ACS Research Committee Report

Suspected Surplus Killing of Harbor Seal Pups by Killer Whales
Source: Gaydos, J.K., Raverty, S., Baird, R.W., and Osborne, R.W. 2005. Suspected surplus killing of harbor seal pups (Phoca vitulina) by killer whales (Orcinus orca). Northwestern Naturalist 86(3), pp. 150-154.

During the period of September 3 through November 10, 2002, five harbor seal pup carcasses were found on beaches of San Juan County, WA. These carcasses had injuries, such as partial or total decapitation, lacerated hind flippers, and/or puncture wounds, which were indicative of predation. The puncture wounds matched the dentition of killer whales. Resident (fish-eating) and transient (mammal-eating) killer whales were both observed in the area at the time that these carcasses washed up.

These injuries were highly unusual; during the years 1982 through 2002, 281 dead harbor seals washed ashore and none demonstrated these injuries. In addition, there were no other observations of similar injuries in the time after November 2002.

It is possible that the injuries were caused by one or more transient killer whales that killed more seals than they could eat, or killed a "surplus."  However, in previous observations of transient killer whales, there were only four cases of the whales leaving more than 1% of the carcass after killing a seal. Another possibility is that these injuries were caused by one or more resident killer whales engaged in an "aberrant" behavior. Either way, it is clear that these harbor seal pups were killed for something besides consumption. It seemed unlikely that these carcasses were the result of whales playing with seals in order to learn hunting skills, being that injuries like these were not seen before or after this five week period. The pattern seen here more closely resembled surplus killing, which has been documented in many terrestrial mammalian predators. Continued monitoring of stranded seals will demonstrate whether this was a one-time event or whether it will occur again. 

Listening for Whales in Alaska
Source: Moore, S.E., Stafford, K.M., Mellinger, D.K., and Hildebrand, J.A. 2006. Listening for large whales in the offshore waters of Alaska. BioScience 56(1), pp. 49-55.

Researchers use autonomous acoustic recorders in the offshore waters of Alaska to listen for the presence of whales. They have learned a great deal about the distribution and seasonality of whale species from these recordings. In 1999, the first year of the study, six recorders were deployed in the Gulf of Alaska and four in the southeastern Bering Sea.

Blue whales were the initial focus of acoustic surveys, because there was little known about the seasonality and population structure of this species. Researchers discovered two types of blue whale calls, perhaps from two distinct populations. Both call types occurred seasonally, and peaked during the period of August through November. The northeast Pacific blue whale call was most common, but the western Pacific call was also found throughout the season.

Sperm whales were also detected in the Gulf of Alaska year round, although only about half as often in the winter as in the summer months. This finding was surprising, because many people believed that all sperm whales migrated to warmer waters during the winter. Fin whales were also heard year round, but they peaked from August to February.

North Pacific right whales were a focus of much of this research, because there was so little known about this highly endangered species. There was one opportunistic sighting of a right whale near Kodiak Island, so acoustic recorders were deployed in this area to complement the others already in the Gulf. There were a total of 60 definite right whale calls identified from all of the recorders; there were an additional ten probable calls found on the recorders near Kodiak Island. The definite calls were detected in August and September on the westernmost recorder in the Gulf, which is an area where right whales were formerly abundant but have not been seen in recent decades. Acoustic recorders were also deployed on the southeastern Bering Sea middle shelf. These recorders found right whale calls from May through October, with a peak in the last two months. Calls occurred in bouts lasting several minutes, followed by quiet periods, suggesting a low number of right whales or that whales were just passing through the area.   

Finally, there were also recorders deployed in the Beaufort Sea slope in the area of opportunistic summer sightings of bowhead whales. Bowhead whales typically migrate to the Beaufort Sea in the late spring and the Alaskan Native subsistence hunters were concerned that changing Arctic climate conditions are affecting bowhead distribution and migration.

Hunters also reported increased numbers of gray whales near Barrow, AK, in the late summer and fall, which could indicate a northward shift in distribution of this species.

Preliminary analyses found bowhead whale calls northeast of Barrow during spring and the presence of gray whales from October through May. This extended occupancy of gray whales suggests that this species has altered its migration and distribution based on climatic changes and may be a good sentinel species for marine ecosystem variability. Analysis of recordings from offshore Alaskan waters is ongoing and is very promising to fill in gaps in scientific knowledge about many whale species. 

