Adnan Tokaç

The effects of different cod-end design on bottom trawl selectivity in Turkish fisheries of the Aegean Sea

Abstract The effect of different cod-end designs on bottom trawl selectivity was studied using the hooped cod-end cover method. The selectivities of three different cod-ends: standard, 15% shortened lastridge rope and narrowed circumference (to 120 mesh from 150 mesh), were measured for red mullet ( Mullus barbatus L., 1758) and annular sea bream ( Diplodus annularis L., 1758) in Turkish territorial waters of the Aegean Sea in June and September 1994. Selection curves and selection parameters were calculated using a logistic model. 50% retention lengths and selection factors for red mullet were higher for the shortened lastridge rope case and narrow cod-end than the standard cod-end. There was no significant difference for annular sea bream. This can be explained by the body shape differences of the two species. The effects of different cod-end designs on the selectivity are discussed.

Turkey: A New Region for Artificial Habitats

The scientific study of artificial reefs is a comparatively new concept in Turkey, starting with the introduction of a reef at Hekim Island (Fig. 1) by the Aegean University Fisheries Faculty in 1991 and followed by the placing of a reef off Foca by Nine September University in 1993. During the 1980s small-scale reefs were deployed by diving clubs and universities, but results remain unpublished. There has also been an attempt by the Izmir Metropolis Municipality to prevent illegal trawling and to generate new fishing opportunities for sport anglers by depositing ten old trolley-bus bodies in Izmir Bay in 1989. Echo sounder studies have shown, however, that the effective height of these last structures has been reduced from 4 m to 1.5 m by sedimentation. A later project carried out by Cesme Municipality in 1995 to improve recreational fishing is too recent to have been fully evaluated. No artificial reef project in Turkey at present is being funded nationally or regionally; existing projects are all based on small-scale reefs.

Evidence of subtle genetic structure in the sympatric species Mullus barbatus and Mullus surmuletus (Linnaeus, 1758) in the Mediterranean Sea

Using thirteen microsatellite loci for Mullus barbatus and Mullus surmuletus collected in the Mediterranean Sea, the biogeographic boundaries, genetic distribution among and within basins and the impact of prolonged exploitation in both species were investigated as a basis for understanding their population dynamics and for improving Mullus spp. stock management. Different level of diversity indices among these co-occurring species were obtained, with M. barbatus showing higher allele richness and higher mean observed and expected heterozygosity than M. surmuletus. Reduced contemporary effective population size (Ne) and M-ratio values found in both species likely reflects recent demographic changes, due to a combination of high fishing pressures, habitat fragmentation and naturally occurring fluctuations in population size. Different patterns of genetic connectivity among populations sampled within the Mediterranean were observed for both species. Higher genetic structure was found for M. barbatus as opposed to a more homogenous pattern observed in M. surmuletus samples. Adriatic populations, previously considered panmictic and isolated from other Mediterranean regions, showed geographical partitioning within the basin but also population connectivity with the northern Ionian and Tyrrhenian Seas. Our results highlight the need for temporal sampling in understanding the complex pattern of population connectivity in the Mediterranean, particularly for management purposes.