Embedding sea surface temperature anomalies into the stock recruitment relationship of red mullet (Mullus barbatus L. 1758) in the Strait of Sicily

Abstract

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 (R²=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.