Dahlheim et al.: Interactions, injuries, and mortalities of Orcinus orca during fishing operations 89 
Figure 8 
Photographs of a killer whale (Orcinus orca) (A) with a cut-off dorsal fin and 
(B) with severe head and lateral injuries in the Bering Sea. The photographs 
were taken as the whale fed off discards during the fishing season in 1994. 
signatus) (Dahlheim!; Yano and Dahlheim, 1995). Because 
these data have not been extrapolated to cover interac- 
tions for the entire fleet, the number of interactions 
reported here is an underestimate of the total number of 
interactions with killer whales occurring in the Alaska 
groundfish fishery. 
During groundfish trawl operations, resident killer 
whales were seen in close proximity (<3 m) to fishing ves- 
sels and feeding off a variety of fish being discarded from 
the vessels. Group size varied for killer whales, and all 
age classes were seen taking part in this feeding. We have 
received multiple reports from fishery observers of both 
individual and groups of killer whales following vessels 
for extended periods (i.e., periods ranging from 3 d to 28 d). 
Over the past 6 decades (from the 1960s to the 2020s) 
in Alaska, fishermen have attempted to either reduce or 
eliminate depredation by killer whales through the use of 
different deterrence methods (see Dahlheim’). Although 
most deterrence efforts occurred during 
longline depredation events, reports of 
killer whales being shot while feeding 
off discards has also been documented 
during longline operations. Despite this 
long-term work by fishermen to protect 
their catch and reduce their financial 
losses, interactions continue to occur. 
We identified the resident killer whale 
ecotype as the ecotype responsible for 
all the interactions reported during 
this study, on the basis of the external 
morphologic characteristics of whales of 
this ecotype, genetic data, photographic 
matches made to well-known resident 
killer whales, and the recognition of one 
distinctly marked individual as a res- 
ident killer whale that linked all killer 
whales by association to that ecotype. 
Little information is known about the 
seasonal occurrence and movements of 
resident killer whales. We documented 
that interactions were occurring every 
year and month, with the highest num- 
ber of interactions reported during the 
spring and summer months. Given that 
fishery interactions with resident killer 
whales are reported throughout the year, 
we now know that killer whales occur in 
these northern areas year-round. Pho- 
tographic matches of individual killer 
whales collected by observers between 
1987 and 2001 (Dahlheim et al., 2002) 
at locations in the Pacific Ocean and the 
Bering Sea indicate that resident killer 
whales moved from south of Unimak 
Pass, north into the Bering Sea along 
the shelf break, and then to waters west 
of St. Matthews Island. Movements by 
individual killer whales also occurred 
from Unimak Pass westward to the cen- 
tral Aleutian Islands and then north into the Bering Sea 
to waters west of St. Matthews Island. 
Killer whales occur in high densities throughout Alaska 
(Leatherwood and Dahlheim’). Zerbini et al. (2007), on the 
basis of surveys of the nearshore waters of the GAO and the 
Aleutian Islands, estimated abundance of resident killer 
whales at 991 individuals (coefficient of variation=0.52), 
with a 95% confidence interval of 380—2585 individuals. 
Based on photo-identification research conducted by the 
MML and the North Gulf Oceanic Society in the Bering 
Sea and western GOA during 2001-2012, a minimum 
count of western Alaska residents is 1475 killer whales 
(Muto et al., 2016). Of this total count, the percentage of 
killer whales or pods involved with fishery interactions 
8 Leatherwood, S. J., and M. E. Dahlheim. 1978. Worldwide distri- 
bution of pilot whales and killer whales. Nav. Ocean Syst. Cent., 
Tech. Rep. 295, 39 p. [Available from website.] 
