Natural Sources

Predation

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The only known current predator of CI belugas is the “transient” or mammal-eating killer whale; there has not been a subsistence hunt by Alaska Natives in Cook Inlet after 2005. However, it is possible that sharks may also occasionally prey upon belugas.

Killer whales are infrequently reported (Table 4) in upper Cook Inlet (Shelden et al. 2003; NMFS, unpub. data), which is now the primary summer range of CI belugas (Rugh et al. 2010). The contraction in CI beluga summer range to the shallow waters of the upper Inlet may reduce the opportunity for killer whales to pursue belugas in this area.

Interviews with people that have fished the upper Inlet for 20 to 50 years reported few sightings of killer whales (Shelden et al. 2003). In his study of TEK, Huntington (2000) interviewed Alaska Native beluga hunters who reported that killer whales were rarely seen in the upper Inlet or near belugas. Currently, beluga sighting networks are scattered along those portions of Cook Inlet shorelines that are road-accessible, and interest among the public is high, so there is an increased opportunity for any killer whale occurrences near Cook Inlet road access points to be reported, especially when these include encounters with belugas.
Additional evidence that killer whale presence in upper Cook Inlet is rare comes from beluga observational and photo-identification work. Between 2004 and 2014, over 30,800 observational hours were logged between May and October in areas that included Turnagain Arm, western upper Cook Inlet, the area west of Fire Island to the Little Susitna, Knik Arm, and around the Kenai River, and no killer whales were observed (McGuire, LGL, unpub. data).

Killer whales have been seen in the upper Cook Inlet in Turnagain Arm and Knik Arm, between Fire Island and Tyonek, and near rivers along the Susitna Delta (Shelden et al. 2003; NMFS, unpub. data). Killer whales have also been reported in areas of the mid and lower Inlet, including near the Chuitna and Kenai Rivers (Table 4) and Kamishak Bay. In addition, Lammers et al. (2013) reported a single detection of a killer at both the Beluga River and Tuxedni Bay. From morphology, behavior, and the small group sizes described in sighting reports, it would appear the killer whales observed in upper Cook Inlet are a transient (marine mammal eating) group. The frequency of sightings in upper Cook Inlet is very low; therefore, killer whales observed in the upper Inlet apparently center their range elsewhere. Killer whales have stranded at least four times in Turnagain Arm since 1990: in May 1991, August 1993, September 2000, and August 2002. During the 1993 stranding event, a large male killer whale regurgitated pieces of beluga and harbor seal (Shelden et al. 2003) and subsequently died.

The number of different killer whales that use the upper Inlet is not known but appears to be small. Photographs taken of killer whales that stranded in Turnagain Arm in 1991, 1993, and 2000 provide evidence that the same adult male was sighted in both 1991 and 1993 (Shelden et al. 2003). Poor quality of additional photographs precluded the identification of other individuals, but they do suggest that the composition of the killer whale pod during these three encounters was similar and the same individuals may be involved in each event. No matches were found between the images of killer whales in Turnagain Arm and those in all available catalogs for Alaska south to Mexico (Shelden et al. 2003).

