Variability of Cetacean Distribution and Habitat Selection in the Alaskan Arctic, Autumn 1982-91

Ten years (1982-91) of autumn sighting data from aerial surveys offshore northern Alaska were analyzed to investigate variability in cetacean distribution and habitat selection. Habitat selection indices were calculated for bowhead, white, and gray whales in heavy, moderate, and light ice conditions; and for high, moderate, and low transport (inflow) conditions at Bering Strait. Bowhead whales selected shallow inner-shelf waters during moderate and light ice, and deeper slope habitat in heavy ice conditions (chi², p < 0.05-0.001). White whales selected slope habitat (chi², p < 0.001), and gray whales selected coastal/shoal and shelf/trough habitat (chi², p < 0.025-0.001), in all ice conditions. In the Alaskan Beaufort Sea, bowheads selected shelf waters and white whales chose slope waters, without regard to transport conditions (chi², p < 0.01-0.001). In the northern Chukchi Sea, gray whales selected coastal/shoal habitat in high transport conditions (chi², p < 0.005), and shelf/trough habitat (chi², p < 0.001) during moderate and low transport conditions. Variability in distribution and habitat selection among these species is likely linked to prey availability at dissimilar trophic levels, although this hypothesis has yet to be rigorously tested. Des données d'observation réalisées en automne sur dix années (1982-1991) grâce à des relevés aériens au large de l'Alaska septentrional ont été analysées dans le cadre de recherches sur la variabilité dans la distribution des cétacés et la sélection de leur habitat. On a calculé les indices de sélection de l'habitat pour la baleine boréale, la baleine blanche et la baleine grise de Californie dans des conditions de glace épaisse, modérée et mince; et pour des conditions de transport (courants de déversement) important, moyen et faible dans le détroit de Béring. La baleine boréale choisissait des eaux peu profondes de l'intérieur du plateau continental durant les conditions de glace modérée et mince, et un habitat plus profond sur la pente durant des conditions de glace épaisse (chi², p < 0,05-0,001). La baleine blanche choisissait l'habitat sur la pente (chi², p < 0,001) et la baleine grise choisissait l'habitat côtier/de hauts-fonds et celui du plateau/des fossés (chi², p < 0,025-0,001), quelles que soient les conditions de glace. Dans la partie alaskienne de la mer de Beaufort, la baleine boréale choisissait les eaux du plateau et la baleine blanche celles de la pente, abstraction faite des conditions de transport (chi², p < 0,01-0,001). Dans la partie septentrionale de la mer des Tchouktches, la baleine grise choisissait un habitat côtier/de hauts-fonds dans des conditions de transport important (chi², p < 0,005) et un habitat de plateau/de fossés (chi², p < 0,001) dans des conditions de transport allant de moyen à faible. La variabilité dans la distribution et la sélection de l'habitat parmi ces espèces est probablement liée à la disponibilité des proies à des niveaux trophiques dissemblables, bien que cette hypothèse doive encore faire l'objet de tests approfondis.

Summer Records of Bowhead Whales in the Northeastern Chukchi Sea

The collation of 26 summer sighting records over years 1975-77, 1984 and 1987-91 suggest that bowhead whales may occupy the northeastern Chukchi Sea in late summer more regularly than commonly believed.Key words: bowhead whale, Balaena mysticetus, Chukchi Sea, outer continental shelfRÉSUMÉ. L'exploitation statistique de 26 observations faites au cours de l'été entre 1975 et 1977, en 1984 et entre 1987 et 1991 donne à penser que la baleine boréale pourrait occuper la partie septentrionale et orientale de la mer des Tchouktches à la fin de l'été de façon plus régulière qu'on ne l'admet généralement.Mots clés: baleine boréale, Balaena mysticetus, mer des Tchouktches, plateau continental extem

Development of Beluga, Delphinapterus leucas, Capture and Satellite Tagging Protocol in Cook Inlet, Alaska

