Offshore Orcas
See: Schorr, G. S., Hanson, M. B., Falcone, E. A., Emmons, C. K., Jarvis, S. M., Andrews, R. D., et al. (2022). Movements and Diving Behavior of the Eastern North Pacific Offshore Killer Whale (Orcinus orca). Front. Mar. Sci. 9, 854893. doi: 10.3389/fmars.2022.854893. The paper is available HERE:
Also: Dalheim, Marilyn, Alisa Schulman-Janiger, Nancy Black, Richard Tenullo, Dave Ellifrit, Kenneth C. Balcomb, III (2008), Eastern temperate North Pacific offshore killer whales (Orcinus orca): Occurrence, movements, and insights into feeding ecology.
A scientist from Canada discovers why a type of killer whale has such bad teeth - a love of shark meat! February 8, 2011 (Practical Fishing)
"We started to speculate perhaps it’s sharks that they’re eating, and sharks have very rough skin – when it dries out, it’s like coarse sandpaper."
Later, while Ford and colleagues were observing the whales, they noticed them engaging in feeding behaviour. Immediately following this they discovered chunks of pink meat on the water's surface which upon genetic analysis turned out to be the meat of at least 16 different Pacific sleeper sharks (Somniosus pacificus).
This discovery, together with the fact that the different lineages have different genetics, do not mix, socialise, or mate together and have learned different hunting strategies (transients travel in small packs and are generally quiet, to help them sneak up on their prey, whereas residents are far more vocal) as well as the fact that they are thought to have different 'languages', means that some scientists are calling for a reclassification into three separate species.
Orcas off B.C.'s coast love the taste of shark
February 4, 2011 B.C. Cetacean Sightings Network
But they're wearing their teeth flat on the abrasive skin of the sleeper shark, study says
This latest study, newly published in the journal Aquatic Biology, proves through DNA evidence that offshore killer whales prey on large Pacific sleeper sharks -- whose skin is so abrasive it is believed to be wearing the whales' teeth flat.
"It's exciting, it's been a detective hunt for so long," said John Ford, lead author of the study and senior research scientist with the federal Pacific Biological Station in Nanaimo. "For so many years we've been pondering on what these offshore killer whales feed on."
Termed Offshores and numbering over 250-300 identified individuals, these whales have been found typically travelling in large groups of 25 or more in continental shelf waters, some ranging from California to Alaska and probably out to hundreds or perhaps thousands of miles offshore. Offshore killer whales were shown to move a one-way distance of at least 4,435 km; a value far exceeding that reported for other killer whale eco-types.
Not much is known about the Offshore orcas of the Eastern North Pacific Ocean. On Sept. 6, 1992, Orca Survey received a call from Seacoast Expeditions that there were a group of approximately 70 whales off Victoria that they could not identify from the ID manuals. Ken Balcomb, Astrid van Ginneken, Diane Claridge, and Dave Ellifrit immediately went over to the locality to get ID pictures. They photographed 67 whales.
This was only the second time they had an offshore killer whale encounter. The first time was on Aug. 20, 1990, and these whales were found 25 miles west of Barkley Sound on the west side of Vancouver Island. 48 whales were photographed during this encounter.
Offshore pods are usually found in groups of 30-60 or more individuals.
They are seldom seen in the protected coastal waters and most encounters have taken place near the Queen Charlotte Islands and 20 to 30 miles off the west coast of Vancouver Island.
They have been photographed all along the Pacific coast from Southern California and S.E. Alaska
Offshore orcas appear to be piscivorous (fish eaters), feeding perhaps on sharks (especially sleeper sharks - see links above).
Offshores have strong genetic and morphological similarity to Residents.
Offshores share a set of calls completely different from those of any other community, resident or transient.
Recent mtDNA evidence suggests that Resident orca derived from founding matrilines of Offshore populations in each of the resident ranges, perhaps in a way analagous to human kin groups radiating into coastal habitats as ice retreated from the Pacific Northwest. Interestingly, the acoustic dialects of the resident orca appear in similar geographic pattern to the linguistic pattern of the native human languages of the Northwest coast: Salishan, Wakashan, and Tlingit from south to north. And, as with the hominids, linguistic and kinship differences were not a complete barrier to gene flow, while matrilineal bonds held society together.