Table 4. Reported killer whale observations in upper Cook Inlet, and reports of killer whale predation on CI belugas Inlet-wide, 1982–2016.
Year
Reported location of killer whale sighting / predation event a
No. reported killer whale sighting / predation events in upper Cook Inlet (including events in mid and lower Cook Inlet if associated with a potential predation event)
No. reported killer whales observed per sighting event b
No. beluga mortalities suspected to be a direct result of killer whale predation b
1982 Knik Arm 1 5 0
1983 No Reports 0 0 0
1984 No Reports 0 0 0
1985 Turnagain Arm 1 1 UNK
1986 No Reports 0 0 0
1987 No Reports 0 0 0
1988 No Reports 0 0 0
1989 No Reports 0 0 0
1990 Chickaloon Bay 1 >3 1
1990 Fire Islandc 1 4 0
1991 Turnagain Arm 1 6 0
1992 Kenai River -1 6 0
1993 Turnagain Arm 1 5 1
1994 Susitna River 1 d UNK 0
1995 Ivan River 1 3 0
1996 Ivan River 1 UNK 0
1997 Ivan River 1 UNK 0
1998 Ivan River 1 UNK 0
1998 Port MacKenzie to Fire Island 1 3 0
1999 Turnagain Arm 1 3 0
1999 Ivan River 1 UNK 0
1999 Chinitna Bay -1 1 1 (2) e
2000 Turnagain Arm 1 3-5 2 (4) e
2000 Kenai River -1 3 1
2000 Kachemak Bay -1 1 UNK
2001 Turnagain Arm 1 1 0
2002 Turnagain Arm 3 1 0
2002 Knik Arm 1 1 0
2002 Chuitna River 1 2 0
2003 Knik Arm 1 2 1
2004 No Reports 0 0 0
2005 No Reports 0 0 0
2006 No Reports 0 0 0
2007 Turnagain Arm 1 3 0
2008 Tyonek 1 2 0
2008 Turnagain Arm 1 2f 1
2009 Turnagain Arm 1 6 0
2010 Point Possession 2 4-5 and 3 1 g
2011 Turnagain Arm 1 1 0
2012 No Reports 0 0 0
2013 No Reports 0 0 0
2014 No Reports 0 0 0
2015 Knik Arm 2 1 and 1 0
2016 No Reports 0 0 0
Totals: 1982-2016 35 Total: 77+ 9
(31 upper CI + 4 mid-lower CI) Average: 2-3 (12 if potentially dependent calves included)

a A predation event is defined as an event during which killer whales were observed chasing belugas, catching belugas, or when a beluga carcass was found with evidence of killer whale tooth marks on it.

b UNK = the information is unknown, undetermined, or unreported

c Year of sighting estimated; this report was from Shelden et al. (2003) and was based upon an anecdotal report of a killer whale sighting in the “early 1990s.”

d This was an unconfirmed sighting of killer whales in the area of the Susitna River; see Shelden et al. (2003) for more details.

e These reports suggest that a dependent calf may have been present. Although there is no evidence the calf was killed, we assume the calf may also have died, either as a direct predation event or due to the death of its mother; thus, we have reported the number of mortalities as a range (1– 2) indicating the possibility that a mom/calf pair died.

f This sighting of killer whales may have been the same two killer whales previously reported near Tyonek.

g The necropsy report for this beluga mortality indicated that killer whale predation may have been a possible cause of death, but poor body condition of the beluga carcass prevented a positive determination.

Sources: Moore et al. 2000, Shelden et al. 2003, Vos and Shelden 2005, NMFS, unpub. data. (Level A stranding and necropsy reports)


Between 1982 and 2016, NMFS received 31 reports of killer whales in upper Cook Inlet, 4 reports of killer whales possibly preying on CI belugas in mid- and lower Cook Inlet, and 9–12 CI beluga mortalities Inlet-wide suspected to be a direct result of killer whale predation (Table 4). The 9–12 CI beluga mortalities suspected to be a direct result of killer whale predation were identified based upon evidence of predation observed on beluga carcasses or eye witness reports. We present this number as a range to indicate our uncertainty regarding the fate of three calves still dependent upon their mothers, which were killed by killer whales. However, there is no evidence available to document the deaths of these three calves.

