Article

Changes in the Numbers of Cetaceans near the Pribilof Islands, Bering Sea, between 1975-78 and 1987-89

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

We compared the number of cetaceans seen during surveys of seabird distribution in the vicinity of the Pribilof Islands, Bering Sea, during two periods, 1975-78 (3867 km surveyed) and 1987-89 (6101 km surveyed). During the 1980s, we saw increased numbers of fin whales (Balaenoptera physalus) (0 to 66 individuals), minke whales (B. acutorostrata) (3 to 38 individuals), humpback whales (Megaptera novaeangliae) (0 to 24 individuals), killer whales (Orcinus orca) (5 to 58 individuals), and Dall's porpoises (Phocoenoides dalli) (101 to 241 individuals). It could not be determined whether these changes reflected changes in the numbers of these species in the Bering Sea, or simply local changes in their foraging or distribution patterns. Fin, humpback and minke whales were seen foraging in the vicinity of large flocks of birds that were eating euphausiids (Thysanoessa raschii and T. inermis). Key words: Fin whale, minke whale, humpback whale, killer whale, Dall’s porpoise, Balaenoptera physalus, Balaenoptera acutorostrata, Megaptera novaeangliae, Orcinus orca, Phocoenoides dalli, Bering Sea, whale foraging

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... In recent years, fin whales have been observed year round off central and southern California, with peak numbers in summer and fall (Dohl et al. 1983;Barlow 1995;Forney et al. 1995), in summer off Oregon (Green et al. 1992), and in summer and fall in the Gulf of Alaska (including Shelikof Strait) and southeastern Bering Sea (Leatherwood et al. 1986;Brueggeman et al. 1990). Their regular summer occurrence has also been noted in recent years around the Pribilof Islands in the northern Bering Sea (Baretta and Hunt 1994). Fin whales have been observed feeding in Hawaiian waters during mid-May (Balcomb 1987; also see Shallenberger 1981), and their sounds have been recorded there during the autumn and winter (Thompson and Friedl 1982; and see Northrop et al. 1968;Shallenberger 1981). ...
... It therefore appears that fin whales remain seriously depleted in these northern waters where they were subject to intense whaling, although the paucity of sightings may also be linked to shifts in distribution or incomplete survey coverage. For example, standardized surveys for seabirds near the Pribilof Islands in the Bering Sea indicated a substantial increase in the local abundance of fin whales from 1975-78 to 1987-89 (Baretta and Hunt 1994). ...
... The dramatic increase in planktivores in 1987-1988 was driven primarily by changes in abundance of short-tailed shearwaters, fork-tailed storm-petrels and red phalaropes, none of which breed at the Pribilof Islands. We also observed high numbers of shearwaters in 1989 (Hunt et al., 1996), as abundance of baleen whales near the Pribilof Islands in the late 1980s was significantly higher than in years prior (Baretta and Hunt, 1994;G.L. Hunt, personal observations). During the late 1980s, shearwaters and thick-billed murres were observed foraging on large aggregations of euphausiids, some of which were also attended by whales (Coyle et al., 1992;Baretta and Hunt, 1994;Hunt et al., 1996). ...
... We also observed high numbers of shearwaters in 1989 (Hunt et al., 1996), as abundance of baleen whales near the Pribilof Islands in the late 1980s was significantly higher than in years prior (Baretta and Hunt, 1994;G.L. Hunt, personal observations). During the late 1980s, shearwaters and thick-billed murres were observed foraging on large aggregations of euphausiids, some of which were also attended by whales (Coyle et al., 1992;Baretta and Hunt, 1994;Hunt et al., 1996). These observations support the hypothesis that in the period 1987/1989 and possibly through 1998, planktonic prey must have been far more available to seabirds foraging near the Pribilof Islands than in either 1977/1978 or 1999/2004. ...
