COPEMED Workshop on Fishing Gear Selectivity

COPEMED
Workshop on Fishing Gear Selectivity
Kerkennah, Tunisia
9 to 11 October 2001
REPORT
1
SUMMARY
The workshop was held on the Island of Kerkennah, Tunisia from 9 to 11 October 2001,
co-ordinated by a FAO COPEMED consultant (Dr Peter Stewart).
BACKGROUND AND OBJECTIVES
One of the main objectives of the project COPEMED has been, right from the
beginning, to assist the Scientific Committees of the multilateral fisheries organisations
on their decision making processes. The idea of this workshop arose as a response to a
need for selectivity studies, expressed at the XXIV General Session of the GFCM,
whose first goal would be to determine fish sizes at first capture then later to search for
common regulations. At that meeting COPEMED decided to start compiling a
bibliography for our area and to plan the organisation of a workshop to analyse the
present status of Gear Selectivity Studies in the Mediterranean.
The organisation of this workshop is one step in the search for solutions that can be
applied to our area to reduce the high mortality of non-target species and unwanted
sizes of fishes and more widely to ensure the conservation and sustainability of our
fisheries.
Programme
The workshop programme consisted of presentations by delegates of their current
national programmes on fishing gear selectivity plus presentations by invited experts
on:
•
•
•
•
•
•
Review of published work on gear selectivity in the Mediterranean, and
Review of methods used elsewhere to improve gear selectivity by Peter Stewart
Selectivity data needed for Mediterranean fish stock asessment by Luis Gil de Sola
Analysis of selectivity data by Rene Holst
Interaction of cetaceans with fishing gears by David Goodson
Techniques for underwater observation of fishing gears by Peter Stewart.
Recommendations
The delegates recommended that the following topics should have priority for study and
funding in the future:
1) The collection of selectivity data for both commercially important and noncommercial species, caught by all types of fishing gears used in the different
Mediterranean countries, with estimates of the variance of the selectivity
parameters. Data collection methods should be standardised to aid comparability
and new methods of analysis, eg bootstrapping, should be used in place of haul
pooling to deal with the problem of low catch per haul for any species.
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2) Investigation of gear selectivity in coastal/artisanal fisheries. The study of
selectivity in regions with several different metiers would allow the selectivity
of the various fishing methods to be compared and the least selective to be
identified. This work would be suitable for a pilot project in a multi-gear fishery.
3) a) Investigation and monitoring of the sampling efficiency and selectivity of the
trawls used in stock assessment surveys
b) Techniques to separate species in towed gears should be developed to reduce
the by-catch of unwanted species, eg grids within the net to separate crustaceans
from fish
c) Development and testing of devices to deter cetaceans from approaching nets
is needed to reduce by-catch and gear damage.
4) In support of these proposals the group considered that progress could be made
more rapidly by:
a) Consulting the fishing industry and seeking their advice and co-operation
when planning new projects to improve gear selectivity. This may assist the
subsequent introduction of new management measures.
b) Obtaining equipment to enable fish behaviour in fishing gears to be observed
underwater. By understanding the processes of capture and escape for each
species effective methods of selection can be developed more efficiently.
c) Training of personnel in the study of fish behaviour and in the analysis of
selectivity data. These methodologies are well developed and could be
applied easily to Mediterranean fishery studies.
Proposed Actions
Considering these recommendations, interested countries and COPEMED should plan
in the near future to:
1) Collect selectivity data for both commercially important and non-commercial
species, caught by all types of fishing gears used in the different Mediterranean
countries with estimates of the variance of the selectivity parameters.
ACTION: all countries.
2) Commission an experienced statistician to apply, to existing data, the new ideas put
forward at the workshop, for the analysis of sparse selectivity data. This is an
essential step for item 3.
ACTION: COPEMED.
3) Meet to agree a protocol for making cod-end selectivity measurements, using the
guidance in ICES Co-operative Report No. 215. This should ensure that the
selection types of trawl to be used (research and commercial), the method of
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measurement (cover type, twin trawl or trouser trawl), the sampling strategy
(number of hauls, catch sampling), method of data analysis, format of report.
ACTION: all countries with some COPEMED support
4) Identify one or more multi-gear artisanal fishery suitable for investigation of the
comparative selectivity of different gear types, then organise studies to expand
knowledge of size and species selectivity in such fisheries and their relative impacts
on the stocks of target and non-target species.
ACTION: countries
5) Conduct trials of sorting grids in demersal trawl fisheries for shrimp to investigate
the capability of this device in the Mediterranean for reducing the by-catch of
juvenile fish In connection with the fishing industry.
ACTION: countries with some COPEMED support
6) Co-ordinate and conduct trials of acoustic devices for scaring dolphins away from
fishing gear, testing both the hand held Tunisian device and electronic pingers.
ACTION: countries interested with some COPEMED support
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AGENDA
DAY 1
• Welcome and Opening of Meeting (Amor el ABED and Kerkennah authorities)
• Overview of COPEMED and the role of gear selectivity studies (Pilar
HERNÁNDEZ)
• Review of published work on gear selectivity in the Mediterranean (Peter
STEWART)
• Priorities for future work - initial discussion.
• Presentations of national programmes of work on fishing gear selectivity,
identifying current fishery management issues and reporting recent results of
studies (Representatives of all COPEMED member states present)
•
Tunisia:
Tunisia:
Tunisia:
Spain:
Morocco:
Algeria:
Libya:
France:
Croatia:
Ridha M’RABET
Lofti BEN NACEUR
Néjla BJAOUi
Luis GIL DE SOLA
Abdelwaheb SLIMANI
Mohamed ABBAS
Ahmed NFATY
Serge MORTREUX
Alen SOLDO
Review of methods used elsewhere to improve gear selectivity (Peter Stewart
and Serge Mortreaux) - Video presentation
DAY 2
• Visit to a “Cherfia” fishery
• Gear selectivity data needed for stock assessment and fishery management (Luis
GIL DE SOLA)
• Analysis of selectivity data (Rene HOLST).
• Acoustic deterrence and fish survival (David Goodson and Peter Stewart) Video presentations.
DAY 3
• Cetaceans and fishing gear interactions (David GOODSON)
• Pelagic Fishing with Light (Ignacio SOLER)
• Techniques for underwater observation of fishing gears (Peter STEWART).
• Identification of research programmes on gear selectivity in Mediterranean
• Discussion and Recommendations
• Closure of Meeting
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PROCEEDINGS
1st Day
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Opening of the Workshop
The workshop was held in Kerkennah Island, Tunisia from 9 to 11 October 2001 at the
kind invitation and excellent organisation of INSTM. It was attended by 34
participants, 23 from Tunisia representing the administration, the industry and the
research sectors, 6 from Spain, France, Morocco, Algeria, Libya and Croatia (this last
representing ADRIAMED area) as well as 3 experts from Denmark, United Kingdom
and Spain who talked about statistical techniques, cetacean deterrence, and fishing with
light respectively. The COPEMED Associated Professional Officer and the contracted
consultant Dr. Peter Stewart also attended, the latter being responsible for the scientific
co-ordination of the meeting. (See Annex I , list of participants).
Prof. El Abed, as chairman, welcomed the participants, thanked the COPEMED
project for facilitating the organisation of the workshop and thanked the Kerkennah
authority delegate for his warm welcome to the island. He stressed the importance and
the need for selectivity studies in Tunisia and in the Mediterranean in general.
Afterwards, he gave the floor to the Kerkennah authority delegate, Peter Stewart and
the COPEMED representative who said a few words of welcome and introduction. On
behalf of the Project Director, who could not attend due to other important simultaneous
commitments, the latter expressed his greetings and best wishes for the success of the
workshop.
Following a proposal by the chairman, Rhida M'rabet from INSTM
Hernández from COPEMED were elected as rapporteurs .
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and Pilar
Introduction of Project COPEMED and the role of Selectivity Studies
The COPEMED officer briefly introduced the project with its main objectives and
development activities . She explained the context in which the workshop was planned
and outlined the objectives expected to be achieved at the present meeting (Annex II).
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Review of published work on gear selectivity in the Mediterranean (Peter
Stewart)
Dr. Peter Stewart presented the terms of reference provided by FAO-COPEMED for
himself as a contracted consultant and for the Workshop. The Terms of Reference are:
1) To review available data on the selectivity of fishing gears used in the Western
Mediterranean Sea and consider the relevance to fisheries in this region of
selectivity studies elsewhere.
