Ocean Regime Shifts Research Articles

Ocean warming as a trigger for irreversible retreat of the Antarctic ice sheet

Warmer ocean conditions could impact future ice loss from Antarctica due to their ability to thin and reduce the buttressing of laterally confined ice shelves. Previous studies highlight the potential for a cold to warm ocean regime shift within the sub-shelf cavities of the two largest Antarctic ice shelves—the Filchner–Ronne and Ross. However, how this impacts upstream ice flow and mass loss has not been quantified. Here using an ice sheet model and an ensemble of ocean-circulation model sub-shelf melt rates, we show that transition to a warm state in those ice shelf cavities leads to a destabilization and irreversible grounding line retreat in some locations. Once this ocean shift takes place, ice loss from the Filchner–Ronne and Ross catchments is greatly accelerated, and conditions begin to resemble those of the present-day Amundsen Sea sector—responsible for most current observed Antarctic ice loss—where this thermal shift has already occurred.

Resolution of the Tetrabothrius jagerskioeldi Cryptic Species Complex among Holarctic Alcidae (Charadriiformes): Cestodes among Fraterculinae—Exploring Marine Diversity, Host Range, and Dynamic Oceanography in the Greater North Pacific

In the biosphere, limits for diversity among species, communities, and biomes are revealed through intensive and extensive field-based inventory and assembly of voucher specimens and associated informatics examined in a phylogenetic, historical, ecological, and biogeographic arena. Archival resources for specimens and information contribute to a cumulative view of faunal structure and assembly under a comparative umbrella. Ultimately, species definitions, and inclusive partitions among populations and lineages, are fundamental in articulating hypotheses that examine interactions about evolution, the nature of organisms, and the condition of environments across space and time. We conclude our proposals establishing species limits for tapeworms of the cryptic complex historically accommodated in Tetrabothrius jagerskioeldi Nybelin, 1916 among Alcidae seabirds (Charadriiformes). Explorations of this facet of marine diversity summarize inventory data for species of Tetrabothrius Rudolphi, 1819 from field collections among 1,976 seabirds of 41 species representing 3 avian orders (Charadriiformes, Suliformes, Procellariiformes) examined across 58 oceanic/geographic localities from the greater North Pacific basin between 1949 and 2019, or over the past 70 years. Cestodes of the complex including T. jagerskioeldi sensu stricto, T. alcae Hoberg and Soudachanh, 2021, and T. sinistralis Hoberg and Soudachanh, 2021, along with 2 previously unrecognized taxa, are documented, occurring in 128 of 1976 seabirds examined (6%) and 17 of 41 marine avian species from 23 insular, coastal, and pelagic sites spanning the North Pacific. In completing an evaluation of this assemblage, we focus on those cestodes among 8 species of medium- to small-bodied alcids, subfamily Fraterculinae. Specimens designated as Tetrabothrius fraterculus n. sp. were observed among puffins (2 species of Fraterculus and Cerorhinca), whereas Tetrabothrius aithuia n. sp. is proposed for tapeworms in auklets (4 species of Aethia and Ptychoramphus) and a puffin (Cerorhinca); both cestodes are currently unknown among the Alcinae species of Cepphus, Uria, Brachyramphus, and Synthliboramphus based on the North Pacific inventory collections. These large-bodied cestodes, typical of the 5 species in the complex, are characterized among 46 currently valid species of Tetrabothrius in avian hosts, based on unique configurations of the genital atrium; male and female genital papillae; terminal genital ducts; numbers of testes; and the structure, position, and dimensions of the vaginal and atrial seminal receptacles. Ancillary characters contributing to differentiation include attributes of the scolex, structure, dimensions, and position of the vitelline gland and relative position of the dorsal and ventral osmoregulatory canals. A suite of complex attributes unequivocally separates 5 respective species that had historically been relegated to a single geographically widespread and morphologically variable taxon under T. jagerskioeldi sensu lato. Host range for respective cryptic species of the T. jagerskioeldi–complex reveal an intricate view of ecological isolation and connectivity across the greater North Pacific basin. Seabirds, marine mammals, and parasites are indicators of changing conditions over space and time. Oceanic regime shifts, prey cascades, and diversity for birds and parasites serve as proxies for revealing accelerating perturbation in marine foodwebs under climate forcing.

