Abstract
The main characteristics concerning distribution, size structure and total mortality of two of the most important decapod crustaceans of commercial interest in the Mediterranean Sea, Nephrops norvegicus and Parapenaeus longirostris, are studied along the European Mediterranean coasts. The study is based on data collected during a series of six trawl surveys performed in spring from 1994 to 1999 from the Gibraltar Straits to the Aegean Sea. The population size structure identified in the different geographical sectors is analysed taking into account two bathymetric sectors: continental shelf and upper slope. Differences in N. norvegicus population demographic structure among geographical sectors, as well as in total mortality, appear to be highly related to different exploitation levels. Size structure in P. longirostris also shows a great heterogeneity throughout the different geographical sectors. Considering that both species are heavily exploited all along the studied area, the observed differences can be interpreted as different responses to exploitation related to the widely differing life history characteristics of the mentioned species. In fact, N. norvegicus is a long-lived, benthic, burrowing species with low growth and mortality rates, and P. longirostris an epibenthic short-lived species characterised by higher rates of growth and mortality.
Highlights
The Norway lobster Nephrops norvegicus and the deep-water pink shrimp Parapenaeus longirostris are two of the main target species of the commercial fisheries in the Mediterranean continental shelf and upper slope and have been the subject of important biological and fishery studies (e.g.Ardizzone et al, 1990; Maynou and Sardà, 1997; Maynou et al, 1996; Sardà, 1995, 1998a,b; Sardà and Lleonart, 1993; Tom et al 1988; Tursi et al., 1998)
The population size structure identified in the different geographical sectors is analysed taking into account two bathymetric sectors: continental shelf and upper slope
Size structure in P. longirostris shows a great heterogeneity throughout the different geographical sectors
Summary
The Norway lobster Nephrops norvegicus and the deep-water pink shrimp Parapenaeus longirostris are two of the main target species of the commercial fisheries in the Mediterranean continental shelf and upper slope and have been the subject of important biological and fishery studies (e.g. Ardizzone et al, 1990; Maynou and Sardà, 1997; Maynou et al, 1996; Sardà, 1995, 1998a,b; Sardà and Lleonart, 1993; Tom et al 1988; Tursi et al., 1998). The spatial component seems to have an important role in the definition of the species population structure This is known to take place between different regions throughout their distribution area (Karlovac, 1953; Chapman and Howard, 1988; Tully and Hillis, 1995; Tuck et al, 1997). Patchiness in population structure characteristics has been detected and appears to be related with heterogeneity in the characteristics of the sediment as well as with variations in fishing effort (Fariña et al, 1994; Tully and Hillis, 1995; Maynou et al, 1996)
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