Spatial distribution pattern of European hake, &lt;em&gt;Merluccius merluccius&lt;/em&gt; (Pisces: Merlucciidae), in the Mediterranean Sea

Letizia Sión ,Chiara Manfredi,Ioannis Thasitis,Francesca Capezzuto,Roberto Carlucci,Angélique Jadaud,Giuseppe Lembo,Zdravko Ikica,George Tserpes,Crescenza Calculli,Isabella Bitetto,Antonio Esteban,José Luis Pérez,Alessandro Ligas,Pierluigi Carbonara,Walter Zupa,Manuel Hidalgo,Cristina Porcu,Panagiota Peristeraki,Germana Garofalo,Beatríz Guijarro ,Maria Cristina Follesa ,Eugenia Lefkaditou ,Igor Isajlović

doi:10.3989/scimar.04988.12a

Abstract

The present study provides updated information on the occurrence, abundance and biomass distribution patterns and length frequencies of Merluccius merluccius in the Mediterranean Sea, by analysing a time series of data from the Mediterranean International Trawl Surveys (MEDITS) from 1994 to 2015. The highest values of abundance and biomass were observed in the Sardinian Seas. The use of a generalized additive model, in which standardized biomass indices (kg km–2) were analysed as a function of environmental variables, explained how ecological factors could affect the spatio-temporal distribution of European hake biomass in the basin. High biomass levels predicted by the model were observed especially at 200 m depth and between 14°C and 18°C, highlighting the preference of the species for colder waters. A strong reduction of biomass was observed since the year 2009, probably due to the strengthening of the seasonal thermocline that had greatly reduced the availability of food. The general decrease in biomass of several stocks of anchovy and sardine, preys of European hake, might be indirectly connected to the decreasing biomass detected in the present study. The length analysis shows median values lower than 200 mm total length of most of the investigated areas.

Highlights

Multispecies fisheries targeting a large number of species represent a management challenge because several biological and ecological parameters must be incorporated in the assessment (Ekerhovd and Steinshamn 2016). This is the case of the Mediterranean fisheries, where the commercial catches are characterized by a high number of target species, among which the most ecologically and economically important one is the European hake, Merluccius merluccius (Linnaeus, 1758) (Orsi Relini et al 2002)
A total of 1880472 M. merluccius individuals were caught in 18470 hauls of the 23748 valid hauls (F=77.8%) carried out in the overall depth range (10–800 m) during the Mediterranean International Trawl Surveys (MEDITS) surveys (1994- 2015) (Table 2)
Table 2. – Number of MEDITS surveys carried out in the period 1994-2015 and total number of positive hauls, depth range (m), frequency of occurrence (F, %), maximum abundance (N km-2) and biomass indices of M. merluccius for each geographical sub-areas (GSAs) involved in the analysis

Summary

Introduction

Multispecies fisheries targeting a large number of species represent a management challenge because several biological and ecological parameters must be incorporated in the assessment (Ekerhovd and Steinshamn 2016) This is the case of the Mediterranean fisheries, where the commercial catches are characterized by a high number of target species, among which the most ecologically and economically important one is the European hake, Merluccius merluccius (Linnaeus, 1758) (Orsi Relini et al 2002). The European hake has always been an important food resource for the population of western Europe throughout history It is caught in mixed fisheries along with blue whiting, megrim, monkfish, shortfin squid, Norway lobster and deep-water rose shrimp by a multirigged fleet. This demersal species is one of the most important commercial resources for trawl and small-scale fisheries (fixed gillnets, bottom longlines) in the Mediterranean basin (STECF 2015). Trawlers mainly catch specimens below 30 cm total length, whereas bottom longlines and gillnets target adults (Sbrana et al 2007)

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Discussion

Conclusion