UCLA

Exploitation of sharks by both commercial and recreational fisheries has caused decreasing numbers resulting in population collapses. Sharks are extremely vulnerable to the effects of exploitation due to life-history characteristics including long lifespans, low fecundities, and late maturities. One family of shark, the Triakidae, has been the subject of global exploitation for greater than 80 years, especially within the eastern Pacific. The Triakidae is a primary component of the eastern Pacific elasmobranch assemblage considered both commercially and recreationally important with several endemic species found within the region including Mustelus albipinnis, M. californicus, M. dorsalis, M. henlei, M. lunulatus, and Triakis semifasciata. In regards to conservation efforts, there is a general paucity of information regarding the status of triakid sharks. As a result of this paucity of information, this study used mitochondrial and nuclear genetic markers to investigate: 1) gene flow among globally distributed populations of the tope shark, Galeorhinus galeus; 2) determine the existence of multiple paternity in M. henlei from within the northern portion of the species' range; and, 3) explore the population connectivity of M. henlei among localities distributed throughout the range of the species from along the northeastern Pacific coast.

A lack of gene flow among globally distributed populations of the tope shark, G. galeus from North America, South America, Western Europe, South Africa, and Australia has been observed based on data from thirteen species-specific microsatellite loci. These data support previous patterns of gene flow based on mitochondrial control region sequence data and indicate the isolated nature of globally distributed populations of G. galeus. As a result, these populations should be managed separately and the currently recognized species status of G. galeus as monotypic should be reconsidered.

The existence of polyandry and multiple paternity within a population of M. henlei at Santa Catalina Island, CA over a period of eight years has been confirmed based on data from 18 litters and four species-specific microsatellites. The observed range of multiple paternity, 0-40%, is significantly lower than that observed in another population of M. henlei from Baja California (93% of 14 litters were observed to be sired by multiple males within a single year). As population sizes differ between the two localities (Baja California > Santa Catalina Island), the rate at which females encounter mates may be responsible for the difference in the frequencies of multiple paternity observed between Santa Catalina Island and Baja California.

Data from six species-specific microsatellites and the mitochondrial control region have detected three distinct populations of M. henlei in the northeastern Pacific (Northern (San Francisco), Central (Santa Barbara, CA, Santa Catalina Island, CA, Punta Lobos, Baja California, Mexico, and San Felipe, Baja California, Mexico), and Southern (Costa Rica)). Reduced mitochondrial genetic diversity was observed in San Francisco and Santa Catalina relative to all other localities. Possible reasons for the observed reductions in genetic diversity may be the recent establishment of isolated populations after Pleistocene glaciations, female philopatry to nursery areas, or a combination of the two. Long-term gene flow was asymmetric among localities with the predominating pattern being from the north to the south. Gene flow within the past two to three generations appears to be virtually nonexistent among localities with the exception of Punta Lobos that demonstrated significant gene flow to all other localities within the central population. This pattern may be the result of changing climate and may reflect the dispersal of tropical M. henlei into subtropical and temperate regions.