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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 (AI), Bering Sea (BS), and Gulf of Alaska (GOA). Killer whale surveys conducted by CAEP between 2001 and 2006 have resulted in encounters with 230 groups of killer whales, belonging to three ecotypes, and 206 tissue samples have been collected. In 2007 we will examine spatial variability in genetic markers from these skin samples to assess killer whale stock structure in the AI/BS/GOA. Our surveys have documented “resident” fish-eating killer whales to be the most abundant ecotype observed in this region, and continued work in 2007 will relate resident distribution, abundance, movements, and demography to key environmental covariates, including interactions with commercial fisheries. However, the primary focus of our killer whale studies will be the foraging movements of mammal-eating “transient” killer whales, with a particular focus on the potential impacts on endangered Steller sea lions. Collaborative studies with the North Gulf Oceanic Society (NGOS) have identified a hot spot in distribution and abundance of transients around the western end of the Alaska Peninsula and in the eastern Aleutians, coinciding with the northbound migration of gray whales into the Bering Sea in late spring. Migrating gray whales have increased in abundance over the past three decades, providing a predictable seasonal food source which may have indirectly increased predation pressure on pinnipeds and other marine mammal species later in the summer. Feeding observations during the summer months have documented the importance of northern fur seals in the diet of killer whales, both in the eastern Aleutian Islands and around the Pribilof Islands. However, the extent of predation on Steller sea lions still remains unclear. In 2007 we propose to focus on the movements and predation behavior of transient killer whales in the AI/BS region, particularly at the time of this seasonal shift at the end of the gray whale migration. A 21-day vessel survey will be conducted in the month of June to locate killer whales around the eastern Aleutian Islands/western Alaska Peninsula and in the southeast Bering Sea around the Pribilof Islands. Emphasis will be placed on deploying satellite tags to provide greater resolution for studying movement patterns, and Passive Acoustic Listeners (PALs) will be deployed 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. One recent hypothesis suggests that killer whale (Orcinus orca) predation may be responsible for these declines, with prey-shifting by killer whales over time as they sequentially deplete populations of available prey species (Springer et al. 2003).  Although there is considerable disagreement over the evidence supporting this hypothesis (DeMaster et al. 2006, Mizroch and Rice 2006, Trites et al. 2006, Wade et al. 2006), this debate has highlighted the need for empirical data on the role of killer whales as predators within these marine ecosystems. 

Surveys conducted by CAEP in the GOA/AI/BS since 2001 have now documented that three ecotypes of killer whales use these waters. More than 200 (206) skin samples have been obtained using remote biopsy techniques (e.g., Barrett-Lennard et al. 1996) and have been sequenced for mitochondrial DNA (mtDNA), documenting the presence of known “resident,” “transient,” and “offshore” haplotypes. Analysis of blubber samples from these biopsies for fatty acids, stable isotopes, and organochlorine contaminants indicate that the consistent dietary specializations persist in this area (Herman et al. 2005), with residents feeding on fish and transients on marine mammals. Furthermore, this suite of chemical markers has provided the first quantitative evidence that the offshore ecotype has a diet that differs from both residents and transients, likely constituting fish of a higher trophic level (Krahn et al. 2007). Genetic variability within the resident and transient ecotypes is also allowing us to assess the population structure of killer whales in this region. All 206 skin samples have now been sequenced for mtDNA.

The ecotypes vary in their abundance in this region. We have had 152 encounters with residents since 2001, 60 with transients, and only 3 encounters with offshores. Line-transect analyses indicate that the abundance of residents in coastal waters between the Kenai Fjords in south central Alaska and Tanaga Pass in the central Aleutians (991; 95% CI 379-2585) is approximately four times the abundance of transients (251; 95% CI 97-644) during the summer months (Zerbini et al. 2007). However, the minimum count of transients in this area from the combined NMML and NGOS photo-ID catalogues is currently 377 whales, and mark-recapture estimates for transients based on photo-identification data are also higher than the “instantaneous” line-transect estimates (Durban et al. in prep). This suggests that a greater number of transient killer whales may visit the study area, perhaps seasonally, but are not always present. In a collaborative project with NGOS, we have identified a large seasonal aggregation (~80 whales annually) of transients around the western end of the Alaska Peninsula and in the eastern Aleutians, coinciding with the northbound migration of gray whales into the Bering Sea in late spring. Migrating gray whales have increased in abundance over the past three decades, providing a predictable seasonal food source. If this has led to an increase in killer whales using this area (either through seasonal immigration or population growth), this may have indirectly increased predation pressure on pinnipeds and other marine mammal species later in the summer once gray whales have migrated from the area (DeMaster et al. 2006). To evaluate this hypothesis, we need to assess the seasonal movement patterns and prey shifting of killer whales using this area. Feeding observations during the summer months have documented the importance of northern fur seals in the diet of killer whales, both in the eastern Aleutian Islands (Matkin et al. 2007) and around the Pribilof Islands in the Bering Sea (CAEP, unpublished data). However, the extent of predation on Steller sea lions still remains unclear.