Atmospheric CO2 Isotopic Variations, with Estimation of Ocean and Plant Source Contributions

This analysis uses both atmospheric CO2 concentrations and the accompanying δ13C isotopic measurements of CO2 over 40 years from 1978 to 2015 observed at ten different latitudes from 90° S to 82 °N. Atmospheric CO2 is separated into two components of CO2 attributable to deep ocean and to plant (including fossil fuel) sources. The isotopic values assigned to the two components are δ13C = 0‰ and −26‰, respectively. The latitude variations in residual source component CO2 show the ocean source component peaking at the equator. This contrasts with the residual plant source component that peaks in the Arctic Circle region. Seasonal comparisons show no change in the ocean component peaking at the equator and no significant changes in its variation with latitude, while the plant component shows seasonal changes of the order of 15 ppm at high latitudes. The ocean component shows clear anomalous behavior in the three years following the 1989 Pacific Ocean regime shift (a shift independently identified from the changed biological time series). By contrast, the residual plant component shows a correlation in the timing of maxima in its annual variations with the timing of El Nino events over the time span of 1985–2015. It also shows a discontinuity in annual variation coinciding with the 1995 AMO phase change. We conclude that the ocean and plant components of atmospheric CO2 relate to independent sources of atmospheric CO2 and have approximately equal magnitudes. The observations are consistent with a hypothesis that variations in the ocean components have an origin from upwelling water from deep ocean currents, and variations in plant components are dominated by a combination of fossil fuel CO2, phytoplankton productivity, and forest and peat fires, which primarily occur in the northern hemisphere.

Ocean Regime Shift is Driving Collapse of the North Atlantic Right Whale Population

Ocean warming linked to anthropogenic climate change is impacting the ecology of marine species around the world. In 2010, the Gulf of Maine and Scotian Shelf regions of the Northwest Atlantic underwent an unprecedented regime shift. Forced by climate-driven changes in the Gulf Stream, warm slope waters entered the region and created a less favorable foraging environment for the endangered North Atlantic right whale population. By mid-decade, right whales had shifted their late spring/summer foraging grounds from the Gulf of Maine and the western Scotian Shelf to the Gulf of St. Lawrence. The population also began exhibiting unusually high mortality in 2017. Here, we report that climate-driven changes in ocean circulation have altered the foraging environment and habitat use of right whales, reducing the population’s calving rate and exposing it to greater mortality risks from ship strikes and fishing gear entanglement. The case of the North Atlantic right whale provides a cautionary tale for the management of protected species in a changing ocean.

Properly designed effort management for highly fluctuating small pelagic fish populations: a case study in a purse seine fishery targeting chub mackerel

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 617-618:265-276 (2019) - DOI: https://doi.org/10.3354/meps12688 Properly designed effort management for highly fluctuating small pelagic fish populations: a case study in a purse seine fishery targeting chub mackerel Momoko Ichinokawa*, Hiroshi Okamura National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa-ku, Yokohama, Kanagawa 236-8648, Japan *Corresponding author: ichimomo@fra.affrc.go.jpAdvance View was available online September 6, 2018 ABSTRACT: Proper fisheries management is difficult in fisheries targeting small pelagic fish that are subject to climate-induced oceanic regime shifts. A favourable regime tends to induce capacity investments, but the results of these investments turn out to be irreducible overcapacity under the next unfavourable regime. The Japanese purse seine fishery studied here, which targets small pelagic fish, is a typical example of such overcapacity. However, we demonstrate that this fishery represents a best practice of properly designed effort management in recent years through its quantitative evaluation. Generalized linear mixed models (GLMMs) applied to daily logbook data revealed that effort restrictions on daily purse seine operations (in terms of the duration and the total number of operations per ship and day) significantly reduced total fishing efforts on chub mackerel. Stochastic simulations based on the parameters estimated in GLMMs quantified the extent of the potential catch reduction by the effort reductions at approximately 20%. Combined with the effect of another concurrently implemented management measure, i.e. day closures, the net effects of the effort management on the total catch reduction were estimated at 30%. Because the quota uptake percentages in this fishery were 60-80% during the study period, we conclude that the effort management helped avoid overshooting of the quota and consequent seasonal closures. KEY WORDS: Input control · Effort limitations · Race to fish · Catch shares Full text in pdf format Supplementary material PreviousNextCite this article as: Ichinokawa M, Okamura H (2019) Properly designed effort management for highly fluctuating small pelagic fish populations: a case study in a purse seine fishery targeting chub mackerel. Mar Ecol Prog Ser 617-618:265-276. https://doi.org/10.3354/meps12688 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 617-618. Online publication date: May 16, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Did a “perfect storm” of oceanic changes and continental anthropogenic impacts cause northern hemisphere anguillid recruitment reductions?