2) Advise on the experimental methodology needed to determine selection parameters
of current fishing methods and co-ordinate a Workshop to consider these issues,
leading to recommendations on actions to improve knowledge of gear selectivity in
the Western Mediterranean.
3) Prepare a written report on the findings of the initial studies and the proceedings of
the Workshop.
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He emphasised that the main aim of the workshop was to identify and recommend
priorities for future work on gear selectivity. Then he explained his review of selectivity
studies and data for the Mediterranean fisheries. This was expanded to cover the whole
Mediterranean as there is significant new work being done in the eastern sector. The
review is available in three documents: a list of selected titles, a second list with
abstracts and a discussion paper The published works chosen for the bibliography are
classified in the following 10 categories, with the numbers of selected papers in
brackets:
General documents and papers (4)
Gear selectivity for demersal fish species (27)
Gear selectivity for shellfish (9)
Selectivity of novel cod-ends (18)
Selectivity of set gear (nets, traps, lines) and artisanal fisheries (11)
Stock assessment, surveys and selectivity of survey gear (15)
Gear performance and catch composition (9)
Techniques of measurement and analysis (7+3)
By-catches of marine mammals and reptiles (4)
Key papers on gear selectivity studies conducted elsewhere (21).
He asked the audience for their help to complete the bibliography by identifying any
relevant papers not included.
To ensure that his comments on the bibliography were clear, he gave a short explanation
of the important terms and definitions on fishing gear selectivity. He then discussed the
papers in each category and identified important issues. There is more published work
than he expected to find, especially investigating novel cod-ends of improved
selectivity. The species for which selection data exist were listed and it was noted that
more work is done on M. barbatus than any other species. One of the problems in
Mediterranean selectivity studies is the difficulty in getting estimates of parameter
variance, since catches are small and several hauls must be pooled to fit selection
curves, which obscures variability. The results of tests of novel cod-ends are
encouraging and indicate that using different mesh shapes has a complex effect on
catches in multi-species fisheries. Sorting grids should be useful for species separation.
He stressed the importance to the fishermen of the economic impact of changing
regulations on mesh sizes and the need to obtain such information for management
purposes.
There is a remarkable lack of work on the selectivity of fixed artisanal gears. The
importance of studies on the selectivity of survey trawls was mentioned and comparison
of the catches in different types of trawl, highlighting the significance of the selective
effects of the different trawl components. Several papers describe improved
measurement techniques and underwater observations on fishing gear, a crucial step in
selectivity studies. Reducing the by-catch of cetaceans is important and recent work was
noted. The final section of the bibliography contains key papers describing progress on
gear selectivity work done elsewhere, including both the results of experiments and the
development of techniques of observation, measurement and data analysis.
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It is important to bear in mind that techniques of improved selectivity are only one tool
of fishery management. There are three methods of controlling fishing mortality: 1)
limiting access, 2) limiting fishing effort and 3) limiting catches which includes the
improvement of gear selectivity. The appropriate methods for a fishery depend on local
circumstances and the co-operation of the fishermen.
•
Priorities for future work - initial discussion.
Having carried out the review, Peter Stewart thought that he could identify some
priorities for future work. He presented a list of possible research topics as a basis for
further discussion during the meeting. He also informed the group of the conclusions
reached by an EU workshop on cod-end selectivity in 1991 which had an important
influence on subsequent work programmes. He suggested that in a multi-species trawl
fishery it might be more productive to concentrate more on species separation by
sorting grids or multi-level nets than on size separation.
The administration delegates from Tunisia expressed their interest in the different
methods used to reduce directly the retention of unwanted fish in the nets and on the
degree of damage caused by trawling.
The consultant asked why there is so little work done on artisanal fixed gears. The
Spanish delegate commented that, maybe because the official way of thinking has been
for a long time to focus on the industrial fisheries, trawlers and gillnets (similar to
ICES), not much attention was paid to the artisanal fisheries which are as important as
those using mobile gears.
He also emphasised the importance of investigating measures other than mesh size
increases to enhance species separation and proposed this for further discussion. There
is a need to enhance and improve the diffusion of information about the experiments
performed in different countries and the benefits that can be obtained when applying
one of these techniques for improving gear selectivity. Video-films and fact sheets were
mentioned and examples of the latter were shown to the group.
A discussion opened about the need for selectivity studies on purse seine nets after a
question from the Algerian representative. The majority of the group thought that there
was little point in raising mesh size in this gear, since the meshes became clogged very
fast and prevented escape but further discussion was suggested.
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Presentations of national programmes of work on fishing gear selectivity
TUNISIA
Rhida M'Rabet, INSTM
He presented the most important INSTM programmes on the selectivity of fishing
gears. These are:
- the improvement of the selectivity of fishing gears used in Tunisia especially the
trawls
- The development of a new selective shrimp trawl with a grid in the gulf of Gabes
For the first programme he studied the effect of cod-end mesh size and compared the
selectivity of diamond and square mesh cod-ends. The results obtained show that the
square mesh cod-end, for the same mesh size, is more selective than the diamond mesh
cod-end. For the selective shrimp trawl net, comparison of the Nordmøre grid and the
INSTM grid shows that the INSTM device is more selective in the fishery of the Gulf
of Gabes
The Algerian representative asked about the possible ways of convincing fishermen to
apply these measures. Dr M'Rabet answered that the only way was to show the method
working at sea and to get them to do some experiments themselves with their own
gear. A representative of the fishing sector asked how long might it take for this grid
system to be adopted by the professional fisherman?. M'Rabet answered that some
improvements will be made and, once the study is finished, the gear will be available.
Lotfi BenNaceur
He described the experiments carried out in Tunisia with the Dolphin scaring tubes
which they have designed, tested and distributed among the fishermen. They include a
booklet with an identification guide for the cetacean species likely to be encountered
and ask for some information about the behaviour of the dolphins. The results have
shown that the degree of avoidance is high. He also described some selective fishing
techniques introduced in Tunisia lately to protect coastal area from trawlers and avoid
unwanted sizes and non target species captures. (See annex VI)
Néhla Bjaoui
Cherfia fisheries in Kerkennah.
The special hydrographic and geomorphological features of the archipelago, with very
shallow water, a muddy bottom and a high tide level by Mediterranean standards, make
the area suitable for this type of trap fishery.
Palm leaves are used to build long leaders and barriers. The traps are made of nylon
netting supported by PVC pipe. The fish are driven towards the traps by the tidal
current. They go from shallow to deep water as the tide goes down and are directed to
the traps by the long lines of palm leaves. It is an artisanal and very typical type of
fishing. The traditional method is preserved with only minor changes in the materials
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used. There has been some decrease in the number of cherfias observed during the last
30 years mainly due to the high costs of the installation and to a decrease in the biomass
captured.
SPAIN
Luis Gil de Sola
He introduced the project MEDITS and invited participants to look at the paper
published in Aquatic Living Resources (1999, 12(3):187-205).. This project concerns
the efficiency and selectivity of sampling trawls used in resource surveys in the western
Mediterranean. He presented the work of different research groups operating in very
localised areas and in two different types of fishery. He commented that there is no
official Spanish programme to perform selectivity studies or are there any selectivity
rules to be applied in Spanish Mediterranean waters. There is an important lack of
selectivity studies in the Mediterranean. The European Commission stated this as one
of the priority lines for research in the last call for proposals. The work on selectivity
carried out during the eighties in the ICES area is still being used to assist the
assessment groups in the Mediterranean. Presently, within the Spanish Institute of
Oceanography (IEO) the possibility of creating a specific research group on fishing
techniques is being considered
MOROCCO
Abdellouah Slimani
presented the programmes of the Institut National de Recherche Halieutique (INRH) on
the technology of fishing gears and indicated that in the new centre of Nador, some
studies were carried out on the fishery resources and the selectivity of fishing gears. He
described also the joint project on dolphin deterrence, between Morocco and Tunisia. .
Long ago, INRH started research on the technology of fishing gears. These studies
cover all the fisheries of the Moroccan coasts. The regional centre in Nador, recently set
up in the Moroccan Mediterranean, studies the fishery resources and there is some
work on gear selectivity. The main studies are recording the activities of the
commercial fishing vessels, the study of interactions between dolphins and fishing nets,
and the selectivity of trawls.
