Barbara L. Taylor

Sperm whale population structure in the eastern and central North Pacific inferred by the use of single-nucleotide polymorphisms, microsatellites and mitochondrial DNA.

We use mitochondrial DNA (mtDNA) (400u2003bp), six microsatellites and 36 single‐nucleotide polymorphisms (SNPs), 20 of which were linked, to investigate population structure of sperm whales (Physeter macrocephalus) in the eastern and central North Pacific. SNP markers, reproducible across technologies and laboratories, are ideal for long‐term studies of globally distributed species such as sperm whales, a species of conservation concern because of both historical and contemporary impacts. We estimate genetic differentiation among three strata in the temperate to tropical waters where females are found: California Current, Hawai`i and the eastern tropical Pacific. We then consider how males on sub‐Arctic foraging grounds assign to these strata. The California Current stratum was differentiated from both the other strata (Pu2003<u20030.05) for mtDNA, microsatellites and SNPs, suggesting that the region supports a demographically independent population and providing the first indication that males may exhibit reproductive philopatry. Comparisons between the Hawai`i stratum and the eastern tropical Pacific stratum are not conclusive at this time. Comparisons with Alaska males were statistically significant, or nearly so, from all three strata and individuals showed mixed assignment to, and few exclusions from, the three potential source strata, suggesting widespread origin of males on sub‐Arctic feeding grounds. We show that SNPs have sufficient power to detect population structure even when genetic differentiation is low. There is a need for better analytical methods for SNPs, especially when linked SNPs are used, but SNPs appear to be a valuable marker for long‐term studies of globally dispersed and highly mobile species.

“Best” Abundance Estimates and Best Management: Why They Are Not the Same

Given the objective of preventing population declines while minimizing restrictions on fisheries, this modeling exercise has shown that including uncertainty in the management regime (the NMIN strategy) is superior. Abundance estimation is difficult for many marine mammal species (Table 7.1). Management objectives are not met for species with high CVs using the NMEAN strategy. If CVs could be reduced to low levels for all species, the NMIN and NMEAN strategies would be similar. Unfortunately, it is often difficult to reduce CVs. As population size decreases, CVs increase (Taylor and Gerrodette 1993). Therefore, threatened, endangered, or depleted populations may be managed poorly by using NMEAN. Species that are difficult to sight (e.g., those with long dive times, that surface with little splashing and no visible blow) may also suffer from chronically high CVs and therefore poor management by using NMEAN. Using NMEAN can also contribute to economic uncertainty for fisheries. For example, the probability of depleting a population is much higher using the NMEAN strategy, which could severely affect fisheries if closures were required for population recovery.