Note: You need to enable scripting and Javascript in your browser settings to best view and navigate our website. Otherwise use our keyboard navigation and search page. Our print link for screen media is scripted. Your computer's normal print command will print this page. Please contact us if you have difficulty in accessing our web pages.
  link to AFSC home page
Mobile users can use the Site Map to access the principal pages


link to NMFS home page link to AFSC home page link to NOAA home page

Project Description

Determining the role of killer whales as apex predators is central to understanding the function and dynamics of marine ecosystems of the Aleutian Islands, Bering Sea and Gulf of Alaska. Killer whale surveys conducted by CAEP between 2001 and 2007 have resulted in encounters with over 250 groups of killer whales, belonging to three ecotypes, and have produced estimates of abundance (Zerbini et al. 2007) and information about prey preferences from chemical ecology studies (Herman et al. 2005, Krahn et al. 2007). The focus of our killer whale studies is on the abundance, population structure, prey preference, and foraging movements of mammal-eating 'transient' killer whales, with a particular focus on the potential impacts on endangered Steller sea lions. In 2007, we surveyed the eastern Aleutian Islands and collected identification photographs that will allow us to estimate abundance for that area using mark-recapture methods (when paired with data collected in 2005). We are now planning to conduct a survey of the central and western Aleutian Islands to provide the second sample for a mark-recapture study (when paired with data collected in that region in 2006). The survey will take place in summer and will be conducted to ensure an adequate sample size for abundance estimation. Upon its completion, this will provide the first estimate of abundance of transient killer whales for the western and central Aleutian Islands. Biopsy samples will be collected during the survey for on-going chemical ecology and genetics studies. We will continue to place an emphasis on deploying satellite tags to provide greater resolution for studying movement patterns (we deployed five tags in 2006-7). In 2008 we will initiate a new research project to deploy Passive Acoustic Listeners (PALs) on fixed moorings around Steller sea lion rookeries. These PALs will be programmed to record killer whale vocalizations for a 12-month period, to examine diurnal and seasonal trends in vocal detections, as a proxy for studying predation rates.

Issues & Justification

The documented declines of several marine mammal species, notably Steller sea lions (Eumetopias jubatus), in the western Gulf of Alaska, Aleutian Islands and Bering Sea have generated a range of hypotheses regarding possible causes, and killer whale predation has been identified as one possible cause. Evaluation and testing of this hypothesis requires empirical data on the population biology and feeding ecology of killer whales in this area.

Surveys conducted by CAEP in the GOA/AI/BS since 2001 have led to estimation of the abundance of transient and resident ecotypes from the Kenai Peninsula to the eastern Aleutians (Zerbini et al. 2007, Durban et al. in review). However, there is currently no abundance estimate available for transients in the western and central Aleutians, an area where Steller sea lions have continued to decline. An abundance estimate is crucial to assessing the potential impact of killer whales on Steller sea lions in this area. We are planning to survey the western and central Aleutian Islands, allowing us to estimate abundance of transients in this region for the first time.

Since 2001 we have obtained more than 225 killer whale skin and blubber samples have been obtained using remote biopsy techniques. Analysis of these samples indicates that transients in the eastern Aleutian Islands have a diet that is consistent with visual observations of predation, with Steller sea lions represent a relatively low percentage of their total prey (Krahn et al. 2007). Genetic analysis of these samples is also allowing us to assess the population structure of killer whales in this region. Relatively few samples have been collected from the central and western Aleutians, so samples collected in this area during the survey will be very valuable for both studies.

Since 2006 we have placed satellite tags on five transient killer whales, leading to the surprising finding that these whales sometimes make movements of 1000 miles or more to warm pelagic waters to the south of the Aleutian Islands during the summer. This puts a new perspective on the foraging range and potential prey base available to these whales. Additional tagging is the only means available for obtaining a large amount of fine-scale foraging and movement data, so we will continue our tagging attempts during the survey.

