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Impact of fishery and environment on hake recruitement in Northwestern Mediterranean.

Objective

The aim of this project is to study the relationships between the recruitment process of European hake (Merluccius merluccius) and its fisheries in the NW Mediterranean.

The project focuses on the recruitment processes of European hake in NW Mediterranean. This project is to be executed in the three-year period 1998-2000. The study is being carried out by means of sampling larvae and juveniles (together with environmental parameters) in various areas off the Tyrrhenian and Ligurian Seas, gulf of Lions and Catalan waters. The reproductive process and fecundity is analysed. Historical data analysis is also envisaged.

The official starting date of this project is January 1st 1998. Hence, it is not possible to present results at the moment. Nevertheless a summary of objectives and tasks and subtasks are exposed.

The geographical scope of the project embraces (see chart) the North Tyrrhenian Sea, Ligurian Sea, Gulf of Lions and Catalonia.
The European hake (Merluccius merluccius) is the most important demersal species (in catch as well as in revenue) in the NW Mediterranean. Its fisheries and population dynamics have been studied by several research teams in the area (see bibliography). This fishery is supported by small immature individuals (mainly ages 0 and 1) caught by trawl. There also exist some minor gears, such as longline or gillnet, which catch aged and sexually mature individuals (3+). A heavy growth overfishing has been demonstrated for this fishery. Higher catches could be obtained if the effort would be reduced or the mesh size enlarged. Hence a selectivity increase (i.e. transferring effort from trawl to other gears) has been suggested in order to improve the yield. Nevertheless there is a danger of recruitment overexploitation if the spawning stock, not available to the trawl at the moment, would become a significant target of the fishermen.
These considerations have lead the researches involved in the project to study in deep the processes of hake recruitment. This study includes all phases of the process (fecundity and reproduction, ichthyoplankton, settlement and ecology of juveniles) and different approaches to the problem: historical data analysis (including environmental series, fisheries statistics and scientific sampling), and sampling environmental parameters and larvae and juveniles by means of scientific cruises.

OBJECTIVES

The main objective of this proposal is to study the relationships between the recruitment process of European hake (Merluccius merluccius) and its fishery in the NW Mediterranean.
This objective is itemised as follows:
1. To analyse the effects of the young hake fishery on the demersal community. This includes the effect of fishing on the demersal communities and the geographic allocation of the fishing effort.
2. Study of the hake recruitment processes. Spatial distribution of eggs and larvae. Settlement process. Juveniles and larval growth and ecology.
3. To analyse the impact of the fishery on the spawning stock.

METHODOLOGY

Tasks and sub-tasks

Task 1.- To analyse the effects of the young hake fishery on the demersal community
Sub-task 1.1.- Definition of ecosystem descriptors among areas with different levels of fishing exploitation (diversity, community structure, size spectrum, biomass distribution).
Sub-task 1.2.- Description of the distribution of fishing effort related to size spectrum of young hake in different areas.
Sub-task 1.3.- Improvement of methodologies for estimation of the spatio-temporal distribution and abundance of the young hake: patchiness and nursery areas.
Sub-task 1.4.- Fishing impact during last decade. Evolution of the fishing effort on juveniles.
Task 2.- Study of hake recruitment processes.
Sub-task 2.1.- Study of the spatio-temporal variations in the trophic relationships of hake: feeding and possible predators.
Sub-task 2.2.- Relationships between the distribution of juveniles and their benthopelagic food resources.
Sub-task 2.3.- Estimation of growth parameters of juveniles and larvae.
Sub-task 2.4.- Determination of the abiotic factors that induced growth, aggregation and recruitment fluctuations.
Sub-task 2.5.- Study of the spatial distribution patterns of eggs and larvae.
Sub-task 2.6.- Analyses of historical environmental data related to hake recruitment.
Task 3.- To analyse the impact of the fishery on the spawning stock.
Sub-task 3.1.- Quantitative size spectrum caught by different gears. Effect on reproductive potential of adult population.
Sub-task 3.2.- Determination of the spawning cycle. Length at first maturity. Estimation of peaks of maturity periods. Fecundity.

Overview on the sample cruise methodology

In the attached map the areas to be covered by the sampling cruises are represented. There are two main areas i.e. Spanish coast (Catalonia) and Italian coast (Ligurian and North Tyrrhenian). These two sampling areas are characterised by different ecological conditions and the hake nursery areas in them extend from 50 to 300 m depth. For this reason juvenile (and ichthyoplankton) sampling schemes will be designed with stations distributed according to geomorphological conditions, environmental characteristics and depth of each area. In order to know the relationship between topography and recruitment processes, areas of different geomorphological features have been chosen: the Catalan coast, the Tuscany Archipelago (North Tyrrhenian) and the Ligurian coast. One of these areas, e.g. the Catalan coast, presents two main topographical features, viz., a very wide continental shelf, in its southern part, and a narrow shelf in its northern part. Whilst each of the other two areas present only one of those features, in the Tuscany Archipelago, the continental shelf is wider than that of the Ligurian Sea. This different geomorphology could be helpful in understanding differences, if any, in settlement and recruitment patterns. From a fisheries point of view, the areas chosen are characterised by different exploitation levels. The areas featuring wide shelves have an homogeneous effort distribution from 50 to 200 m, while in areas of narrow shelf, the effort is concentrated deeper than 100 m. On the other hand, the sampling strategy will include experimental fishing shallower than 50 m, on the basis that these depths are little affected by fishing. The comparison of these three scenarios will contribute to clarify the ecological and fisheries mechanisms at work during recruitment of juvenile hake.