Attempts to capture and place satellite tags on belugas, Delphinapterus leucas, in Cook Inlet, Alaska were conducted during late spring and summer of 1995, 1997, and 1999. In 1995, capture attempts using a hoop net proved impractical in Cook Inlet. In 1997, capture efforts focused on driving belugas into nets. Although this method had been successful in the Canadian High Arctic, it failed in Cook Inlet due to the ability of the whales to detect and avoid nets in shallow and very turbid water. In 1999, belugas were successfully captured using a gillnet encirclement technique. A satellite tag was attached to a juvenile male, which subsequently provided the first documentation of this species’ movements within Cook Inlet during the summer months (31 May–17 September)

Incidental Sighting of a Ribbon Seal (Phoca fasciata) in the Western Beaufort Sea

On 29 August 1983, an adult ribbon seal (Phoca fasciata) was seen by one of us (EIB) resting on ice in the western Beaufort Sea (71 41 N, 152 41 W), during the course of an aerial survey. The seal did not move from the ice when over-flown at 200 m, and was positively identified by its distinctive pelage. Ribbon seals are commonly found along the ice front in the Bering Sea in winter and early spring, then disperse in late spring as the sea ice breaks up and presumably become solitary and pelagic with poorly known distribution in the summer (Wilke, 1954; Naito and Konno, 1979; Burns, 1970, 1981; Stewart and Everett, 1983). Ribbon seals are rarely seen or taken by Eskimo hunters from coastal villages north of the Bering Strait, and sightings at Wainwright and Point Barrow in the northern Chukchi Sea have been described as "most unusual" (Burns, 1981). ... The observed ribbon seal may have drifted north and east with the ice from the Chukchi Sea during the summer. To our knowledge, this report constitutes the northeasternmost record of a ribbon seal

Estimates of Bowhead Whale (Balaena mysticetus) Numbers in the Beaufort Sea during Late Summer

Broad estimates of bowhead whale numbers in Beaufort Sea outer continental shelf (OCS) waters were calculated based on raw counts of whales seen during aerial surveys conducted in late summer 1982-84, corrected by factors accounting for surface area not sampled, surfaced whales missed by observers, and whales too deep to be seen. Annual estimates ranged from roughly 700-1200 to 3000-3500 whales for the latter half of August and from 2000-2200 to 1600-2900 whales for the first half of September. Additionally, estimates of up to 3000 whales were calculated for subregions of the Beaufort Sea for two separate two-week periods, with adjacent-period estimates of only several hundred whales in the same subregions, implying that whale concentrations were highly transitory. The highest estimate (ca. 3500 whales) accounts for less than half of the estimated 7800 whales in the Bering Sea bowhead population. If the population estimate of 7800 whales is valid, then either a substantial number of whales summered outside Beaufort Sea OCS waters in 1982-84 or bowhead numbers are routinely underestimated by the methods used here, or some combination of both.Key words: bowhead whale, Beaufort Sea, outer continental shelf, abundance estimates, aerial surveysMots clés: baleine franche, mer de Beaufort, au large du plateau continental, évaluations de la quantité, relevés aérien