A review of the original sightings reports has resulted in a change of opinion about some mortalities originally attributed to killer whale predation. Shelden et al. (2003) reported that two CI belugas died on October 6, 1992 with “killer whale teeth marks on their flukes.” Although there were reports of killer whales in the Kenai River in September 1992, a review of the original Level A stranding reports for the two belugas reveal that there were “no gross injuries” observed and no mention of killer whale teeth marks on either beluga. A comparison of the photographs taken of the October 1992 beluga carcasses against photographs of CI beluga carcasses with confirmed killer whale teeth marks from 2000 led NMFS AKR to determine that the whales stranded in the Kenai River in October 1992 were “not attacked by killer whales” (NMFS, unpub. data; Level A stranding report). Additionally, Moore et al. (2000) reported that in early September 2000 a CI beluga carcass was documented near Nikiski with “possible orca teeth marks” (reproduced in Shelden et al. 2003). However, after review of the original Level A stranding report, NMFS AKR confirmed the report never mentioned possible orca (a.k.a., killer whale) teeth marks, and given that the report states the whale was “very decomposed”, “skeletal remains were visible”, and it was “too deteriorated to collect skin for genetics” testing, there would be too little skin available to see teeth marks from a killer whale. Despite the person reporting the dead whale speculating that a “killer whale took bites from its belly”, without evidence supporting killer whale predation, the stranding event in Nikiski in 2000 cannot be deemed to be the result of killer whale predation. Finally, Shelden et al. (2003) indicated “killer whale teeth marks [were] evident” on a dead beluga found June 20, 1991, based on a report by Moore et al. (2000) that the beluga was found with teeth marks and a piece of its tail missing. However, after review of the original Level A stranding report, NMFS AKR found that the “bitemark” noted in the report was qualified as “may have been.” Without additional corroborating information, there is insufficient evidence to deem this stranding to be the result of killer whale predation. Thus, although previously considered evidence of killer whale predation on CI belugas (see Moore et al. 2000 and Shelden et al. 2003), the mortalities from June 1991, October 1992, and September 2000 are not included in Table 4 as mortalities suspected to be the direct result of killer whale predation.

Since 2001, only three CI beluga deaths have been suspected to be a result of killer whale predation: one in Knik Arm in August 2003; one in Turnagain Arm in September 2008; and one near Point Possession in June 2010. However, the 2010 mortality necropsy report stated although predation was a possible cause of death, it could not be positively determined due to the poor condition of the beluga carcass.

Killer whales in the vicinity or actively chasing belugas could also cause CI belugas to strand alive. Such events may have contributed to several more CI beluga mortalities beyond those listed in Table 4 (strandings are discussed in the next section). For instance, in August of 1999, approximately 60 belugas live stranded in Turnagain with reports of killer whales in the vicinity prior to the stranding. Five mortalities were associated with that stranding event. However, in the absence of trained observers documenting killer whales’ pursuit of belugas directly to the location of a stranding, it is not possible to definitively attribute a mortality after a live stranding event to killer whale predation without physical evidence of predation on the carcass. Therefore, any mortalities associated with a live stranding event, despite reported killer whale presence in the area, are not included in Table 4.

There have been anecdotal reports and other observations of killer whales attacking or chasing CI belugas in lower Cook Inlet when belugas were more frequently observed in lower Cook Inlet. For instance, one person reported in 2002 that in 1999 they saw a killer whale dragging an adult beluga by its flipper from Chinitna Bay into deeper water, with the beluga’s calf following; and another person recalled seeing a killer whale chasing a beluga in Kachemak Bay in 2000 (Shelden et al. 2003; included in Table 4). Hobbs and Shelden (2008) and NMFS (2008a) also reported that killer whales chased and fed on a beluga near Anchor Point on June 14, 2007. However, after follow-up interviews and a review of additional photos and video, it was determined that it was a minke whale that was killed by killer whales near Anchor Point, and not a CI beluga.

In directed killer whale surveys in lower Cook Inlet in July 2008 and July 2009, there were eleven encounters with resident type killer whales (fish-eaters) and five encounters with transient type killer whales (mammal-eaters; Matkin et al. 2009). During these directed, and other opportunistic, observations of killer whales in lower Cook Inlet, transient killer whales were recorded killing minke whales, harbor porpoises, and harbor seals, and attacking sea otters and humpback whales (Matkin et al. 2009; C. Matkin, North Gulf Oceanic Society, unpub. data). No beluga predation was observed during directed or opportunistic observations by researchers or the public in the lower Inlet during this time period (Matkin et al. 2009).