Some scientists are going on board commercial vessels to get information on their
fishing activities. Observations on vessels fishing swordfishwith long-lines or gillnets
aims to learn about the by-catch species (mammals, turtles, ..) On trawlers observation
allows estimates to be made of discard ratesof small fish.
This study, aims at the reduction of catches of dolphins in the nets, has been carried as
a co-operative project between Tunisia and Morocco. The objective is to assist the
fishermen by the reduction of damage caused by dolphins to the fishing nets. This is
achieved by using the deterrent tubes developed by INSTM in Tunisia. These tubes
produce sound waves that annoy the dolphins, making them flee. Several exercises have
been carried out at the ports of Ras Kebdana, Nador and Alhoceïma, and some meetings
with professional fishermen have taken place. The deterrent tubes have been produced
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and are ready to be distributed to the fishermen with a log book during November
2001.
A study of the selectivity of the bottom trawls used in the Moroccan Mediterranean has
been programmed for 2002.
Mr. Said Benchoucha described work on gillnet selectivity carried out during a
research visit to Japan (Annex III)
LIBYA
Mr. Ahmed Nfaty presented a short review of thefishing techniques used to target
different species.,
Information collected during the survey field work on Melates showing seasonality in
the species composition of catches according to the type of gear used. A total of 51
species including worms, clams, lobsters and sponges were recorded to be captured with
25 different fishing and collecting gears.
Among the groups of fish caught by longline: groupers, dentex, shark and white bream
are the main target species . Other non-target species are cumbers, breams and weavers.
Fishes caught by trammel nets are red mullets, breams, dentex, pandora, sharks, saupes,
weavers and wrasses. As the trammel net is a non-selective passive gear, it collects a
wide variety of fishes, some of them (wrasses and weavers) not targeted originally, but
frequently taken as bycatch.
Gillnets are selective gears according to the mesh size used. They are used to catch
mainly small tuna, barracuda, saupe and small amberjack (<0.5 kg).
Handlines are employed to catch a variety of species including combers, weavers, white
bream and Pandora.
Polelines are mainly used from the shore and seem to be rather unselective, though grey
mullets, breams and white bream are caught at a slightly higher rate than other species.
Lampara fishing employs a lamp boat working in association with a larger seine net
craft at night . It captures sardine, mackerel, bogue and horse mackerel.
Polelines and handlines are respectively the first and second most commonly used gear
by foot fishers. Spear guns and explosives seem to share the rank of third most frequent
type of fishing techniques employed in Libyan waters.
ALGERIA
Mohamed Abbas
said that there are fishing regulations in Algeria but these need to be revised. There is a
project to study the selectivity of fishing gears used in Algeria. He is responsible for a
study of the selectivity of gillnets and the results will be communicated as soon as
possible.
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FRANCE
Mr. Serge Mortreux reviewed recent IFREMER projects on selectivity (Annex IV).
These studies are conducted with the aim of achieving sustainable management of the
fish stocks. IFREMER is well equipped for this work, having underwater vehicles and
cameras to study fish behaviour in gears; two flume tanks in which new selective gears
can be observed and developed; instrumentation for measuring the physical
performance of gears.
In project SELMED, the selectivity of fixed nets was studied in relation to mesh size
and net height. An extensive investigation of the MEDITS trawl took place in project
ESMED, involving underwater observation of fish behaviour, determination of escape
rates in the forward parts of the trawl, selectivity measurements with a small mesh cover
and catch comparison with a commercial trawl.
In northern waters, studies have been made of the effect on selectivity of cod-end twine
dimensions and, at the request of fishermen, of the use of sorting grids to release
juvenile fish. Prototype grids were tested in the flume tank then at sea. A second codend was used to catch escaping fish and assess the separation achieved. An enveloping
cover with kites was also used to obtain selection data. Various grid types and rigging
have been tested with good results and the concept could be tried in the Mediterranean.
CROATIA.
Dr. Alen Soldo reviewed work in Croatia.
Due to great diversity of fish species living in the Adriatic Sea, of which 420 species
have been identified so far, a large number of fishing gear types and techniques have
been developed. Nowadays, there are about 120 commercial species, including
crustaceans, cephalopods and molluscs, caught with 55 different types of fishing gear
in Croatian fisheries.
According to the Law of Marine Fisheries of the Republic of Croatia, commercial
fishing, small-scale fishing and fishing for sports and recreation are recognised .
Commercial fishing is a profit-making activity, which means that it is conducted on a
professional basis. All 55 types of fishing gear are allowed to be used in this category.
Small-scale fishing is performed for individual needs and catches taken by the smallscale gear must not be traded. It is not a professional activity, and therefore the types
and quantity of gear are limited to several gillnets, trammel nets, seine nets, traps and
hooks. Gears used in the category of sports and recreation are similar to those used in
other countries of the Mediterranean.
The Institute of Oceanography and Fisheries, as the main institution for marine research
in the Eastern Adriatic, has performed studies in which most of fishing gear types have
been used. Unfortunately, most of those studies were conducted for biological
purposes, and the fishing gear was used only as a tool for the collection of samples.
Therefore, the data necessary for the proper statistical analysis of fishing gear selectivity
were not collected. Although there is no funding for gear selectivity projects, during the
last few years biological studies were used for collecting data on gear selectivity,
whenever it was possible. Since 1999, funds were available for a project on trawl
selectivity . The poor selectivity of (“tartana”) trawl is one of the greatest problems in
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Croatian fisheries. This is a typical Mediterranean type of trawl used evenly on both
sides of the Adriatic. Therefore, a new type was designed, with double panels as used
in northern fisheries. According to the first results obtained, new directions for fishery
management (increasing mesh size and use of selective panels) were determined, but
the project, because of lack of funding, is currently halted. The project was proposed, as
of general concern for the whole Adriatic, to be part of the FAO AdriaMed programme,
so that all the countries of the Adriatic could benefit from the results.
Along with that project, the selectivity of other fishing gears was also the subject of
research. Currently, data on the selectivity of pots for Norway lobster, Nephrops
norvegicus, pots and gillnets for common spiny lobster, Palinurus elephas, gillnets for
hake, Merluccius merluccius and bogue, Boops boops are in process of analysis, while
some results are awaiting publication (eg the “tramata” fishing or fishing using only
ropes).
Much attention has been paid in the study of gear selectivity elsewhere, to underwater
observation of fish behaviour in response to fishing gear. Such observations, along with
data obtained by other techniques could give more reliable results in Mediterranean
fisheries that would lead to improvement in the selectivity of fishing gear. Furthermore,
such improved fishing gear, which would have reduced catches of immature specimens
and unwanted species of fish and other marine organisms, would enable better
protection and management of fish in the eastern Adriatic.
Video-Films
Four video-films on aspects of fishing gear selectivity were presented by Peter Stewart
and Serge Mortreaux:
a) "Conservation Measures" reviewed the techniques used throughout the world to
improve fishing gear selectivity and reduce discarding.
b) Set nets on various types of sea bed, showing catches.
c) Sorting grids in trawl cod-ends in the EUROGRID Project, with many shots of
escaping fish
d) Square mesh escape panels in trawl cod-ends.
These films clarified many of the issues raised during the day and stimulated much
further discussion.
2nd Day
Morning: Visit to Cherfia Fishery
The group visited a “cherfia” fishery and had the opportunity of watching the catch
being collected from the traps set on the corners of the cherfia rooms. A variety of
mugilidae, sciaenids, some sparids and some cephalopods was collected from each trap.
Another set of traps with crabs as bait had been set on a line close to the cherfia. Those
traps contained only octopus. The total catch of the full operation was about 15 kg.
The experience of seeing a traditional artisanal fishery in operation and fishing from a
sailing boat was greatly valued by the group It was interesting to see how this traditional
fishery survives and to note its minimal impact on the ecosystem.
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Continuation of the sessions
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Data needed for Selectivity studies in the Mediterranean
Dr. Luis Gil de Sola described the size and species selectivity of some of the fishing
gears used in the Mediterranean (Annex V). The fleets can be divided into metiers
specialising in different depth strata and using different gears to catch their target
species. He noted the complex short and long term effects of changing minimum mesh
sizes in multi-species fisheries and the problematic assumption for stock management,
that fishermen always use the legal minimum mesh size. Often they do not as they are
fishing for the size ranges of the species required by the market. Estimates of the effect
of increasing mesh size on the stocks are then flawed. He reviewed some of the work of
IEO and described the type of selectivity data needed for stock assessment studies:
•
•
•
•
•
•
•
•
•
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Length composition of the catch (by country).
