Killer Whales (Orcinus orca) Chasing Gray Whales (Eschrichtius robustus) in the Northern Bering Sea

Sixteen killer whales (Orcinus orca) were observed for 90 minutes as they approached and then chased gray whales (Eschrichtius robustus) in the Bering Sea north of St. Lawrence Island, Alaska. The killer whales swam in four discrete lines that blew synchronously as they approached an area in which gray whales were feeding. Once in the gray whales' feeding area, the killer whales broke into small groups and dispersed. The gray whales, which had been dispersed while feeding, formed groups of three to six and swam away from the killer whales, except for one individual. That whale was pursued by four killer whales swimming nearly abreast in a loose crescent formation with about 300 m between individuals. Although a sonobuoy was deployed throughout the observation period, no sounds were recorded from either species. The absence of whale sounds raises questions about how the whales detected one another and communicated between nearby conspecifics.Key words: killer whale (Orcinus orca), gray whale (Eschrichtius robustus), Bering Sea, predator/prey, acousticsMots clés: épaulard (Orcinus orca), baleine grise de Californie (Eschrichtius robustus), mer de Béring, prédateur/proie, acoustiqu

Observations on the Behavioral Responses of Bowhead Whales (Balaena mysticetus) to Active Geophysical Vessels in the Alaskan Beaufort Sea

The responses of bowhead whales to controlled approaches by geophysical vessels producing airgun blasts were observed during the course of four field experiments conducted in the Alaskan Beaufort Sea in September 1984. Behavioral responses included shorter surfacing and dive times, fewer blows per surfacing, longer blow intervals and subtle to overt changes in surface behaviors. Subtle behavioral responses occurred at 3.5 and 8.2 km with received airgun noise levels of 142 and 157 dB respectively (all levels in dB re 1 micro Pa). Partial avoidance (i.e., some whales leaving the observation area while others remained) occurred at ranges of 3.5 and 7.6 km, with sound levels of 142 and 158 dB respectively. Total avoidance (i.e., all whales leaving the observation area) occurred at 1.3, 7.2, 3.5 and 2.9 km, with corresponding sound levels of 152, 165, 178 and 165 dB. The similarities among experiments reported here support the conclusion that short-term behavioral changes occur when bowhead whales are exposed to airgum blasts from approaching geophysical vessels at ranges <10 km. These disturbance efforts wane within one hour after a disturbance; long-term effects on social, behavioral or physiologic parameters are not known at this time.Key words: bowhead whale, Balaena mysticerus, geophysical vessel, bioacoustics, airgunsMots clés: baleine franche, Balaena mysticetus, navire de prospection géophysique, bioacoustique, canons à ai

Summer Distribution of Bowhead Whales, Balaena mysticetus, Relative to Oil Industry Activities in the Canadian Beaufort Sea, 1980-84

Aerial surveys in 1980-84 showed that summer distribution of bowheads in the Beaufort Sea varied markedly between years. Distribution varied both outside and within the "main industrial area" (MIA), the area of island construction, drilling and intensive ship and helicopter traffic. Numbers of bowheads in the MIA were high in 1980, lower in 1981, near zero in 1982 and very low in 1983-84. The few whales in the MIA in 1983-84 were mainly near its edges, contrary to 1980-81. These data, plus limited evidence from 1976-79, indicate that bowheads were numerous in the centre of the MIA in 3 of 5 years from 1976-80 (1976-77, 1980) vs. 0 of 4 years from 1981-84. One hypothesis is that progressively increasing industrial activities affected bowhead distribution after 1980. However, bowheads probably also react to variations in their zooplankton prey, which may be affected by year-to-year changes in oceanography and weather. Influences of natural factors on zooplankton and bowheads need to be better understood in order to assess whether oil exploration caused any of the observed changes in bowhead distribution.Key words: bowhead whale, Balaena mysticetus, Beaufort Sea, oil exploration, seismic exploration, aerial surveysDes relevés aériens effectués entre 1980 et 1984 ont montré que la répartition estivale des baleines franches dans la mer de Beaufort varie nettement d’année en année. Elle varie à fois à l’extérieure et à l’intérieur de la “zone industrielle principale” (ZIP), qui est la zone de construction de l’île, de forage et de circulation intense de bateaux et d’hélicoptères. Le nombre de baleines franches dans la ZIP était élevé en 1980, plus bas en 1981, près de zéro en 1982, et très bas en 1983 et 1984. Les quelques baleines présentes dans la ZIP en 1983 et 1984 étaient principalement à la périphérie, contrairement à 1980 et 1981. Ces données, jointes à des évidences plus limitées de 1976 à 1979, indiquent que les baleines franches étaient nombreuses au centre de la ZIP pendant 3 années sur 5, allant de 1976 à 1980 (1976, 1977 et 1980), par rapport à aucune année sur les quatre allant de 1981 à 1984. On avance l’hypothèse que les activités industrielles progressivement croissantes ont affecté la répartition des baleines franches après 1980. Cependant, les baleines franches ont probablement réagi aussi aux variations de zooplancton qui constitue leur nourriture et qui peut être affecté par les changements qui ont lieu d’année en année dans l’océanographie et le climat. I1 est nécessaire de mieux comprendre l’influence des facteurs naturels sur le zooplancton et les baleines franches afin d’évaluer si l’exploration pétrolière a provoqué l’un quelconque des changements observés dans la répartition de ces baleines.Mots clés: baleine franche, Balaena mysticetus, mer de Beaufort, exploration pétrolière, exploration sismique, relevés aérien