From: Offshore Killer Whale Teeth, On August 29, 1997 a dead killer whale was reported drifting 17 miles offshore. It took the Strawberry Isle Marine Research Society's small research boat eleven hours to tow the carcass to Strawberry Isle, with many re-fueling visits from whale-watching boats. The 5.5m (18ft) female orca's saddle patch and dorsal fin identified her as O120, a member of the elusive offshore group of killer whales. No clear cause of death was found, though her heavily worn teeth and thin blubber suggest that she may have been old and far removed from her home in more southern waters. After a year of bleaching the bones in the sun, Society member Dominique Dupuis (Pipot) and a crew of volunteers put in close to 700 hours scrubbing and treating the bones with a non-toxic penetrating epoxy. Pipot and Robinson Cook created the ingenious orca-sized framework that supports the skeleton. The Build-A-Whale exhibit has inspired people in classrooms and at community events all over Vancouver Island, and will continue touring after it leaves the BC Experience.
Below is from NMFS' U.S. Pacific Marine Mammal Stock Assessments: 1999
Revised 09/30/99
KILLER WHALE (Orcinus orca): Eastern North Pacific Offshore Stock
STOCK DEFINITION AND GEOGRAPHIC RANGE
Figure 1. Killer whale sightings based on aerial and shipboard surveys off California, Oregon and Washington, 1989-96. Sightings include killer whales from all stocks found in this region. Dashed line represents the U.S. EEZ, thick line indicates the outer boundary of all surveys combined. Greater effort was conducted off California (south of 42 / N) and in the inshore half of the U.S. EEZ. See Appendix 2 of Barlow et al. (1997) and Barlow (1997) for data sources and information on timing and location of survey effort
Killer whales
Killer whales have been observed in all oceans and seas of the world (Leatherwood and Dahlheim 1978). Although reported from tropical and offshore waters, killer whales prefer the colder waters of both hemispheres, with greatest abundances found within 800 km of major continents (Mitchell 1975). Along the west coast of North America, killer whales occur along the entire Alaskan coast (Braham and Dahlheim 1982), in British Columbia and Washington inland waterways (Bigg et al. 1990), and along the outer coasts of Washington, Oregon and California (Green et al. 1992; Barlow1995, 1997; Forney et al. 1995). Seasonal and year-round occurrence has been noted for killer whales throughout Alaska (Braham and Dahlheim 1982) and in the intracoastal waterways of British Columbia and Washington State, where pods have been labeled as 'resident', 'transient' and ‘offshore' (Bigg et al. 1990, Ford et al. 1994) based on aspects of morphology, ecology, genetics and behavior (Ford and Fisher1982; Baird and Stacey 1988; Baird et al. 1992, Hoelzel et al.1998).
Through examination of photographs of recognizable individuals and pods, movements of whales between geographical areas have been documented. For example, whales identified in Prince William Sound have been observed near Kodiak Island (Heise et al. 1991) and whales identified in Southeast Alaska have been observed in Prince William Sound, British Columbia, and Puget Sound (Leatherwood et al. 1990, Dahlheim et al. 1997). Movements of killer whales between the waters of Southeast Alaska and central California have also been documented (Goley and Straley 1994).Offshore killer whales have more recently also been identified off the coasts of California, Oregon, and rarely, in Southeast Alaska (Ford et al. 1994, Black et al. 1997, Dahlheim et al. 1997). They apparently do not mix with the transient and resident killer whale stocks found in these regions (Ford et al. 1994, Black et al. 1997).
Studies indicate the ‘offshore' type, although distinct from the other types (‘resident' and `transient'), appears to be more closely related genetically, morphologically, behaviorally, and vocally to the ‘resident' type killer whales (Black et al. 1997, Hoelzel et al. 1998; J. Ford, pers. comm.; L. Barrett-Lennard, pers. comm.). Based on data regarding association patterns, acoustics, movements, genetic differences, and potential fishery interactions, five killer whale stocks are recognized within the Pacific U.S. EEZ 1) the Eastern North Pacific Northern Resident stock - occurring from British Columbia through Alaska,2) the Eastern North Pacific Southern Resident stock - occurring within the inland waters of Washington State and southern British Columbia, 3) the Eastern North Pacific Transient stock - occurring from Alaska through California, 4) the Eastern North Pacific Offshore stock - occurring from Southeast Alaska through California (this report), and 5) the Hawaiian stock. ‘Offshore' whales in Canadian waters are considered part of the Eastern North Pacific Offshore stock. The Stock Assessment Reports for the Alaska Region contain assessments of the Eastern North Pacific Northern Resident stock, and the most recent assessment for the Hawaii Stock can be found in Barlow et al. (1997).
