New study coins the term ‘bright extinction’ to describe the failure of Southern Resident killer whales to recover

Raincoast, in collaboration with a team of international scientists, authored a new study on the potential to recover the critically endangered population of Southern Resident killer whales. This study updates an analysis undertaken 8 years ago, which estimated the population of 80 killer whales had a 24% chance of extinction within 100 years.

The updated study, “Warning sign of an accelerating decline in critically endangered killer whales” published this week in Nature’s Communications Earth and Environment, employs a Population Viability Analysis to assess how factors like the age of females, calf survival rate, and salmon abundance affect recovery of the population. The study was conducted on a population of 74 individuals.

We explore the consequences to Southern Residents from three well documented primary threats; prey limitation (Chinook salmon), underwater noise that disrupts successful foraging, and accumulation of contaminants. We found that over the next 100 years, the population will likely decline between 1% -2% annually under the current habitat conditions. While initially slow, this rate of decline increases after two generations, about 40 years, a pattern typical of populations headed towards extinction.

The authors determined that habitat degradation through underwater noise, high concentrations of industrial chemicals, and declining quality and quantity of Chinook salmon still inhibit population recovery.

These urban whales must find food in busy, noisy and polluted waters. It seems as though every time we deal with one harmful industrial chemical, we have a thousand new ones to consider. Southern Resident killer whales keep reminding us about the need for a true ecosystem approach.

In addition to the updated understanding of threats the team also identified a phenomenon they call ‘bright extinction’ to signify a precipitous decline in a well understood population. Bright extinction contrasts with ‘dark extinction’, the loss of species that are poorly studied and data limited.

The failure of the Southern Resident killer whales to recover can be attributed in large part to a reluctance to make difficult decisions. In a declining population, however, the greater the lag time between knowledge and mitigation, the more draconian the recovery actions needed. Ultimately, such actions often come with a higher social cost, and with increased risk that threat reduction efforts might not work.

In the end, the team concluded that 11th hour recovery is still possible, but more serious conservation efforts will be required.

Read the research

Citation

Williams, R., Lacy, R.C., Ashe, E. Lance Barrett-Lennard*, Tanya M. Brown, Joseph K. Gaydos, Frances Gulland, Misty MacDuffee*, Benjamin W. Nelson, Kimberly A. Nielsen, Hendrik Nollens, Stephen Raverty, Stephanie Reiss, Peter S. Ross*, Marena Salerno Collins, Raphaela Stimmelmayr & Paul Paquet*. 2024. Warning sign of an accelerating decline in critically endangered killer whales (Orcinus orca). Commun Earth Environ 5, 173 https://doi.org/10.1038/s43247-024-01327-5

*denotes Raincoast authors

Abstract

Wildlife species and populations are being driven toward extinction by a combination of historic and emerging stressors (e.g., overexploitation, habitat loss, contaminants, climate change), suggesting that we are in the midst of the planet’s sixth mass extinction. The invisible loss of biodiversity before species have been identified and described in scientific literature has been termed, memorably, dark extinction. The critically endangered Southern Resident killer whale (Orcinus orca) population illustrates its contrast, which we term bright extinction; namely the noticeable and documented precipitous decline of a data-rich population toward extinction. Here we use a population viability analysis to test the sensitivity of this killer whale population to variability in age structure, survival rates, and prey-demography functional relationships. Preventing extinction is still possible but will require greater sacrifices on regional ocean use, urban development, and land use practices, than would have been the case had threats been mitigated even a decade earlier.

Select figures

Figure 1 Southern Resident killer whale population growth, gene diversity and abundance over time.

Population growth rate (r) (Fig. 1a) and number of whales and proportion of current gene diversity projected (Fig. 1b) over 100 years and averaged across 1000 iterations of the Baseline model of the SRKW population. The expected growth rate is in blue, the projected decline is in red, and the horizontal dashed line represents the mean rate. Note the bifurcation around 50 years (two killer whale generations) indicative of an accelerating decline, even without accounting for increasing threats⁵. Shading represents the 95% confidence intervals around SRKW abundance (dark blue line) and gene diversity (light blue line).

Figure 2 Relationship of survival and reproductive rates [with the Pacific Salmon Commission] Chinook Abundance Index.

Annual survival rates (Fig. 2a) and reproductive rates (the proportion of breeding age females producing a calf) (Fig. 2b) for SRKW of different age-sex classes (Table 1) predicted from logistic regressions against the Chinook salmon prey abundance. Calf survival is in yellow, post-reproductive female is in red, older male is in green, older female is in orange, subadult survival is in dark blue, young female is in light blue, and young male is in blue.

Figure 4. Southern Resident killer whale population size projected 100 years in the future

Projections of SRKW population size, averaged across 1000 iterations for six scenarios that range from optimal to pessimistic:
• “Road to recovery” (in blue) assumes direct and indirect human impacts on the whales and their habitats re removed (1.5× Chinook, no climate change effects, no noise, human-caused mortalities prevented, no PCBs or other contaminants);
• “Slow recovery” (in yellow) assumes lesser but still considerable improvements to threats (1.3× Chinook, no climate change, no noise, no human-caused mortalities, environmental PCBs reduced with 25-year half-life);
• “Persistence” (in light blue) assumes each threat reduced to half as much as in “Slow recovery”; “Current decline” (in orange) is the Baseline;
• “Decline toward extinction” (in dark blue) adds further threats (8% reduction in prey size, climate change decimating Chinook salmon stocks, total contaminants 1.67× PCB, a low probability of oil catastrophic spills);
• “Worst case” (in red) adds further plausible increases in threats (0.7× Chinook, noise disturbance 100% of time, oil spills at higher frequency).

Authors and affiliations

Rob Williams¹, Robert C. Lacy², Erin Ashe¹, Lance Barrett-Lennard³, Tanya M. Brown⁴, Joseph K. Gaydos^5,6, Frances Gulland⁶, Misty MacDuffee³, Benjamin W. Nelson, Kimberly A. Nielsen¹, Hendrik Nollens⁷, Stephen Raverty⁸, Stephanie Reiss¹, Peter S. Ross³, Marena Salerno Collins¹, Raphaela Stimmelmayr⁹ & Paul Paquet³

Oceans Initiative
Chicago Zoological Society
Raincoast Conservation Foundation
Fisheries and Oceans Canada
SeaDoc Society
Wildlife Health Center
San Diego Zoo Wildlife Alliance
Animal Health Center
Department of Wildlife Management

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