engleski

Marine turtles and fisheries in the Mediterranean: are we missing something?

We analyzed data on the by-catch of 59 loggerhead sea turtles Caretta caretta in coastal gill nets in the eastern Adriatic Sea, in the period 2000-2002. We divided the year into two periods: the "warm period"” (from the beginning of May to the end of October) and the "cold period" (from the beginning of November to the end of April), and tested the temporal distribution of by-catch by means of a chi-square test. Data on the gill net fishing fleet were obtained from the Directorate of Fisheries, the Ministry of Agriculture and Forestry of Croatia and through personal interviews with fishermen in Slovenia. We found a significant association between by-catch in gill nets and the warm period (chi-sq = 4.33, p = 0.03, d.f. = 1), which implies that loggerheads in the eastern Adriatic are mostly involved with gill nets during the period of increased activity, between the end of April and November. Furthermore, our study showed that gill nets affect both small juveniles (<50 cm CCL) and large, benthic size-classes (>50 cm CCL), in the ratio 1.2:1, respectively. The mean mortality was 54.9% (n=51). Out of about 2, 400 fishing vessels that operate with gill nets along about 3, 000 km of the total coastline of Croatia, 89.4% are less than 12 m in length. A total of 12, 142 km of gill nets are registered, which gives about 5 km of gill nets per boat, or 3.3 to 6.2 times more than is allowed by the law, depending of the type of net. About 60 gill netters are registered along 44 km of Slovenian coast, fishing with 2-4 km of gill nets per boat. In total, between 120 and 240 km of gill nets are set along 44 km of Slovenian coastline, causing a direct mortality of loggerheads of 65.4%. Considering the high mortality rates, it is quite possible that the cumulative lethal effect of numerous small coastal gill net fisheries could have a direct mortality level equivalent to that of larger, commercial fisheries. A loggerhead population model showed that a reduction of mortality in the large juvenile and subadult stages would contribute most to population recovery. Therefore, assessment and management of gill net fisheries in the Mediterranean and a reduction of mortality through time and/or area closures should be emphasized as a conservation priority, particularly in foraging and inter-nesting habitats, and along the migration pathways of marine turtles.

sea turtles; by-catch; mortality; Adriatic fisheries; Mediterranean; conservation

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