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

Beluga, Delphinapterus leucas, Habitat Associations in Cook Inlet, Alaska

A review of available information describing habitat associations for belugas, Delphinapterus leucas, in Cook Inlet was undertaken to complement population assessment surveys from 1993-2000. Available data for physical, biological, and anthropogenic factors in Cook Inlet are summarized followed by a provisional description of seasonal habitat associations. To summarize habitat preferences, the beluga summer distribution pattern was used to partition Cook Inlet into three regions. In general, belugas congregate in shallow, relatively warm, low-salinity water near major river outflows in upper Cook Inlet during summer (defined as their primary habitat), where prey availability is comparatively high and predator occurrence relatively low. In winter, belugas are seen in the central inlet, but sightings are fewer in number, and whales more dispersed compared to summer. Belugas are associated with a range of ice conditions in winter, from ice-free to 60% ice-covered water. Natural catastrophic events, such as fires, earthquakes, and volcanic eruptions, have had no reported effect on beluga habitat, although such events likely affect water quality and, potentially, prey availability. Similarly, although sewage effluent and discharges from industrial and military activities along Cook Inlet negatively affect water quality, analyses of organochlorines and heavy metal burdens indicate that Cook Inlet belugas are not assimilating contaminant loads greater than any other Alaska beluga stocks. Offshore oil and gas activities and vessel traffic are high in the central inlet compared with other Alaska waters, although belugas in Cook Inlet seem habituated to these anthropogenic factors. Anthropogenic factors that have the highest potential negative impacts on belugas include subsistence hunts (not discussed in this report), noise from transportation and offshore oil and gas extraction (ship transits and aircraft overflights), and water quality degradation (from urban runoff and sewage treatment facilities). Although significant impacts from anthropogenic factors other than hunting are not yet apparent, assessment of potential impacts from human activities, especially those that may effect prey availability, are needed

Cetacean Habitat Selection in the Alaskan Arctic during Summer and Autumn

Ten years (1982-91) of sighting data from aerial surveys offshore of northern Alaska were analyzed to investigate seasonal variability in cetacean habitat selection. Distinct habitats were described for bowhead whales (Balaena mysticetus), white whales (Delphinapterus leucas), and gray whales (Eschrichtius robustus) on the basis of habitat selection ratios calculated for bathymetric and ice cover regimes. In summer, bowheads selected continental slope waters and moderate ice conditions; white whales selected slope and basin waters and moderate to heavy ice conditions; and gray whales selected coastal/shoal waters and open water. In autumn, bowheads selected inner shelf waters and light ice conditions; white whales selected outer shelf and slope waters and moderate to heavy ice; and gray whales selected coastal and shoal/trough habitats in light ice and open water. Habitat differences among species were significant in both seasons (ANOVA F > 28, p < 0.00001). Interseasonal depth and ice cover habitats were significantly different for bowhead whales (p < 0.00002), but not for gray whales (p > 0.35). White whale depth habitat was significantly different between seasons (p < 0.00002), but ice cover habitat was not (p < 0.08). Des données d'observation réalisées sur dix années (1982-1991) grâce à des relevés aériens au large de l'Alaska septentrional ont été analysées dans le cadre de recherches sur la variabilité saisonnière dans la sélection de l'habitat des cétacés. On a décrit des habitats distincts pour la baleine boréale (Balaena mysticetus), la baleine blanche (Delphinapterus leucas) et la baleine grise de Californie (Eschrichtius robustus) en se fondant sur les taux de sélection de l'habitat calculés pour le régime bathymétrique et celui de la couverture de glace. En été, la baleine boréale choisissait les eaux de la pente continentale et des conditions de glace modérée; la baleine blanche choisissait les eaux de la pente continentale et du bassin océanique, et des conditions de glace allant de modérée à épaisse; et la baleine grise choisissait des eaux côtières et de hauts-fonds ainsi que l'eau libre. En automne, la baleine boréale choisissait les eaux intérieures du plateau continental, où se trouvait une faible concentration de glace; la baleine blanche choisissait les eaux à l'extérieur du plateau et sur la pente, ainsi qu'une glace allant de modérée à épaisse; et la baleine grise choisissait des habitats côtiers et de hauts-fonds ou des fossés à faible concentration de glace et à eau libre. Les différences d'habitat entre les espèces étaient importantes durant les deux saisons (ANOVA F > 28, p < 0,00001). D'une saison à une autre, les habitats différaient sensiblement quant à la profondeur et à la couverture de glace pour la baleine boréale (p < 0,00002), mais pas pour la baleine grise (p > 0,35). La profondeur de l'habitat pour la baleine blanche variait sensiblement d'une saison à une autre (p <0,00002), mais pas la couverture de glace (p < 0,08).