CPUE for medium sizes.
Selection factors.
Growth rate of the target species.
biomass and density of the most exploited groundfish
Proportion of the stock dying each year by causes other than fishing (Natural
mortality).
Proportion caught at age in the international fishery (Fishing mortality).
Discarding
Incidental catches (not only classical endangered species)
Data Analysis
Rene Holst's presentation is summarised in Annex VII. He discussed the three key
factors for conducting successful selectivity studies: planning, modelling and analysis.
Great care must be taken in planning this type of work, starting with the design of the
fishing gear and the method used to collect and sample escaping fish. To obtain a valid
rather than a misleading result, it is essential to scale the exercise correctly and to have a
clear experimental plan. The data to be collected and the catch sub-sampling protocol
must be clearly defined.
He explained the most common statistical methods used for analysing selectivity data.
Both physically realistic and pseudo-models can be used for curve fitting. Fryer's model
of between haul variation and the SELECT model are presently applied to all gears
and selectivity measurement methods (small mesh covers, trouser trawls, inter-gear
comparison). Some examples were given.
Multi-species fisheries present additional problems to the analyst and he discussed
suitable methods. His suggestions were to pool data for species of similar body shape,
to use bootstrapping for sparse data, and to pool data from adjacent length classes. In
discussion it was thought that these methods were promising and could be applied to
existing Mediterranean selectivity data to test their effectiveness. Also this work would
be an excellent topic for an EU funded project.
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Video-Films
Films were presented by David Goodson and Peter Stewart.
a) Studies of acoustic methods of scaring cetaceans
b) Survival of fish escaping from cod-ends.
These films again stimulated interest and discussion. Peter Stewart agreed to provide
copies of his films to the Tunisian delegates.
3rd Day
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Cetaceans-fishing gear interactions
Dave Goodson presented a comprehensive review of the problems caused by these
interactions, to the fishing gear as well as to the cetaceans populations, and suggested
possible solutions.
The following points were discussed:
-
Cetacean interactions with different fisheries- problems of bycatch and predation
Recent EU projects: “ BioEco”, “CetaSel”, “Bycare”, “Epic” and “Adepts”.
Methods of studying dolphin behaviour near to fishing nets
Acoustic deterrents - design and experiments
Managing unwanted dolphin interactions: habituation, habitat denial, noise
pollution, and other oft quoted concerns
- Future research – some new problems to solve.
The only project in Mediterranean waters (ADEPTs) is carried out on the coast of
Sicily. This was described in more detail and results summarised as follows:
•
•
•
A two year study of the trammel and gillnet fisheries in the Egadi Islands and
Catania monitored the weight of landings and net damage caused by dolphins.
Wideband acoustic deterrents (AQUAmark100) were introduced during the second
year to evaluate their effect.
The predating dolphin species was found to be exclusively bottlenose dolphins
(Tursiops truncatus) with most net damage occurring during the spring and least in
summer months.
Attaching a simple pre-production AQUAmark pinger provided very significant
protection to the nets and correlated with an increase in landed catch weights by
both trammel and gillnet boats at both geographic locations.
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Light fishing
Prof. Captain Ignacio Soler gave a multi-media presentation showing two fishing
procedures with a purse seine: one in winter, when the fish are distributed closer to the
surface and need only a short time to be concentrated, and one in summer when fish are
below the thermocline and a longer period of illumination is needed in order to make
the fish rise and concentrate.
He presented technical features of the gears used under Spanish regulations.
Summarising the Regulations in Spain since 1984 for this type of fishing, the
requirements are:
- Minimum tonnage of boats: 20 tonnesMaximum power: 450 hp
- Maximum net dimensions:
•
Length: 300 m
•
Height: <80 m
- Maximum light intensity: 6 kW
- Minimum distance between light boats: 500 m
- Time schedule: All year long at night, between 9-11 pm and 8-10 am.
- Minimum landing sizes for the target species:
•
Anchovy (Engraulis encrasicholus) : 9 mm
•
Sardine (Sardina pilchardus) : 11 mm
He also gave a short description of some of the modern acoustic instruments used by
part of the fleet. Many participants showed a great interest in the technical details of the
operation. Mr. Soler commented that there are many factors that have to be adjusted
very sensitively in every haul, depending on the weather, the currents, and the species
targeted.
-
Underwater observation techniques
Peter Stewart referred to the Film "Conservation Measures" , shown on the 1st day of the
workshop and emphasised that the significant progress recorded there had come about
as a result of observing fish and fishing gears underwater. It is essential to know how
fish behave in front of and within a net if the aim is to design nets of improved
efficiency or selectivity. He then illustrated the typical fish reactions to fishing gears
observed in previous studies. These depend on the visual stimulus, towing speed, fish
size and species. One study showed three gadoid species with different reactions when
exhausted and how this could be used to separate the species during trawling. Escape
from cod-ends is a complex process and he listed the factors affecting fish escape,
biological (fish condition, species), environmental (light level, water temperature) and
mechanical (net structure, towing speed). This type of information is needed for
Mediterranean fisheries to provide a sound scientific basis for the development of
improved fishing gears.
To obtain such knowledge it is essential to have equipment for underwater observation.
It is complex and expensive to observe fishing gears underwater but scientifically
rewarding. The alternative is to design new gears based on speculation about fish
behaviour. This is unsatisfactory as then the only way to test the ideas is by exhaustive
and expensive fishing trials. The most commonly used techniques of observation are:
16
Divers: Either free diving or with a towed body for protection;
Remotely Operated Vehicles (ROV): either towed or independent;
Fixed cameras: using small cameras linked to a recorder on the net.
He discussed the advantages and disadvantages of these methods for Mediterranean
fishery studies and drew attention to a small ROV designed and built in Finland. This is
a hydrofoil with moveable fins for steering, supporting an adjustable TV camera. It is
limited in depth but he thought the device could be used in Mediterranean fisheries. It is
less expensive than a large ROV and more adaptable than a fixed camera.
In response to questions raised informally at the workshop, he then compared the
function of escape panels and grids on trawls. These are alternative options for
improving selectivity and are a source of discussion among scientists. Panels are less
complex and cheaper than grids but rely on fish being induced to make active escape
attempts. Grids are set within the net where fish must confront them and either pass
through or be released.
-
Identification of relevant programmes of research
The European Commission has recently published a volume entitled "Dissemination of
the results of biological studies" which describes several recent programmes
investigating gear selectivity and by-catch reduction in the Mediterranean. These
include:
•
•
•
•
•
•
•
•
•
Discards of the Western Mediterranean Trawl Fleets (94/027);
Analysis of Trawl Discard operations in the Central and Eastern Mediterranean Sea
(94/065);
Selectivity of Square Mesh Windows in Fish and Nephrops Trawls (94/084);
Trammel and Gill net Selectivity in the Adriatic and Tyrrenhian Sea (94/086);
Selectivity of Static Nets in the Mediterranean (95/012);
Efficacy and Selectivity of the Trawl used for the MEDITS Project (95/029);
Analysis of Trawl Discard Operations in the central and eastern Mediterranean Sea
(95/061)
Comparative Fixed Gear Selectivity Studies in Portugal and Greece (96/065);
The Composition and Fate of Discards from Nephrops Trawling in Scottish and
Italian Waters (96/092).
In addition, David Goodson informed the group of some recent EU projects aimed
wholly or partly at reducing cetacean by-catch:
•
•
•
•
•
Prevention of By-catch of small cetaceans in pelagic trawls (CETASEL 94/2423)
Elimination of porpoise incidental catch (EPIC 97/0006)
Acoustic deterrents to eliminate predation on trammels (ADEPTS 98/019)
Reducing by-catch in trawls and set nets (BIO-ECO)
By-catch reduction (BY-CARE)
The group noted these programmes and their relevance to the present discussions.
17
DISCUSSION AND RECOMMENDATIONS
The group discussed the list of ideas for future work on fishing gear selectivity
suggested by Peter Stewart on Day 1The Spanish delegate pointed out the high costs of
some of the measurement techniques in use (hooped covers, twin nets). He also stressed
the importance on carrying out selectivity studies on artisanal fisheries.
He asked Peter Stewart whether he had information on the importance placed by the
EU on selectivity studies nowadays. Peter Stewart replied that several major
programmes on selectivity are in progress and that the Commission is laying much
stress on new gear regulation to improve selectivity for the North Sea and NE Atlantic.
