Evaluating anthropogenic threats to endangered killer whales to inform effective recovery plans

Abstract

Understanding cumulative effects of multiple threats is key to guiding effective management to conserve endangered species. The critically endangered, Southern Resident killer whale population of the northeastern Pacific Ocean provides a data-rich case to explore anthropogenic threats on population viability. Primary threats include: limitation of preferred prey, Chinook salmon; anthropogenic noise and disturbance, which reduce foraging efficiency; and high levels of stored contaminants, including PCBs. We constructed a population viability analysis to explore possible demographic trajectories and the relative importance of anthropogenic stressors. The population is fragile, with no growth projected under current conditions, and decline expected if new or increased threats are imposed. Improvements in fecundity and calf survival are needed to reach a conservation objective of 2.3% annual population growth. Prey limitation is the most important factor affecting population growth. However, to meet recovery targets through prey management alone, Chinook abundance would have to be sustained near the highest levels since the 1970s. The most optimistic mitigation of noise and contaminants would make the difference between a declining and increasing population, but would be insufficient to reach recovery targets. Reducing acoustic disturbance by 50% combined with increasing Chinook by 15% would allow the population to reach 2.3% growth.

Approaches to reduce noise from ships operating in important killer whale habitats

“…Our convoy model suggests that a speed limit of 11.8 kt reduces the time SRKWs receive peak levels of ship noise (>110 dB) by ~70 min/day, but also decreases their "quiet time" (<103 dB) by ~15-30 min/day. Population modelling tools are available to explore the likely consequences to SRKWs of predicted effects of noise on foraging (Lacy et al 2017). Before evaluating this tradeoff, an explicit policy statement is needed on both the desired noise reduction target and its intended benefit to whales.…”

“…This sensitivity to ship noise is problematic, because a number of large-scale industrial developments are pending that, if approved, would increase ship traffic in SRKW critical habitat (Gaydos et al 2015). Some level of noise reduction will be needed to ensure that additional ship traffic does not cause a net increase in noise levels in SRKW critical habitat; in fact, some currently unspecified level of net reduction in noise will be needed to promote recovery given predictions of the SRKW trajectory under status quo conditions (Velez-Espino et al 2014, Lacy et al 2017.…”

Survival of Salmonids from an Experimental Commercial Fish Trap

“…Despite these efforts and many others, ESA-listed wild salmonid stocks have not recovered, and fishing opportunities have become increasingly limited (Lichatowich et al 2017;Price et al 2017;Gayeski et al 2018a). The populations of southern resident killer whales Orcinus orca and other apex predators have declined to historic lows due to reductions in the quantity and size of marine prey (e.g., Chinook Salmon) and other factors (Ford et al 2010;Ayres et al 2012;Lewis et al 2015;Lacy et al 2017). The populations of southern resident killer whales Orcinus orca and other apex predators have declined to historic lows due to reductions in the quantity and size of marine prey (e.g., Chinook Salmon) and other factors (Ford et al 2010;Ayres et al 2012;Lewis et al 2015;Lacy et al 2017).…”

“…Failure to achieve Pacific salmonid recovery and the continued mixed-stock harvest of salmon in marine settings have further altered ecosystem dynamics. The populations of southern resident killer whales Orcinus orca and other apex predators have declined to historic lows due to reductions in the quantity and size of marine prey (e.g., Chinook Salmon) and other factors (Ford et al 2010;Ayres et al 2012;Lewis et al 2015;Lacy et al 2017).…”

Fisheries Volume 44 Number 9 September 2019

“…Failure to achieve Pacifi c salmonid recovery and the continued mixed-stock harvest of salmon in marine settings have further altered ecosystem dynamics. The populations of southern resident killer whales Orcinus orca and other apex predators have declined to historic lows due to reductions in the quantity and size of marine prey (e.g., Chinook Salmon) and other factors (Ford et al 2010 ;Ayres et al 2012 ;Lewis et al 2015 ;Lacy et al 2017 ).…”