AbstractThe three northern hemisphere anguillid eel species experienced recruitment declines at similar times beginning in the 1970s and 1980s, but the exact causes of the declines have remained unclear. Attention focused on two categories of possible causes that included (i) anthropogenic impacts on eel growth habitats, such as dam construction, degradation and pollution of habitats, introduction of parasites, overfishing and (ii) changes in ocean-atmospheric conditions affecting their marine life-history stages. The cumulative effects of reaching peaks in dam construction, levels of pollution, and eutrophication just before the eel declines likely had reduced eel production in many areas, and contamination by metallic and organic compounds and parasites may have reduced reproductive success. Shifts in ocean-atmospheric conditions also occurred just before the eel declines that could have reduced feeding success of larvae or disrupted larval transport. If oceanic regime shifts reduced production of the marine snow food of eel larvae, it may have affected larval survival and recruitment success, especially if there is a critical time-window for successful larval first feeding when marine snow particles need to be abundant. A reduction of these particles could result in density-dependent early mortality of the larvae of each spawning event, and competition for marine snow particles with sympatrically spawning mesopelagic eel larvae would amplify this effect. Nutrient reductions causing shifts in the relative abundance of phytoplankton contributing to marine snow production and of ubiquitous cyanobacteria may mediate levels of larval survival in areas with high spawning activity. Reductions of eels reaching the spawning area from species range margins that spawn outside of peak spawning periods could have reduced recruitment further. It appears likely that a variety of impacts, oceanic and anthropogenic occurred simultaneously causing sudden declines of these eel populations.

Asynchronous responses of fish assemblages to climate-driven ocean regime shifts between the upper and deep layer in the Ulleung basin of the East Sea from 1986 to 2010

Past studies suggested that a basin-wide regime shift occurred in 1988–1989, impacting marine ecosystem and fish assemblages in the western North Pacific. However, the detailed mechanisms involved in this phenomenon are still yet unclear. In the Ulleung basin of the East Sea, filefish, anchovy and sardine dominated the commercial fish catches in 1986–1992, but thereafter common squid comprised > 60% of the total catch in 1993–2010. To illuminate the mechanisms causing this dramatic shift in dominant fisheries species, I related changes in depth-specific oceanographic conditions from 0 to 500 m to inter-annual changes in the fish assemblage structure from 1986 to 2010. In the upper layer of 50–100 m depths, water temperature suddenly increased in 1987–1989, and consequently warm-water epi-pelagic species (anchovy, chub mackerel, and common squid) became dominant, while sardine, relatively cold-water epi-pelagic species, nearly disappeared. An annual index of the volume transport by the Korea Strait Bottom Cold Water, originating from the deep water of the Ulleung Basin, displayed a sudden intensification in 1992–1993, accompanied by decreased water temperature and increased water density in the deep water and replacement of dominant bentho-pelagic species from filefish, warm-water species, to herring and cod, cold-water species. The results suggest that climate-driven oceanic changes and the subsequent ecological impacts can occur asynchronously, often with time lags of several years, between the upper and the deep layer, and between epi-pelagic and deepwater fish assemblages.

