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- Assessment of radiometric dating for age validation of deep-water dogfish (Order: Squaliformes) finspines
- Vertebrae of most deep-water sharks are too poorly calcified to record visible growth bands and therefore are not useful for age determination. Most dogfish species (Order: Squaliformes) possess dorsal finspines and several recent studies have shown that these structures offer potential for age determination. Age validation should be central to any age determination study, yet to date no age and growth study of deep-water sharks has included a complete validation of age estimates. In this study we sought to age two deep-water dogfish species by analyzing 210Pb and 226Ra incorporated into the internal dentin of the finspines. These radiometric age estimates were compared with counts of internal growth bands observed in the finspines. A pilot study indicated that dorsal finspines of Centroselachus crepidater are too small and thus offer insufficient mass for the radiometric techniques employed in this study. For ageing larger finspines of Centrophorus squamosus, the lead-radium disequilibria method (ingrowth of 210Pb from 226Ra) was found to be inapplicable due to exogenous uptake of 210Pb in the finspine. Therefore, to approximate age, we measured the decay of 210Pb within the dentin material at the tip of the finspine (formed in utero), relative to the terminal material at the base of the finspine. Results with this method proved to be inconsistent and did not yield reliable age estimates. Hence the use of 210Pb and 226Ra for radiometric age determination and validation using dorsal finspines from these deep-water dogfishes was deemed unsuccessful. This outcome was likely due to violations of the consistent, life-long isotopic uptake assumption as well as the provision that the finspine must function as a closed system for these radioisotopes. Future improvements in analytical precision will allow for smaller samples to be analyzed, potentially yielding a better understanding of the fate of these radioisotopes within finspine dentin throughout the life of the shark. © 2013 Elsevier B.V., Fish and Fisheries
- Cotton, Andrews, Cailliet, Grubbs, Irvine, Musick
- Protection of marine fish stocks at risk of extinction,
- The American Fisheries Society (AFS) recommends that regulatory agencies closely scrutinize both marine fish and invertebrate stocks that may be at risk of extinction and take remedial action before populations are threatened or endangered. Initial AFS analyses of marine stocks at risk in North America show at least four primary geographic "hot spots" with stocks at risk-the Florida Keys; the Indian River Lagoon area of Florida; Puget Sound, Washington and adjacent Canadian waters; and the Gulf of California. Further AFS analyses show that certain groups of fishes are particularly vulnerable because they have slow growth and late maturity. Severe population declines have been documented for several snappers and groupers (Lutjanidae, Serranidae) in the Atlantic and the Gulf of California, several rockfishes (Sebastinae) in the Pacific, and some sharks (Selachei), skates (Rajidae), and sawfishes (Pristidae). Regulatory agencies should be apprised that these groups are extraordinarily vulnerable, and priority management should be given to these species. The greatest threat to many long-lived marine species may be bycatch (including regulatory discard) in fisheries targeting other, often more-productive species. Regulatory agencies must monitor bycatch of long-lived species and move to implement conservation actions if population declines are recorded. The most effective management strategy for some species taken as bycatch and for targeted species such as deeper-water groupers and Pacific rockfishes, may be establishment of large, protected marine reserves to supplement traditional management practices outside of the protected areas. The AFS supports the development, use, and evaluation of large marine reserves or Marine Protected Areas to protect and rebuild vulnerable populations. These reserves must have clearly defined goals, include a wide variety of environmental conditions, be of sufficient number to protect marine ecosystems within each region, allow adaptive management, and be large enough to be self-sustaining. The AFS encourages its members to become involved by providing technical information needed for protection of at-risk marine stocks to international, federal, state, and provincial policy makers, so decisions are made on a scientific, rather than emotional or political, basis., Cited By (since 1996):22, Source: Scopus, ,
- Musick, Berkeley, Cailliet, Camhi, Huntsman, Nammack, Warren Jr.