Article
Full-text available
We examined trends in the abundance and distribution of 12 species of marine birds around the Pribilof Islands, southeastern Bering Sea, over the period from 1977 to 2004. We contrasted patterns among piscivores and planktivores and related these to known and hypothesized changes in the abundance and distribution of prey in the vicinity of the islands. Planktivorous and piscivorous species of marine birds showed different patterns of abundance over time. Planktivorous seabirds that breed away from the Pribilof Islands (e.g., short-tailed shearwaters [Puffinus tenuirostris], fork-tailed storm-petrels [Oceanodroma furcata] and red phalaropes [Phalaropus fulicarius]) were scarce in the 1970s, were abundant in the 1980s, and declined in abundance in the 1990s and from 1999 to 2004. Planktivorous alcids combined (parakeet [Aethia psittacula], crested [A. cristatella] and least [A. pusilla]) that breed on the Pribilof Islands showed a similar remarkable four-fold increase from the 1970s to the 1980s, but then a small increase into the 1990s followed by a rapid decline in the 2000s to numbers similar to those present during the 1970s. The abundance of piscivores kittiwakes (Rissa spp.) and murres (Una spp.) was high in the 1970s and declined through the 1980s, 1990s and 2000s. In 1999 and 2004, the total number of all seabirds at sea around the Pribilof Islands was well below the numbers seen at any other survey period. We hypothesize that changes in the abundances and types of seabirds present through time reflect changes in the structure of the marine ecosystem of the eastern Bering Sea shelf. We suggest that changes in pathways of energy flow may be responsible for these shifts, though the possibility that there has been a reduction in productivity cannot be ruled out given the scarcity of available data.
... Evidence for a decline includes fewer birds breeding on the Pribilof Islands (Hunt and Byrd, 1999) and recent decreases in the average size of adult salmon 6 in western Alaska (Kruse, 1998). As the numbers of planktivorous marine mammals on the Bering Sea shelf continue to rebound from decades of whaling (Baretta and Hunt, 1994; Tynan, 1998) and biomass of another plankton predator (Scyphomedusae ) remains high after recent rapid increases (Brodeur et al., 1999), food may become a limiting resource for established populations such as walleye pollock (i.e. the opposite of the cascade hypothesis; Merrick, 1995 Merrick, , 1997 National Research Council, 1996 ). If this happens , then atmospherically-forced ecosystem perturbations that affect the production of zooplankton and their availability to apex predators may have an even greater effect on the structure of trophic webs than was observed in 1997. ...
Article
In 1997, the Bering Sea ecosystem, a productive, high- latitude marginal sea, demonstrated that it responds on very short time scales to atmospheric anomalies. That year, a combination of atmospheric mechanisms pro- duced notable summer weather anomalies over the eastern Bering Sea. Calm winds, clear skies, and warm air temperatures resulted in a larger-than-normal transfer of heat to surface waters and the establishment of a shallow mixed layer. In spring, significant new production occurred below the shallow pycnocline over the Middle Shelf, depleting the subpycnocline nutrient reservoir that normally exists during summer. Following the depletion of nitrate and silicate from the system, a sustained (‡ 4 months) bloom of cocco- lithophores (Emiliania huxleyi) was observed - a phe- nomenon not previously documented in this region. Summer Middle Shelf Domain copepod concentrations were higher for some species in 1997 than in the early 1980s. Warmer surface water and lack of wind mixing also changed the basic distribution of hydrographic regimes on the south-eastern shelf and altered the strength and position of fronts or transition zones where apex predators seek elevated food concentra- tions. The Inner Front was well inshore of its normal position, and adult euphausiids (the primary prey of short-tailed shearwaters, Puffinus tenuirostris )w ere unavailable at, and shoreward of, the front in autumn. High shearwater mortality rates followed the period of low euphausiid availability. Some, but not all, of these anomalous conditions re-occurred in 1998. These observations are another demonstration that the structure and function of marine ecosystems are inti- mately tied to forcing from the atmosphere. Alteration of climatological forcing functions, expressed as wea- ther, can be expected to have large impacts on this ecosystem and its natural resources.
... the zooplankton standing stock around the Pribilof Islands in summer 1999, compared to a consumption of o1% in 1982 . Second, the numbers of baleen whales, such as humpback (Megaptera novaengliae) and minke (Balaenoptera acutorostrata) whales also have increased over the shelf since the 1970s (Baretta and Hunt, 1994). The diet composition of these whales in the eastern Bering Sea is not known, and their impact on zooplankton has yet to be determined. ...
