Killer whales ( Orcinus orca ) are large predators that occupy the top trophic position in the world's oceans and as such may have important roles in marine ecosystem dynamics. Although the possible top-down effects of killer whale predation on populations of their prey have received much recent attention, little is known of how the abundance of these predators may be limited by bottom-up processes. Here we show, using 25 years of demographic data from two populations of fish-eating killer whales in the northeastern Pacific Ocean, that population trends are driven largely by changes in survival, and that survival rates are strongly correlated with the availability of their principal prey species, Chinook salmon ( Oncorhynchus tshawytscha ). Our results suggest that, although these killer whales may consume a variety of fish species, they are highly specialized and dependent on this single salmonid species to an extent that it is a limiting factor in their population dynamics. Other ecologically specialized killer whale populations may be similarly constrained to a narrow range of prey species by culturally inherited foraging strategies, and thus are limited in their ability to adapt rapidly to changing prey availability.

Killer whales were photographed in oil after the 1989 'Exxon Valdez' oil spill, but preliminary damage assessments did not definitively link mortalities to the spill and could not evaluate recovery. In this study, photo-identification methods were used to monitor 2 killer whale populations 5 yr prior to and for 16 yr after the spill. One resident pod, the AB Pod, and one transient population, the AT1 Group, suffered losses of 33 and 41%, respectively, in the year following the spill. Sixteen years after 1989, AB Pod had not recovered to pre-spill numbers. Moreover, its rate of increase was significantly less than that of other resident pods that did not decline at the time of the spill. The AT1 Group, which lost 9 members following the spill, continued to decline and is now listed as depleted under the Marine Mammal Protection Act. Although there may be other contributing factors, the loss of AT1 individuals, including reproductive-age females, accelerated the population's trajectory toward extinction. The synchronous losses of unprecedented numbers of killer whales from 2 ecologically and genetically separate groups and the absence of other obvious perturbations strengthens the link between the mortalities and lack of recovery, and the 'Exxon Valdez' oil spill. KEY WORDS: Killer whales · 'Exxon Valdez' oil spill · EVOS · Southern Alaska · Fishery interactions · Residents · TransientsResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 356: 269-281, 2008 bottlenose dolphins relied on vision to detect thick oil, tactile response was the primary factor in avoidance. Smultea & Wursig (1995) found that dolphins apparently did not detect sheen oil and that although they detected slick oil, they did not avoid traveling through it. Evans (1982) observed that gray whales Eschrichtius robustus typically swam through oil seeps off California. Although the gray whales modified their swim speeds and breathing rates, there was no consistent pattern of behavior in regard the presence of the oil. Lack of an olfactory system likely contributes to the difficulty cetaceans have in detecting oil.Loughlin (1994a) included a number of studies evaluating the impact of the oil spill on cetaceans (e.g. , Harvey & Dahlheim 1994, Loughlin 1994b, von Ziegesar et al. 1994. described a decline in the largest identified fish-eating 'resident' killer whale pod, AB Pod, but concluded that a direct link to the oil spill was equivocal. Effects on the genetically distinct mammal-eating 'transient' population, the AT1 Group, were not assessed.In this paper, we examine the impact of the EVOS on killer whales based on long-term population monitoring. We examine the population trajectories of 2 groups of genetically and ecologically distinct killer whales in Prince William Sound to re-evaluate the confidence with which their decline and lack of recovery can be attributed to the EVOS. We examine the possible vectors for oil contamination in killer whales and assess their vulnerability to oil s...