Changes in size and trends of North American sea duck populations associated with North Pacific oceanic regime shifts

Broad-scale multi-species declines in populations of North American sea ducks for unknown reasons is cause for management concern. Oceanic regime shifts have been associated with rapid changes in ecosystem structure of the North Pacific and Bering Sea. However, relatively little is known about potential effects of these changes in oceanic conditions on marine bird populations at broad scales. I examined changes in North American breeding populations of sea ducks from 1957 to 2011 in relation to potential oceanic regime shifts in the North Pacific in 1977, 1989, and 1998. There was strong support for population-level effects of regime shifts in 1977 and 1989, but little support for an effect of the 1998 shift. The continental-level effects of these regime shifts differed across species groups and time. Based on patterns of sea duck population dynamics associated with regime shifts, it is unclear if the mechanism of change relates to survival or reproduction. Results of this analysis support the hypothesis that population size and trends of North American sea ducks are strongly influenced by oceanic conditions. The perceived population declines appear to have halted >20 years ago, and populations have been relatively stable or increasing since that time. Given these results, we should reasonably expect dramatic changes in sea duck population status and trends with future oceanic regime shifts.

Perspectives on wild and hatchery salmon interactions at sea, potential climate effects on Japanese chum salmon, and the need for sustainable salmon fishery management reform in Japan

Pacific salmon (Oncorhynchus spp.) play an important role as a keystone species and provider of ecosystem services in the North Pacific ecosystem. We review our studies on recent production trends, marine carrying capacity, climate effects and biological interactions between wild and hatchery origin populations of Pacific salmon in the open sea, with a particular focus on Japanese chum salmon (O. keta). Salmon catch data indicates that the abundance of Pacific salmon increased since the 1976/77 ocean regime shift. Chum and pink salmon (O. gorbuscha) maintained high abundances with a sharp increase in hatchery-released populations since the late 1980s. Since the 1990s, the biomass contribution of hatchery returns to the total catch amounts to 50% for chum salmon, more than 10% for pink salmon, and less than 10% for sockeye salmon (O. nerka). We show evidence of density-dependence of growth and survival at sea and how it might vary across spatial scales, and we provide some new information on foraging plasticity that may offer new insight into competitive interactions. The marine carrying capacity of these three species is synchronized with long-term patterns in climate change. At the present time, global warming has positively affected growth and survival of Hokkaido populations of chum salmon. In the future, however, global warming may decrease the marine carrying capacity and the area of suitable habitat for chum salmon in the North Pacific Ocean. We outline future challenges for salmon sustainable conservation management in Japan, and recommend fishery management reform to sustain the hatchery-supported salmon fishery while conserving natural spawning populations.

Magnitude and Trends in Abundance of Hatchery and Wild Pink Salmon, Chum Salmon, and Sockeye Salmon in the North Pacific Ocean

AbstractAbundance estimates of wild and hatchery Pacific salmon Oncorhynchus spp. are important for evaluation of stock status and density‐dependent interactions at sea. We assembled available salmon catch and spawning abundance data for both Asia and North America and reconstructed total abundances of pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka during 1952–2005. Abundance trends were evaluated with respect to species, regional stock groups, and climatic regimes. Wild adult pink salmon were the most numerous salmon species (average = 268 × 106 fish/year, or 70% of the total abundance of the three species), followed by sockeye salmon (63 × 106 fish/year, or 17%) and chum salmon (48 × 106 fish/year, or 13%). After the 1976–1977 ocean regime shift, abundances of wild pink salmon and sockeye salmon increased by more than 65% on average, whereas abundance of wild chum salmon was lower in recent decades. Although wild salmon abundances in most regions of North America increased in the late 1970s, abundances in Asia typically did not increase until the 1990s. Annual releases of juvenile salmon from hatcheries increased rapidly during the 1970s and 1980s and reached approximately 4.5 × 109 juveniles/year during the 1990s and early 2000s. During 1990–2005, annual production of hatchery‐origin adult salmon averaged 78 × 106 chum salmon, 54 × 106 pink salmon, and 3.2 × 106 sockeye salmon, or approximately 62, 13, and 4%, respectively, of the combined total wild and hatchery salmon abundance. The combined abundance of adult wild and hatchery salmon during 1990–2005 averaged 634 × 106 salmon/year (498 × 106 wild salmon/year), or approximately twice as many as during 1952–1975. The large and increasing abundances of hatchery salmon have important management implications in terms of density‐dependent processes and conservation of wild salmon populations; management agencies should improve estimates of hatchery salmon abundance in harvests and on the spawning grounds.