Article
Full-text available
We propose a new hypothesis, the Oscillating Control Hypothesis (OCH), which predicts that pelagic ecosystem function in the southeastern Bering Sea will alternate between primarily bottom-up control in cold regimes and primarily top-down control in warm regimes. The timing of spring primary production is determined predominately by the timing of ice retreat. Late ice retreat (late March or later) leads to an early, ice-associated bloom in cold water (e.g., 1995, 1997, 1999), whereas no ice, or early ice retreat before mid-March, leads to an open-water bloom in May or June in warm water (e.g., 1996, 1998, 2000). Zooplankton populations are not closely coupled to the spring bloom, but are sensitive to water temperature. In years when the spring bloom occurs in cold water, low temperatures limit the production of zooplankton, the survival of larval/juvenile fish, and their recruitment into the populations of species of large piscivorous fish, such as walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus) and arrowtooth flounder (Atheresthes stomias). When continued over decadal scales, this will lead to bottom-up limitation and a decreased biomass of piscivorous fish. Alternatively, in periods when the bloom occurs in warm water, zooplankton populations should grow rapidly, providing plentiful prey for larval and juvenile fish. Abundant zooplankton will support strong recruitment of fish and will lead to abundant predatory fish that control forage fish, including, in the case of pollock, their own juveniles. Piscivorous marine birds and pinnipeds may achieve higher production of young and survival in cold regimes, when there is less competition from large piscivorous fish for cold-water forage fish such as capelin (Mallotus villosus). Piscivorous seabirds and pinnipeds also may be expected to have high productivity in periods of transition from cold regimes to warm regimes, when young of large predatory species of fish are numerous enough to provide forage. The OCH predicts that the ability of large predatory fish populations to sustain fishing pressure will vary between warm and cold regimes.The OCH points to the importance of the timing of ice retreat and water temperatures during the spring bloom for the productivity of zooplankton, and the degree and direction of coupling between zooplankton and forage fish. Forage fish (e.g., juvenile pollock, capelin, Pacific herring [Clupea pallasii]) are key prey for adult pollock and other apex predators. In the southeastern Bering Sea, important changes in the biota since the mid-1970s include a marked increase in the biomass of large piscivorous fish and a concurrent decline in the biomass of forage fish, including age-1 walleye pollock, particularly over the southern portion of the shelf. Populations of northern fur seals (Callorhinus ursinus) and seabirds such as kittiwakes (Rissa spp.) at the Pribilof Islands have declined, most probably in response to a diminished prey base. The available evidence suggests that these changes are unlikely the result of a decrease in total annual new primary production, though the possibility of reduced post-bloom production during summer remains. An ecosystem approach to management of the Bering Sea and its fisheries is of great importance if all of the ecosystem components valued by society are to thrive. Cognizance of how climate regimes may alter relationships within this ecosystem will facilitate reaching that goal.
... (3) The existence of a clockwise circulation pattern around the Pribilof Islands, which can retain young fish near the Pribilof Islands (Kowalik and Stabeno, 1999; Stabeno et al., 1999). (4) The great abundance of piscivorous seabirds (Decker and Hunt, 1996) and marine mammals (Baretta and Hunt, 1994; Robson, 2002) that breed and feed in the Pribilof Islands region, and have diets dominated by pollock (Dragoo et al., 2000). (5) The presence of pollock spawning areas near the Pribilof Islands (e.g., Pribilof Canyon) that can deliver pollock larvae to the Pribilof region earlier than those arriving by drift along the shelf break (Napp et al., 2000). ...
Article
The Pribilof Islands region is recognized to be a major nursery for age-0 walleye pollock (Theragra chalcogramma) in the eastern Bering Sea. However, the Pribilof Islands’ importance for the recruitment of pollock in the Bering Sea has not been quantified. In this paper, we define the geographic extent of the Pribilof Islands region based on ocean circulation, location of major fronts, and trophic interactions. The abundance and distribution by oceanographic habitat (nearshore, frontal and offshore), of acoustically determined age-0 pollock are compared between the Pribilof Islands and the Inner Front of the eastern Bering Sea, for the summers of 1997–1999. Net samples collected during surveys in 1995–2002 are used to compare the abundance of age-0 pollock in the Pribilof Islands region to locations eastward along the Bering Sea shelf.We found densities of age-0 pollock near the Pribilof Islands to be generally higher than on the surrounding shelf, and higher or non-significantly different from the Inner Front. Through synthesis of our data and inferences of pollock growth and mortality, we estimate the Pribilof Islands region to have comprised 12.5% (1997), 53.7% (1998), and 24.7% (1999) of the total stock of age-0 pollock in the eastern Bering Sea. Since the Pribilof Islands region comprises only 14% of the total eastern Bering Sea area, evidence is given that a disproportionally large fraction of the age-0 pollock population inhabits the Pribilof Islands nursery.