Goals

  • Examine the foraging movements and predation behavior of transient killer whales in the GOA/AI/BS region, particularly at the time of this seasonal shift at the end of the gray whale migration.

Specific Goals of 2007 survey:

  • Deploy up to 10 satellite tags on transient killer whales for high resolution data on movement patterns.
  • Deploy Passive Acoustic Listeners (PALs) on fixed moorings around Steller sea lion rookeries (3 or 4), to obtain year-round detections of killer whale vocalizations as a proxy for predation behavior.
  • Collect photo-identification data to assess movement patterns of killer whales through examination of matches of individuals to established regional catalogues.
  • Collect skin and blubber samples from killer whales for molecular genetic analyses of stock structure and chemical analyses of diet.
  • Collect morphometric measurements from free-ranging killer whales to assess body condition and geographic/ecotypic size differences.
  • Conduct detailed statistical analyses of spatial mtDNA variability for both residents and transients to assess the population structure in the Gulf of Alaska, Aleutian Islands, and Bering Sea.
  • Continue entering individual photo-identification data from resident and transient killer whales into a database in order to estimate abundance, movement patterns, and demographic parameters. Once compiled, these estimates will be used to evaluate the importance of transient killer whales as apex predators and the interaction between resident killer whales and commercial fishing operations.

Methods

A 21-day vessel survey will be conducted in the month of June to locate killer whales around the eastern Aleutian Islands/western Alaska Peninsula and in the southeast Bering Sea around the Pribilof Islands. Visual and acoustic survey techniques will be employed; 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. 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. Three satellite tags were deployed on transient killer whales during the CAEP killer whale cruise in 2006, providing high quality location data for 14 days, 38 days, and 54 days. In 2007 we aim to deploy as many as 10 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. We will also measure killer whale morphometrics, using laser beam pointers (Durban and Parsons 2006), to compare the sizes of killer whales of different ecotypes and different geographical regions and to assess stock structure and body condition.

The vessel survey will also be used to deploy Passive Acoustic Listeners (PALs) on fixed moorings around Steller sea lion rookeries at Amak, Ugimak, and Clubbing Rocks (and possibly Bogoslof Island). PALs have been deployed on moorings off Cape Flattery and in Haro Strait, WA, to monitor killer whales, and they have successfully recorded both resident and transient type killer whales (Nystuen 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. 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. 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 eastern Aleutians in 2007/08 will serve as the first year of a multi-year comparative study. In summer 2008, PALs will be deployed in the western Aleutians at Steller sea lion rookeries to provide a comparison of transient killer whale daily presence/absence in a region where Steller sea lions are still declining (western Aleutians) versus an area where they are stable or increasing (eastern Aleutians).

Skin samples collected in 2007 will be integrated with the samples from previous years to assess patterns of genetic variability. DNA will be extracted and sequenced for mtDNA haploytpes and incorporated into an analysis of stock structuring in coastal waters of the North Pacific. Photo-identification and photogrammetric images from 2001-2007 will continue to be archived in a relational database to link sighting histories of known individual killer whales to movement patterns, population demography, and morphometric parameters.

Citations

Barrett-Lennard, L.G., T.G. Smith, and G.M. Ellis. 1996. A cetacean biopsy system using lightweight pneumatic darts, and its effect on the behavior of killer whales. Mar. Mammal Sci. 12:14-27.