Effects of local and global change on an inland sea: the Strait of Georgia, British Columbia, Canada

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 40:1-21 (2009) - DOI: https://doi.org/10.3354/cr00819 Effects of local and global change on an inland sea: the Strait of Georgia, British Columbia, Canada S. C. Johannessen*, R. W. Macdonald Department of Fisheries and Oceans, Institute of Ocean Sciences, 9860 West Saanich Road, Sidney, British Columbia V8L 4B2, Canada *Email: sophia.johannessen@dfo-mpo.gc.ca ABSTRACT: Global changes manifest themselves in coastal waters depending on local oceanography and ecosystems. In this paper, we consider the Strait of Georgia as a case study. After examining physical and chemical processes and trends, we discuss consequences of change on geochemical cycling and biota. Several components of the system are vulnerable. Declines in pH and O2 of basin waters, partly imported from the shelf and partly supported by carbon cycling within the strait, could reduce benthic and pelagic habitat. Sea level rise and storms will interact with coastal development to place critical habitat, such as low-lying estuaries, intertidal zones and mudflats, at risk. The decrease and earlier peak in zooplankton biomass may lead to changes in the food web that cascade to higher trophic levels such as fish and birds. Anadromous fish, already showing declines, are vulnerable to ocean regime shifts, increasing river temperatures, habitat destruction, harvesting and contaminants. For southern resident killer whales Orcinus orca, a species at risk, decline in Chinook salmon Oncorhynchus tshawytscha together with marine traffic and biomagnifying contaminants will lead to extirpation if no action is taken. Some stressors can be controlled only through international action to mitigate climate change. However, we have local control of fishing, habitat destruction, release of some contaminants and, to some extent, river flow and temperature. Acting to control these stressors will support resilience of biota in the face of inevitable global changes. KEY WORDS: Climate change · Strait of Georgia · Temperature · Anoxia · Coastal development · pH · Fish · Marine mammals Full text in pdf format NextCite this article as: Johannessen SC, Macdonald RW (2009) Effects of local and global change on an inland sea: the Strait of Georgia, British Columbia, Canada. Clim Res 40:1-21. https://doi.org/10.3354/cr00819 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 40, No. 1. Online publication date: September 24, 2009 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2009 Inter-Research.

Contrasting responses in larval and juvenile growth to a climate–ocean regime shift between anchovy and sardine

Anchovy and sardine populations have fluctuated alternately with decadal changes in climatic and oceanic states, although the mechanisms remain unclear. In the western North Pacific, anchovy and sardine share nursery grounds in the Kuroshio–Oyashio transitional waters, where the subtropical and subarctic currents converge from the south and north, respectively. We found that northward expansion of the subtropical waters simultaneously changed the local environment in the nursery grounds to be favorable for late larvae and early juveniles of anchovy, but not for those of sardine during 1996–2002. Increased temperature enhanced growth and survival for anchovy, whereas reduced food availability diminished those for sardine. Northward expansion of the subtropical waters have been linked with wind-forced anomaly of sea-surface height in the central North Pacific. After 1988, when anchovy flourished and sardine collapsed in the western North Pacific, previous studies by other researchers documented similar changes in air–sea interaction. Our results suggest that contrasting responses in growth and survival processes to wind-forced oscillation of the current structures caused the alternate population dynamics between anchovy and sardine in the western North Pacific.