... In the late-1990s, the biomass of large predatory fish appeared to decline. The biomass of baleen whales on the shelf increased between the mid-1970s and the late-1980s (Baretta & Hunt, 1994 ). Populations of piscivorous marine birds and pinnipeds declined, particularly in the vicinity of the Pribilof Islands (Hunt et al., 2002). ...
Article
We examine how coupling between physical and biological processes influences the production and transfer of energy to upper trophic-level species in the southeastern Bering Sea. We review time series that illustrate changes in the marine climate of the southeastern Bering Sea since the mid-1970s, particularly variability in the persistence of sea ice and the timing of its retreat. Time series (1995 – 2001) from a biophysical mooring in the middle domain of the southeastern shelf support the hypothesis that retreat of the winter sea ice before mid-March (or the failure of ice to be advected into a region) results in an open water bloom in May or June in relatively warm water (≥3°C). Conversely, when ice retreat is delayed until mid-March or later, an ice-associated bloom occurs in cold (≤0°C) water in early spring. These variations are important because the growth and production of zooplankton and the growth and survival of larval and juvenile fish are sensitive to water temperature. The Oscillating Control Hypothesis (OCH) recently proposed by Hunt et al. (2002), predicts that control of the abundance of forage fish, and in the case of walleye pollock (Theragra chalcogramma), recruitment of large piscivorous fish, will switch from bottom-up limitation in extended periods with late ice retreat to top-down in warmer periods when ice retreat occurs before mid-March. In support of this hypothesis, we review recent data from the southeastern Bering Sea that show 2- to 13-fold changes in copepod abundance with changes in spring water temperatures of 3 to 5°C. We also provide indirect evidence that the abundance of adult pollock on the eastern Bering Sea shelf negatively affects the abundance forage fishes (including juvenile pollock) available to top predators. Although there is evidence that pollock year-class strength is positively related to temperature, we lack the time series of pollock populations in extended periods (8 – 10 years) of cold-water blooms necessary to test the OCH.
Article
Full-text available
The global distribution of fin whales Balaenoptera physalus is not fully understood. Existing maps can be divided into two conflicting categories: one showing a continuous global distribution and another showing an equatorial hiatus (gap in the global distribution) between approximately 20°N and 20°S. Questions also remain about the seasonal distribution of fin whales.To explore the suggested equatorial hiatus and seasonal distribution patterns, we synthesised information on fin whale distribution in the post-whaling era (1980–2012) from published literature, publicly available reports and studies conducted by various organisations. We created four seasonally stratified maps showing line-transect density estimates, line-transect survey effort, acoustic detections, and sightings.An equatorial hiatus in the global distribution of fin whales during the post-whaling era is supported by numerous line-transect surveys and by the rarity of equatorial acoustic detections and sightings, and corroborated by whaling era reports, morphological analyses, and genetic analyses.Our synthesis of post-whaling era data is consistent with results from other studies indicating that fin whales are more abundant at higher latitudes during warmer months and more abundant at lower latitudes (although these latitudes are still greater than 20°) during colder months. However, our synthesis and results from other studies also indicate that some fin whales in both hemispheres remain in higher latitudes (50°–60° north or south) during colder months and in lower latitudes (to approximately 20°–30° north or south) during warmer months, indicating that seasonal fin whale movements differ from the seasonal migrations of blue whales Balaenoptera musculus and humpback whales Megaptera novaeangliae.Our maps of global fin whale distribution provide a comprehensive picture of current knowledge and highlight important geographical and temporal data gaps. Surveys should be conducted within the identified data gaps in order to increase fine-scale spatial and temporal knowledge of distribution patterns, improve fin whale taxonomy, and identify areas of elevated fin whale densities that may require management of threats, such as ship strikes.
