Why are some protected species failing to recover?
New study uses integrated population models to predict extinction risk for Cook Inlet beluga whales and lend insight into factors limiting the recovery of protected populations.
Sparse monitoring data and persistent knowledge gaps can hamper conservation efforts aimed at recovering depleted wildlife populations. In a new study, researchers from the UW School of Aquatic and Fishery Sciences (SAFS) set out to tackle this issue for federally endangered Cook Inlet beluga whales by developing an integrated population model that capitalizes on all available information to understand factors that may be affecting survival, reproduction, and population viability.
Listed as endangered under the U.S. Endangered Species Act, the Cook Inlet beluga whale (Delphinapterus leucas) population has declined approximately 75% since the 1970s. The major results from the new study, published on Oct. 6 in the journal Animal Conservation, indicate that the population will likely continue to decline, with a 17-32% probability of extinction in 150 years and a low probability of reaching recovery targets in that time frame. The researchers also found that survival of non-breeding whales and overall reproduction in Cook Inlet may be depressed compared to other beluga populations, suggesting that these demographic rates may be behind the ongoing declines. Researchers highlighted the potential benefit of bolstering reproduction in particular, though identifying and implementing conservation actions that might facilitate that is challenging.
SAFS PhD student Amanda Warlick led the effort, along with USGS Washington Cooperative Fish and Wildlife Research Unit Leader and Associate Professor Sarah Converse. SAFS researchers teamed up with biologists from Montana State University, the Cook Inlet Beluga Whale Photo-ID Project, and the NOAA Alaska Fisheries Science Center’s Marine Mammal Laboratory to develop a Bayesian integrated population model using mark-resight and aerial count data from 2004-2018. The turbid waters and unpredictable weather conditions in Cook Inlet make collecting these data difficult. Moreover, the permanent scars and marks used to individually identify belugas and build mark-resight datasets only reliably show up in older animals. These data limitations, coupled with the complexity of the life history of these whales, made model development challenging. However, given the difficulties of collecting the data, getting the most from them is critical. Integrated population models are designed to do just that, by bringing together all available data to better understand demography, threats, and population viability.
Dr. Warlick and the research team also examined the effects of salmon prey availability and oceanographic conditions on beluga vital rates. They found that reproduction was correlated with metrics of prey availability, with lower reproduction in years of poorer prey availability. Further study is needed to better understand the link between prey populations and beluga demography.
Many questions remain about why protected populations sometimes fail to recover despite managers’ best efforts. This study highlights the utility of integrated population modeling for maximizing the usefulness of available data to identify factors limiting the recovery of declining wildlife populations. The hope is that this model can be used on an ongoing basis to better understand what is happening with Cook Inlet belugas as more data become available, while also inspiring the development of similar models for other declining species.
