Assessment of sea cucumber populations from the Aegean Sea (Turkey): first insights to sustainable management of new fisheries

Sea cucumber stocks have been overfished in many countries. As a consequence, several species (Holothuria polii, Holothuria tubulosa and Holothuria mammata) are now caught in Turkish waters without adequate knowledge on their biology and ecology. Here, we address their morphometry, relationships among gutted length and weight, population dynamics, temporal evolution of catches, and we provide the first insights about technical aspects of their fisheries. The largest size classes of H. polii are missing from our sampling collection, possibly due to the heavy fishery pressure on this species. Significant differences in the eviscerated length and weight were found among the Turkish sampled localities for H. polii and H. tubulosa, respectively. These differences could be explained by higher food availability in some areas and/or differential fishery pressure. The size and weight of H. tubulosa specimens were smaller than those registered for the same species in Greek waters, where this species is not fished. All the studied species showed allometric growth. In the last two years, the sea cucumber fishery in Turkey has been increasing rapidly, reaching a total production of ca. 555 000 kg in 2012 (80% H. polii and 20% H. tubulosa plus H. mammata). For a correct management of these species, we recommend: 1) the reestablishment of species-specific closed fishery season according to the specific reproductive cycle; 2) the assessment of the exploited stocks from the Northern Turkish coasts with estimates of recovery time of their populations; 3) the reduction of fishery efforts, mainly on H. polii and H. tubulosa and 4) the establishment of protected areas (where sea cucumber fisheries are forbidden) to conserve healthy populations which will favour the recruitment on nearby areas.

Age and growth, mortality and reproduction of the striped sea bream, Lithognathus mormyrus Linnaeus 1758, from the south coast of Portugal (Algarve)

The striped sea bream, Lithognathus mormyrus, used for this population dynamics study were obtained from longline catches and market sampling in the Algarve (south Portugal). The macroscopic analysis of the gonads and the gonad somatic index showed that the south Portuguese population of L. mormyrus spawns mainly between late spring and summer (June to August). The length at first maturity was similar for males and females and the value for both sexes combined was estimated to be 16.08 cm, corresponding to an age between 1 and 2 years. Fish age classes (0 to 13) were determined by reading growth rings on whole otoliths. Age determination was validated by marginal increment analysis. The estimated parameters of the von Bertalanffy growth equation were L infinity = 35.30 cm, K = 0.264 and t(0) = -0.809. Mortality rates were calculated for fish captured with longlines, and the estimated parameters were M = 0.356, Z = 0.622 and F = 0.266. From an Algarve fishery management perspective, these results suggest the need for an increase in the minimum landing size (from 15 to 17 cm), which should be beneficial for the sustainability and conservation of this species. The results also showed that fishing with longlines off the Algarve coast may allow for a sustainable use of the resource.