| Striped marlin, Tetrapturus audax, is an Indo-Pacific pelagic fish that is valuable to commercial and recreational fisheries throughout its range. Populations of striped marlin are starting to show strain from intensified fishing pressure over the past few decades, and the management of this fishery is at a critical point for sustaining this resource. However, the stock structure of this highly migratory species is still in question, and this has limited the ability to manage this fishery. This research is aimed at resolving patterns of spatial and temporal variation, and thus the stock structure, of striped marlin populations in the Pacific using molecular markers. In Chapter 1, the development of 10 microsatellite markers was described. These first striped marlin-specific microsatellites were developed to increase resolution of genetic variation in subsequent analyses. Using 12 microsatellites and mitochondrial control region sequences, Chapter 2 examined geographic genetic heterogeneity of striped marlin samples collected from 7 locations around the Pacific. Microsatellite and sequence results revealed small, but significant overall spatial subdivision among locations (FST =0.0145 and KST =0.06995, respectively). Pair-wise microsatellite analysis revealed 4 stocks (1-Japan-Southern California-Immature Hawaii, 2-Mature Hawaii 3-Mexico-Central America, and 4-New Zealand-Australia); sequence results were similar but did not detect significant structure between Mature Hawaii and the Japan-Southern California-Immature Hawaii group. Temporal variability among year-classes of striped marlin was determined in Chapter 3. Overall genetic drift did not increase at points separated by longer periods of time, and temporal variation, Fs', shifted widely between/among year-classes. Significant variation was found in several year-class comparisons, however factorial correspondence analyses of location/year-classes showed temporal stability in spatial patterns detected in Chapter 2. Effective population sizes, corrected for overlapping generations, were remarkably small (e.g. 16-76); and this, in addition to the observed shifting Fs' estimates, strongly suggests highly variable reproductive success among cohorts. Finally, in Chapter 4, the heterogeneity detected in striped marlin was compared to other pelagic species in the Pacific in order to determine if any common patterns could help explain population subdivision patterns in these fish. Although no single parameter was identified, certainly the number, size and specificity of spawning locations and the duration of spawning events play a role in the heterogeneity pattern of a species throughout its distribution. The results from this dissertation provide a much clearer picture of the stock structure of striped marlin in the Pacific and of the processes determining that structure. |
