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: Lf = 31.46(1 − e−0.228 (t+3.034)) (L∞ = 31.46 cm, k = 0.228 per year, t0 = −3.034 years); for male Lf = 27.43(1 − e−0.422 (t+1.747)) (L∞ = 27.43 cm, k = 0.422 per year, t0 = −1.747 years) and for female Lf = 31.70(1 − e−0.227 (t+2.196)) (L∞ = 31.70 cm, k = 0.227 per year, t0 = −2.916 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 Wt = a*Lb; a = 9.89*10−5 and b = 2.37 for the sexes combined.

Sampling was carried out in the Celtic Sea in May 1987 over Great Sole and Cockburn Banks, and in June 1991 over Little Sole Bank, to study relationships between bank topography, hydrography and plankton distribution.

Over Great Sole and Cockburn Banks, there were various patterns in the hydrography and plankton which could be related to the banks, although there were no significant correlations with water depth. Away from the shelf-edge, stratification was lower over the banks. Higher water temperatures (at 5 m and 100 m depth) and increased concentrations of copepod nauplii and adults occurred on either side of Cockburn Bank. Abundance of mackerel (Scomber scombrus) eggs and larvae increased towards the shelf-edge, with lower numbers over Cockburn Bank.

Over Little Sole Bank, water column stratification was negatively correlated with water depth. However, this was strongly influenced by shelf-edge mixing, which was reflected in reduced stratification towards the shelf-edge. Background levels of chlorophyll-a also increased from on-shelf towards the shelf-edge. Copepod adults and nauplii, as well as mackerel eggs and larvae were more abundant with distance onto the shelf.

There was partial retention of four Argos tracked drift buoys on the south-east flank of Little Sole Bank. The mean displacement rate of the buoys was 1.35 km day−1 over 10 days, with a mean dispersion of 1.2 km day−1. A simple one-dimensional coupled physical–biological model showed the potential influence of banks resulting in earlier stratification and resultant spring bloom. Considerations of the delay in transfer of production from primary to secondary production and the effects of drift and diffusion, suggested it was unlikely that any influence of the banks on production would be directly related to bank topography, but there might be some regional enhancement of production.

A method for acoustic abundance estimation by horizontal guided sonar of fish schooling close tosurface is presented. The basic principle is to measure the horizontal area of schools in situ, and derive the school biomass subsequently through a school area to school biomass relationship. The application of the method is exemplified through a sonar survey in the eastern North Sea-Skagerrak in September 1990. The areas of recorded schools were measured by the estimate function of a Furuno CSH-70 sonar, and selected schools were captured by purse seine to establish a school-area to school-biomass relationship. In the actual region, the biomass of herrig (Clupea harengus) and mackerel (Scomber scombrus) was estimated to about 90 000 and 43 0000 tons, respectively. The accuracy of the method is discussed and improvements are suggested.