CI belugas may also be susceptible to shark predation, although attacks have not been witnessed, nor has clear evidence of shark predation been documented. Wounds from possible shark attacks have been observed in photographs of CI belugas (T. McGuire, LGL, unpub. data). Salmon sharks and Pacific sleeper sharks are found in Cook Inlet, although neither has been determined to attack free-swimming cetaceans. Salmon shark jaw and tooth structure is indicative of a fish predator and it is highly unlikely they would attack a marine mammal (K. Goldman, Alaska Department of Fish and Game [ADF&G], pers. comm.to C. Goertz). Pacific sleeper sharks are known to feed on whale carcasses (Barrett-Lennard et al. 2011), and although cetacean remains have been found in their stomachs, this was apparently the result of scavenging and conclusive evidence of predation on live cetaceans is lacking (Sigler et al. 2006). A counterpart in the Atlantic Ocean, the Greenland shark, apparently consumes live pinnipeds (Sigler et al. 2006), but is not known to be a predator of free swimming cetaceans. It is possible that great white sharks make rare visits to the area (Martin 2005), but they are very unlikely to pose a threat to belugas due to their rarity.

Strandings

CI beluga strandings include beached or floating carcasses as well as live animals found in waters too shallow to permit them to swim. An extensive review of the NMFS AKR Level A stranding reports resulted in some updates to the CI beluga stranding data presented in Moore et al. (2000), Vos and Shelden (2005), and NMFS (2008a and 2008b). The total number of CI beluga carcasses reported in Table 5 reflects the most current information available regarding the number of reported, non-subsistence related mortalities since 1988.

Beluga whale live strandings in upper Cook Inlet are not uncommon, with a majority occurring in Turnagain Arm and Knik Arm (Table 5). Live stranded whales are often opportunistically spotted from the Seward Highway off of Turnagain Arm, or from small aircraft traveling over Cook Inlet. Between 1988 and 2016, 214 dead CI belugas were reported, and at least 876 belugas were involved in live strandings in Cook Inlet (some individual belugas were likely involved in multiple live stranding events over the years; Table 5). Mass strandings (involving two or more whales) primarily occurred in Turnagain Arm and often coincided with extreme tides or killer whale sighting reports (Shelden et al. 2003). In 2003, an unusually high number of beluga live strandings (five separate events in Turnagain Arm involving between 2 and 46+ whales) and mortalities (n = 20) occurred in Cook Inlet (Vos and Shelden 2005).

Table 5. CI beluga stranding records (for beach-cast or floating carcasses, and live strandings), 1988–2016.
Year
Reported location of killer whale sighting / predation event a
No. reported killer whale sighting / predation events in upper Cook Inlet (including events in mid and lower Cook Inlet if associated with a potential predation event)
No. reported killer whales observed per sighting event b
No. beluga mortalities suspected to be a direct result of killer whale predation b
1982 Knik Arm 1 5 0
1983 No Reports 0 0 0
1984 No Reports 0 0 0
1985 Turnagain Arm 1 1 UNK
1986 No Reports 0 0 0
1987 No Reports 0 0 0
1988 No Reports 0 0 0
1989 No Reports 0 0 0
1990 Chickaloon Bay 1 >3 1
1990 Fire Islandc 1 4 0
1991 Turnagain Arm 1 6 0
1992 Kenai River -1 6 0
1993 Turnagain Arm 1 5 1
1994 Susitna River 1 d UNK 0
1995 Ivan River 1 3 0
1996 Ivan River 1 UNK 0
1997 Ivan River 1 UNK 0
1998 Ivan River 1 UNK 0
1998 Port MacKenzie to Fire Island 1 3 0
1999 Turnagain Arm 1 3 0
1999 Ivan River 1 UNK 0
1999 Chinitna Bay -1 1 1 (2) e
2000 Turnagain Arm 1 3-5 2 (4) e
2000 Kenai River -1 3 1
2000 Kachemak Bay -1 1 UNK
2001 Turnagain Arm 1 1 0
2002 Turnagain Arm 3 1 0
2002 Knik Arm 1 1 0
2002 Chuitna River 1 2 0
2003 Knik Arm 1 2 1
2004 No Reports 0 0 0
2005 No Reports 0 0 0
2006 No Reports 0 0 0
2007 Turnagain Arm 1 3 0
2008 Tyonek 1 2 0
2008 Turnagain Arm 1 2f 1
2009 Turnagain Arm 1 6 0
2010 Point Possession 2 4-5 and 3 1 g
2011 Turnagain Arm 1 1 0
2012 No Reports 0 0 0
2013 No Reports 0 0 0
2014 No Reports 0 0 0
2015 Knik Arm 2 1 and 1 0
2016 No Reports 0 0 0
Totals: 1982-2016 35 Total: 77+ 9
(31 upper CI + 4 mid-lower CI) Average: 2-3 (12 if potentially dependent calves included)

a Known subsistence harvested belugas are not included.

