Limits...
Distinguishing the impacts of inadequate prey and vessel traffic on an endangered killer whale (Orcinus orca) population.

Ayres KL, Booth RK, Hempelmann JA, Koski KL, Emmons CK, Baird RW, Balcomb-Bartok K, Hanson MB, Ford MJ, Wasser SK - PLoS ONE (2012)

Bottom Line: The inadequate prey hypothesis argues that the killer whales have become prey limited due to reductions of their dominant prey, Chinook salmon (Oncorhynchus tshawytscha).Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability.Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery.

View Article: PubMed Central - PubMed

Affiliation: Despartment of Biology, Center for Conservation Biology, University of Washington, Seattle, Washington, United States of America. kayres@harveyecology.com

ABSTRACT
Managing endangered species often involves evaluating the relative impacts of multiple anthropogenic and ecological pressures. This challenge is particularly formidable for cetaceans, which spend the majority of their time underwater. Noninvasive physiological approaches can be especially informative in this regard. We used a combination of fecal thyroid (T3) and glucocorticoid (GC) hormone measures to assess two threats influencing the endangered southern resident killer whales (SRKW; Orcinus orca) that frequent the inland waters of British Columbia, Canada and Washington, U.S.A. Glucocorticoids increase in response to nutritional and psychological stress, whereas thyroid hormone declines in response to nutritional stress but is unaffected by psychological stress. The inadequate prey hypothesis argues that the killer whales have become prey limited due to reductions of their dominant prey, Chinook salmon (Oncorhynchus tshawytscha). The vessel impact hypothesis argues that high numbers of vessels in close proximity to the whales cause disturbance via psychological stress and/or impaired foraging ability. The GC and T3 measures supported the inadequate prey hypothesis. In particular, GC concentrations were negatively correlated with short-term changes in prey availability. Whereas, T3 concentrations varied by date and year in a manner that corresponded with more long-term prey availability. Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability. Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery.

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Temporal trends in variables used to test the inadequate prey and vessel impacts hypotheses.Temporal variation in Fraser River Chinook salmon catch per unit effort at the Albion test fishery (a); vessel traffic in proximity to Southern resident killer whales (b); physiological stress (indexed by fecal glucocorticoid concentrations) (c); nutrition (indexed by fecal triiodothyronine concentrations) (d). Trend lines determined using general linear model selection with predictor variables year, Julian date (linear, quadratic, cubic, etc.; see Table S1) and the interactions between year and Julian date parameters. Hashed lines indicate 95% confidence intervals. Dotted vertical lines indicate Julian day 230 (August 18), the time of maximum vessel traffic and approximately ten days before the maximum Chinook salmon catch each year. Horizontal dotted lines indicate dependent variable marginal means for each year on day 230 within the individual model.
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pone-0036842-g001: Temporal trends in variables used to test the inadequate prey and vessel impacts hypotheses.Temporal variation in Fraser River Chinook salmon catch per unit effort at the Albion test fishery (a); vessel traffic in proximity to Southern resident killer whales (b); physiological stress (indexed by fecal glucocorticoid concentrations) (c); nutrition (indexed by fecal triiodothyronine concentrations) (d). Trend lines determined using general linear model selection with predictor variables year, Julian date (linear, quadratic, cubic, etc.; see Table S1) and the interactions between year and Julian date parameters. Hashed lines indicate 95% confidence intervals. Dotted vertical lines indicate Julian day 230 (August 18), the time of maximum vessel traffic and approximately ten days before the maximum Chinook salmon catch each year. Horizontal dotted lines indicate dependent variable marginal means for each year on day 230 within the individual model.

Mentions: While in the Salish Sea from May through September, the SRKW primarily eat Chinook salmon heading to the Fraser River system [20]. Fraser River Chinook salmon counts are relatively low when the whales first arrive sometime in the late spring and early summer, as are the number of vessels in the area (Figure 1a and 1b respectively). Both Fraser River Chinook salmon counts and vessel abundance peak around August-September, progressively declining thereafter. These coincident peaks allow us to use GC and T3 measures to distinguish between the inadequate prey and vessel impact hypotheses. Under the inadequate prey hypothesis, GC concentrations should be relatively high upon SRKW arrival when Fraser River Chinook salmon counts arelow. GC concentrations should reach their nadir around August-September–the peak of Fraser River Chinook salmon counts–and then increase as Fraser River Chinook salmon decline thereafter. The vessel impact hypothesis makes the opposite prediction. GC concentrations should be relatively low due to low vessel traffic when SRKW arrive in late Spring, peak around August-September with the peak in vessel abundance, and decline with declining vessel traffic thereafter. If prey availability and vessel impacts act cumulatively, we predict an interaction between Fraser River Chinook salmon counts and vessel abundance on GC concentrations. Specifically, GC concentrations should show a steeper positive correlation with vessel abundance during years of low Fraser River Chinook salmon returns.


