Gear selectivity and discards are important issues related to fisheries management but separately modelled. This work examines for the first time the overall size-selection pattern on the total amount of individuals of a species entering the trawl codend. An innovative approach was used based on modelling the escapement through the codend in the sea and the subsequently selection process by the fisher on the deck of the fishing vessel resulting into the discards and landings. Three different trawl codends and three species were investigated in the case study conducted. A dual sequential model accounting for both gear size-selectivity and the subsequent fisher-size-selectivity was applied, under the hypothesis that a fish entering the codend can follow a multinomial distribution with three probabilities, the escape, the discard and the landing probability, respectively. The model described the escape probability through the gear and the landing probability by the fisher as S-shaped curves leading to a bell-shaped curve for the discard probability affected by both gear and fisher selection. The model described well the experimental data in all cases. Sampling scheme of three compartments proved adequate. The model provides at the same time selectivity and discards parameters useful in fisheries management.
Commercial bycatch species and their exploitation pattern in the Mediterranean trawl fishery are little studied. The present work examines the overall size-selection pattern, both regarding the trawl in the sea and the fisher onboard the vessel, for seven commercial bycatch species using different codends. The applied selection model predicted the escape, discard, and landing probability for each species simultaneously, a useful method for providing information important for fisheries management under the ecosystem approach. Among the studied codends, the 40-mm diamond mesh codend, still in use in non-EU Mediterranean fleets, was found unsuitable for the stocks in all cases. The 40-mm square mesh codend (40S) was found appropriate for blue whiting (Micromesistius poutassou), comber (Serranus cabrilla), and bogue (Boops boops) sustainability. The 50-mm diamond mesh codend (50D) was more suitable than the square mesh codend only for the spotted flounder (Citharus linguatula). Both the 40S and the 50D codends were appropriate for picarel (Spicara smaris), whereas none ensured sustainable exploitation for the blackbelly rosefish (Helicolenus dactylopterus), and the streaked gurnard (Chelidonichthys lastoviza). The results are discussed in relation to juvenile protection, discard mitigation, and fisher selection behaviour, important factors for the sustainability of stocks and fisheries in the Common Fishery Policy for the Mediterranean Sea.
Since July 2019, Gyaros island in the central Aegean Sea, enjoys the status of a partial Marine Protected Area (MPA), allowing for exploitation by small-scale fishers following specific spatio-temporal restrictions. The need for assessing the effectiveness of the MPA in the future, led MAVA Foundation to fund a knowledge survey project aiming to serve as a baseline for future reference. A series of experimental fishing surveys took place with static nets, the outcomes of which are presented herein. From June 2018 to September 2020, a series of 8 fishing excursions with a total of 40 experimental fishing sets with bottom static nets were realized in 5 set locations around Gyaros island, inside the MPA protection zone. A total of 75 species were identified; the most abundant species, in terms of biomass, being: parrotfish-Sparisoma cretense, red scorpionfish-Scorpaena scrofa, common spiny lobster-Palinurus elephas, red porgy-Pagrus pagrus, little tunny–-Euthynnus alletteratus, Mediterranean moray-Muraena helena, lesser spotted dogfish -Scyliorhinus canicula, forkbeard-Phycis phycis, surmullet-Mullus surmuletus, common cuttlefish-Sepia officinalis and common Pandora-Pagellus erythrinus. A comparison with similar data in adjacent areas outside the MPA allowed for assessing the effectiveness of the MPA based on four indicators: species diversity index, species relative biomass index, key predator species abundance, and alien fish abundance. Based solely on the experimental fishing trials, the MPA seems to be functioning, since both species diversity and abundance were higher within the protected area. However, its performance may still not be considered as optimal, as this is indicated by the large proportion of undersized key predators (e.g. groupers), although more abundant and larger than the ones residing outside the MPA.
Currently, seven dasyatid species have been described in the Mediterranean Sea: Bathytoshia lata, Dasyatis marmorata, Dasyatis pastinaca, Dasyatis tortonesei, Himantura uarnak, Pteroplatytrygon violacea and Taeniura grabata. Papaconstantinou (2014) listed four species of Dasyatidae occurring in Greece (P. violacea, D. pastinaca, D. tortonesei and D. centroura; the latter was a case of misidentification and it is currently identified as B. lata, according to genetic analysis). However, the marbled stingray (D. marmorata) was not amongst them. Here, the presence of D. marmorata was examined for the first time in Greece. The present study provides updated information on the geographical distribution of D. marmorata in the Eastern Mediterranean Sea. A juvenile male stingray was captured in February 2019, during an onshore survey in Maliakos Gulf, located in the central Aegean Sea, Greece. The ray was examined at the Fisheries laboratory of the Hellenic Centre for Marine Research (HCMR) in Athens and was identified as D. marmorata. Morphological characters were recorded and DNA barcoding was applied to confirm the species identification. The combination of the two methods verified the occurrence of the marbled ray in the Greek waters. This is the first record of D. marmorata from the Aegean Sea.
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