Map of the study area with location of the sampling zones where juvenile research cruises will be done

(For the map contact the Coordinator)

The Catalan zone is disjoint regarding the juvenile sampling cruises, whilst for the ichthyoplankton sampling purposes the area to be covered includes also the central zone.
Samples for fecundity estimates and adult fisheries will be taken in the same areas. This sampling schedule will allow us to understand the mechanism(s) involved in recruitment and especially, why hake is heavily concentrated in particular areas. For other purposes, like analyses of historical data and definition of present exploitation level of juveniles the Gulf of Lions area will also be considered.

BIBLIOGRAPHY

Aldebert, Y. & L. Recasens. 1996. Comparison of methods for stock assessment of European hake Merluccius merluccius in the Gulf of Lions (Northwestern Mediterranean). Aquat. Living Resour., 9: 13-22.
Aldebert, Y., L. Recasens & J. Lleonart. 1993. Analysis of gear interactions in a hake fishery: the case of the gulf of Lyons. Northwestern Mediterranean Fisheries, Sci.Mar., 57(2-3):207-217.
Biagi, F. Cesarini A., Sbrana M. & Viva C. 1995 - Reproductive biology and fecundity of Merluccius merluccius (L., 1758). Rapp. Comm. int. Mer Medit., 34: 237.
Bozzano, A., L. Recasens & P. Sartor. 1997. Diet of the European hake Merluccius merluccius (Pisces: Merlucciidae) in the western Mediterranean (Gulf of Lions). Scientia Marina (in press).
Cesarini, A. 1994. Biologia riproduttiva e fecondita di Merluccius merluccius (Linneo, 1758) nel mar Tirreno Settentrionale. Tesi di laurea. Universita'degli studi di Pisa, 136 pp.
Morales-Nin, B. & Y. Aldebert. 1997. Assessment of growth and hatchdate distribution of juvenile Merluccius merluccius in the Gulf of Lions (NW Mediterranean) determined by otolith microstructure and length frequency distribution. Fisheries Research, (in press).
Oliver, P.- 1991. Dinamica de la poblacion de merluza (Merluccius merluccius L.) de Mallorca (reclutamiento, crecimiento y mortalidad). Ph.D. Thesis, Univ. Balearic Islands, 392 pp.
Oliver, P.- 1993. Analysis of fluctuation observed in the trawl fleet landings of the Balearic Islands. Northwestern Mediterranean Fisheries, Sci.Mar., 57(2-3): 219-227
Oliver, P. and E. Massuti. 1995. Biology and fisheries of western Mediterranean hake (M. merluccius). In: Hake. Fisheries, ecology and markets. J.Alheit and T.J. Pitcher eds. Chapman and Hall. Fish and Fisheries Series 15. pp. 181-202.
Orsi-Relini, L., M. Cappanera & F. Fiorentino. 1989. Spatial-temporal distribution and growth of Merluccius merluccius recruits in the Ligurian Sea. Observations on the 0 group. Cybium, 13 (3): 263-270.
Orsi-Relini, L., F. Fiorentino & M. Cappanera. 1986. The timing of recruitment of Merluccius merluccius in the Ligurian Sea. Rapp. Comm. int. Mer Medit., 30 (2): 224.
Recasens, L. 1992. Dinamica de poblacions i pesqueria del lluc (Merluccius merluccius) al golf de Lleo i la mar Catalana. Ph. D. Thesis. Univ. Barcelona. 398 pp.
Sarano, F. 1983. La reproduction du merlu Merluccius merluccius (L.): Cycle ovarien et fecondite. Cycle sexuel de la population du golfe de Gascogne. Ph.D. Thesis. Universite de Poitiers, 168 pp.
Sarano, F. 1984. Cycle ovaryen du merlu, Merluccius merluccius, poisson a ponte fractionee. Revue Travaux Institut Peches Maritimes, 48 (1-2): 65-76.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
Address
S/n,passeig Joan De Borbo S/n
08039 Barcelona
Spain

Participants (4)

Consejo Superior de Investigaciones Cientificas
Spain
Address
Km 7.5,Carretera Valldemossa Km 7,5
07071 Palma De Mallorca
Consorzio per il Centro Interuniversitario di Biologia Marina ed Ecologia Applicada
Italy
Address
Piazzale Mascagni, 1
57127 Livorno
IFREMER
France
Address
1, Rue Jean Vilar
34200 Sete
Universita degli Studi di Genova
Italy
Address
Via Balbi, 5
16126 Genova