Nantes, the 3^rd – 5^th November 1999

The Medits group met in Nantes (France) at the Ifremer Centre, the 3^rd to 5^th of November 1999. This meeting was preceded by a Medits steering committee the 3rd November 1999. This report presents the conclusions of the two above-mentioned meetings.

The following scientists have taken part in the general meeting:

Alvaro Abella, Italy

Pere Abello, Spain

Gianni Ardizzone, Italy

Andrea Belluscio, Italy

Jacques Bertrand, France (chairman)

Giulio Cosimi, Italy

Laura Di Turi, Italy

Pierre-Yves Dremiere, France

Eduardo Ferrandis, Spain

Fabio Fiorentino, Italy

Jean-Claude Gaertner, France

Luis Gil de Sola, Spain

María Gonzàlez, Spain

Pilar Hernandez, Spain

Angélique Jadaud, France

Stjepan Jukic, Croatia

Argyris Kallianotis, Greece

Eugenia Lefkaditou, Greece

Giuseppe Lembo, Italy

Iole Leonori, Italy

Porzia Maiorano, Italy

Alessandro Mannini, Italy

Chiara Marano, Italy

Matteo Murenu, Italy

Michele Panza, Italy

Costas Papaconstantinou, Greece

Panagiota Peristeraki, Greece

Corrado Piccinetti, Italy

Gabriela Piccinetti Manfrin, Italy

Chrissi-Yianna Politou, Greece

Sergio Ragonese, Italy

Giulio Relini, Italy

Javier Rey, Spain

Paola Rinelli, Italy

Marie-Joelle Rochet, France

Marco Rossi, Italy

A. Slimani, Maroc

Kosmas Sophronidis, Greece

Arnauld Souplet, France

Maria Teresa Spedicato, Italy

Ali Srairi, Maroc

George Tserpes, Greece

Angelo Tursi, Italy

Nicola Ungaro, Italy

Paulos Vidoris, Greece

Alessandro Voliani, Italy

Loïc Antoine, Ifremer, Director, Fishery research Department (part time)

The chairman has opened the meeting welcoming the participants, especially the new partners from Morocco. He made the apologies for some colleagues, particularly from Albania and Slovenia, who intended to participate but were unable to join the meeting.

The Medits '99 survey has been carried out applying the same general schedule as the one used for the previous surveys. Nevertheless, the following modifications have been introduced. The survey has been enlarged to cover the Mediterranean Moroccan coast, thanks to the contribution of our Moroccan colleagues and Copemed's support. The survey has been disrupted in the Adriatic due to the conflict in the Balkan area: postponement in some areas and cancelling along the Croatian coast, despite very strong efforts done by our colleagues to maintain the series. In some areas, bad weather conditions have also disrupted the survey. Nevertheless, a total of 1139 hauls have been carried out.

Applying the same process as the one chosen during the previous meetings, the analysis of the survey results has been managed during the meeting by three working groups respectively in charge of fish (Co-ordinator: N. Ungaro), crustaceans (Co-ordinator: M.T. Spedicato), and cephalopods (Co-ordinator: E. Lefkaditou). Each group has written comments on (i) the results of the Medits '99 survey, and (ii) the variation observed from 1994 to 1999. The analyses were done from abundance (biomass and density) indices and length distribution. Length distributions have been studied for the main Medits areas, and two bathymetric zones (10-200 m & 200-800 m). To make easier the comparisons, length distributions have been characterised by using three parameters: mean, mode and median class. All the analyses were basically conducted by species.

Each of the working groups was provided with tables and figures presenting the different indices usually used to prepare the Medits annual reports and bottom temperature recorded during the hauls. Furthermore, the basic Medits data were available to each of the groups who were able to elaborate them as they wished to complete their analyses. The reports done by these working groups will be included in the final Medits '99 report.

A project has been presented to the 1999 CFP call for proposals for continuing the Medits surveys in 2000 and 2001, and enlarging them to the Malta area (Co-ordinator: A. Souplet). The EC-DGXIV has expressed its wish to support the survey in 2000, but no one in 2001. The EC-DGXIV intends to incite the group in developing data analyses during 2001. The Steering committee has decided to react by modifying the proposal, in the way of the Commission's request, cancelling the survey 2001 and introducing analyses focused on nursery areas and characterisation of homogenous fishery areas from the Medits data. These works will be mainly based on cluster and multi-table analyses, as well as GIS tools. Furthermore, the Co-ordination committee has been commissioned to send to the Commission a message drawing the attention on the negative consequences that imply the decision to cut in on the series.

