Meeting Abstract

19.2  Thursday, Jan. 3  Population structure and gene flow in the scalloped hammerhead shark, Sphyrna lewini along the Eastern Pacific NANCE, H.A.*; MARKO, P.B.; KLIMLEY, A.P.; Clemson Univ.; Clemson Univ.; Univ. of California, Davis hnance@clemson.edu

Large, cosmopolitan marine fishes appear to have great potential for panmixia throughout their geographic ranges via long-distance migration. One common method of assessing connectivity among natural populations is through the use of genetic markers, which can be used to characterize population structure and make inferences regarding gene flow. In the scalloped hammerhead shark, Sphyrna lewini, previous genetic analyses have shown very low mitochondrial gene flow across oceans. At smaller spatial scales however, such as along individual continental margins, population structure and migration rates remain undescribed in detail for this species. In the Eastern Pacific (EP) where this shark is heavily exploited, resulting in recent IUCN listing as �endangered globally�, large aggregations of S. lewini form with seasonal regularity at distinct sites from the Gulf of California to northern Peru. To understand the degree to which these distinct, yet temporally ephemeral aggregations represent �open� or �closed� populations with respect to one another, we are using microsatellite loci to characterize spatial patterns of population genetic subdivision in the EP. To determine whether sharks return to the same sites annually, we are also sampling EP sites across years. Preliminary data show some spatial structure among EP populations, but no temporal differences in their genetic composition. These data suggest that S. lewini exhibits site fidelity, but that gene flow between sites of aggregation is low. Additional analyses with more loci we are developing can potentially shed more light on whether migration rates are small enough to result in demographically independent populations along the EP.