Distinguishing the impacts of inadequate prey and vessel traffic on an endangered killer whale (Orcinus orca) population.

Ayres KL, Booth RK, Hempelmann JA, Koski KL, Emmons CK, Baird RW, Balcomb-Bartok K, Hanson MB, Ford MJ, Wasser SK - PLoS ONE (2012)

Temporal trends in variables used to test the inadequate prey and vessel impacts hypotheses.Temporal variation in Fraser River Chinook salmon catch per unit effort at the Albion test fishery (a); vessel traffic in proximity to Southern resident killer whales (b); physiological stress (indexed by fecal glucocorticoid concentrations) (c); nutrition (indexed by fecal triiodothyronine concentrations) (d). Trend lines determined using general linear model selection with predictor variables year, Julian date (linear, quadratic, cubic, etc.; see Table S1) and the interactions between year and Julian date parameters. Hashed lines indicate 95% confidence intervals. Dotted vertical lines indicate Julian day 230 (August 18), the time of maximum vessel traffic and approximately ten days before the maximum Chinook salmon catch each year. Horizontal dotted lines indicate dependent variable marginal means for each year on day 230 within the individual model.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3368900&req=5

pone-0036842-g001: Temporal trends in variables used to test the inadequate prey and vessel impacts hypotheses.Temporal variation in Fraser River Chinook salmon catch per unit effort at the Albion test fishery (a); vessel traffic in proximity to Southern resident killer whales (b); physiological stress (indexed by fecal glucocorticoid concentrations) (c); nutrition (indexed by fecal triiodothyronine concentrations) (d). Trend lines determined using general linear model selection with predictor variables year, Julian date (linear, quadratic, cubic, etc.; see Table S1) and the interactions between year and Julian date parameters. Hashed lines indicate 95% confidence intervals. Dotted vertical lines indicate Julian day 230 (August 18), the time of maximum vessel traffic and approximately ten days before the maximum Chinook salmon catch each year. Horizontal dotted lines indicate dependent variable marginal means for each year on day 230 within the individual model.
Mentions: While in the Salish Sea from May through September, the SRKW primarily eat Chinook salmon heading to the Fraser River system [20]. Fraser River Chinook salmon counts are relatively low when the whales first arrive sometime in the late spring and early summer, as are the number of vessels in the area (Figure 1a and 1b respectively). Both Fraser River Chinook salmon counts and vessel abundance peak around August-September, progressively declining thereafter. These coincident peaks allow us to use GC and T3 measures to distinguish between the inadequate prey and vessel impact hypotheses. Under the inadequate prey hypothesis, GC concentrations should be relatively high upon SRKW arrival when Fraser River Chinook salmon counts arelow. GC concentrations should reach their nadir around August-September–the peak of Fraser River Chinook salmon counts–and then increase as Fraser River Chinook salmon decline thereafter. The vessel impact hypothesis makes the opposite prediction. GC concentrations should be relatively low due to low vessel traffic when SRKW arrive in late Spring, peak around August-September with the peak in vessel abundance, and decline with declining vessel traffic thereafter. If prey availability and vessel impacts act cumulatively, we predict an interaction between Fraser River Chinook salmon counts and vessel abundance on GC concentrations. Specifically, GC concentrations should show a steeper positive correlation with vessel abundance during years of low Fraser River Chinook salmon returns.

Bottom Line: The inadequate prey hypothesis argues that the killer whales have become prey limited due to reductions of their dominant prey, Chinook salmon (Oncorhynchus tshawytscha).Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability.Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery.

View Article: PubMed Central - PubMed

Affiliation: Despartment of Biology, Center for Conservation Biology, University of Washington, Seattle, Washington, United States of America. kayres@harveyecology.com

ABSTRACT
Managing endangered species often involves evaluating the relative impacts of multiple anthropogenic and ecological pressures. This challenge is particularly formidable for cetaceans, which spend the majority of their time underwater. Noninvasive physiological approaches can be especially informative in this regard. We used a combination of fecal thyroid (T3) and glucocorticoid (GC) hormone measures to assess two threats influencing the endangered southern resident killer whales (SRKW; Orcinus orca) that frequent the inland waters of British Columbia, Canada and Washington, U.S.A. Glucocorticoids increase in response to nutritional and psychological stress, whereas thyroid hormone declines in response to nutritional stress but is unaffected by psychological stress. The inadequate prey hypothesis argues that the killer whales have become prey limited due to reductions of their dominant prey, Chinook salmon (Oncorhynchus tshawytscha). The vessel impact hypothesis argues that high numbers of vessels in close proximity to the whales cause disturbance via psychological stress and/or impaired foraging ability. The GC and T3 measures supported the inadequate prey hypothesis. In particular, GC concentrations were negatively correlated with short-term changes in prey availability. Whereas, T3 concentrations varied by date and year in a manner that corresponded with more long-term prey availability. Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability. Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery.

Show MeSH
Related in: MedlinePlus