New paper published titled “Accounting for sampling bias reveals a decline in abundance of endangered false killer whales in the main Hawaiian Islands” Full 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. 2025. Accounting for sampling bias reveals a decline in abundance of endangered false killer whales in the main Hawaiian Islands. Endangered Species Research 57:325-340https://doi.org/10.3354/esr01423. This is an open-access paper available from https://www.int-res.com/abstracts/esr/v57/esr01423 or from our Hawai‘i publication page https://cascadiaresearch.org/hawaii_publications/ ABSTRACT: We estimated abundance of the endangered main Hawaiian Islands (MHI) insular population of false killer whales Pseudorca crassidens from 1999–2022 using a modeling technique that incorporates animal availability in a capture–recapture analysis. The population was sampled using different sampling methods, resulting in yearly encounter histories of 265 individuals and 53 satellite-tagged whales. Survey effort and animal location data were separately analyzed using kernel density estimators, and the degree of overlap between these 2 processes was used to model detection probability in a Bayesian Jolly-Seber population model. This approach better addresses spatiotemporally variable sampling effort than traditional capture–recapture methods, improving the estimation of reliable abundance trends. Using simulated data, the model was robust to many sampling and ecological complications, such as variable low detectability, unequal tag deployment lengths, and variable social group sizes. Fitting the model to the MHI false killer whale data set, we found that the insular population of false killer whales remains small, with an estimated 139 individuals (95% credible interval, CRI = [114, 162]) in 2022. The population appears to be in decline throughout the study period, with a mean annual percent change of –1.09 (95% CRI = [–2.11, –0.023]) over the entire time series and –3.51 (95% CRI = [–5.08, –1.88]) since 2013, when the population was listed as endangered. Given the magnitude of the decline, identifying which of the many factors affecting this population is most responsible is key in order to guide potential management responses. HŌ‘ULU‘ULU MANA‘O: Koho mākou i ka nui o nā pū‘uo ‘anehalapohe o nā koholā ‘āhuka iwi poʼo like (Pseudorca crassidens) a puni ka paeʼāina ‘o Hawai‘i (MHI) mai nā makahiki 1999-2022 ma o kekahi ‘ōnaehana e kālailai ana i ka loa‘a ‘ana o ka holoholona i kekahi kālailai loa‘a-loaʼa hou. Mai nā makahiki 1999-2022 mai, he mau ki‘ina ‘ohi hāpana i nānā ‘ia a ‘o ka loa‘a, ‘ike kūmakahiki ‘ia he 265 koholā iwi po‘o like a he 53 mea i poelele lepili ‘ia. Kālailai pākahi ‘ia ke anapū‘uo a me ka ‘ikepili henua ma o nā koho pa‘apū kenele, a ‘o ka nui o ke kaulapa ma waena o ia mau ‘elua, ua ho‘ohana ‘ia i kumu ho‘ohālike i ka papaha ‘ikena ma ka pū‘uo ho‘ohālike Bayesian Jolly-Sever. ‘Oi aku ka maika‘i o kēia hana ma mua o nā hana loa‘a-loa‘a hou ma‘amau no ka nānā ‘ana i nā ‘ano ao henua ‘ohi hāpana, a he ho‘oikaika i ke koho i ka ‘aui ‘ana o nā lawa kūpono. Ma ka ho‘ohana ʼana i ka ‘ikepili ho‘okūkohukohu ‘ia, he kumu ho‘ohālike maika‘i nō kēia i ka nui ‘ohi hāpana a me ka nui o nā hopena kaiaola, e la‘a ho‘i me ke kumuloli ‘ikena ha‘aha‘a, ka lō‘ihi o ka lepili ‘oko‘a, a me ke kumuloli o ka nui pū‘ulu launa. Ma ka launa ‘ana o ia kumu ho‘ohālike me ka ‘ikepili o ko Hawai‘i pae‘āina koholā ‘āhuka iwi po‘o like, ‘ike mākou i ka li‘ili‘i mau o ka pū‘uo koholā ‘āhuka iwi po‘o like ‘ane‘ane puni ‘ia e ke kai, ma kahi o 139 (95% CRI = [114, 162]) ma ka makahiki 2022. Ma o ka wā kālailai, kohu mea lā, emi mai ka pū‘uo, he -1.09 pākēneka loli (95% CRI = [-2.11, -0.023]) ‘awelike o ka makahiki, a he -3.51 (95% CRI = [-5.08, -1.88]) mai ka makahiki 2013, i ka wā i helu ‘ia ai ka pū‘uo he mea ‘anehalapohe. No ka nui o ia ‘ano emi ‘ana, ko‘iko‘i nō ka ‘ike ‘ana i nā mea e pā nui ana i kēia pū‘uo i mea e alaka‘i aku ai i nā hāpane ho‘oponopono. There is also a feature story on this publication on the NOAA Fisheries website at https://www.fisheries.noaa.gov/feature-story/endangered-population-false-kil... -- Robin W. Baird, Ph.D. Hawai‘i Program Director Cascadia Research Collective<https://cascadiaresearch.org/> 218 ½ W. 4th Avenue Olympia, WA 98501 USA Donate to support our work<https://cascadiaresearch.org/donations/> Follow us on Facebook<https://www.facebook.com/CascadiaResearch/> Updates on our June O‘ahu field project<https://cascadiaresearch.org/hawaii-update/june2025/> Recent publications on our work<https://cascadiaresearch.org/hawaii_publications/>: 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. 2025. Accounting for sampling bias reveals a decline in abundance of endangered false killer whales in the main Hawaiian Islands. Endangered Species Research https://doi.org/10.3354/esr01423 Baird, R.W. 2025. Out of sight, out of mind: false killer whale populations are at risk<https://cascadiaresearch.org/files/Baird_2025_Pseudorca-conservation_Whalewatcher.pdf>. Whalewatcher 45(1):76-82. Corsi, E., R.W. Baird, A.E. Harnish, A.M. Gorgone, J.J. Currie, S.H. Stack, and J.J. Kiszka. 2025. Variation in social structure among multiple stocks of island-associated common bottlenose dolphins (Tursiops truncatus) in Hawaiian waters. Marine Mammal Science e70051. https://doi.org/10.1111/mms.70051 Henderson, E.E., M.A. Kratofil, R.W. Baird, C.R. Martin, A.E. Harnish, G.C. Alongi, S.W. Martin, and B.L. Southall. 2025. Exposure and response of satellite-tagged Blainville’s beaked whales to mid-frequency active sonar off Kaua‘i, Hawai‘i. Movement Ecology 13:29. https://doi.org/10.1186/s40462-025-00550-9 Mahaffy, S.D., U. Gorter, and R.W. Baird. 2025. Neonatal facial pigmentation of pygmy killer whales (Feresa attenuata): a description from repeated observations of individuals in the wild. Aquatic Mammals 51:138-143. https://doi.org/10.1578/AM51.2.2025.138 Walker-Milne, N.L., Y.P. Papastamatiou, S.D. Mahaffy, and R.W. Baird. 2025. Dynamics of foraging interactions between cookiecutter sharks (Isistius spp). and short-finned pilot whales (Globicephala macrorhynchus) in Hawai‘i. Marine Biology 172:63. https://doi.org/10.1007/s00227-025-04633-4