The Effects of Aquaculture on Bottlenose Dolphins
Source: Watson-Capps, J.J. and Mann, J. 2005. The effects of aquaculture on bottlenose dolphin (Tursiops sp.) ranging in Shark Bay, Western Australia. Biological Conservation 124, pp. 519-526.

Aquaculture, the farming of finfish or shellfish, has grown 11% in the last ten years. In 2002, it produced 37.8 million metric tons of fish and shellfish and 55.7 billion U.S. dollars. Shellfish farms have open areas that are large enough to allow small cetaceans to swim through. Nevertheless, cetaceans may avoid these areas because of ropes, equipment, human noise, water clarity, or other factors.

This study looked at whether the ranging patterns of bottlenose dolphins were altered by an oyster farm in Shark Bay, Australia. Dolphin movements near the farm before and during its operation were analyzed to look for any differences.

The dolphins showed a significant decrease in the use of the study area when the oyster farm was introduced. Analysis of detailed movement of individuals confirmed the overall finding that the farm displaced dolphins. Adult females were less likely to go into areas where farming occurred compared to areas of similar ecology nearby. In several instances, females remained on the periphery of the farm instead of traveling through it.

Displacement of habitats by aquaculture may be particularly detrimental to dolphins that are specialized foragers. For example, a subset of female dolphins uses marine sponges to dig out prey from the sea floor in deep water channels in the study area. If they were displaced from these channels, they would be prevented from using their primary foraging strategy. Although this study took place in only one location, the results found here could be extrapolated to other areas where aquaculture and small cetaceans overlap. 

Killer Whales and Whaling: the Scavenging Hypothesis
Source: Whitehead, H. and Reeves, R. 2005. Killer whales and whaling: the scavenging hypothesis. Biology Letters 1, pp. 415-418.

It has been proposed that the decline of some pinniped species and sea otters in the Pacific Ocean is due to increased predation by killer whales. In this scenario, killer whales switched their primary prey from large whales, made scarce by commercial whaling, to these smaller marine mammal species.

In a review of whaling literature, the authors found that accounts of killer whales scavenging on whaled carcasses were very common and were geographically widespread, especially during modern whaling. The accounts agreed that the tongues of large whales were the main target of this scavenging, which parallels observations of killer whales consuming prey they caught themselves.

Through estimates in the literature and through the authors’ extrapolations, they discovered that there were many more carcasses, and a much higher biomass, produced by whaling than by natural mortality during the middle of the twentieth century. However, this carcass availability fell dramatically between 1970 and 1980.

For scavenging killer whales, large whales that were killed through whaling had several potential advantages over animals that died naturally. Whaled carcasses were generally healthier, more nutritious animals; they were more likely to be baleen whales, which have a larger tongue than sperm whales; whaled carcasses were temporarily spatially clustered; and their availability was advertised by loud acoustic signals such as from engines, winches, harpoon guns, etc.

Killer whales are known to specialize on certain prey types and it is likely that scavenging was a specialization for some killer whales. Large whales dying of natural causes were most likely not enough to survive on exclusively, but when modern whaling made available carcasses more plentiful, killer whales could make a living on this specialization alone. Even non-scavenging killer whales may have started scavenging during this period and other ways of getting nutrients may have receded in the population.

By 1980, whaled carcasses were suddenly no longer available to these killer whales and they had to switch prey in order to survive. It is reasonable to conclude that killer whales may have shifted to pinnipeds, living large whales, and sea otters, although the extent of impact that this change may have had on marine mammal populations is unknown. 

The Effect of Radio Tagging on the Survival of Small Cetaceans
Source: Martin, A.R., da Silva, V.M.F., and Rothery, P.R. 2006. Does radio tagging affect the survival or reproduction of small cetaceans?; Marine Mammal Science 22(1), pp.17-24.

It is important to understand the effects of research techniques on the cetaceans that are being studied.