Bowhead Whales Along the Chukotka Coast in Autumn

Bowhead whales (Balaena mysticetus) were seen in autumn 1992 and 1993 only along the northern coast of Chukotka, Russia, although an extensive area of the Chukchi Sea was searched during ship cruises. Single-day counts for 76 and 50 bowheads were made on 1 October 1992 and 3 October 1993, respectively, with only a few whales seen on other days. Whales seen between Cape Schmidt and Cape Vankarem on 1 October 1992 appeared to be feeding, but there was no means to detect or sample subsurface forage that year. On 3 October 1993, bowheads appeared to be feeding in an area where a 5 m x 8 km patch of zooplankton was identified, via acoustics, at 25-30 m in water 35 m deep. A vertical-tow sample near the patch indicated the euphausiid Thysanoessa rachii, a common bowhead prey species, was abundant in the water column. The location of the zooplankton patch corresponded with a sharp salinity (proxy density) gradient. In addition, whale distribution coincided with a surface thermal boundary, identified by satellite-borne Advanced Very High Resolution Radiometer (AVHRR) imagery. The confinement of bowhead sightings to the northern coast of Chukotka in 1992-93 corresponds to reports from autumn surveys in 1979, 1980 and 1990, while the association of whales with physical oceanographic fronts is similar to findings from a study of bowhead feeding areas in the southern Beaufort Sea. These observations suggest that the Chukotka coast may be an important feeding or staging area for the Bering Sea stock and that oceanographic patterns influencing whale occurrence may be identifiable from standard oceanographic measurements.Key words: bowhead whale, Balaena mysticetus, migration, Chukchi Sea, Bering Sea, Chukotka, Thysanoessa rachii, satellite imagery, AVHRRDurant l'automne de 1992 et celui de 1993, on n'a pu observer de baleines boréales (Balaena mysticetus) que le long de la côte nord de Chukotka (Russie), bien que des recherches aient eu lieu dans une zone étendue de la mer des Tchouktches lors de croisières en bateau. Des comptages de 76 et 50 baleines boréales ont été obtenus respectivement le 1er octobre 1992 et le 3 octobre 1993, alors qu'on n'en a observé que quelques-unes les autres jours. Les baleines observées entre Cape Schmidt et Cape Vankarem le 1er octobre 1992 semblaient être en train de s'alimenter, mais on ne disposait pas de moyens pour détecter le genre de nourriture sous la surface, ni pour en prélever un échantillon cette année-là. Le 3 octobre 1993, les baleines semblaient s'alimenter là où une plaque de zooplancton de 5 m x 8 km avait été identifiée par méthode acoustique entre 25 et 30 m de profondeur, dans une zone de 35 m de fond. Un échantillon prélevé par hâlage vertical près de la plaque a indiqué que l'euphausiacé Thysanoessa rachii, une proie courante de la baleine boréale, était abondant dans la colonne d'eau. L'emplacement de la plaque de zooplancton correspondait à un fort gradient de salinité (approximation par la densité). De plus, la distribution des baleines coïncidait avec une limite thermique de surface identifiée au moyen de l'imagerie par radiomètre perfectionné à très haute résolution, transporté par satellite. Le confinement des observations de baleines à la côte nord de Chukotka en 1992-93 correspond aux rapports des relevés d'automne de 1979, 1980 et 1990, tandis que l'association des baleines à des fronts physiques océanographiques cadre avec les résultats d'une étude des zones d'alimentation de la baleine boréale dans le sud de la mer de Beaufort. Ces observations suggèrent que la côte de Chukotka pourrait être une importante zone d'alimentation ou de rassemblement pour la population de la mer de Béring, et que les caractéristiques océanographiques qui influencent la présence des baleines pourraient être identifiables à partir des mesures océanographiques courantes.Mots clés: baleine boréale, Balaena mysticetus, migration, mer des Tchouktches, mer de Béring, Chukotka, Thysanoessa rachii, imagerie par satellite, radiomètre perfectionné à très haute résolutio