Some participants from Tunisia stressed their need of education and training for
biologists in fish behavior and in analytical techniques .The COPEMED representative
said that the project is always ready to consider proposals, but outlined the better idea of
collecting data and having projects in which any training could be immediately applied,
rather than organising formal courses. This is the view after a survey was conducted
amongst students who attended some of the courses provided by the project.
Mr R. Holst: commented that there is a substantial job to do in adapting classical
analytical technique to the special features of Mediterranean fisheries. He mentioned
the FTFB working group of ICES, meeting once a year to comment and provide
information on such items. It would be valuable to have a similar group in the
Mediterranean. He pointed out the importance of good experimental design. Without
this, it is possible to waste large amounts of money collecting data that cannot provide
useful estimates of selectivity. He referred to the EU SELDAT Project which is defining
how the data have to be collected and stored. David Goodson commented on the value
of searchable databases of this type, accessible to all those interested in the topic.
Both Mr Holst and Dr Stewart stressed the value of the ICES Co-operative Research
Report No. 215 published in 1996 (ISSN 1017-6195): Manual of methods of measuring
the selectivity of towed fishing gears. This document gathers together the experience in
gear selectivity research gained by the scientsists in ICES countries during the last 20
years, and is an excellent guide for anyone seeking to start new work on gear selectivity.
The Croatian delegate pointed out that underwater observations are too expensive for
many countries to undertake. He thinks that fish behavior studies are not so necessary,
that you can draw some conclusions from the results of surveys. He thinks that one of
the major priorities would be to reinforce contacts with the fishing industry. Peter
Stewart disagreed with this view as it can be very time consuming and costly to collect
enough catch data to demonstrate that a new technique really improves selectivity.
Direct observation of fish reacting to nets on the other hand shows whether an idea
works.
Peter Stewart asked about the current interest of COPEMED partners in the separation
of species in trawls. The delegates from Spain and France commented that it needs to
be studied further.
The Tunisian delegate considered it very important to add a recommendation about
testing the different deterrent devices for dolphins that they think are very much needed,
18
especially, according to David Goodson's comments , in artisanal fisheries, where the
economic loss caused by dolphin predation can be important.
The discussion identified the topics listed below, in order of priority, which the group
considered to be of major importance to the scientific investigation and management of
Mediterranean fisheries. These include both specific themes for study and general issues
concerning project planning, facilities and training.
Recommendations
1) The collection of selectivity data for both commercially important and noncommercial species, caught by all types of fishing gears used in the
Mediterranean, with estimates of the variance of the selectivity parameters. The
aim is to provide information on age at first capture for stock assessment. On
towed nets, the new types of small mesh cod-end cover should be used to ensure
that the data are not biased by the cover obstructing the cod-end meshes and
hindering fish escape. Data collection methods should be standardised to aid
comparability and new methods of analysis, eg bootstrapping, should be used in
place of haul pooling to deal with the problem of low catch per haul for any
species.
2) Investigation of gear selectivity in coastal/artisanal fisheries. These fisheries are
widespread and economically and socially important. The catches in total may
contribute significantly to stock mortality. The study of selectivity in regions
with several different metiers would allow the selectivity of the various fishing
methods to be compared and the least selective to be identified. This work
would be suitable for a pilot project in a multi-gear fishery.
3) a) Investigation and monitoring of the sampling efficiency and selectivity of the
trawls used in stock assessment surveys should continue to ensure that they
provide reliable estimates of relative stock abundance and to expand knowledge
of trawl selection for various species.
b) Techniques to separate species in towed gears should be developed to reduce
the by-catch of unwanted species, eg grids within the net to separate crustaceans
from fish. These methods show promise when used to separate fauna of differing
body form but require adaptation for specific fisheries.
c) Development and testing of devices to deter cetaceans from approaching nets
is needed to reduce by-catch and gear damage. These are serious problems in
some fisheries and the techniques recently developed have been shown to
provide effective deterrence.
4) In support of these proposals the group considered that progress could be made
more rapidly by:
a) Consulting the fishing industry and seeking their advice and co-operation
when planning new projects to improve gear selectivity. This may assist the
subsequent introduction of new management measures.
19
b) Obtaining equipment to enable fish behaviour in fishing gears to be observed
underwater. By understanding the processes of capture and escape for each
species, effective methods of selection can be developed more efficiently.
c) Training of personnel in the study of fish behaviour and in the analysis of
selectivity data. These methodologies are well developed and could be applied
easily to Mediterranean fishery studies.
Closure of Meeting
In the absence of Prof el Abed, Peter Stewart thanked all the participants for their
contributions to the proceedings, the INSTM staff for their excellent organisation and
hospitality and the Rapporteurs for their efforts. He expressed his satisfaction with the
clarity of the recommendations produced by the workshop, considering them to be a
useful basis for the planning of future work. He requested all participants to submit
summaries of their presentations as soon as possible. He then closed the meeting.
20
ANNEX I
ATELIER DE TRAVAIL SUR LES TECHNIQUES
DE PECHE SELECTIVES EN MEDITERRANEE
KERKENNAH 9 – 11 octobre 2001
LISTE DES PARTICIPANTS
NOM ET PRENOM
Pilar HERNANDEZ
Amor ELABED
Serge MORTREUX
Ignacio SOLER
Dave GOODSON
René HOLST
Mohamed ABBES
Abdelouhab SLIMANI
Saïd BEN CHOUCHA
Luis Gil DE SOLA
Ahmed NFATI
Alan SOLDO
Peter STEWART
Ridha MRABET
Lotfi BEN NACEUR
Nejla BEJ AOUI
Othman JARBOUI
Habib LANGAR
Sofia EZZEDDINE
Mohamed GHORBEL
Nédra ZAMOURI
Selim RIVEILL
Mohamed HMANI
Nehla ALAYMI
Othman ZOGHLAMI
Ridha AMIMI
Taieb BOU AFIF
Abdelmajid SHEL
Mohamed TILA
Nidhal MLAOUAH
Hamadi BEL AIBA
Touhami EL MEKKI
Mohsen AJMI
Mejdi MANOUCHI
PAYS D’ORIGINE
INSTITUTION
ESPAGNE
TUNISIE
FRANCE
ESPAGNE
ANGLETERRE
DANEMARK
ALGERIE
MAROC
MAROC
ESPAGNE
LIBYE
CROATIE
ECOSSE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
TUNISIE
COPEMED
INSTM
IFREMER
C.F.P Maritime
LUEC
CONSTAT
M.P.R.H
INRH
INRH
IEO
MBCT
IOR
ADRESSE ELECTRONIQUE
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
INSTM
INSTM
INAT
INSTM
INSTM
INSTM
INSTM
INSTM
INSTM
DGPA
APIA
CRDA, La Goulette
CRDA, Mahdia
CRDA, Sfax
CRDA, Sousse
CRDA, Zarzis
CRDA, Béja
CRDA, Gabès
CRDA, Kerkennah
AVFA
GIPP
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
ANNEX II
OVERVIEW OF COPEMED AND THE ROLE OF GEAR
SELECTIVITY STUDIES
By Pilar Hernández
APO of the project COEPEMED
One of the main objectives of the project COPEMED has been right from the beginning
to assist the Scientific Committees of the multilateral fisheries organisations on their
decision making processes. According to it, COPEMED has launched and maintained a
series of regional research programs among which we would like to mention: Large
Pelagics, Deep sea shrimps, Artisanal Fisheries, GIS application to Fisheries, Gear
Selectivity, Socio-economic indicators and others devoted to certain species (lobster,
dolphinfish, among others). In general these programs include three steps to follow:
First to gather the existing information , second to organise a workshop in which this
information is put forward and updated by the different parties and third to analyse the
needs of investigation and propose activities to be undertaken. These actions can be
either co- financed by the project in an important percentage or in a desirable
progressive way by the countries themselves.
The idea of this workshop arose as response to a need of selectivity studies expressed at
the XXIV General Session by the GFCM whose first goal would be to determine fish
sizes at first catches and at a later extent to search of common regulations. At that
meeting COPEMED decided to start compiling the existing bibliography in our area and
to take in charge the organization of a workshop to analyse the present status of Gear
Selectivity Studies in the Mediterranean. With this objective in mind COPEMED
contacted with an expert in this studies Dr. Peter Stewart to commission the information
gathering and the analysis of this information. The report accordingly elaborated, would
serve as a basis for discussions and for the identification of needs in an eventual ad-hoc
meeting.
