Studying population dynamics and research strategies for endangered Cook Inlet Belugas

Studying population dynamics and research strategies for endangered Cook Inlet Belugas

Tuesday, February 25th at 2:00 PM (PST) in FSH 203

Stephanie Thurner and Amanda Warlick

Cook Inlet belugas (Delphinapterus leucas, CIB) are a small, geographically isolated population in Cook Inlet, Alaska. In the 1990s, the CIB population experienced a notable decline and despite the cessation of hunting in 2005, there is limited evidence of recovery to date, with most recent surveys estimating further decline. Consequently, CIB are listed as endangered under the U.S Endangered Species Act. To examine population viability, identify factors limiting recovery, and further evaluate the potential contribution of research activities designed to monitor the CIB population status we are (1) developing an integrated population model and (2) analyzing research strategies. Today, we will talk about our work to date and hope to garner feedback as we continue to engage on these projects.

Integrated population modeling to examine population dynamics and viability – Amanda Warlick

Substantial monitoring effort and resources have been invested to conduct aerial and mark-resight surveys of the CIB population, yet considerable uncertainty still exists about demographic rates, population abundance, and potential factors limiting recovery. One way to improve our understanding of population dynamics and future viability is through integrated population modeling, where multiple sources of information are combined to reduce bias and improve precision in life-history parameter estimates. Here we build on a recent integrated population model to estimate time-varying adult survival, fecundity, and abundance using aerial and mark-resight survey data collected from 2004-2018. We outline a framework for conducting a population viability analysis (PVA) to quantify the magnitude of change in extinction probabilities across a range of demographic rates estimated in the integrated model. The PVA will be used in the future to examine the potential effects of anthropogenic mortality, decreased fecundity, or reduced carrying capacity due to the unquantified and unknown effects of stressors such as underwater noise, prey depletion, or habitat range contraction. This information will help identify factors limiting recovery and what, if any, management actions could ameliorate the effects of the most impactful anthropogenic activities.

Research strategy analysis – Stephanie Thurner

We are conducting a Research Strategy Analysis to evaluate the potential contribution of research actions designed to monitor CIB population status, as required by the CIB Recovery Plan. Aerial surveys of marine wildlife species that aggregate in groups are generally susceptible to four major sources of bias that could lead to underestimation of population abundance: (1) group availability bias, (2) group perception bias, (3) individual availability bias, and (4) individual perception bias. We evaluate the potential for accurate and precise estimation of CIB abundance and trends using aerial surveys involving a new aerial survey design that is standardized to ensure consistent coverage across years and provides spatially and temporally replicated counts. Preliminary results show that both linear regression and Multivariate Auto-Regressive State-Space models were able to distinguish stable (0% annual growth), increasing (~2% annual growth), and decreasing (~2% annual decrease) trends, despite various types of availability and detection bias as long as there were no long-term trends in bias. A Bayesian N-mixture-type model was able to estimate unbiased annual abundance under various types of availability and detection bias acting together; but performance deteriorated when sources of bias occurred individually.

Posted in Fisheries Think Tank.

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