Aerial censuses of harbour seals (Phoca vituiina) were conducted in the Strait of Georgia (1966–88), the lower Skeena River (1977–87), off the southwest coast of Vancouver island (1976–87), off the northeast coast of the Queen Charlotte Islands (1986), in Jervis Inlet (1987), and at the entrance to Queen Charlotte Strait (1988). The estimated number of seals in the Strait of Georgia, the primary study area, increased from 2170 in 1973 to 15 810 in 1988; the number in the lower Skeena River from 520 in 1977 to 1590 in 1987; and the number off south western Vancouver Island from 210 in 1976 to 1130 in 1987. The trends indicated that populations throughout British Columbia had been increasing at a rate of about 12.5% ∙yr−1 since 1973. Based on the density of seals in the areas surveyed, and the relative distribution of bounty and commercial kills, the total post-pupping population in British Columbia was estimated to have numbered 75 000–88 000 in 1988, compared with 9000–10 500 when the species was protected in 1970. Despite the recent increases, which probably reflect the recovery from historic kills, there was no evidence of density-dependent changes in the population growth rate.

Abstract. Polymerase chain reaction techniques were developed and applied to identify DNA from .40 species of prey contained in fecal (scat) soft-part matrix collected at terrestrial sites used by Steller sea lions (Eumetopias jubatus) in British Columbia and the eastern Aleutian Islands, Alaska. Sixty percent more fish and cephalopod prey were identified by morphological analyses of hard parts compared with DNA analysis of soft parts (hard parts identified higher relative proportions of Ammodytes sp., Cottidae, and certain Gadidae). DNA identified 213 prey occurrences, of which 75 (35%) were undetected by hard parts (mainly Salmonidae, Pleuronectidae, Elasmobranchii, and Cephalopoda), and thereby increased species occurrences by 22% overall and species richness in 44% of cases (when comparing 110 scats that amplified prey DNA). Prey composition was identical within only 20% of scats. Overall, diet composition derived from both identification techniques combined did not differ significantly from hard-part identification alone, suggesting that past scat-based diet studies have not missed major dietary components. However, significant differences in relative diet contributions across scats (as identified using the two techniques separately) reflect passage rate differences between hard and soft digesta material and highlight certain hypothesized limitations in conventional morphological-based methods (e.g., differences in resistance to digestion, hard part regurgitation, partial and secondary prey consumption), as well as potential technical issues (e.g., resolution of primer efficiency and sensitivity and scat subsampling protocols). DNA analysis of salmon occurrence (from scat soft-part matrix and 238 archived salmon hard parts) provided species-level taxonomic resolution that could not be obtained by morphological identification and showed that Steller sea lions were primarily consuming pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Notably, DNA from Atlantic salmon (Salmo salar) that likely originated from a distant fish farm was also detected in two scats from one site in the eastern Aleutian Islands. Overall, molecular techniques are valuable for identifying prey in the fecal remains of marine predators. Combining DNA and hard-part identification will effectively alleviate certain predicted biases and will ultimately enhance measures of diet richness, fisheries interactions (especially salmonrelated ones), and the ecological role of pinnipeds and other marine predators, to the benefit of marine wildlife conservationists and fisheries managers.

We describe an experiment conducted to assess the impact of the sound generated by an acoustic harassment device (AHD) on the relative abundance and distribution of harbor porpoises (Phocoena phocoena) in Retreat Passage, British Columbia. During control periods when the AHD was inactive, the mean number of porpoises observed in the study area was 0.39 for broad area scans conducted with the naked eye and 0.48 for narrow sector scans conducted with binoculars. Abundance declined precipitously when the AHD was activated, to 0.007 porpoises per broad area scan and 0.018 per narrow sector scan. The mean number of porpoise resightings while tracking their movements also declined from 12.2 to 13.6 per sighting during control periods to 1.1–1.9 per sighting when the AHD was activated, which suggested that the few porpoises that ventured into the study area spent less time within it when the AHD was activated. The effect of the AHD diminished with distance. No porpoises were observed within 200 m of the AHD when it was activated. The number of sightings and resightings observed when it was activated was less than 0.2% of the number expected had there been no AHD effect at a range of 200–399 m, 1.4% the number expected at a range of 400–599 m, varied between 2.5% and 3.3% of the number expected at a range of 600–2,499 m, and was 8.1% the number expected at a range of 2,500–3,500 m, which suggested that the impact of the AHD extended beyond our maximum sighting range of 3.5 km.