The Medits group was informed of a new project (SAMED project) co-ordinated by G. Lembo. This project will be supported by the EC-CFP in 2000 and 2001. The aim of this project is:

• Re-classification of the Medits data-base, taking into account the new sub-divisions in macroareas adopted by the Scientific Advisory Committee of FAO-GFCM;
• Characterisation of the above mentioned macroareas as concerns abundance indices, length frequency distributions, sex pattern, and multispecies size spectra as an indicator of fishing mortality;
• Estimation of the demographic parameters and prediction by analytical model (e.g. Thompson and Bell, as in the Sanders' approach);
• Estimation of demographic parameters and production under non equilibrium approach.

This project will involve scientists from Italy, Spain, France and Greece.

To favour emergence of new approaches in the characterisation of bottom resources in the Mediterranean, different suggestions have been made available to the group. M.J. Rochet has presented some perspectives for the analysis of survey data in a fishery ecology context. Her presentation was devoted to three main approaches: multispecific size spectra, analysis of variability of age and length at maturity, and potential use of life history traits as indicators of population variability (cf. appendix 2.2.1). A. Abella proposed a combination of indirect and direct methods for assessment of multispecies resources. An incitement to develop trophic studies was suggested by J. Rey (cf. appendix 2.2.2). Finally, the group will take benefit of the reflection developed in the Italian group on statistical methodology (GRUND programme) (cf. the proposal by G. Lembo in appendix 2.2.3).

From a proposal made by P. Abello, the Medits group has decided to engage the realization of a special volume to be published in Scientia Marina. It is foreseen that the volume will be made in three parts.

• An introductory part will be dedicated to a general presentation of the Medits programme, including some general biological results as well as most recent knowledge concerning the sampling gear.
• The second part will be devoted to a monograph of the most important groups of bottom species studied during the Medits survey. In this part, the information should be presented taking into account the whole Medits area at least. The main topics of each chapter would be the same and the authors of each chapter would have at their disposal the same basic information from the Medits surveys (tables on biomass indices, length distribution, figures, etc.). Nevertheless, the authors will be free to adapt their presentation taking into account this information and the available bibliography, as well as the characteristics of the studied species (or group of species). The distribution of the tasks for this part will be managed from the schedule defined below.

Å coordinator of the group working on a species or more

• The third part will be devoted to "independent" papers. Nevertheless, advisability of request for papers on specific topics (eg applying new methods and technologies to characterise the dynamics of the species and their relationship with environment, ecosystemic approaches, etc.) is in debate.

In both cases, the terms of reference will have to strictly respect the Scientia Marina's Instructions for authors. Their final acceptance will be established through the Scientia Marina's evaluation procedure.

The project will be managed by the Medits Co-ordination committee and P. Abello. P. Abello will be the contact person with Scientia Marina.

The present proposal will be submitted to the Scientia Marina's Editor in chief.

The chairman of the GFCM-SAC (J. Camiñas) has requested the Medits team to contribute in the next SAC-Demersal working group (Sète, 21-23 March 2000). Actually, the GFCM shows consideration towards the status of juveniles in the Mediterranean (cf. inset below).

The Medits co-ordination team intends to answer this request by (i) preparing an updated version of the paper entitled "Distribution of juveniles of some demersal species in the Northern Mediterranean", presented as working paper at the GFCM-SAC-SCSA (7-10 June 1999, Rome, Italy), and (ii) inciting scientists involved in the Medits programme to prepare papers according to the terms of reference of the foreseen Sète meeting. To favour the presentation of those papers by their authors, the Medits co-ordinators will try to pay the travel of these scientists through the Medits programme. This approach implies that the terms of reference of this meeting will be available soon. The Medits Co-ordinator was commissioned to ask them to the Stock Assessment Sub Committee Co-ordinator (J. Lleonart).

