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Book (series)Handbook on fish age determination: a Mediterranean experience 2019
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No results found.Fish age, among other biological parameters, is one of the most relevant pieces of data in reaching sustainable exploitation of fishery resources. Indeed, most analytical methods used in stock assessment require knowledge of demographic structure according to the age of stocks, as well as to recruitment, growth, maturity, natural mortality, etc., which are strictly linked to information on age and age structure. The literature on ageing analysis shows some gaps regarding ageing schemes, criteria and methodologies used in preparing calcified structures. These aspects affect both the precision and accuracy of age estimation. One action that could be taken to overcome this gap was to formalize a handbook that clarified approaches to ageing schemes, criteria and preparation methods. Having a common protocol is fundamental to decreasing relative/absolute bias associated with the activities of age determination and to improving the precision (reproducibility and reduction of the coefficient of variation) of age readers from the various laboratories. In the light of these considerations, this handbook aims to be a guideline to standardizing the methods used in fish ageing studies. The document is focused on a description of the general principles on which age analysis relies (assignment of birth date, preparation methods, aging scheme reading and identification of true and false rings). Moreover, common shared analysis methods can enable a high level of calibration among the diverse institutes involved, thus improving the quality and reliability of results. The volume is subdivided into five main sections: Small Pelagic Species, Demersal Species, Cartilaginous Species, Large Pelagic Species and the European Eel. For each section, information on extraction and storage, preparation method, interpretation of age (age scheme) and ageing criteria are provided by species. In total, 30 species were analysed: 6 small pelagic, 12 demersal, 5 cartilaginous, 6 large pelagic and the European eel. These species represent some of the most important fish from an economic and ecological point of view. Thus this volume represents one of the most complete outlooks for fish ageing analysis in the Mediterranean context. -
DocumentReproductive potential of yellowfin tuna (Thunnus albacares) in the western Indian Ocean 2013
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No results found.The reproductive biology of Yellowfin Tu (Thunnus albacares) in the western Indian Ocean was investigated from samples collected in 2009 and 2010. In our study, 1012 female Yellowfin Tu were sampled: 320 fish on board a purse seiner and 692 fish at a Seychelles cannery. We assessed the main biological parameters that describe reproductive potential: maturity, spawning seasolity, fish condition, and fecundity. The length at which 50% of the female Yellowfin Tu population matures (L50) was estimat ed at 75 cm in fork length (FL) when the maturity threshold was established at the cortical alveolar stage of oocyte development. To eble comparison with previous studies, L50 also was estimated with maturity set at the vitellogenic stage of oocyte development; this assessment resulted in a higher value of L50 at 102 cm FL. The main spawning season, during which asynchrony in reproductive timing among sizes was observed, was November–February and a second peak occurred in June. Smaller females ( <100 cm FL) had shorter spawning periods (December to February) than those (November to February and June) of large individuals, and signs of skipspawning periods were observed among small females. The Yellowfin Tu followed a “capital-income” breeder strategy during ovarian development, by mobilizing accumulated energy while using incoming energy from feeding. The mean batch fecundity for females 79–147 cm FL was estimated at 3.1 million oocytes, and the mean relative batch fecundity was 74.4 oo cytes per gram of god-free weight. Our results, obtained with techniques defined more precisely than techniques used in previous studies in this region, provide an improved understanding of the reproductive cycle of Yellowfin Tu in the western Indian Ocean. -
Book (series)Elasmobranchs of the mediterranean and black sea: status, ecology and biology, biographic analysis 2012
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No results found.The authors have compiled published information on taxonomy, distribution, status, statistics, fisheries, bycatch, biologic and ecologic parameters on age and growth, food and feeding habits, reproductive biology and stock assessment of elasmobranchs in the Mediterranean and Black Sea. This bibliographic analysis, through 661 papers dealing with elasmobranchs in the GFCM area, shows that cartilaginous species, including sharks, rays and chimaeras, are by far the most endangered group of marine fish in the Mediterranean Sea, with 31 species (40 percent of all) critically endangered, endangered or vulnerable. The biological characteristics of elasmobranchs (low fecundity, late maturity, slow growth) make them more vulnerable to fishing pressure than most teleost fish. Overfishing, wide use of non-selective fishing practices and habitat degradation are leading to dramatic declines of these species in the Mediterranean Sea. In general, elasmobranchs are not targeted but are caught incidentally. In many fisheries they are, however, often landed and marketed. The study also highlights the following points: – Works are concentrated mainly in the western Mediterranean. Few works concern endangered species and those of the GFCM priority list; – Much systematic confusion persists for some species and some others are doubtful; – The IUCN red list shows clearly the vulnerability of elasmobranchs and the lack of data; – A decline in cartilaginous fish speci es landings has been observed while fishing effort has generally increased; – A standardization of methods and expression of results on the biology should be generalized in the whole Mediterranean; – Papers on biologic parameters concern few species primarily in the occidental and central Mediterranean areas. Therefore, recommendations to fill gaps in order to protect and manage elasmobranchs stocks are proposed in this document. In fact, better understanding of the composition of incidental and targeted catches of sharks by commercial fisheries and biological and ecological parameters are fundamentally important for the conservation of these populations. Moreover, problems encountered by elasmobranchs in the GFCM area are highlighted and conservation measures are suggested.
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