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Age determination of elasmobranchs, with special reference to Mediterranean species: a technical manual

Studies and Reviews. General Fisheries Commission for the Mediterranean. No. 94. Rome, FAO 2014









Campana S.E. Age determination of elasmobranchs, with special reference to Mediterranean species: a technical manual. Studies and Reviews. General Fisheries Commission for the Mediterranean. No. 94. Rome, FAO 2014. 38 p.


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    Elasmobranchs of the mediterranean and black sea: status, ecology and biology, biographic analysis 2012
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    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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    Bycatch in longline fisheries for tuna and tuna-like species: a global review of status and mitigation measures 2014
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    This publication is the third in a series on bycatch in global tuna fisheries. Dealing with longline fisheries, its scope is defined taxonomically to comprise only non-tuna and non-tuna-like species. The history of longline fishing illustrates the role of new technologies, the expansion of fishing grounds, and the operational characteristics of the fleets in shaping today’s fishery. More recently, management regulations, the price of oil, the cost of labour, and market demand have also exerted a n influence. No more than 23 percent of the tuna in each ocean is longline-caught. However, there may be up to 7 500 tuna longliners globally with almost 60 percent of them less than 24 m in length. Available data suggest that elasmobranch catches have fallen 14 percent since their peak in 2003. In longline fisheries, shark catch rates may be determined by bait type, soak time, hook shape, leader length and material, depth at which the hook is fished, and whether special gear is deployed to targ et sharks. Vulnerability to hooking, and resilience to haulback and handling, vary by species, size, area and fleet operational practices. Tuna regional fisheries management organizations (t-RFMOs) assess the status of shark populations but data limitations often hinder firm conclusions. There is little information on the implementation or effectiveness of finning bans and no-retention measures. Mitigation measures have been tested but results vary. Six of the seven species of sea turtles are th reatened with extinction, and while longline fisheries may have less impact than net-based fisheries, significant populationlevel impacts may be occurring in some regions. The greatest concern is associated with loggerhead–longline interactions in the Atlantic. Circle hooks and using finfish bait have proved effective mitigation techniques either by reducing hooking or hook swallowing. Other methods require further development. Interactions with pelagic longline fisheries kill 50 000–100 000 sea birds annually. Many of these species, particularly albatrosses, are threatened with extinction. Recent advances in tracking technologies have facilitated mapping of where interactions are most likely. The Western and Central Pacific contains more than 45 percent of the global total albatross and giant petrel breeding distributions. The most promising mitigation methods appear to be night setting, side-setting, line weighting and streamer lines, but further research is needed. All five t-RFMOs r equire use of one or more of these methods in areas that overlap albatross distributions. However, compliance data are limited and improved observer coverage is essential. Marine mammals’ interactions with longline fisheries are detrimental to the fishery but may be positive or negative for the mammals. Although it is often unclear which species are involved, pilot whale interactions in the western Atlantic and false killer whale interactions off Hawaii have triggered national mitigation plans. No t-RFMO has adopted management measures for marine mammal interactions. Research and testing of mitigation measures continue in order to ameliorate both marine mammal impacts and economic losses to industry from depredation. At least 650 species of other bony fishes may be caught in association with pelagic longline fisheries, e.g. dolphinfish, opah, oilfish, escolar and ocean sunfish. Some of these stocks are important as local food supplies. However, it is unclear whether these stocks or the ecosystem they help structure is at risk. More attention should focus on improving fishery statistics and initiating basic monitoring of these stocks’ status. The diversity of pelagic longline gear designs and fishing methods, the variety of habitats they are deployed in, the thousands of marine species they may interact with, v and the different mechanisms and behaviours that govern those interactions provide an array of topics to be addressed in any discussion of bycatch mitigation. Scientifi c and technical issues in mitigation including effects across taxa, effects of combinations of measures, economic and safety considerations, underlying biological mechanisms, handling and post-release mortality, and non-fishery impacts must all be addressed. In addition, it is also necessary to consider issues such as who takes the lead for ensuring mitigation is sufficient for the population as a whole, how to devise effective mitigation implementation strategies, and whether gear modification should be used in concert with more sweeping measures.
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    Management techniques for elasmobranch fisheries. 2005
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    This publication describes the scientific principles and techniques used for resource management of elasmobranch fisheries with emphasis on the particular context of elasmobranchs. The management characteristics of these fishes are described – their common bycatch character and their biological constraints on productivity (low growth rate, late maturity and low fecundity). Stock assessment of elasmobranchs is described in the context of management objectives in a wide management contex t. Special attention is given to accurate species identification given the prevalent aggregating of landings data across species, genera and often families in this group. Techniques and experiences for tagging elasmobranchs for population estimation are described as well as methods of genetic techniques for stock identification. Methods and problems involved in determining age, growth, fecundity and mortality rates are described and their use in age-structured models within the conte xt of the reproductive biology of these fishes. Demographic models to determine the productivity of elasmobranch resources are described. Use of surveys to complement information derived from fisheries is described together with management measures. Last, practices of shark utilization are noted.

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