Suchergebnisse

Most reintroduction and restocking programs consist of releasing captive-raised juveniles. The usefulness of these programs has been questioned, and therefore, quality control is advisable. However, evaluating restocking effectiveness is challenging because mortality estimation is required. Most methods for estimating mortality are based on tag recovery. In the case of fish, juveniles are tagged before release, and fishermen typically recover tags when fish are captured. The statistical models currently available for analyzing these data assume either constant mortality rates, fixed tag non-reporting rates, or both. Here, instead, we proposed a method that considers the mortality rate variability as a function of age/size of the released juveniles. Furthermore, the proposed method can disentangle natural from fishing mortality, analyzing the temporal distribution of the captures reported by fishermen from multiple release events. This method is demonstrated with a restocking program of a top-predator marine fish, the meagre (Argyrosomus regius), in the Balearic Islands. The estimated natural mortality just after release was very high for young fish (m = 0.126 day for fish 180 days old), but it was close to zero for large/old fish. These large/old fish were more resilient to wild conditions, although a long time was needed to achieve a relevant reduction in natural mortality. Conversely, these large/old fish were more vulnerable to fishing, creating a trade-off in survival. The release age that maximizes the number of survivors after, for example, one year at liberty was estimated to be 1,173 days. However, the production cost of relatively old fish is high, and only a few fish can be produced and released within a realistic budget. Therefore, in the case of the meagre, increasing the number of released fish will have no or scarce effects on restocking success. Conversely, it is advisable implement measures to reduce the high natural mortality of young juveniles and/or the length of time needed to improve fish resilience. ; This work was financially supported by >Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria> (INIA) belonging to >Ministerio de Economía y Competitividad> (Spanish Government), through the projects RTA-2007 00033-C02-01 and RTA-2011 00056-C02-00 ; Peer Reviewed

Because the meagre (Argyrosomus regius) is not currently found around the Balearic Islands (western Mediterranean), the Balearic government is carrying out a restocking programme to recover its population. The success of this programme is critically dependent on improved knowledge of the meagre's life cycle, and particularly its reproductive biology. Data on key reproductive parameters based on both reared and wild specimens are reported here. Histological examinations and gonadosomatic indices from 342 reared specimens demonstrated that 1) the potential reproductive season ranged from April to June and peaked in May, and 2) length at maturity (L50) was 49.3 cm for males and 57.2 cm for females, age at maturity (A50) was 2.7 years for males and 3.5 years for females, and weight at maturity (W50) was 1396 g for males and 1892 g for females. Histological examinations of 37 wild fish from Cádiz (SW Spain) demonstrated that the meagre has determinate fecundity. The annual potential fecundity of reared females ranged from 0.9 to 4.2 million oocytes, which is exponentially dependent upon female size. ; This work has been funded by the Plan Nacional de Cría de Corvina 2005-2007 (JACUMAR MAPA-CC.AA.) and by the INIA projects RTA-2007 00033-C02-01 and RTA-2011 00056-C02-00 ; Peer Reviewed

The cuttlefish (Sepia officinalis) trammel net fishery is one of the most important small-scale fisheries in the Mediterranean Sea. Here we describe the main catch, by-catch and discard patterns found in this fishery on Mallorca Island by onboard surveys of 1005 netting walls from 23 fishing trips. The number of items captured, their size and their subsequent use, i.e. kept for sale or discarded, were recorded. Furthermore, the immediate survival of the unwanted items (i.e. vitality state when the gear came on board) and the medium-term survival of a subsample were assessed. The cuttlefish was the dominant species in the commercial fraction of the catch, particularly during the fishing season peak (March). However, S. officinalis catches quickly decreased further into the season, with other high-value fish, such as Scorpaena scrofa, increasing in the commercial fraction of the catch. As species composition is continuously changing, it is often difficult to determine the main target species of this fishery. This strategy possibly complicates management but maximizes fishing revenue, which was an average of €175 per trip. With respect to discards, up to 104 different species were caught but not commercialized. The most abundant were Holothuria sp. and Torpedo marmorata. Their immediate survival was 100% and 20%, respectively. In both cases, the medium-term survival and the vitality status were high after seven days in monitored captivity. Therefore, in these cases, their immediate release to the sea should be promoted, given that they are exempt from the EU landing obligation. Interviews with fishers revealed that the perceived quantity of discards was lower than the amount recorded by the present study. Currently, just a small percentage (1.5%) of these discards will be affected by the landing obligation enforced by the new European discards ban. ; This study is a result of the Associated Unit LIMIA-IMEDEA. It received funding from the European Commission's Horizon 2020 Research and Innovation Programme under Grant Agreement No. 634495 for the Science, Technology, and Society Initiative to Minimize Unwanted Catches in European Fisheries (MINOUW). G. Catanese was supported by a postdoctoral research contract from INIA-CCAA. H. Hinz was supported by a Ramón y Cajal Fellowship (grant funded by the Ministerio de Economía y Competitividad de España and the Conselleria d'Educació, Cultura i Universitats de la Comunidad Autónoma de las Islas Baleares). ; Peer reviewed