Synchrony of Marine Fish Catches and Climate and Ocean Regime Shifts in the North Pacific Ocean

AbstractCatches of 19 marine fish species from the eastern and western portions of the North Pacific Ocean during 1970–2004 were examined to determine whether there was synchrony in their responses to the generally accepted climate regime shifts that occurred during that period. Catches for these species represented approximately 55% of the total fish catch in the North Pacific in the 1990s. Five distinct groups were apparent in the data, and each group exhibited a different response to the climate regime shifts of 1977, 1989, and 1998. Some species appeared to have responded only to the regime shift in 1977, others responded only to the shift in 1989, and a few species responded to both. The trends in the time series of catches for these five groups were not random, and shifts in catch generally coincided with regime shifts as identified by the Pacific Decadal Oscillation and other indices of climate change. Although this study examined the relationship of fisheries to trends in climate, there is an obvious linkage to the population dynamics of a particular species. Understanding how climate affects these linkages may help improve our ability to reliably forecast population and fishery trends in the future.

Multi-species regime shifts reflected in spawning temperature optima of small pelagic fish in the western North Pacific

Small pelagic fish have exhibited cyclic population dynamics in complex marine ecosys- tems worldwide. These fish regime shifts have been associated with ocean regime shifts; however, the biological mechanisms have remained unresolved and have been considered to depend mainly on multi-step processes through food webs. In the present study, we focus on species-specific temper- ature optima and show that similarities and differences in spawning temperature optima reflect those in the long-term population dynamics among multi-species pelagic fish in the western North Pacific. Spawning temperature optima were examined for anchovy, sardine, mackerel and jack mackerel, based on the occurrence of eggs and larvae, using a long-term (1978 to 2004) data set of egg and lar- val surveys off the Pacific coast of Japan. Anchovy exhibited a plateau-like spawning temperature pattern with a peak at ca. 22°C. In contrast, sardine and mackerel exhibited steeply peaked patterns with marked peaks at ca. 16 and 18°C, respectively. On the contrary, jack mackerel showed a very similar spawning temperature pattern to anchovy. These relationships were consistent with their flourish and collapse in long-term population dynamics. Furthermore, sardine and mackerel with stenothermal spawning patterns showed dramatic fluctuations relative to anchovy and jack mackerel with more eurythermal features. The multi-species comparisons extracted a simple and direct path- way: if viewed at large scales, direct temperature impacts on vital parameters provide a plausible explanation of multi-species regime shifts of small pelagic fish in the western North Pacific.

Response of the Gulf of Alaska 3D winter circulation to oceanic climate shifts: Ecosystem implications

Recent measurements of zooplankton biomass and biological productivity in the Gulf of Alaska have raised a number of questions regarding possible linkages between climate and availability of renewable resources. In this article we compare 3 abrupt oceanic regime shifts in the Gulf of Alaska, the 1976–1977 warming shift, the 1998 cooling episode, and the 1998 to 1999 El Niño to La Niña transition, against concomitant changes in biological conditions reported in the literature. After the 1976–1977 warming shift, changes in the Gulf's 3D circulation, i.e., interior upwelling, onshore transport and coastal downwelling, had the same sign as their climatological means, thus providing a candidate explanation to the observed increased productivity of the upper ocean. Warming and cooling transitions have associated with them very different patterns of both horizontal and vertical circulation, where the latter is confirmed to be linked to the wind stress curl variability. Important shifts in the local biology have been reported in the literature (warming of 1976–1997 and El Niño to La Niña transition of 1998–1999) when climatological shifts in our simulated vertical velocities were large; in turn, when they were small, the ecosystem did not show significant changes and this was in part due to the resilience set by the 1976–1977 shift through the strengthening of the GOA's mean 3D circulation.

