Abstract
Many fisheries management and conservation plans are based on the genetic structure of organisms in pelagic ecosystems; however, these structures tend to vary over time, particularly in cyclic ocean currents. We performed genetic analyses on the populations of the pelagic fish, Megalaspis cordyla (Osteichthyes: Carangidae) in the area surrounding Taiwan during 2000–2001. Genotyping was performed on M. cordyla collected seasonally around Taiwan as well as specimens collected from Singapore (Malacca strait) and Indonesia (Banda Sea). Gonadosomatic indices (GSI) revealed that M. cordyla does not spawn near Taiwan. Data related to the mitochondrial control region revealed that the samples from Singapore and Indonesia represented two distinct genetic cohorts. Genotyping revealed that during the summer (June–August 2000), the Indonesian variant was dominant in eastern Taiwan (presumably following the Kuroshio Current) and in the Penghu region (following the Kuroshio Branch Current). During the same period, the Singapore genotype was dominant along the western coast of Taiwan (presumably following the South China Sea Current); however, the number dropped during the winter (December–February 2001) under the effects of the China Coast Current. Divergence time estimates indicate that the two genetic cohorts split during the last glacial maximum. Despite the fact that these results are based on sampling from a single year, they demonstrate the importance of seasonal sampling in unravelling the genetic diversity in pelagic ecosystems.
Highlights
Management plans for fisheries and the conservation of biodiversity in pelagic ecosystems are commonly based on geospatial data related to a target species[1,2,3]
Despite the fact that these results are based on sampling from a single year, our findings clearly illustrate the importance of using serial sampling to identify changes in cryptic genetic structures associated with oceanographic dynamics as well as the important implications this can have for conservation
A correlation was observed between seasonal ocean current cycles and the genetic diversity of M. cordyla captured throughout the study period (2000–2001)
Summary
Management plans for fisheries and the conservation of biodiversity in pelagic ecosystems are commonly based on geospatial data related to a target species[1,2,3]. The fact that the genetic structures observed in many pelagic fish are associated with oceanographic d ynamics[4,5] means that the conclusions drawn from genetic diversity and heterogeneity among populations are often attributed to connectivity among populations. We sampled the pelagic fish stocks of torpedo scad, Megalaspis cordyla (Linnaeus, 1758) (Perciform: Carangidae) in the offshore ocean currents surrounding Taiwan. Some of the pelagic migratory species with life histories similar to that of M. cordyla present discrete genetic structures, despite the fact that they are widely dispersed throughout the West Pacific and East Asian oceans. The M. cordyla in the Indo-Pacific oceans and the amalgamation of the cohorts from different source populations in the offshore waters around Taiwan provide a rare opportunity to test the hypothesis that seasonal dynamics in the genetic structures of highly migratory pelagic organisms are associated with cyclic ocean currents. Our results clearly demonstrate the importance of performing sampling at multiple timepoints in order to capture time-sensitive fluctuations in the genetic structure of migratory pelagic organisms and thereby elucidate the corresponding cryptic genetic diversity
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