The great diversity of gears and species fished and even of type of vessels used in the
Mediterranean make the fisheries management special and not comparable in what
regulations are concerned to other higher latitudes fisheries as has been evidenced by
Peter Stewart’s report. The high variety of species caught by haul do not favour
generalization of mesh size limits, one mesh size being suitable only for one or two
species and not for others. Solutions that may be valid for other areas are not applicable
to the Mediterranean case. That is why it deserves special attention. COPEMED playing
its role as SAC supporter has worked towards an involvement of the fisheries institutes
in such type of studies. The organisation of this workshop is one step towards the search
for solutions that can be applied to our area in order to reduce the high mortality of nontarget species and non wanted size s of fishes and on the later extent to ensure the
conservation and sustainability of our fisheries.
Our hostess today, the Director of INSTM expressed his high interest on the issue and
his willingness on becoming organiser of this event and has facilitated since the very
beginning the holding of the workshop for what we all are very grateful.
The work elaborated by Peter Stewart is a very good launching ground to jointly
analyse the situation and to identify priorities of research for the near future. He has
carried out an exhaustive critical review with all the available information (published
ANNEX II
and unpublished works) from in and out the Mediterranean and has elaborated some
final recommendations that have to be commented and eventually, taken into
consideration for future research lines. Although COPEMED priorities up to 2004 are
still to be decided by the end of present year, very likely will be outlined during our
Steering Committee meeting next week, we hope that selectivity studies can be included
as priority line to be considered for co- funding.
Mr. Rafael Robles, the Project Director would have liked very much to attend this
workshop, but some other simultaneous activities (preparation of S.C. and fisheries
regulations workshop) kept him in Spain. However he wants to transmit you his
greetings and best wishes for the fruitful development of this workshop. He was very
keen on the idea of holding it with a previous review of the existing information and so
he expressed in the SAC meeting last year. Since then he started the search of experts
and Peter Stewart finally accepted, for what we are very happy and grateful. The kind
invitation of INSTM as the hostess institution by Prof. Amor El Abed was very
welcome and we want to thank as well all the INSTM staff their effort to set up all the
infrastructure with the added difficulty of being in an island.
ANNEX III
SELECTIVITE DU FILET MAILLANT SELON LA METHODE
DES PROBABLITES BASEE SUR LES MENSURATIONS
DU PERIMETRE DU CORPS
(RESUME DE LA METHODOLOGIE)
Par : Said BENCHOUCHA
Institut National de Recherche Halieutique, Maroc
Comme tous les engins passifs, le filet maillant a une courbe de sélectivité modale qui
ressemble à une courbe de distribution normale. Le principal facteur qui régit la sélectivité du
filet maillant est la taille de la maille. La sélectivité du filet maillant dépend aussi du matériel
constituant le filet, les filets constitués d’un fil double et mince ont une courbe de sélectivité
déplacée vers la droite due à la grande magnitude d’élongation de ce matériel pour les grandes
tailles. Les filets constitués de monofilament ont une courbe de sélectivité étroite. Les forces
de flotaison et de descente du filet ne sont pas encore étudiées.
La courbe de sélectivité des filets maillants est variable pour la même espèce, due au
changement de la forme du poisson selon le sexe, la croissance et les saisons.
Plusieurs auteurs ont évalué la sélectivité du filet maillant de différentes manières. Cependant,
la méthode actuelle (méthode de Kawamura révisée par Matsuoka et al.) est la plus facile à
appliquer. Cette méthode repose sur le calcul des probabilités basée sur les mensurations du
périmètre du corps. Elle présente plusieurs avantages :
-
Les individus peuvent être échantillonnés par n’importe quelle manière et sans conditions,
L’échantillonnage peut se faire sur des engins de pêche autres que le filet maillant,
L’échantillonnage peut se faire également au niveau des supermarchés, tant que la forme
du poisson n’a pas été déformée,
La pêche expérimentale est obligatoire uniquement pour déterminer la section antérieure
retenue par le filet.
Un nombre minimale de 50 mailles doit être utilisé pour la mesure du périmètre moyen des
mailles du filet maillant. Le double du maillage peut être utilisé pour l’estimation du
périmètre moyen des mailles. Des mensurations du périmètre du corps sont effectuées sur les
individus capturés au niveau de la partie antérieure (exemple : l’opercule ou le pré-opercule)
et au niveau de la section maximale, ces mensurations doivent être faites à l’aide d’un
monofilament qui est enroulé autour du poisson, les deux extrémités du fil, une fois jointes
doivent être coupées en même temps. Le poisson une fois capturé, doit être mesuré pour éviter
la déformation du corps avec le temps. Cependant, un échantillon constitué de 400 à 500
individus (6 à 7 classes de tailles) est nécessaire pour le calcul des équations de régression et
des coefficients de variation entre les périmètres du corps et la taille (longueur) du poisson.
Un minimum de 200 individus peut être utilisé mais avec un degré de fiabilité faible. Les
individus échantillonnés sont séparés en trois groupes :
-
Les individus retenus par leur partie antérieure.
Les individus retenus par la section maximale.
Les individus capturés par les nageoires, par les dents ou par une autre partie du corps.
1
ANNEX III
Généralement, le poisson est capturé dans les deux conditions suivantes :
- La section antérieure du corps est retenue par la maille, en un autre terme lorsque le
périmètre antérieur G1 est plus petit que celui de la maille.
- La section maximale est stoppée par la maille (le périmètre maximal G2 est plus grand que
celui de la maille).
La probabilité pour que la première condition soit satisfaite est appelée P1, celle de la
deuxième condition est appelée P2. Des coefficients de calibration sont calculés pour
l’estimation des poissons retenus par d’autres parties du corps (nageoires, dents etc.). Ces
coefficients sont intégrés dans le calcul des probabilités P1 et P2.
La méthode actuelle est basée sur le calcul de la probabilité Ps lorsque les deux conditions P1
et P2 sont réalisées.
Se référant aux probabilités P1 et P2, la probabilité Ps à une certaine taille L est .
Ps(L) = P1(L) × P2(L)
2
ANNEX IV
Présentation de quelques uns des travaux réalisés par l'IFREMER au plan
national sur la sélectivité des engins de pêche.
Par Serge Mortreux
Une gestion durable de la ressource est un des principaux objectifs que s'est fixé l'IFREMER.
L'étude de la sélectivité des engins de pêche est un des moyens d'y parvenir.
Le matériel
Parmi les différents matériels mis à la disposition des chercheurs de l'IFREMER pour faciliter
la réalisation de ces études on trouve:
Des moyens de prise de vue pour la réalisation d'images sous- marines:
- l’EROC, ensemble remorqué, offre la possibilité de filmer le train de pêche en action
afin de mieux appréhender son comportement ainsi que celui du poisson face au
chalut.
- Le VECOC, peu encombrant, pouvant être fixé à différents endroits du chalut, permet
l’observation in situ du comportement d’un dispositif sélectif en pêche ainsi que celui
du poisson face à ce dernier
Deux bassins d'essais dont un de 4m le large, 2m de haut et 18m de longueur utile avec une
vitesse maximale pouvant atteindre 4 nœuds permet de visualiser le comportement de
maquettes de chaluts et, avant des essais en mer, autorise l'observation à l'échelle 1 des
prototypes de dispositifs sélectifs à l'étude
En mer, une batterie complète de capteurs apporte les informations nécessaires au contrôle de
la géométrie des chaluts et gréements. Entre autres, des inclinomêtres fixés sur les grilles
fournissent leur angle d'inclinaison durant l'action de pêche.
Les travaux réalisés
En Méditerranée
L'IFREMER a participé au projet européen SELMED sur l'étude de la sélectivité de certains
métiers de filets calés méditerranéens et plus spécialement ceux ciblant le merlu et le rouget.
Entre autres résultats, des courbes de sélection ont été établies pour ces espèces en fonction
du maillage et de la hauteur des filets. Un film vidéo a également été réalisé montrant les
modes de capture des différents filets et reprenant le travail réalisé durant le déroulement du
projet.