From an analysis of trawl depth trajectory in one region, P.Y. Dremière indicated different factors which could explain the variability obtained when driving the gear. Furthermore, he drew the attention on the fact that, in shallow waters, the submersion level of the sounder transducer is not always taken into account on board, when giving the water depth; in the deepest waters, the distance between the vessel and the trawl could explain some variations, mostly in case of a sharp slope. He also highlighted that, in deep waters: (i) the long time of net descending motion can be connected with the very low density differential between the net material and the sea water; (ii) the long time between the end of haul (beginning of handling) and gear takeoff mainly corresponds to taking-up of warp slack, even the net then stopped and not fishing because not really towed itself on the bottom at that stage.

From these considerations, it was strongly suggested to use, as often as possible, devices like Scanmar, and the following recommendations have been explained. (i) All the teams were incited to analyse the data already obtained from their sensor with the objective to assess the effective motion of the gear in their own area. They should take advantage in discussing the results with the captain of their vessel. (ii) This work should be extended to a sensitivity analysis of the effect of swept area estimate on abundance indices. (iii) During the next survey, a particular attention should be done to strictly respect the procedure described in the Medits handbook concerning the gear motion. (iv) In the future, sampling and/or analysis protocols could be improved taking into account the results obtained from the previous items.

The following short agenda has been established.

1. Transmission of the regional technical reports Medits ‘99 (SCM>GC) 30/11/1999

1. Transmission of the regional biological report Medits ‘99 (SCM>GC) 30/11/1999

1. Final report (project) (GC>SCM) January 2000

1. Medits 2000 survey May-July 2000

1. General meeting, Italy (place to be proposed by the Italian partners) November 2000

1. Symposium in Malaga, Spain (proposal from Spain) End of 2001

SCM: Steering committee member; GC: General co-ordinator

The Co-ordinator thanked all the participants for their strong and very helpful contribution to the meeting as well as for the work done all during the first six years of the Medits programme. He explained his satisfaction of having co-ordinate the so kind Medits group during these six years. He presented his best wishes to Arnauld Souplet for continuing the co-ordination of the programme. As the elder member of the group, Giulio Relini warmly thanked Jacques Bertrand for the work done during this period and expressed his wish for the continuation of collaboration in the future. He welcomed Arnauld Souplet in his new job.

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By Marie-Joëlle Rochet (IFREMER, Nantes, France)

1. Multispecific size spectra: an index of ecosystem exploitation on a large spatial scale?

Multispecies size spectra are constructed from scientific trawl surveys by combining the length distributions of all fish species caught. Over large ecosystems, there is considerable regularity and stability of the numbers at length in each year. Examination of size spectra from various ecosystems has shown that log numbers per size class are often linearly related to log size of fish. It has been suggested that the slope of this relationship might depend on fishing intensity. Therefore the slope of size spectra has been recommended as an index of fishing effects on exploited communities.

Two questions were examined: i) why should size spectra of fish communities be linear? ii) should fishing change the slope of the size spectrum or change its shape, towards a convex relationship? Following previous time-dependent models of energy flux in the pelagic ecosystem, we accept that size spectra may be linear because the main processes that govern energy transfer from smaller to larger particles, growth, predation and loss, are allometric (power functions of body size). However, exploited communities suffer additional loss due to fishing, therefore their size spectra should not be linear. Standardized sampling collection and data analysis methods are needed to allow to test this hypothesis.

2. Analysis of the variability of age and length at maturity in time and space: causes and consequences.

Spatial and temporal variations in age and length at maturity in four species of North Sea Gadoids were analysed. The data were extracted from the International Bottom Trawl Survey data, for 1983-1995 cohorts in 9 round-fish areas of the North Sea. An analysis of variance shows that there are significant spatial and temporal effects on age and length at maturity in cod and haddock, with no interaction. The factors potentially determining these patterns were investigated among temperature, salinity, stock abundance, individual growth and fishing mortality. Temperature was the only factor with consistent effects among the four stocks examined: low temperatures induce a later maturity. In addition, in cod a faster growth is associated with earlier maturity. Taking into account spatial and temporal variability of age at maturity leads to different (usually lower) estimates of the spawning stock biomass.

3. Potential use of life history traits as indicators of population viability: importance in fisheries with poor or no catch statistics.