Deecke, V.B., J.K.B. Ford, and P.J.B. Slater. 2005. The vocal behaviour of mammal-eating killer whales: communicating with costly calls. Anim. Behav. 69:395-405.

DeMaster, D.P., A.W. Trites, P. Clapham, S. Mizroch, P. Wade, R.J. Small, and J. Ver Hoef. 2006. The sequential megafaunal collapse hypothesis: Testing with existing data. Prog. Oceanogr. 68:329-342.

Durban, J.W., and K.M. Parsons. 2006. Laser-metrics of free-ranging killer whales. Mar. Mammal Sci. 22:735-743.

Durban, J., D. Ellifrit, M. Dahlheim, J. Waite, C. Matkin, L. Barrett-Lennard, G. Ellis, R. Pitman, R. LeDuc, and P. Wade. In prep. Clustered mark-recapture analysis of mammal-eating killer whales around the Aleutian Islands and Gulf of Alaska. Ecol. Appl.

Herman, D.P., D.G. Burrows, P.R. Wade, J.W. Durban, C.O. Matkin, R.G. LeDuc, L.G. Barrett-Lennard, and M.M. Krahn. 2005. Feeding ecology of eastern North Pacific killer whales Orcinus orca from fatty acid, stable isotope, and organochlorine analyses of blubber biopsies. Mar. Ecol. Prog. Ser. 302:275-291.

Krahn, M.M., D.P. Herman, C.O. Matkin, J.W. Durban, L. Barrett-Lennard, D.G. Burrows, M.E. Dahlheim, N. Black, R.G. LeDuc, and P.R. Wade. 2007. Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales. Mar. Environ. Res. 63:91-114.

Matkin, C.O., L.G. Barrett-Lennard, H. Yurk, D. Ellifrit, and A.W. Trites. 2007. Ecotypic variation and predatory behavior among killer whales (Orcinus orca) off the eastern Aleutian Islands, Alaska. Fish. Bull., U.S. 105:74-87.

Mizroch, S.A., and D.W. Rice. 2006. Have North Pacific killer whales switched prey species in response to depletion of the great whale populations? Mar. Ecol. Prog. Ser. 310:235-246.

Nystuen, J.A. 2006. Marine mammal monitoring for Northwest fisheries. Final report N00024-02-D-6602. 20 p. Available from Northwest Fisheries Science Center, NMFS, 2725 Montlake Blvd. East, Seattle, WA 98112-2097.

Springer, A.M., J.A. Estes, G.B. Van Vliet, T.M. Williams, D.F. Doak, E.M. Danner, K.A. Forney, and B. Pfister. 2003. Sequential megafaunal collapse in the North Pacific Ocean: An ongoing legacy of industrial whaling? Proc. Nat. Acad. Sci. U.S.A. 100:12223-12228.

Trites, A.W., V.B. Deecke, E.J. Gregr, J.K.B. Ford, and P.F. Olesiuk. 2006. Killer whales, whaling, and sequential megafaunal collapse in the North Pacific: A comparative analysis of the dynamics of marine mammals in Alaska and British Columbia following commercial whaling. Mar. Mammal Sci. (OnlineEarly Articles). doi: 10.1111/j.1748-7692.2006.00076.x

Wade, P.R., V.N. Burkanov, M.E. Dahlheim, N.A. Friday, L.W. Fritz, T.R. Loughlin, S.A. Mizroch, M.M. Muto, D.W. Rice, L.G. Barrett-Lennard, N.A. Black, A.M. Burdin, J. Calambokidis, S. Cerchio, J.K.B. Ford, J.K. Jacobsen, C.O. Matkin, D.R. Matkin, A.V. Mehta, R.J. Small, J.M. Straley, S.M. McCluskey, and G.R. VanBlaricom. 2006. Killer whales and marine mammal trends in the North Pacific—a re-examination of evidence for sequential megafauna collapse and the prey-switching hypothesis. Mar. Mammal Sci. (OnlineEarly Articles). doi: 10.1111/j.1748-7692.2006.00093.x

Zerbini, A.N., J.M. Waite, J.W. Durban, R. LeDuc, M.E. Dahlheim, and P.R. Wade. 2007. Estimating abundance of killer whales in the nearshore waters of the Gulf of Alaska and Aleutian Islands using line-transect sampling. Mar. Biol. 150:1033-1045.
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