Le projet européen ESMED avait pour objectif l'évaluation de l'efficacité et de la sélectivité du
chalut standard d'échantillonnage utilisé durant les campagnes MEDITS à travers une série
d'observations vidéo sous- marines et des pêches comparatives entre ce chalut et un chalut
commercial de type italien utilisé pour les campagnes d'évaluation GRUND en Italie. Au cours
des essais en mer, les observations vidéo réalisées à l' aide de l'EROC ont permis de vérifier de
comportement des chaluts. Une double poche en petit maillage à été utilisée pour l'étude de
sélectivité du chalut commercial de référence. De plus, six petites poches additionnelles ont
été fixées à l’extérieur sur la périphérie à l’avant des chaluts dans le but de quantifier les
échappements. Dans l’ensemble, le chalut MEDITS s’est avéré moins efficace que le chalut
italien pour les espèces benthiques mais plus efficace que ce dernier pour les espèces
ANNEX IV
dégagées du fond. Enfin, les poches additionnelles ont montré un échappement significatif
dans la partie basse des faces de côté du chalut MEDITS.
En Atlantique et Mer du Nord
Une série de campagnes SELECT destinées a étudier la sélectivité de la nature et du diamètre
du ou des fils constituant la poche du chalut a été réalisée. La technique des chaluts jumeaux a
été retenue pour ces essais.
Un chalut sélectif équipé d'une grille pour la sauvegarde des juvéniles de lotte à été
développé.
L'objectif du projet SAUPLIMOR était de développer une grille sélective permettant la
sauvegarde, durant le chalutage, de plies et morues de petite taille dans une pêcherie multispecifique. Ce projet a été mis en oeuvre à la demande des professionnels. C'est
principalement la méthodologie employée qu'il apparaît intéressant de développer car elle
pourrait servir de base de réflexion à l'élaboration de futures études de sélectivité en
Méditerranée.
Ce projet, programmé sur deux ans, a été scindé en deux parties.
Durant la première année, différents prototypes ont été testés en bassin d'essais et à la mer
afin de comparer leur efficacité.
Pour cela, une poche additionnelle
du même maillage que celui du cul
Poche additionnelle
du chalut a été fixée au dessus de
l'emplacement
prévu
pour
l'échappement des petits individus
passés à travers la grille. Ainsi la
somme des captures des deux
Cul du chalut
poches était équivalente à la
capture d'un chalut standard sans
Zone couverte
grille (donc à une pêche
par la poche additionnelle
commerciale). Différents types de
grilles ont été comparés pour
lesquels ont varié les positions,
du rapport de recherches collectives "Manual of Methods of
angles
d'inclinaison
et (inspiré
Measuring the Selectivity of Towed Fishing Gears" publié par le CIEM)
espacements
entre
barres.
Plusieurs systèmes de guidage du
poisson vers la grille ont
également été testés.
A l'issue de ces tests, durant la seconde année du projet, les études de sélectivité ont été
réalisées sur le dispositif ayant obtenu les meilleurs résultats et sur le chalut standard sans
grille.
La méthode de la double poche a été employée. Celle-ci, en petit maillage, couvrait la totalité
de la poche du chalut (rallonge et cul). Afin de ne pas obstruer les mailles de la poche du
chalut ainsi que l'échappement du dispositif sélectif pour permettre le passage des poissons,
des cerfs-volants (développés par nos collègues danois du DIFTA ) ont été fixés sur la double
poche, écartant cette dernière de la poche du chalut.
ANNEX IV
6 cerfs volants
Cul du chalut
Grille
2 lests de 15kg
Double poche
De plus, des observations vidéo sous-marines avec le VECOC ont permis de vérifier le bon
fonctionnement du dispositif sélectif ainsi que le comportement du poisson face à ce dernier.
Une grille en aluminium en deux parties de 1.20 x 0.70 m avec un angle d'inclinaison de 45°
et des espacements entre barres de 25mm a ainsi été développée. Elle a permis, au printemps,
la sauvegarde de 35% de plies et 25% de morues de taille non commerciale. A l'automne,
25% de ces plies ont été sauvegardées alors que pour la morue, l'utilisation du dispositif
sélectif n'apparaît pas nécessaire puisque la quasi totalité des individus capturés avait une
taille supérieure à la taille minimale légale.
Avec le projet européen EUROGRID actuellement en cours, dont l'objectif est la mise au
point d'une grille sélective permettant la sauvegarde des gadidés juvéniles en mer du nord et
mers adjacentes, une grille en polyamide est en développement. Sa flexibilité, et son faible
poids sont des atouts importants pour sa manœuvrabilité et la sécurité de l'équipage.
Tout récemment, suite aux décisions européennes sur la sauvegarde de la morue et du merlu,
des essais sur des fenêtres en mailles carrées ont été entrepris.
Toutes ces études mont rent que la sélectivité des engins de pêche est, depuis plusieurs années,
un des axes principaux de recherche pour le service de technologie des pêches de l' IFREMER.
ANNEX V
Selectivity data needed for Mediterranean fish stock assessment
Luis Gil-de-Sola
Instituto Español de Oceanografía, Apdo 285, 29640 Fuengirola, Spain.
[email protected]
As a consequence of the intensive fishing effort in a Mediterranean trawl fishery (Pearse,
19801), especially in its north and western regions with wider continental shelf, a 40 mm
stretched cod end mesh size was recommended by GFCM (6th Session 1973) and
accepted by member countries.
The term selectivity is often used in two different ways. A trawl may be adapted in away
that allows it to catch flatfish (benthonic strictly) more efficiently than hake or red mullet.
This feature of trawl design has sometime been referred to as providing selectivity for the
target species. This preferential rate of capture is dependent on differences in behaviour
or availability of the fish (different species) to the gear.
In its more usual sense the term selectivity refers to the mechanical selection of different
sizes of fish as a consequence of the mesh size in use. Each type of gear has its own
selectivity or selection pattern. For example prawn trawlers catch virtually everything that it
encloses and is therefore unselective. As the other extreme, on the shelf (20-60 m) it
catches only the fish which are just near bottom (0-0,5 m) and they are highly selective
(although they are forbidden and are highly dangerous for the populations of fish).
For trawls there are different methods, which allow one to quantitatively relate the
selectivities of different fish species to different mesh sizes.
The effects of an increase in mesh size can be grouped under two headings: short-term
and long-term effects. In the Mediterranean area there are not an example of both. But, like
a literature related, short-term effect may be a reduction in marketable catches, brought
about because some of the smaller marketable fish, which had previously been retained
by the cod-end, can now escape through the meshes. By how much the catch is reduced
depends upon the extent of the mesh increase and on the abundance of fish in the
selection range. Among the few experiments in the Mediterranean area the
implementation of the minimum legal size has contrasting effects on the landed catch. For
the hake the major part of the catch is below the legal limit (if exist in the country) and has
1
Pearse, P.H., 1980. Regulation of fishing effort with special reference to Mediterranean trawl fisheries.
FAO Fish.Tech.Pap.(41)Rev.1:65 p.
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ANNEX V
not to be discarded. In the case of whiting almost all the catch is of legal size but, being
unmarketable, has to be discarded.
For national fleets the actual mesh size in use is often not known, except that it may well be
greater than the minimum by some margin which safeguards the fishermen from chance
prosecution. In certainly countries with reglamentation it is difficult to quantify what the real
short-term loss would be.
Many fishermen commonly use mesh sizes well in excess of the minimum stipulated.
When the scientists recommending changes in the mesh size, in most cases, assume that
the minimum mesh size is in use. Their calculation of short-term loss is therefore likely to
be an overestimate, but it would be an underestimate if substantial catches were being
taken with undersize meshes, whether taken either with blinded trawls or illegally in smallmeshed fisheries.
The long-term effect, theory says, arises because fish released due to the increase in
mesh size are allowed to growth bigger before being caught. In the Mediterranean there
are not many examples of this.
As there are clearly defined three strata of depth where the whole fleet of the
Mediterranean works, defined three classes of nets that are adapted to those bottoms and
the species objective are. The general stratums are:
•
•
•
A) <160 m
B) 30-250 m
C) >200 m
These strata generate fleet segments that they have an objective clearing:
•
•
•
A) Mullidae, M. Merluccius and Octopus vulgaris
B) M. merluccius and Parapenaeus longirostris
C) Nephrops norvegicus and/or Aristeus antennatus.
With these species like objective, the meshes are very different among if. A ship that he
will fish Norway lobster doesn't use that trawl for the Octopus.
