U.S. Pacific pelagic longline fisheries operating in the central North Pacific have been subject to a series of regulations to reduce bycatch of protected species, including seabirds and sea turtles. Cetaceans are also occasionally caught, and the bycatch of false killer whales, Pseudorca crassidens, in the Hawaii‐based deep‐set longline fishery currently exceeds allowable levels under the Marine Mammal Protection Act (MMPA). In this study, we examined longline observer data collected between 1994 and 2009, with emphasis on 2003–2009, to identify patterns of cetacean bycatch and depredation in relation to area, time, vessel, habitat variables, fishing gear, and set characteristics. The objectives of these analyses were to identify relationships amongst fishery interaction rates and variables that could provide opportunities to reduce depredation by cetaceans, reduce the likelihood of incidentally catching a cetacean when present, or reduce the severity of injuries to cetaceans if caught. The results of this study were provided to the False Killer Whale Take Reduction Team, convened under the MMPA, as they developed a plan to reduce serious injury and mortality of false killer whales in these fisheries. No correlates were identified that could markedly reduce depredation rates, but a slight (16%) reduction in repeat depredation within a fishing trip was evident when vessels moved at least 100 km following a depredation event. The most practical option for reducing bycatch of false killer whales was determined to be the use of small (14/0–16/0) circle hooks, which could result in an estimated 6% reduction in bycatch and a greater likelihood of releasing animals with non‐serious injuries. Additional research is needed to address unresolved questions relating to processes involved in depredation events and hookings or entanglements of false killer whales.

The first cetacean circovirus, beaked whale circovirus (BWCV), was recently reported in a Longman’s beaked whale (Indopacetus pacificus) stranded in Hawai‘i and represents an emergent disease with unknown population impacts. In other species, circovirus infection may cause mortality or opportunistic co-infection by other pathogens. We report on a targeted surveillance of stranded cetaceans in the Pacific basin, including archived beaked whale species, strandings where pathological findings suggested disease presence, mass stranded animals, and additional individuals to represent a broad range of Hawaiian cetacean species. Archived tissues primarily from the brain, kidney, liver, lung, spleen, and lymph nodes of individuals stranded between 2000 and 2020 (n=30) were tested by PCR for the presence of BWCV. Suspect positive tissue amplicons were confirmed as BWCV through sequencing. Of the screened individuals, 15 animals tested positive in one or more tissues, with a single striped dolphin (Stenella coeruleoalba) testing positive in all six tissues. The highest rate of detection among positive cases was found in the brain (69%), followed by lymph (67%) and lung tissues (64%). Additionally, co-infections of cetacean morbillivirus (n=3), Brucella ceti (n=1), and Toxoplasma gondii (n=1) were found among the positive cases. These results expand the potential host range for BWCV into ten additional odontocete species. New host species include a dwarf sperm whale (Kogia sima) that stranded on O‘ahu in 2000, predating the initial case of BWCV. The results broaden the known geographic range of BWCV to Saipan in the Western Pacific, and American Samoa in the South Pacific, where stranded Cuvier’s beaked whales (Ziphius cavirostris) tested positive. Although the clinical significance is currently unknown, this study demonstrates that BWCV has a high prevalence within targeted cetacean screening efforts. Infectious diseases pose a major threat to cetaceans and BWCV may represent an important emerging disease within populations spanning the central, Western, and South Pacific.