There is increasing knowledge that fishing affects life history traits in flatfish and other teleosts. Fish compensate for fishing mortality by faster growth, earlier maturity and increased fecundity. Concern has been raised that the widely used spawning biomass might not be a sensitive index of the reproductive potential of exploited populations. Indices incorporating parameters such as fecundity or egg viability should improve stock projections. A good index of population sustainability is Lotka's intrinsic population growth rate r, because it incorporates all vital rates involved in population growth. However, monitoring such an index would be costly, because it requires annual estimates of age-specific survival and fecundity rates, including juvenile survival. An alternative approach would be to monitor vital rates that both are affected by fishing and have a high contribution to the population growth rate. Traits meeting both criteria were investigated among age at maturity, fecundity and growth by a retrospective sensitivity analysis in the framework of matrix population models.

This approach was used for comparing vital rates and population growth rates of flatfish populations between periods characterized by different fishing pressures.

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by Javier Rey and Luis Gil de Sola (Instituto Oceanografico de Málaga)

The trophic ecology of fish is clearly a central issue for many aquatic habitats and it assumes particular importance in systems where fish play a central role in determining community structure (Hall et al., 1995) The stomach content data are the most obvious source of information. The feeding ecology of fish shows how changes in predator density are likely to have important consequences for prey abundance. In dermersal systems most fishes have not a migratory behaviour so interrelations between predators and prey population densities are much closer. Fishery has an enormous influence on demersal populations from what we can consider it as a non selective predator also liable to suffer these community changes.

A large scale stomach-sampling programme also provide high quality information on the diet of predatory species in a form suitable for the testing and development of multispecies assessment models even of virtual population analyses (ICES, 1991).

After six years performing Medits surveys in the Mediterranean most of initial goals have been reached. With such data collection and results we have a strong base to propose new scientific and technical possibilities.

In some Mediterranean areas trophic research have been achieved in the last twenty years (Macpherson, 1977, 1980; Bello, 1990, 1991; Carrassón, 1994; Sartor, 1995; Bozzano et al., 1997) but most of them lacks of continuity on time and are reduced to a small area.

Medits experience should be used to support another common projects (first a working group) so we present the proposal "Stomach Contains Analysis in Fishes for the Medits Area" as a new research level for the Mediterranean work team.

MATERIAL AND METHODS

In the last spanish Medits survey (May 1999) stomach sampling and analysis on board have been carried out. In this first experience hake and some chondrichthyans have been selected because of the size of it preys. A total of 853 stomachs were analysed (table 1). Preys had been determined to the lowest taxonomic level when possible. Each species is counted and mesured (in mm) as well as expressed as a proportion (%) of the whole stomach content (cc). A volumetric method is used on board measuring each content with a trofometer (Olaso, 1990). Data were computed in a dBase program designed by the Santander trophic team who are working in the Cantabric Sea with the ICES group for ten years (Velasco, 1998).

Table 1. Number of stomachs analysed in the Medits-ES 9905 survey.

REFERENCES

A meeting was held in Messina the 28-30 October 1999, on the Multispecies approach for the stock assessment in the Mediterranean.

The guest speaker was Jorge Csirke that is actually the chief of the Marine Resources Service of the FAO.

We discussed about the contribution of direct and indirect methods to the assessment and management of multispecies resources in the Mediterranean context, on the basis of the Italian experience. Considering the difficulties in accounting for the biological interactions, such as prey-predator or competitors relationships, the discussion was mainly focused on the technical interactions, such as those related to the effects of a gear on different species. This way presents a higher level of feasibility also because the standard models can be applied.

The yield per recruit equation for one species was considered, in the discussion, as the first step of the analyses, that could be expanded to several species, by summing the different yields per recruit. This approach has the advantage of using well known methods of analysis, while the disadvantage consists in the equilibrium assumption. Moreover, the yield per recruit equations can easily be transformed into age-structured dynamic equations such as those of Thompson and Bell. This kind of model can be used for dynamic forward projections and for simulating various scenarios derived by different management options, such as change of mesh size and/or fishing ban.

During the meeting the role of information coming from the direct and indirect methods was also discussed, and the importance of a complementary approach was underlined.

A preliminary model was prepared for the meeting to allow simulations and evaluation within the working groups. This model was designed to combine information coming from trawl surveys (such as age structure) and from indirect approach (such as effort estimates).

The discussion gave useful suggestions for further improvements of the model that will be ready, in a preliminary release, within the next April. We hope it will be possible to have an occasion to discuss about it among the colleagues of Medits in order to receive further suggestions and comments.

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