In 2008 and 2009 we will deploy Passive Acoustic Listeners (PALs) on fixed moorings around Steller sea lion rookeries. These PALs will be programmed to record killer whale vocalizations for a 12-month period, to examine diurnal and seasonal trends in vocal detections, as a proxy for studying predation rates. The ability to detect predation events and transient killer whale presence at a Steller sea lion rookery on a continuous basis for an entire year will bring a new level of information to studying the impact of killer whales on Steller sea lions. Data from rookeries in the western and central Aleutians will be compared to data from deployments at rookeries in the eastern Aleutians.

Abundance, prey preferences, and movement information will be synthesized in an energetic analysis to evaluate the current impact of predation on Steller sea lions.

Goals

  • Deploy two Passive Acoustic Listeners (PALs) on fixed moorings around Steller sea lion rookeries to obtain year-round detections of killer whale vocalizations as a proxy for predation behavior.
  • Design and plan a killer whale survey in the central and western Aleutian Islands
  • Collect skin and blubber samples from killer whales for molecular genetic analyses of stock structure and chemical analyses of diet.
  • Analyze identification photographs for mark-recapture abundance estimation and to assess movement patterns of killer whales through examination of matches of individuals to established regional catalogues.
  • Completion energetics study and manuscript on the potential impact of transients killer whales on prey populations in the Aleutians Islands, particularly Steller sea lions
  • Deploy up to 8 satellite tags on transient killer whales for high resolution data on movement patterns.

Methods

A 30-day vessel survey will be designed and planned for the June/July to locate killer whales around the central and western Aleutian Islands. Visual and acoustic survey techniques will be employed, and when killer whales are encountered, a skiff will be launched if weather permits to allow close approaches for tagging, photo-identification, biopsy and acoustic sampling. By surveying this region (first surveyed in 2006) we will be able to collect a second photographic sample of identified individuals, which will allow us to estimate abundance for this region by applying mark-recapture methods to the combined datasets.

During the survey, emphasis will be placed on deploying satellite tags to the dorsal fins of transient killer whales to provide greater resolution for studying movement patterns beyond the time frame of the vessel operations. Five satellite tags were deployed on transient killer whales during the CAEP killer whale cruises in 2006-7, providing high quality location data for up to 54 days. On the survey we aim to deploy as many as 8 tags. Photo-identification data will be compared to existing catalogues from other areas maintained by NMML and NGOS. Tissue samples will be used for mtDNA and microsatellite genetic analyses, as well as for stable isotope, fatty acid, and contaminant analyses. Acoustic recordings of killer whales will be used along with genetic and photographic data to assess the ecotype and population identity of recorded groups. If opportunities allow, we will also measure killer whale morphometrics using laser beam pointers (Durban and Parsons 2006), to compare the size of killer whales of different ecotypes and in different geographical regions, to assess stock structure and body condition.

We will deploy Passive Acoustic Listeners (PALs) on fixed moorings around Steller sea lion rookeries at two rookeries in the Aleutian Islands (at sites such as Amak, Ugamak, Kiska and the Delarof Islands). PALs were developed by Dr. Jeff Nysteun at the University of Washington, and they have been deployed on moorings off Cape Flattery and in Haro Strait, WA, to monitor killer whales where they have successfully recorded both resident and transient type killer whales (Nysteun, 2006). Because transient killer whales feed on marine mammals that have sensitive underwater hearing, they are typically silent when they hunt, and are only vocally active after making a kill (Deecke et al., 2005). For this reason, acoustic monitoring of vocal activity may offer a powerful approach to studying predation behavior throughout all seasons. The PALs will be programmed to record killer whale vocalizations for a 12-month period, to examine diurnal and seasonal trends in vocal detections, as a proxy for studying predation rates. This, in combination with the tracking of individual whales seen near Steller sea lion rookeries with satellite tags, can potentially provide more direct evidence of the magnitude of predation on Steller sea lions than has previously been available.

The acoustic data collected from the PALs in the Aleutians in 2008 will serve as the first year of a multi-year comparative study, as in future years PALS will be deployed in other locations in the Aleutian Islands.
Webmaster | Privacy | Disclaimer | Accessibility