Abstract
SUMMARY: In the Strait of Sicily, red mullet (Mullus barbatus L. 1758) is one of the most important resources for the bottom trawlers exploiting the shelf fishing grounds. At present, the younger age groups (groups 0-1) represent most of the catches. In order to give more effective advice for fisheries management in the area, this paper is aimed at further investigating the stock-recruitment relationship for red mullet by including environmental information. Indices of the mean abundance of red mullet older than 1 year (spawners) and younger (recruits) were obtained from autumn trawl survey samples by analyzing the length-frequency distributions. Sea surface temperature (SST), expressed as the average monthly anomalies over the period from May to September (referring to 1961-90 climatology), was considered as a proxy for oceanographic processes affecting recruitment. An exploratory analysis was performed using three stock-recruitment relationships (Cushing, Ricker and Beverton-Holt), with and without the effect of SST. The best fit (R 2 =0.80) was obtained with a Ricker modified curve (lnR = ln(70.17113) + lnS ‐ 0.063812S + 0.060544(S · E)), including SST anomalies in July and August as a masking factor. Results showed that, for a given spawning stock level, higher recruitment levels corresponded to warmer than average SST in early life stages.
Highlights
It is widely recognized that Mediterranean demersal fisheries exploiting several species use various types of gear, but mainly prefer small mesh size trawling (Caddy, 1990; Farrugio and Papaconstantinou, 1998)
The maps show the relative densities of both spring spawners and autumn recruits, and reveal two distinct spawning areas roughly corresponding to Adventure Bank and Malta Bank
Spring spawners were more abundant at deeper levels, though in the western sector they even occurred within 50 m depth (Fig. 3a)
Summary
It is widely recognized that Mediterranean demersal fisheries exploiting several species use various types of gear, but mainly prefer small mesh size trawling (Caddy, 1990; Farrugio and Papaconstantinou, 1998). Since many Mediterranean demersal species of fish and cephalopods are recruited to fishery as 0. It is well known that spawner stock and recruitment relationships (SRR) are one of the most complex issues in the dynamics of exploited resources. The Strait of Sicily connects the two main, western and eastern basins of the Mediterranean. The upper layer, called “Modified Atlantic Water” (MAW), is identified by water with a relatively low salinity flowing from the western to the eastern basin. The lower layer, called “Levantine Intermediate Water” (LIW), is identified by water with a relatively high salinity flowing in the opposite direction, like an undercurrent (Bethoux, 1980; Manzella et al, 1988; Onken and Sellshopp, 1998). Measurements have shown that the mesoscale signal prevails in the upper layer, with the presence of eddies and meanders
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