Growth of the blue mackerel Scomber scombrus in Tunisia using the otolith microstructure

This paper studies the age and the growth of male and female of the Tunisian blue mackerel Scomber scombrus during 2004-2006. The age was determined by interpreting and counting daily increments on the otoliths sagitta of 320 individuals sampled from landings caught by different gears specially by purse seine. The parameters of the Von Bertalanffy growth curve were estimated for sexes combined: L-f = 31.46(1 - e(-0.228) ((t+3.034))) (L-infinity = 31.46 cm, k = 0.228 per year, t(o) = -3.034 years); for male L-f = 27.43(1 - e (-0.422) ((t+1.747))) (L-infinity = 27.43 cm, k = 0.422 per year, t(o) = -1.747 years) and for female L-f = 31.70(1 - e(-0.227) ((t+2.196))) (L-infinity = 31.70 cm, k = 0.227 per year, t(o) = 22.916 years) for the whole study period. The difference between the growth of male and female is not significant. The relationship between length and weight shows a length growth faster than of the weight with parameters of the equation W-t = a*L-b; a = 9.89*10(-5) and b = 2.37 for the sexes combined

Predictive distribution models of European hake in the south-central Mediterranean Sea

The effective management and conservation of fishery resources requires knowledge of their spatial distribution and notably of their critical life history stages. Predictive modelling of the European hake (Merluccius merluccius L., 1758) distribution was developed in the south-central Mediterranean Sea by means of historical fisheries-independent databases available in the region. The study area included the international waters of the south-central Mediterranean Sea and the territorial waters of Italy, Malta, Tunisia and Libya. Distribution maps of predicted population abundance index, and probabilistic occurrence of recruits and large adults were obtained by means of generalized additive models using depth and seafloor characteristics as predictors. Presence/absence data of the two life stages was obtained using threshold values applied to the mean weight of the survey catches. Modelling results largely matched previously reported knowledge on habitat preference of the species and its critical life phases. Hake recruits showed an occurrence peak at 200 m depth with preference for soft bottoms. Large adults preferred deeper and harder bottom substrates. Prediction maps allowed to improve our knowledge on the distributional patterns of one of the most important shared stocks in the south-central Mediterranean. This knowledge is essential for an appropriate development of regional-spatial-based management plans