McGOWAN and RICHARDS: BLUEFIN TUNA LARVAE 



recruitment of its temporal and spatial variabil- 

 ity can be tested by comparing the fishery inde- 

 pendent-variations in habitat with recruitment 

 indices based on the catch statistics of commer- 

 cial and recreational fisheries. 



CONCLUSIONS 



Larval bluefin tuna caught in the South At- 

 lantic Bight in 1985 were in Gulf Stream water. 

 Bluefin tuna larvae previously captured near 

 Cape Hatteras were also in Gulf Stream water 

 which meandered over the shelf edge. Larvae 

 previously collected near Miami were primarily 

 in the high velocity core of the Stream or in 

 onshore meanders of the Stream. Therefore 

 most bluefin tuna larvae off the southeastern 

 U.S. were advected to the area, not spawned 

 there. Although some unspent adults may 

 spawn while migi-ating from the Gulf of Mexico 

 to New England feeding gi-ounds, only one of 

 the larvae collected off the southeastern U.S. in 

 1985 had to have been spawned north of Miami 

 based on its estimated age and rate of advec- 

 tion. The estimates of ages and advection do not 

 falsify a hypothesis of local spawning with re- 

 tention in recirculating currents, but the most 

 hkely conclusion considering all the evidence is 

 that the South Atlantic Bight is not a major 

 spawning area for western Atlantic bluefin 

 tuna. 



In addition, the habitat off the southeastern 

 U.S. seems less favorable for bluefin tuna larvae 

 because higher temperatures here than in the 

 Gulf of Mexico would increase food require- 

 ments, and upweUing events over the shelf ap- 

 parently do not lead to favorable food chains for 

 larval tunas. Larvae may need to develop in re- 

 tention areas outside the Loop Current in the 

 Gulf of Mexico in order to synchronize their sub- 

 sequent migration as schools of juveniles to 

 nursery areas. These retention areas would be 

 expected to vary in size and location with fluc- 

 tuations in the Loop CuiTent flow. The varia- 

 tions in amount of habitat for larvae could deter- 

 mine recruitment and thus affect the population 

 dynamics of the bluefin tuna. 



More research is needed to determine the sur- 

 vival rate of the larvae which are advected out of 

 the Gulf of Mexico, to establish whether or not 

 they recruit to the adult stock, to refine the 

 definition of habitat for bluefin tuna larvae 

 within the Gulf of Mexico, and to test if this 

 habitat controls recruitment and population 

 dynamics of the stock. 



ACKNOWLEDGMENTS 



We want to acknowledge the inspiration of the 

 work of Dr. Reuben Lasker on larval fish habitat 

 and the benefit of our discussions with him on 

 the ecological, evolutionary, and fishery implica- 

 tions of the coincidence in space and time of fish 

 larvae and the conditions necessary for their sur- 

 vival and gi'owth. 



We are grateful to Karen Lecke and Rick 

 Minkler of the Southeast Fishery Center, 

 Pascagoula Laboratory, for providing the cruise 

 report, the temperature-salinity plots, and ac- 

 cess to the environmental data for RV Oregon 

 II, Cruise 152. Steve Baig, NOAA National 

 Hurricane Center, Miami, provided copies of the 

 Gulf Stream Position charts. Leslie Rosenfeld, 

 University of Miami Cooperative Institute for 

 Marine and Atmospheric Studies, guided us to 

 relevant physical oceanogi'aphic literature, made 

 many helpful suggestions in its interpretation, 

 and extensively criticized an early draft of the 

 paper. Two anonymous reviewers made con- 

 structive criticisms which helped separate sub- 

 stance from speculation in the manuscript. This 

 research was funded in part through the Cooper- 

 ative Institute for Marine and Atmospheric 

 Studies by the National Oceanic and Atmos- 

 pheric Administration under Cooperative 

 Agi-eement NA85WC-H-016334. 



LITERATURE CITED 



.\nonynious. 



1986. Report of the bluefin working group. Miami, 

 Florida, U.S.A. September 1985. Int. Comm. Con- 

 serv. Atl. Tunas, Coll. Vol. Sci. Pap.. Madrid 24:11. 



1987. Report for the biennial period 1986-87, Part 

 1. Int. Comm. Conserv. Atl. Tunas. Madrid, 

 Spain. Appendi.x 5 to Annex 8. Recommendation 6, p. 

 98. 



Atkinson, L. P. 



1985. Hydrography and nutrients of the southeastern 

 U.S. continental shelf, hi L. P. Atkinson, D. W. 

 Menzel, and K. A. Bush (editors), Oceanography of 

 the southeastern U.S. continental shelf, p. 77-92. Am. 

 Geophys. Union, Wash, D.C. 

 Atkinson, L. P., and D. W. Menzel. 



1985. Introduction: oceanogi'aphy of the southeast 

 United States continental shelf. In L. P. Atkinson, 

 D. W. Menzel, and K. A. Bush (editors), Oceanog- 

 raphy of the southeastern U.S. continental shelf, p. 

 1-9. Am. Geophys. Union, Wash, D.C. 

 Atkinson, L. P., T. N. Lee, J. O. Blanton, and G. A. 

 Paffenhofer. 



1987. Summer upwelling on the southeastern conti- 

 nental shelf of the U.S.A. during 1981: hydrogi-aphic 

 observations. Prog. Oceanogi-. 19:231-266. 



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