The defined species as of high-priority study for the GFCM are: M. merluccius, Mullus
barbatus, Pagellus erythrinus, Aristeomorpha foliacea, Aristeus antennatus,
Parapenaeus longirostris, Nephrops norvegicus, Eledone spp., Sparidae and T.
trachurus.
The fisherman looks for spawning and growing areas to capture the species and the sizes
that the marked demand. This characteristic is very normal in areas of massive tourist
concentration.
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ANNEX V
Discussion
Therefore in the Mediterranean area they need to be carried out selectivity experiences.
On the other hand also it is necessary to know the following factors:
•
•
•
•
•
•
•
•
•
Length composition of the catch (by country).
CPUE for medium sizes.
Selection factors.
Growth rate of the target species.
Groundfish more prospected and rates (biomass and density)
Proportion of the stock dying each year from causes other than fishing (Natural
mortality).
Proportion caught at age in the international fishery (Fishing mortality).
Discarding
Incidental catches (not only classical endangered species)
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3
ANNEX VI
Résumé des activités de recherche en matière de pêche côtière
Par Ben Naceur Lotfi
1 - Sujets
- L’utilisation de l’acoustique pour la réduction des interaction entre dauphin et filet de pêche.
- Introduction de nouvelles techniques de pêche côtière sélectives et rentables.
II - Termes de références
(7mots) : Interaction, dauphin, acoustique , tube dauphin, set-net, nasses, palangres).
III - Méthodes d’étude
III – 1 - Interactions entre dauphins et filets de pêche :
- Améliorer certaines performances techniques du générateur d’ondes mécaniques .
- Assurer l’utilisation adéquate de cet engin auprès de la profession.
- Sensibiliser les utilisateurs de l’espace marin sur la nécessité de protéger les dauphins.
- Mener une étude exhaustive portant sur l’écologie, l’éthologie et l’abondance des
delphinidés.
- Mener une étude sur le degré et l’impact réel des interactions entre les dauphins et les
pêcheries.
III – 2 - Engins de pêche :
- Mener des actions de pêche pilote avec l’AVFA et l’UTAP pour introduire et vulgariser
certaines techniques japonaises de pêche côtière auprès des professionnels.
IV - Résultats obtenus
IV - 1 - L’utilisation de l’acoustique pour la réduction des interaction entre dauphins et
filets de pêche.
Après avoir assurer l’utilisation adéquate du tube dauphin auprès de la profession et
après les avoir sensibiliser sur le rôle joué par les dauphins dans l’équilibre de l’écosystème
marin et la nécessité de protéger les cétacés, nous avons obtenu les résultats suivants :
* Les ondes acoustiques transmises en profondeur par le tube dauphin sont efficaces en deçà
de 60 à 80 m et peuvent sensiblement varier avec la nature des fonds.
* Les ondes de surface sont limitées entre 800 m et 1000 m à la ronde du lieux de leur
émission et peuvent couvrir parfois des distances allant jusqu'à 1500 m. Les filets placés au
delà de cette zone sont facilement attaqués par les dauphins.
* Bien que les réclamations concernant les dégâts causés aux filets de pêche soient signalées
dans tous les ports de pêche , la région du Nord-Est semble la plus touchée.
* Les unités de la pêche au feu travaillant dans les grandes profondeurs ne semblent pas être
affectées par cette interaction (région de Chebba et Mahdia) ; or pour les unités de la région
Nord - Est opérant au niveau des bancs, cette interaction est encore signalée.
* Les sennes tournantes des unités de la pêche au feu des petits pélagiques sont les plus
affectées par le problème de déchirure des filets de pêche.
ANNEX VI
* Les embarcations de la pêche côtière utilisant les filets trémails ne semblent être affectées
par les déchirures des filets que dans les faibles profondeurs (inférieur à 70 m) et seulement
dans certaines zones de pêche.
* Sur les six espèces de dauphin citées à ce jour par (Ktari-Chakroun.1980 et 1982 ;
Chakroun.1994), trois ont été reconnues comme présentes sur les côtes tunisienne. Le grand
dauphin est à chaque fois facilement identifié par les pêcheurs alors que les deux autres
espèces aussi identifiées ( le dauphin commun et le dauphin bleu et blanc) sont le plus souvent
confondus à cause de leur ressemblance.
* Aucune mention n’a été faite pour le dauphin de risso, signalé par ( Bradaî 2000), ainsi que
sur le globicéphale noir et l’orque signalés par Chakroun en 1994.
IV – 2 - Introduction de nouvelles techniques de pêche côtière.
* Préparation d’une étude technico-économique et impact écologique concernant
l’exploitation d’une pêcherie fixe (set–net) en Tunisie.
* Vulgarisation de certaines techniques de pêches dans la région nord de la Tunisie, notament
la palangre verticale et les nasses à poissons et crustacés.
IV - Impact des résultats obtenus
La réduction des effets des interactions entre dauphins et filets de pêche a permis de
réduire les dégâts causés aux filets de pêche, d’augmenter la production et d’honorer
l’engagement de la Tunisie pour la protection de ces mammifères marins.
L’introduction de la pêcherie fixe (set-net) en Tunisie permet de protéger le littoral des
incursions des chalutiers dans les faible s profondeurs, de protéger la faune et la flore marine
contre la pêche a outrance non sélective et de fournir au marché Tunisien une nouvelle
gamme de produit à haute valeur commerciale (poisson vendu dans des aquariums).
ANNEX VII
COPEMED
Workshop on Gear Selectivity Research
Kerkennah 9-11 October 2001
Selectivity Analysis
by
René Holst
ConStat
[email protected]
Abstract
The presentation was originally planned to focus on practical exercises with data from previous
experiments. This was however changed, due to a last-minute change of the agenda whereby this
item was reduced from a full day to a three-hours presentation.
The speach aimed at providing an overview over central statistical aspects related to gear selectivity
research. The main topics were:
• Planning
• Modelling
• Analysis
In addition to this the specific problems related to small catches with multiple species were
addressed
Planning
A number of different aspects relating to the planning of gear-selectivity experiments were
mentioned:
• Identification of the problem
• Design of the gear
• Scaling of the experiment
o Sub-sampling
o Number of hauls
• Experimental plan
• Sampling protocol
o Variables to record
o Exchange format
o Operational scheme
It was emphasized that proper planning is essential for obtaining valid data. Valid data means data
that can be used for getting answers to the questions tha t the experiments address.
Modelling
General definitions of models, mathematical models and statistical models were used as an
introduction to the more specific modelling of data from gear selectivity experiments. This served
ANNEX VII
the purpose of making a dis tinction between models that reflect the mechanisms by which the data
have been generated and pseudo- models that merely involve curve- fitting and mathematical
convenience.
Statistical modelling of gear-selectivity experiments has reached a well-defined state within the
ICES community during the past 10 years. The main components are the SELECT model and
Fryer’s model of between-haul variation. The SELECT model is a general model that enables
estimating the selectivity from indirect experiments with fishing gear, including towed gears, with
two or more compartments (trouser trawl, twin-trawl, covered codend, trawls with grids etc) and
passive gears (gillnets, trammel nets, pots, traps, hooks etc.). This model handles however only
individual hauls (or sets) and gives no guidance concerning aggregation of multiple hauls within an
experiment. Fryer’s model of between-haul variation was constructed for this purpose and separates
the within- haul variation from the between-haul variation. This provides much more realistic
confidence intervals and tests for differences between gear types.
Analysis
A few examples of analysing data from gear selectivity experiments were demonstrated. It was
shown how the choice of the selectivity curve could affect the goodness of fit. This did also include
inspection of the residuals.
Small Catches – Multiple Species
It is well-known that the Mediterranean fishery is characterised by small catches and a multitude of
different species. This can impede the estimation of the selectivity using the models described so
far. These problems were addressed with a few suggestions including:
• Pooling of species with similar morphology.
This solution could be justified by Baranov’s principle of geometrical similarity, which
states that the selectivity only depends on the geometry of the fish relative to that of the
mesh. It is anticipated to cause some over-dispersion.
• Bootstrapping techniques.
A relatively new technique, that has gained much attention for sparse data. The approach
can be adapted to accommodated both between-haul variation and within haul variation. A
general stepwise scheme was outlined.
• Pooling of adjacent length-classes.
The purpose of pooling adjacent length classes is obviously to reduce the number of length
group and increase the number of observations in each of these. This can possibly facilitate
the estimation although it is also likely to cause an increased variance.