5
Conclusions and Recommendations

GENERAL RECOMMENDATIONS

In response to its charge, the committee makes the following recommendations:

  1. Available biological evidence of stock structure although sparse is consistent with a single stock hypothesis for bluefin tuna in the North Atlantic Ocean, with at least two spawning areas. Furthermore, the committee's reevaluation of tagging results confirms that movement of bluefin tuna between the western and eastern Atlantic Ocean is sufficient to alter the previous SCRS stock assessments. The committee recommends that NOAA/NMFS conduct new scientific assessments explicitly to include mixing of Atlantic bluefin tuna between eastern and western fishing grounds.

  2. In response to the first question posed to the committee by NOAA, the committee concludes that recent ICCAT Standing Committee on Research and Statistics (SCRS) assessments of abundance of eastern and western Atlantic bluefin tuna do not provide the most defensible interpretations of available scientific data. The committee's reanalyses show that there is no evidence that abundance of western Atlantic bluefin tuna has changed significantly between 1988 and 1992. The committee recommends that NOAA/NMFS use alternative methods of data management, data analyses, and peer review for estimating abundance indices, movement rates, and mixed population assessments (as discussed in Chapters 3 and 4 of this report).

  3. The committee notes that the ICCAT SCRS uses a variety of uncertainty



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OCR for page 109
An Assessment of Atlantic Bluefin Tuna 5 Conclusions and Recommendations GENERAL RECOMMENDATIONS In response to its charge, the committee makes the following recommendations: Available biological evidence of stock structure although sparse is consistent with a single stock hypothesis for bluefin tuna in the North Atlantic Ocean, with at least two spawning areas. Furthermore, the committee's reevaluation of tagging results confirms that movement of bluefin tuna between the western and eastern Atlantic Ocean is sufficient to alter the previous SCRS stock assessments. The committee recommends that NOAA/NMFS conduct new scientific assessments explicitly to include mixing of Atlantic bluefin tuna between eastern and western fishing grounds. In response to the first question posed to the committee by NOAA, the committee concludes that recent ICCAT Standing Committee on Research and Statistics (SCRS) assessments of abundance of eastern and western Atlantic bluefin tuna do not provide the most defensible interpretations of available scientific data. The committee's reanalyses show that there is no evidence that abundance of western Atlantic bluefin tuna has changed significantly between 1988 and 1992. The committee recommends that NOAA/NMFS use alternative methods of data management, data analyses, and peer review for estimating abundance indices, movement rates, and mixed population assessments (as discussed in Chapters 3 and 4 of this report). The committee notes that the ICCAT SCRS uses a variety of uncertainty

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An Assessment of Atlantic Bluefin Tuna analyses. The committee recommends that NOAA/NMFS and ICCAT SCRS act to include transatlantic movement of fish and adaptive management techniques in future uncertainty analyses. The committee cannot determine the maximum sustainable yield (MSY) for Atlantic bluefin tuna under a one-stock hypothesis with two spawning grounds. Available biological information on stock structure, mixing on the spawning and fishing grounds, spawning site fidelity, and spawner/recruit relationships is too sparse. We do know that the present abundance of bluefin tuna in the western Atlantic Ocean is lower than that in the early 1970s although the committee did not analyze similar data for the bluefin tuna in the eastern Atlantic Ocean. We also know that the present abundance and fishing mortality are much higher in the eastern Atlantic Ocean than in the west, and that some physical mixing occurs between the fishing grounds in the eastern and western Atlantic Ocean. The committee recommends that NOAA/NMFS reevaluate MSY for Atlantic bluefin tuna. RESEARCH RECOMMENDATIONS The committee notes that research on the biology of Atlantic bluefin tuna is not continuing at an intensity necessary to answer major biological questions pertaining to the management of the fisheries. Therefore, the committee recommends that NOAA/NMFS carry out the research described below using the best available science and techniques within and outside NOAA. For example, research supported by other U.S. government agencies, including the National Science Foundation, the Department of Energy, and the Office of Naval Research, could contribute to the goals of the studies funded by NOAA. Finally, the committee urges NOAA/NMFS to work cooperatively with ICCAT to implement these research recommendations. The following recommendations are not listed in order of importance or priority. Tagging data show that there is movement of bluefin tuna between the eastern and western Atlantic fishing grounds, but the degree of gene flow between spawning areas is not known. Such knowledge is essential in defining population genetic structure and useful for refining stock assessments. The committee recommends that the one-stock hypothesis be tested rigorously, using the most appropriate technologies capable of detecting contemporary population genetic structure. Estimates of spawning fidelity to a particular area are essential for stock assessments. The committee recommends that microconstituent analysis and archival tags be used to provide information on spawning fidelity. Stock assessments can be refined by better estimates of life history characteristics such as spawning biomass, larval abundance, sex ratio, age at maturity, fecundity, and recruitment. The committee recommends that spawning

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An Assessment of Atlantic Bluefin Tuna biomass, sex ratio, age at maturity, and fecundity in the spawning grounds be estimated and that larval performance, as affected by environmental conditions, be studied. The committee recognizes that knowledge of movement patterns is essential for estimating abundance and distribution and that movement rates and patterns may change over time. The committee recommends that a tagging program be undertaken, with an appropriate combination of conventional, PIT, acoustic, and archival tags to provide improved estimates of the magnitude and patterns of movement. This program should be designed to answer scientific questions pertinent to stock assessment and should be coordinated among all nations involved in the bluefin tuna fishery. Estimates of abundance are confounded by the interaction between fishing and changes in distribution caused by interdecadal climatic and oceanic variability. The committee recommends a synthesizing analysis of existing data on distributions of bluefin tuna in relation to spatial and temporal dynamics of major oceanographic features. The committee notes that a greater use of peer review would have improved the quality of some of the research reviewed during the preparation of this report. The committee recommends that review of all research proposals and resulting manuscripts include a process of external peer review.

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