Article
Baleen whales typically migrate to high-latitudes to feed during summer in regions of predictably high concentrations of their zooplankton or fish prey. Therefore, their presence in shelf systems is a good indicator of productive food webs. Line-transect surveys of cetaceans conducted during the late 1990s in the SE Bering Sea (160.32 to 171.08° W) indicate that the middle shelf (50 m < z < 100 m) now supports the highest whale biomass in this region. In recent decades, whales were rare and hence their ecological role on the shelf was limited. During July 1997, the density and abundance (N) of humpback whales Megaptera novaeangliae and fin whales Balaenoptera physalus were highest on the middle shelf between 163.7 and 168.1° W: 0.0236 humpback whales km -2, N = 1308 (coefficient of variation, CV = 0.65), and 0.00924 fin whales km-2, N = 513 (CV = 0.61), respectively. Similarly, during June 1999, fin whales were the most numerically dominant species of large whale in the SE Bering Sea, with highest densities and abundance in the 'central' middle shelf (163.7 to 168.1° W): 0.0169 fin whales km-2, N = 938 (CV = 0.54). During the summers of 1997 and 1999, 65 and 79 % of the prey consumption by fin whales in the SE Bering Sea occurred on the central middle shelf. Prey biomass consumed by fin and humpback whales on the SE Bering Sea shelf and slope in 1997 (264474 to 723504 metric tons, mt) is equivalent to 34-94% of the 1997 echo-integration trawl estimate of walleye pollock Theragra chalcogramma biomass (age 1+) for the shelf east of 170° W (0.77 × 106 mt). Large whales were much more abundant on the middle shelf during the late 1990s than during preceding decades and, therefore, their foraging may have impacted trophic dynamics, carbon pathways and nutrient cycling. The partitioning of available carbon and energy in the pelagic and benthic systems of the shelf, as determined previously during the 1970s, when whales were rare, should now be reexamined relative to the increased ecological impact of these top-level predators. Fluxes of carbon that involve pathways through whales should be incorporated in shelf and oceanic carbon budgets.
Chapter
Full-text available
Did the removal of megatons of upper-trophic-level consumers significantly alter food-web dynamics by removing significant levels of predatory controls over prey populations, removing an important prey resource for predator populations, and changing the sensitivity of the ecosystem to physical forcing because of new predator-prey functional relationships? In order to address this question, it is necessary to understand where and when whales were harvested in the North Pacific Ocean, and how this ultimately affected whale distribution. Whales were not uniformly distributed across this broad region, and the roles they played were concentrated in relatively small areas. This chapter shows where great whales formerly were found in abundance in the North Pacific, relates those distributions to oceanography, and briefly explores some examples of the magnitude of change that might have resulted from the loss of great whales in the Aleutian Islands and Bering Sea.
Article
Results from 2004 field observations, integrated with those from prior studies, allow definition of a unique “Pribilof Domain” in the southeastern Bering Sea. This domain results from its geographic location and bathymetry that supply water from the outer shelf and slope that is replete with dissolved and planktonic material. We highlight temporal variability in this domain and place this in the broader context of mechanisms identified as potentially important in regulating the flow of energy and material in this shelf ecosystem.
Article
Full-text available
Populations of seals, sea lions, and sea otters have sequentially collapsed over large areas of the northern North Pacific Ocean and southern Bering Sea during the last several decades. A bottom-up nutritional limitation mechanism induced by physical oceanographic change or competition with fisheries was long thought to be largely responsible for these declines. The current weight of evidence is more consistent with top-down forcing. Increased predation by killer whales probably drove the sea otter collapse and may have been responsible for the earlier pinniped declines as well. We propose that decimation of the great whales by post-World War II industrial whaling caused the great whales' foremost natural predators, killer whales, to begin feeding more intensively on the smaller marine mammals, thus "fishing-down" this element of the marine food web. The timing of these events, information on the abundance, diet, and foraging behavior of both predators and prey, and feasibility analyses based on demographic and energetic modeling are all consistent with this hypothesis.
Article
Full-text available
A high mortality of juvenile and adult female north- ern fur seals (Callorhinus ursinus) is believed to be responsible for the most recent decline of the Pribilof population which began in the early 1970s. The two most likely explanations for the high mortality rates are related to 1) commercial fishing of major fur seal prey species in the Bering Sea and Gulf of Alaska, and 2) entrapment of seals in lost and discarded fish- ing gear. A review of the entanglement hypothesis found many of the assertions made about the extent of entanglement mortality were poorly supported by the available data and were inconsistent with the dynamics of other pinniped populations. The build up of commercial fishing is consistent with the timing of the fur seal decline, but studies of growth (lengths and weights of pups, subadults and adults) and the duration of foraging trips by lactating mothers suggest per capita increases in food abundance. These fur seal observations suggest food resources in the spring are sufficient to meet the needs of the currently low population as the seals migrate north through the coastal waters of British Columbia and Alaska. However, the data are also consistent with the view that per capita fish abundance is insufficient for young fur seals during the fall migration as the seals swim south through the Aleutian archipelago. It is hypothesized that reduced food availability for young fur seals in the Gulf of Alaska during this stage of the seal's life cycle creates a bottleneck for the entire population, which can account for the decline of the Pribilof herd. This possibility is supported by the sharp decline in numbers of Steller sea lions and harbour seals along the Alaskan panhandle.