Population Size
Off British Columbia, approximately 200 offshore killer whales were identified between 1989 and 1993 (Ford et al. 1994), and 20 of these individuals have also been seen off California (Black et al. 1997). Using only good quality photographs that clearly show characteristics of the dorsal fin and saddle patch region, an additional 11 offshore killer whales that were not previously known have been identified off the California coast, bringing the total number of known individuals in this population to 211. This is certainly an underestimate of the total population size, because not all animals in this population have been photographed. In the future, it may be possible estimate the total abundance of this transboundary stock using mark-recapture analyses based on individual photographs. Based on summer/fall shipboard line-transect surveys in 1991, 1993 and 1996 (Barlow 1997), the total number of killer whales within 300 miles of the coasts of California, Oregon and Washington was recently estimated to be 819 animals (CV=0.38). There is currently no way to reliably distinguish the different stocks of killer whales from sightings at sea, but photographs of individual animals can provide a rough estimate of the proportion of whales in each stock.
A total of 161 individual killer whales photographed off California and Oregon have been determined to belong to the transient (105 whales) and offshore (56 whales) stocks (Black et al. 1997). Using these proportions to prorate the line transect abundance estimate yields an estimate of 56/161 * 819 = 285 offshore killer whales along the U.S. west coast. This is expected to be a conservative estimate of the number of offshore killer whales, because offshore whales apparently are less frequently seen near the coast (Black et al. 1997), and therefore photographic sampling may be biased towards transient whales. For stock assessment purposes, this combined value is currently the best available estimate of abundance for offshore killer whales off the coasts of California, Oregon and Washington.
Minimum Population Estimate.
The total number of known offshore killer whales along the U.S. West coast, Canada and Alaska is 211 animals, but it is not known what proportion of time this transboundary stock spends in U.S. waters, and therefore this number is difficult to work with for PBR calculations. A minimum abundance estimate for all killer whales along the coasts of California, Oregon and Washington can be estimated from the 1991-1996 line-transect surveys as the 20th percentile of the abundance estimate, or 601 killer whales. Using the same prorating as above, a minimum of 56/161 * 601 = 209 offshore killer whales are estimated to be in U.S. waters off California, Oregon and Washington.
Current Population Trend
No information is available regarding trends in abundance of Eastern North Pacific offshore killer whales.
Human-Caused Mortality and Serious Injury
A summary of recent fishery mortality and injury for this killer whale stock is shown in Table 1. More detailed information on these fisheries is provided in Appendix 1 of Barlow et al. (1997). In the California drift gillnet fishery, no offshore killer whales have been observed entangled (Julian and Beeson 1998, Julian 1997, Cameron 1998), but one killer whale from the Eastern North Pacific Transient Stock was observed taken in 1995, and offshore killer whales may also occasionally be entangled. Additional potential sources of killer whale mortality are set gillnets and longlines. In California, an observation program between July 1990 and December 1994 monitored 5-15% of all sets in the large mesh (>3.5") set gillnet fishery for halibut and angel sharks, and no killer whales were observed taken. Based on observations for longline fisheries in other regions (i.e. Alaska; Yano and Dahlheim 1995), fishery interactions may also occur with U.S. West coast pelagic longline fisheries, but no such interactions have been documented to date. Set and drift gillnet fisheries for swordfish and sharks exist along the entire Pacific coast of Baja California, Mexico and may take animals from the same population. Quantitative data are available only for the Mexican swordfish drift gillnet fishery, which increased from two vessels in 1986 to 29 vessels in 1992 (Sosa-Nishizaki et al. 1993). The total number of sets in this fishery in 1992 can be estimated from data provided by these authors to be approximately 2700, with an observed rate of marine mammal bycatch of 0.13 animals per set (10 marine mammals in 77 observed sets; Sosa-Nishizaki et al. 1993). This overall mortality rate is similar to that observed in California driftnet fisheries during 1990-95 (0.14 marine mammals per set; Julian and Beeson, in press), but species-specific information is not available for the Mexican fisheries. Table 1. Summary of available information on the incidental mortality and injury of killer whales (Eastern North Pacific Offshore Stock) in commercial fisheries that might take this species.
Historical mortality
California coastal whaling operations killed five killer whales between 1962 and 1967 (Rice 1974). An additional killer whale was taken by whalers in British Columbian waters (Hoyt 1981). It is unknown whether any of these animals belonged to the Eastern North Pacific Offshore stock.
Status of Stock
The status of killer whales in California in relation to OSP is unknown, and there are insufficient data to evaluate trends in abundance. No habitat issues are known to be of concern for this species. They are not listed as "threatened" or "endangered" under the Endangered Species Act nor as "depleted" under the MMPA. There has been no documented human-caused mortality of this stock, and therefore they are not classified as a "strategic" stock under the MMPA. The total fishery mortality and serious injury for offshore killer whales is zero and can be considered to be insignificant and approaching zero mortality and serious injury rate.
References
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