Identifying social clusters of endangered main Hawaiian Islands false killer whales
Authors: Mahaffy SD , Baird RW , Harnish AE , Cullins T , Stack SH , Currie JJ , Bradford AL , Salden DR , Martien KK 
Published: June 2023

The presence of distinct social groups within an animal population can result in heterogeneity in many aspects of its life history and ecology. The ability to accurately assess social group membership increases with the number of times individuals are identified, but obtaining sufficient sightings of rarely encountered species can be difficult. Three social clusters were previously identified for the endangered population of false killer whales Pseudorca crassidens around the main Hawaiian Islands, using modularity among associations within a 12 yr photographic dataset with no restrictions on the number of times seen. In this study, we used photo-identification data over a 23 yr period to reassess the number and membership of social clusters, restricted to individuals seen on at least 5 different days. We compared the robustness of clustering assignments from 6 community detection algorithms using modularity and found that the 3 highest-ranking algorithms all identified the same number (4) and membership of social clusters. Spatial use of clusters varied among the islands, with 3 of the 4 clusters encountered regularly only off 1 or 2 of the 3 main island study areas. Comparison of genetic differentiation among social clusters revealed significant differentiation in nuclear DNA. Furthermore, all individuals in 2 of the clusters possess the same mitochondrial DNA haplotype, while in the other 2 clusters, approximately 40% of animals possess a second haplotype. This level of clustering and associated heterogeneity within the population may have implications for mark-recapture abundance estimation, as well as for mitigating exposure to anthropogenic activities, including interactions with fisheries.HŌ‘ULU‘ULU MANA‘O: Pili nā ‘ano like ‘ole o ka nohona a me ke kālaikaiaola o nā pū‘uo holoholona i ka loa‘a ‘ana o nā pū‘ulu kiko‘ī. Pi‘i a‘e ka hiki ke helu kūpono‘ia ka māhuahua ‘ana o nā heluna o ia mau pū‘ulu i ka helu ‘ana i nā wā e ‘ike ‘ia ai kēlā me kēia holoholona, ‘o ka lawa ‘ana na‘e o ka ‘ike ‘ana i nā lāhulu ‘ane halapohe kekahi ālaina. Hō‘ia ‘ia ‘ekolu pū‘ulu o ke koholā ‘ane halapohe, ‘o ka Pseudorca crassidens, a puni nā mokupuni nui ‘ewalu o Hawai‘i, ma ka ho‘owae‘anona ‘ana i ka pilina i loko o kekahi ‘ikepili ki‘a he ‘umikūmālua makahiki me ke kāohi ‘ole i ka nui o ka ‘ike ‘ia ‘ana. Ma kēia kilo ‘ana, ua ho‘ohana mākou i ka ‘ikepili ma o nā makahiki he iwakāluakūmākolu i mea e hō‘oia hou ai i ka heluna a me nā lālā o nā pū‘ulu launa i loko o kekahi pū‘uo holoholona, a pāpā ‘ia nā kālailaina i nā mea i ‘ike ‘ia ma ‘elima mau lā ‘oko‘a ma ka li‘ili‘i loa. Ho‘ohālikelike mākou i ke ‘ano me ka ikaika o kēia mau pū‘ulu launa ma ka ho‘ohana ‘ana i ka ho‘owae‘anona ‘ana ma ‘eono pū‘ulu ha‘ilula a ‘o ka mea i loa‘a, ‘o ia ho‘i ka ‘ike ‘ana, ma o nā ha‘ilula nui ‘ekolu, i ka heluna a me ka lālā ho‘okahi o nā pū‘ulu launa. Loli ka ho‘ohana ‘ana i ke koana o nā pū‘ulu ma waena o nā mokupuni, ‘ike ‘ia ‘ekolu pū‘ulu ma ho‘okahi a ‘elua paha mokupuni mai loko mai o nā mokupuni nui ‘ekolu e kālailai ‘ia ana. Ma ka ho‘ohālikelike ‘ana aku i nā hi‘ohi‘ona ōewe ‘oko‘a o nā pū‘ulu launa, ‘ike ‘ia ka ‘oko‘a ‘ano nui ma ka piko ōewe o nā pū‘ulu. A no laila, loa‘a i nā mea a pau o ia mau pū‘ulu ‘elua ke ōewe ho‘oilina ho‘okahi, a ma nā pū‘ulu ‘ē a‘e ‘elua, loa‘a he hi‘ohi‘ona ōewe ‘elua i nā holoholona he 40 pākēneka. Hiki nō paha i kēia ‘ano ho‘opū‘ulu ‘ana me kēia ‘ano wae‘anona ōewe ho‘opili ma kekahi pū‘uo ke pili i ke kuhi ‘ana i ka nui ma ka hopu kaha ‘ana, a i ke kāohi a ho‘ēmi ‘ana mai i nā hopena o nā hana kanaka, e la‘a ho‘i me ka hana ma ke kai lawai‘a.