Article
Full-text available
An unusual number of killer whales appeared in inshore waters of the south-eastern Bering Sea in summer 1989 and 1990. Multiple sightings occurred in Bristol and Kuskokwim bays where killer whales had been seen only rarely in previous years. Three animals became stranded on mud flats in Kuskokwim Bay but were able to free themselves on a high tide. Killer whales were observed interacting with salmon, harbor seals, SteIler sea lions, walruses, and beluga whales. Detailed observations were made of killer whales attacking belugas in the Naknek River. Local conditions and behavioral adaptations may reduce the susceptibility of belugas to killer whale predation. Continued killer whale activity in this area would be unlikely to affect fish resources, but might have some influence on beluga whales.
Article
Full-text available
In the summer and fall of 1986 a total of 257 humpback whales Megapteranovaeangliaewere individually identified during nonsys­ tematic vessel surveys of southeast­ ern Alaska. The majority of adult animals (n 130, 54.6%) identified in 1986 had been identified previously in southeastern Alaska during the years 1979-85. Capture-recapture estimates suggested that this region­ al subpopulation increased in abun­ dance from 1979 to 1986, and in­ cluded 547 individual whales (95% CL: 504-590) at the time of the 1986 surveys. An average reproduction rate of 0.36 calves/mature female' year- 1 (95% CL: 0.28-0.43) was es­ timated for this regional subpopula­ tion using individual identification records collected during 1980-86. In the Frederick Sound-Stephens Pas­ sage area, the largest number of whales was found during August and their predominant prey appeared to be euphausiids. In the Glacier Bay­ Icy Strait area, the relative abun­ dance of whales was greatest in June and July and their predominant prey appeared to be schooling fish. Low levels of interchange between sur­ veyed areas for much of the summer season indicated strong preferences for local habitats among individual whales. The documented presence of some individual whales for at least 6 months is evidence that southeast­ ern Alaska is the primary feeding ground for many of the whales iden­ tified in these surveys.
Article
Full-text available
For about a month every spring, most of the northwest Atlantic population of right whales (Eubalaena glacialis) is found in the Great South Channel off New England. We hypothesized that the whales aggregate in this region during the spring because of the increased abundance or aggregation of their major food item, the copepod Calanus finmarchicus. During a 4-day cruise in May 1986 to the Great South Channel, we located a group of surface-feeding right whales spatially associated with a large, dense, nearly monospecific concentration of copepods, primarily C. finmarchicus. A 200 kHz acoustic system showed that these copepods formed an extensive, nearly continuous surface layer that may have occupied an area of over 2,500 km2. The copepod layer began about 20 km north of a front and extended northward at the surface in the region where water depth was deeper than 100 m. In MOCNESS plankton tows, a maximum copepod biomass of 23.6 g wet wt·m−3 and abundance of 41,600 copepods·m−3 were found, with highest abundances in the upper 20 m. The dominant developmental stage was the copepodite IV, but developmental stages from nauplius II to adult males and females were also present. The patch was a regional abundance maximum for the older developmental stages, but relative abundances of different stages changed with depth. The range of diel vertical migration of Calanus in the patch was small, and maximum abundances occurred near the surface day and night. The lower and side borders of the patch could be distinct and abrupt. Calanus abundance inside the patch was about 83 times higher than immediately below the patch and 311 times higher than immediately adjacent to the patch. Several biological and physical mechanisms, interacting with copepod behavior, may be important in the formation of the patch and the maintenance of its edges.
