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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Physiological stress correlates with year, Chinook availability, vessel abundance and an interaction between Chinook and vessel abundance.According to the best-fit mixed effects model, glucocorticoid concentrations decreased with increased Chinook salmon CPUE, after taking into account a 10-day lag time for fish to swim from the study site to the test fishery (column A). The best-fit model also includes an interaction between Chinook counts and vessel abundance on glucocorticoids, whereby fecal glucocortiods are always high at times of low Chinook counts. However, an increase in glucocorticoids with increasing vessel abundance is observed only during times of relatively high Chinook counts (column B set to the Chinook value indicated by the vertical line in the corresponding panel of column A). The y-axis represents glucocorticoid concentration marginal means predicted from the best-fit model. The hashed blue lines indicate 95% confidence intervals. Vertical red dotted 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 red dotted lines indicate dependent variable marginal means for each year on day 230 within the model.
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pone-0036842-g002: Physiological stress correlates with year, Chinook availability, vessel abundance and an interaction between Chinook and vessel abundance.According to the best-fit mixed effects model, glucocorticoid concentrations decreased with increased Chinook salmon CPUE, after taking into account a 10-day lag time for fish to swim from the study site to the test fishery (column A). The best-fit model also includes an interaction between Chinook counts and vessel abundance on glucocorticoids, whereby fecal glucocortiods are always high at times of low Chinook counts. However, an increase in glucocorticoids with increasing vessel abundance is observed only during times of relatively high Chinook counts (column B set to the Chinook value indicated by the vertical line in the corresponding panel of column A). The y-axis represents glucocorticoid concentration marginal means predicted from the best-fit model. The hashed blue lines indicate 95% confidence intervals. Vertical red dotted 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 red dotted lines indicate dependent variable marginal means for each year on day 230 within the model.

Mentions: We tested for effects of prey and vessel traffic on GC concentrations by fitting fecal GC concentrations to Fraser River Chinook CPUE, vessel abundance, Julian date, sex, pod and fecal T3 concentrations, including individual identity as a random effect. The best-fit models are presented in Table 2, however more detailed model selection data can be found in Tables S2 and S3. Fecal GC concentrations were best modeled as a response to year, Fraser River Chinook CPUE (with a 10-day time lag), vessel abundance in proximity to whales and the interaction of prey and vessel abundance (Table 2; GC Top model A). Chinook CPUE was the only significant main effect in this model, however less variance was explained by the model if any of the other parameters were removed. There was a highly significant negative relationship between GC concentrations and Fraser River Chinook CPUE each year; GC concentrations consistently decreased as Chinook counts increased (Figure 2a). Both year and Chinook CPUE were significant if vessel abundance and its interactions were removed, with GCs being significantly lower in 2007 compared to 2009 (Table 2; GC Top model B). Sex, pod and fecal T3 concentrations did not improve any of the tested models.


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)

Physiological stress correlates with year, Chinook availability, vessel abundance and an interaction between Chinook and vessel abundance.According to the best-fit mixed effects model, glucocorticoid concentrations decreased with increased Chinook salmon CPUE, after taking into account a 10-day lag time for fish to swim from the study site to the test fishery (column A). The best-fit model also includes an interaction between Chinook counts and vessel abundance on glucocorticoids, whereby fecal glucocortiods are always high at times of low Chinook counts. However, an increase in glucocorticoids with increasing vessel abundance is observed only during times of relatively high Chinook counts (column B set to the Chinook value indicated by the vertical line in the corresponding panel of column A). The y-axis represents glucocorticoid concentration marginal means predicted from the best-fit model. The hashed blue lines indicate 95% confidence intervals. Vertical red dotted 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 red dotted lines indicate dependent variable marginal means for each year on day 230 within the model.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0036842-g002: Physiological stress correlates with year, Chinook availability, vessel abundance and an interaction between Chinook and vessel abundance.According to the best-fit mixed effects model, glucocorticoid concentrations decreased with increased Chinook salmon CPUE, after taking into account a 10-day lag time for fish to swim from the study site to the test fishery (column A). The best-fit model also includes an interaction between Chinook counts and vessel abundance on glucocorticoids, whereby fecal glucocortiods are always high at times of low Chinook counts. However, an increase in glucocorticoids with increasing vessel abundance is observed only during times of relatively high Chinook counts (column B set to the Chinook value indicated by the vertical line in the corresponding panel of column A). The y-axis represents glucocorticoid concentration marginal means predicted from the best-fit model. The hashed blue lines indicate 95% confidence intervals. Vertical red dotted 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 red dotted lines indicate dependent variable marginal means for each year on day 230 within the model.
Mentions: We tested for effects of prey and vessel traffic on GC concentrations by fitting fecal GC concentrations to Fraser River Chinook CPUE, vessel abundance, Julian date, sex, pod and fecal T3 concentrations, including individual identity as a random effect. The best-fit models are presented in Table 2, however more detailed model selection data can be found in Tables S2 and S3. Fecal GC concentrations were best modeled as a response to year, Fraser River Chinook CPUE (with a 10-day time lag), vessel abundance in proximity to whales and the interaction of prey and vessel abundance (Table 2; GC Top model A). Chinook CPUE was the only significant main effect in this model, however less variance was explained by the model if any of the other parameters were removed. There was a highly significant negative relationship between GC concentrations and Fraser River Chinook CPUE each year; GC concentrations consistently decreased as Chinook counts increased (Figure 2a). Both year and Chinook CPUE were significant if vessel abundance and its interactions were removed, with GCs being significantly lower in 2007 compared to 2009 (Table 2; GC Top model B). Sex, pod and fecal T3 concentrations did not improve any of the tested models.

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