We estimated abundance from 1999-2021 for the endangered main Hawaiian Island (MHI) insular population of false killer whales using a modeling technique that incorporates animal
availability into a capture-recapture model. Since 1999, this population has been sampled by a variety of dedicated systematic, nonsystematic, and opportunistic methods that have resulted in the yearly encounter histories of 202 individuals and 52 satellite telemetry tag deployments used in this analysis. Survey efforts and animal location data from telemetry deployments were separately analyzed using kernel density estimators, and the degree of overlap between these two processes was used this overlap as a covariate for detection probability within a Jolly-Seber open population model in a Bayesian framework. Using simulated data, we found this model estimates abundance with a higher degree of accuracy and precision than conventional methods and is robust to many sampling and ecological complications, such as variable tag deployment lengths, low detectability, and variable social group sizes. Upon fitting the model to the false killer whale dataset, we found that the insular population of false killer whales remains small, with an estimated 138 individuals (95% CRI: [120, 160]) in the population in 2021. The population appears to be in decline throughout the study period, with an estimated trend of -3.51 (95% CRI: [-8.40, 2.04]) over the entire time series and -5.53, 95% CRI = [-9.91, -1.61] over the past 10 years. As this modeling approach addresses the spatiotemporal variability in sampling effort, these updated abundance estimates provide improved inputs for management frameworks
Citation:
Badger, J.J., R.W. Baird, D.S. Johnson, A.L. Bradford, S.D. Mahaffy, M.A. Kratofil, T. Cullins, J.J. Currie, S.H. Stack, and E.M. Oleson. 2024. Accounting for Spatiotemporal Sampling Bias in a Long-Term Dataset Establishes a Decline in Abundance of Endangered False Killer Whales (Pseudorca crassidens) in the Main Hawaiian Islands. Document PSRG_2024_06 submitted to the Pacific Scientific Review Group, NOAA Fisheries.
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