Long-term changes in the fish community structure from the Tsushima warm current region of the Japan/East Sea with an emphasis on the impacts of fishing and climate regime shift over the last four decades

Japanese fisheries production in the Japan/East Sea between 1958 and 2003 increased to their peak (1.76 million tons) in the late 1980s and decreased abruptly with the collapse of Japanese sardine. Catch results for 58 fisheries and various environmental time-series data sets and community indices, including mean trophic level (MTL) and Simpson’s diversity index (DI), were used to investigate the impacts of fishing and climate changes on the structure of the fish community in the Tsushima warm current (TWC) region of the Japan/East Sea. The long-term trend in fisheries production was largely dependent on the Japanese sardine that, as a single species, contributed up to 60% of the total production in the Japanese waters of the Japan/East Sea during the late 1980s. Excluding Japanese sardine, production of the small pelagic species was higher during 1960s and 1990s but lower during 1970s and 1980s. This variation pattern generally corresponds with the trend in water temperature, warmer before early 1960s and after 1990s but colder during 1970s and 1980s. The warm-water, large predatory fishes and cold water demersal species show opposite responses to the water temperature in the TWC region, indicating the significant impact of oceanic conditions on fisheries production of the Japan/East Sea. Declines in demersal fishes and invertebrates during 1970s and 1980s suggested some impact of fishing. MTL and DI show a similar variation pattern: higher during 1960s and 1990s but lower during 1970s and 1980s. In particular, the sharp decline during the 1980s resulted from the abundant sardine catches, suggesting that dominant species have a large effect on the structure of the fish community in the Japan/East Sea. Principal component analysis for 58 time-series data sets of fisheries catches suggested that the fish community varied on inter-annual to inter-decadal scales; the abrupt changes that occurred in the mid-1970s and late 1980s seemed to correspond closely with the climatic regime shifts in the North Pacific. These results strongly suggest that the structure of the fish community in the Japan/East Sea was largely affected by climatic and oceanic regime shifts rather than by fishing. There is no evidence showing “fishing down food webs” in the Japan/East Sea. However, in addition to the impacts of abrupt shifts that occurred in the late 1980s, the large predatory and demersal fishes seem to be facing stronger fishing pressure with the collapse of the Japanese sardine.

UNUSUAL MORTALITY IN THE DEPLETED COOK INLET BELUGA (DELPHINAPTERUS LEUCAS) POPULATION

In 2003, an unusually high number of beluga (Delphinapterus leucas) deaths occurred in Cook Inlet, Alaska. This small population of whales is segregated geographically and genetically from all other populations of belugas in Alaska waters (O'Corry-Crowe and others 1997). Cook Inlet belugas display strong site fidelity and many remain year-round in the Inlet (Rugh and others 2004), making this population vulnerable to impacts from anthropogenic and environmental hazards (Calkins 1983; Moore and DeMaster 2000; Moore and others 2000). Factors that may presently impact the Cook Inlet beluga population include harvest by Alaska Natives, contaminants, boat traffic, killer whale (Orcinus orca) predation, strandings, disease, forage base decline, human-induced habitat changes, and an ocean regime shift (Vos 2003). The National Marine Fisheries Service

ASSESSING SEABIRD MORTALITY FROM CHRONIC OIL DISCHARGES AT SEA

Chronic marine oil pollution is an ongoing global problem, yet no model currently exists to assess seabird mortality from continuous low-level inputs of oil. Taking into account persistence and detection rates of birds on beaches, and the wind-dependent proportion of birds lost at sea, we present a general mathematical Oiled Seabird Mortality Model (OSMM) to assess seabird mortality due to chronic oil pollution along a given coastline, using birds counted during systematic beached-bird surveys. We applied our OSMM to Newfoundland, Canada, where the incidence of chronic oil pollution is among the highest in world. We estimated that between 1998 and 2000, an average of 315,000 ± 65,000 murres (common [Uria aalge] and thick-billed [U. lomvia]) and dovekies (Alle alle) were killed annually in southeastern Newfoundland due to illegal discharges of oil from ships. Thick-billed murres that overwinter on the Grand Banks made up 67% of this kill. This species already is subject to extensive summer and winter hunting in Greenland, as well as winter hunting in Newfoundland, which harvests an additional 250,000–300,000 birds/year. Although populations remain stable, these levels of sustained mortality make thick-billed murre populations vulnerable to pulse perturbations and ocean regime shifts and hamper our ability to set harvest at sustainable levels.