Article
Full-text available
Populations of several species of marine birds and mammals in the Bering Sea and Gulf of Alaska have been declining since the mid-1970s, with numbers of one, the Steller sea lion (Eumetopias jubatus), so depressed it was listed as threatened under the Endangered Species Act in spring 1990. All of the declining populations depend to an important extent on walleye pollock (Theragra chakogramma) for food, although they eat numerous other species as well. In contrast, certain animals that compete with pollock for common prey have been increasing in abundance. All of these changes could be related through food web connections mediated by pollock. Pollock is also important to people–it presently supports the largest single-species commercial fishery in the world, in large part because of its great biomass, which has averaged about 15 × 106t in the Bering Sea over the past 15 years. Pollock consume an inordinate proportion of the pelagic production in the Bering Sea, which further supports the conclusion that it is a key species in the ecosystem. However, there are conflicting hypotheses about the importance of the roles played by pollock as predator and prey, and about the effect that changes in pollock abundance might have on biomass yield at higher trophic levels.
Article
High concentrations of 2 murre species (Uria aalge and U. lomvia) were observed foraging over a submarine ridge on the east side of St. George Island, Bering Sea, usually in the morning. Simultaneous measurements of tidally generated current velocity and acoustically determined biomass along transects over the ridge demonstrated that the murres were concentrating over a dense epibenthic sound-scattering layer near the ridge crest on southward ebb tide currents. Samples taken by net tows through the layer contained high numbers of euphausiids (Thysanoessa inermis and T. raschii). Stomachs of murres collected in the area contained predominantly euphausiids. When tidal currents reversed from southward to northward, the sound-scattering layer was carried northward off the ridge and the murres left the area. We hypothesize that the euphausiid aggregations resulted from the interaction of the diel downward migration of euphausiids in the morning, bottom topography and tidal currents.
Article
SUMMARY Lawley (1956) describes how asymptotic likelihood ratio tests can in general be improved by multiplying the −2logλtest statistic by a multiplier chosen so that the null distribution of the modified statistic is better approximated by its asymptotic X2 distribution. This paper applies this technique to asymptotic likelihood ratio tests of hypotheses concerning complete contingency tables. Improved tests are derived for hypotheses with closed form maximum likelihood estimators.
Article
Aerial surveys were conducted in the Northwestern Gulf of Alaska and southeastern Bering Sea to determine the abundance, distribution, and habitat use patterns of endangered cetaceans and other marine mammals. Four species of cetaceans listed by the Federal Government as endangered were observed: gray, humpback, finback, and sperm whales. Sightings were also made to seven nonendangered species of cetaceans: minke, Cuvier's beaked, Baird's beaked, belukha, and killer whales, and Dall and harbor porpoises. Results show that the project area is an important feeding ground for relatively large numbers of humpback and finback whales and lower numbers of gray whale migration route between seasonal ranges. The project area also supports a variety of other marine mammals both seasonally and annually.
Article
Inshore abundance of baleen whales along the Newfoundland coasts changed considerably during the period 1973–83. In particular, large numbers of humpbacks were present along the northeast coast each summer between 1977 and 1980. This influx led to entrapment of whales in fishing gear. Counts of humpback (Megaptera novaeangliae), finback (Balaenoptera physalus), and minke (Balaenoptera acutorostrata) whales during standard surveys along the coast are used as indices of inshore abundance, and are related to the year-class strengths of capelin (Mallotus villosus), their major food in the Newfoundland region. Whales are found inshore when there are few immature capelin offshore. Minke whale distributions seem more closely related to the abundance of 1- to 2-yr-old, immature capelin, but humpback and finback whales are found inshore with low abundances of 2- to 3-yr-old, mainly immature capelin. We suggest that estimates of capelin year-class strength predicted from abiotic variables can be used to predict inshore whale abundance, at least 1 yr in advance. The extreme influx of humpbacks of the late 1970s is unlikely to recur in the short term. The analysis suggests that finback populations in the area are declining.
Article
Significant changes in the biomass of sandlance Ammodytes spp. and in the abundance of the copepod Calanus finmarchicus in the southern Gulf of Maine co-occurred with a shift in the occurrence and abundance of four species of baleen whales in the region. During 1982-88, abundance of sandlance was negatively correlated to abundance of C. finmarchicus. Abundance of C. finmarchicus and sandlance was at a regional maximum during 1986 and 1988, respectively. Abundance of humpback Megaptera novaeangliae and fin Balaenoptera physalus whales were marginally correlated to each other. Abundance of humpbacks was negatively correlated with right Eubalaena glacialis and sei Balaenoptera borealis whales. Patterns of occurrence for right and sei whales were significantly related to each other, these whales were common in the region only during 1986, when copepod abundance reached a regional maximum and sandlance abundance a regional minimum. -from Authors
basin environment and possible consequences of planned offshore oil and gas development
  • H W Braham
  • G W Oliver
  • C Fowler
  • K Frost
  • F Fay
  • C Cowles
  • K Schneider
BRAHAM, H.W., OLIVER, G.W., FOWLER, C., FROST, K., FAY, F., COWLES, C., SCHNEIDER, K., and CALKINS, D. 1992. Marine mammals. In: Hameedi, M.J., ed. The St. George basin environment and possible consequences of planned offshore oil and gas development. U.S. Department of Commerce, U.S. Department of the Interior, Outer Continental Shelf Environmental Assessment Program, Juneau, Alaska. 55-81.