b NA indicates there were no live strandings reported to NMFS that particular year.

c On May 26, 2014 NMFS received a report of two dead belugas on the shore of Kincaid Park along Turnagain Arm; although there was no live stranding event reported, the necropsy of these two whales suggests they were recently live stranded and that the live stranding may have contributed to their death.

Source: Moore et al. 2000; NMFS 2008a, 2008b; NMFS AKR, unpub. data (CI beluga stranding database).


Marine mammals strand alive for a variety of reasons. Belugas may intentionally ground themselves in shallow waters to more easily rub off molting skin, to avoid predation or other perceived threats (e.g., acoustic disturbances, vessel traffic, or other anthropogenic activity), when chasing prey, or as a result of an inability to properly navigate or maneuver when debilitated by injury or disease (Smith et al. 1992, Moore et al. 2000, Shelden et al. 2003, Vos and Shelden 2005, Burek-Huntington et al. 2015). A prolonged period out of the water may ensue if animals strand during outgoing tides, especially with the extreme/rapid tidal changes and gently sloping mudflats of Cook Inlet. The perception is that belugas tolerate such events better than other cetaceans due to their relatively small size and flat abdomens which spread out their weight and allow them to remain upright, their light color which minimizes the absorption of heat from sunlight, and their ability to create wallows in the mud to retain at least some water to help them stay cool and moist. While belugas often appear calm and seem to float off without incident with the incoming tide, these animals have not been assessed or tracked other than during the stranding itself and from a great distance.

However, carcasses found following documented mass strandings, as well as carcasses found in the absence of such events, have shown evidence of death as a result of a live stranding. Findings from 38 CI belugas necropsied between 1998 and 2013 indicated nine died following a live stranding (Burek-Huntington et al. 2015; note Table 5 documents a total of 13 belugas may have died after a live stranding event; not all of these belugas were accessible and necropsied, but were included in the table due to the close timing of a dead beluga with a reported live stranding event). Five of these nine belugas were found dead shortly after documented mass strandings. Some of these dead belugas appeared to have been robust and otherwise healthy, with no other definitive causes of death. However, they did have debris deep in their airways suggesting forceful inspiration of mud while alive, such as might occur during a live stranding (Burek-Huntington et al. 2015; NMFS AKR, unpub. data). In May 2014, two belugas found dead near Anchorage also had sand deposited within their airways suggesting a recent live stranding event (NMFS AKR, unpub. data), although no live stranding event was reported.

Four additional individual carcasses had extensive post-mortem sampling and analyses which did not reveal a pre-existing health problem or other cause of death; however, sand and silt was found in the airways, again suggesting forceful inspiration of mud as might occur during a live stranding. In addition to the obstructive inhalation of debris leading to asphyxia (lack of oxygen), live strandings could also lead to death due to stress, hyperthermia (abnormally elevated temperature), pressure necrosis (cellular death due to excessive pressure) of internal organs, aspiration pneumonia (pneumonia due to inhaled material), and kidney damage secondary to myopathy (muscular damage) or muscle compartment syndrome (muscular swelling constricted by surrounding tissue resulting in reduction of blood supply). Some of these conditions may take weeks to months to fully develop and cause death. They may also exacerbate pre-existing conditions, making it difficult to determine whether death was caused by a previous live stranding. Understanding the true impact of live stranding on animals that survive the ordeal requires a more directed assessment and tracking of those animals. Live belugas have not been observed to strand in SLE and deaths attributed to such events have not been identified there (S. Lair, pers. comm. to C. Goertz).