This study focused on botos, Amazon river dolphins, captured in the central Brazilian Amazon during annual three-week campaigns, usually in November. The botos were captured using nets to herd them into shallow beaches and then onto floating processing laboratories. The total time between capture and release was approximately 12 to 16 minutes, on average. During this process, the animals were weighed, measured, photographed, freeze branded, sampled for blood and tissue, and, in some cases, tagged with radio tags attached with pins to the dorsal fins.

There were a total of 52 botos captured and not tagged and 51 captured and tagged. There was no significant impact on the survival of tagged animals. Out of 51 tagged botos, 47 (92.2%) survived for three years after the tag was placed; in comparison, 42 (82.4%) of the 52 botos without tags survived for three years. There also was no difference in reproduction; many of the females that were tagged went on to produce multiple calves.

Short term effects were relatively minor and included migration of the pins out of the dorsal fin leaving linear tears in the fin, or the pins remaining in the fin after the tag fell off. 

Sexual Dimorphism in Botos
Source: Martin, A.R. and da Silva, V.M.F. 2006. Sexual dimorphism and body scarring in the boto (Amazon river dolphin) Inia geoffrensis. Marine Mammal Science 22(1), pp. 25-33.

Botos were studied in the central Brazilian Amazon from 1994 through 2004. Males were found to be 16% longer and 55% heavier than females, making botos one of the most sexually dimorphic (different between the sexes) of any cetacean. Botos are found to be much more sexually dimorphic than any other river dolphin and they are the only river dolphin in which males are larger than females. This difference indicates that there may be a large evolutionary distance between botos and other river dolphins.

Species with larger males than females usually demonstrate male-male aggression, most likely for mating opportunities. In botos, this aggression was confirmed by the high degree of physical damage, including rake marks, found in males.

The body color of botos was different between the sexes, as well, with the males being significantly pinker than the females. Male botos lose their dark color with age, so the pinkness of a male may advertise its maturity. On the other hand, scars in botos appear pink on either sex and the pinkness of males may be an artifact of their extensive scarring, such as is found in Risso’s dolphins.

Males also were found to have cobblestone skin lesions. It is unknown what the cause or function of these lesions were, but the authors propose that they were a form of callous used as a weapon against other males. Scarred females did not have these lesions and, in males, they were not in locations with increased scarring; both findings indicated that the lesions were not caused by injury. On males, these lesions were usually located in areas that could be used as weapons, but were not likely to be attacked. 

Dissolving Stock Boundaries with Satellite Tracking of Bowhead Whales
Source: Heide-Jorgensen, M.P., Laidre, K.L., Jensen, M.V., Dueck, L., and Postma, L.D. 2006. Dissolving stock discreteness with satellite tracking: bowhead whales in Baffin Bay. Marine Mammal Science 22(1), pp. 34-45.

Bowhead whales in the northwest Atlantic Ocean are currently considered by the International Whaling Commission to be two stocks: the Davis Strait/Baffin Bay and the Foxe Basin/Hudson Bay stocks. The rationale for this distinction is that the summering areas of Baffin Bay and Foxe Basin are separated and there is an assumption that baleen whales migrate north to south and not east to west. Historic whaling data, however, do not support this distinction.

In this study, six bowhead whales were tagged in Disko Bay, western Greenland, in 2002 and three in 2003. All tagged whales departed the Bay by the end of May and all traveled northwest across Baffin Bay. All but three tags lost contact in June when the whales were on the western side of Baffin Bay along Baffin Island. Three tags kept transmitting until November. All of these three bowheads traveled south along Baffin Island in July, perhaps to avoid ice. In August, one male turned north again and stayed north of Baffin Island until early October, then moved south until it entered Hudson Strait in mid November. Two females stayed on eastern Baffin Island during August and then moved south in September, arriving in Hudson Strait in mid November. One female even moved to the western side of Hudson Strait, almost into Hudson Bay. All three of these tagged animals went into Hudson Strait in the fall, indicating that this area may be an important wintering area for Baffin Bay bowhead whales. Hudson Strait is also thought to be a wintering area for the Foxe Basin/Hudson Bay stock, meaning that these animals may all intermingle during portions of the year. The extent of the movements, from the Canadian High Arctic to Hudson Strait, of these tagged animals, as well as the overlap of these two stocks during part of the year seriously questions whether there should be a distinction into two stocks of bowhead whales in the northwest Atlantic. 

   

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