Marine mammal data documentation for the Platforms of Opportunity Program and Outer Continental Shelf Environmental Assessment Program
  • L D Consiglieri
CONSIGLIERI, L.D., and BOUCHET, C. 1981. Marine mammal data documentation for the Platforms of Opportunity Program and Outer Continental Shelf Environmental Assessment Program. In: NOAA/OCSEAP Environmental Assessment of the Alaskan Continental Shelf. Final Reports of Principal Investigators 20:265 -364.
Murre foraging, epibenthic sound scattering and tidal advection over a shoal near
  • K O Coyle
  • G L Hunt
  • Jr
  • M B Decker
COYLE, K.O., HUNT, G.L., Jr., DECKER, M.B., and WEINGARTNER, T.J. 1992. Murre foraging, epibenthic sound scattering and tidal advection over a shoal near St. George Island, Bering Sea. Marine Ecology Progress Series 83:1-14.
Distribution of marine mammals in the coastal zone of the Bering Sea during summer and autumn
  • K J Frost
  • L F Lowry
  • J J Burns
FROST, K.J., LOWRY, L.F., and BURNS, J.J. 1982. Distribution of marine mammals in the coastal zone of the Bering Sea during summer and autumn. In: NOAA/OCSEAP Environmental Assessment of the Alaskan Continental Shelf. Final Reports of Principal Investigators 26:356 -561.
Foraging ecology of shorttailed shearwaters near the Pribilof Islands
  • G L Hunt
  • Jr
  • K O Coyle
  • S Hoffman
  • M B Decker
  • E Unpubl
HUNT, G.L., Jr., COYLE, K.O., HOFFMAN, S., DECKER, M.B., and FLINT, E. Unpubl. manuscript. Foraging ecology of shorttailed shearwaters near the Pribilof Islands. Available from G.L. Hunt Jr. at Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92717, U.S.A.
Reproductive ecology, foods and foraging areas of seabirds nesting on the Pribilof Islands
  • G L Hunt
  • Jr
  • Z Eppley
  • B Burgeson
HUNT, G.L., Jr., EPPLEY, Z., BURGESON, B., and SQUIBB, R. 1981. Reproductive ecology, foods and foraging areas of seabirds nesting on the Pribilof Islands, 1975-1979. In: NOAA/OCSEAP Environmental Assessment of the Alaskan Continental Shelf. Final Reports of Principal Investigators 12:1-257.
Aerial surveys of marine mammals in the southeastern Bering Sea
  • S Leatherwood
  • A E Bowles
LEATHERWOOD, S., BOWLES, A.E., and REEVES, R.R. 1983. Aerial surveys of marine mammals in the southeastern Bering Sea. In: NOAA/OCSEAP Environmental Assessment of the Alaskan Continental Shelf. Final Reports of Principal Investigators 42:147-473.
Behavior of individually-identified sei whales Balaenoptera borealis during an episodic influx into the southern Gulf of Maine in 1986
  • M R Schilling
  • I Seipt
  • M T Weinrich
  • S E Frohock
  • A E Kuhlberg
SCHILLING, M.R., SEIPT, I., WEINRICH, M.T., FROHOCK, S.E., KUHLBERG, A.E., and CLAPHAM, P.J. 1992. Behavior of individually-identified sei whales Balaenoptera borealis during an episodic influx into the southern Gulf of Maine in 1986. Fishery Bulletin 90:749-755.
Catalog of Alaskan seabird colonies
  • A L Sowls
  • S A Hatch
SOWLS, A.L., HATCH, S.A., and LENSINK, C.J. 1978. Catalog of Alaskan seabird colonies. Anchorage: US. Fish and Wildlife Service. FWS/085-78/78.