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Prince William Sound (prince + william_sound)
Selected AbstractsLENGTH-MASS AND TOTAL BODY LENGTH OF ADULT FEMALE SEA OTTERS IN PRINCE WILLIAM SOUND BEFORE AND AFTER THE EXXON VALDEZ OIL SPILLMARINE MAMMAL SCIENCE, Issue 4 2002Lisa Mignon Rotterman Abstract After the 1989 T/V Exxon Valdez oil spill (EVOS), the body condition of non-pregnant female sea otters (Enhydra lutris) ages 4 yr and older in the EVOS-affected region of western Prince William Sound, Alaska (WPWS), was significantly poorer than that of individuals captured in the same or adjacent habitat in WPWS approximately a decade earlier, and than that of individuals inhabiting unoiled habitat in eastern PWS (EPWS) between 1984 and 1990. However, the body condition of females of this age category captured in WPWS prior to EVOS was not significantly different from that of pre-and postspill EPWS females. The mean total body length (TBL) of non-pregnant females captured prespill in WPWS was significantly less than that of pre-and postspill EPWS and postspill WPWS females. Evidence from this and other studies suggests that the body condition of at least some classes of sea otters was negatively affected by one or more EVOS-related factors. [source] Risk of weathered residual Exxon Valdez oil to pink salmon embryos in Prince William SoundENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2007Ernest L. Brannon Abstract It has been hypothesized that pink salmon eggs incubating in intertidal streams transecting Prince William Sound (PWS) beaches oiled by the Exxon Valdez oil spill were exposed to lethal doses of dissolved hydrocarbons. Since polycyclic aromatic hydrocarbon (PAH) levels in the incubation gravel were too low to cause mortality, the allegation is that dissolved high-molecular-weight hydrocarbons (HPAH) leaching from oil deposits on the beach adjacent to the streams were the source of toxicity. To evaluate this hypothesis, we placed pink salmon eggs in PWS beach sediments containing residual oil from the Exxon Valdez oil spill and in control areas without oil. We quantified the hydrocarbon concentrations in the eggs after three weeks of incubation. Tissue PAH concentrations of eggs in oiled sediments were generally <100 ppb and similar to background levels on nonoiled beaches. Even eggs in direct contact with oil in the sediment resulted in tissue PAH loads well below the lethal threshold concentrations established in laboratory bioassays, and very low concentrations of HPAH compounds were present. These results indicate that petroleum hydrocarbons dissolved from oil deposits on intertidal beaches are not at concentrations that pose toxic risk to incubating pink salmon eggs. The evidence does not support the hypothesis that interstitial pore water in previously oiled beaches is highly toxic. [source] Ecosystem controls of juvenile pink salmon (Onchorynchus gorbuscha) and Pacific herring (Clupea pallasi) populations in Prince William Sound, AlaskaFISHERIES OCEANOGRAPHY, Issue 2001Robert T. Cooney Abstract Five years of field, laboratory, and numerical modelling studies demonstrated ecosystem-level mechanisms influencing the mortality of juvenile pink salmon and Pacific herring. Both species are prey for other fishes, seabirds, and marine mammals in Prince William Sound. We identified critical time-space linkages between the juvenile stages of pink salmon and herring rearing in shallow-water nursery areas and seasonally varying ocean state, the availability of appropriate zooplankton forage, and the kinds and numbers of predators. These relationships defined unique habitat dependencies for juveniles whose survivals were strongly linked to growth rates, energy reserves, and seasonal trophic sheltering from predators. We found that juvenile herring were subject to substantial starvation losses during a winter period of plankton diminishment, and that predation on juvenile pink salmon was closely linked to the availability of alternative prey for fish and bird predators. Our collaborative study further revealed that juvenile pink salmon and age-0 herring exploit very different portions of the annual production cycle. Juvenile pink salmon targeted the cool-water, early spring plankton bloom dominated by diatoms and large calanoid copepods, whereas young-of-the-year juvenile herring were dependent on warmer conditions occurring later in the postbloom summer and fall when zooplankton was composed of smaller calanoids and a diversity of other taxa. The synopsis of our studies presented in this volume speaks to contemporary issues facing investigators of fish ecosystems, including juvenile fishes, and offers new insight into problems of bottom-up and top-down control. In aggregate, our results point to the importance of seeking mechanistic rather than correlative understandings of complex natural systems. [source] Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, AlaskaFISHERIES OCEANOGRAPHY, Issue 2001T. M. Willette Abstract Our collaborative work focused on understanding the system of mechanisms influencing the mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska. Coordinated field studies, data analysis and numerical modelling projects were used to identify and explain the mechanisms and their roles in juvenile mortality. In particular, project studies addressed the identification of major fish and bird predators consuming juvenile salmon and the evaluation of three hypotheses linking these losses to (i) alternative prey for predators (prey-switching hypothesis); (ii) salmon foraging behaviour (refuge-dispersion hypothesis); and (iii) salmon size and growth (size-refuge hypothesis). Two facultative planktivorous fishes, Pacific herring (Clupea pallasi) and walleye pollock (Theragra chalcogramma), probably consumed the most juvenile pink salmon each year, although other gadids were also important. Our prey-switching hypothesis was supported by data indicating that herring and pollock switched to alternative nekton prey, including juvenile salmon, when the biomass of large copepods declined below about 0.2 g m,3. Model simulations were consistent with these findings, but simulations suggested that a June pteropod bloom also sheltered juvenile salmon from predation. Our refuge-dispersion hypothesis was supported by data indicating a five-fold increase in predation losses of juvenile salmon when salmon dispersed from nearshore habitats as the biomass of large copepods declined. Our size-refuge hypothesis was supported by data indicating that size- and growth-dependent vulnerabilities of salmon to predators were a function of predator and prey sizes and the timing of predation events. Our model simulations offered support for the efficacy of representing ecological processes affecting juvenile fishes as systems of coupled evolution equations representing both spatial distribution and physiological status. Simulations wherein model dimensionality was limited through construction of composite trophic groups reproduced the dominant patterns in salmon survival data. In our study, these composite trophic groups were six key zooplankton taxonomic groups, two categories of adult pelagic fishes, and from six to 12 groups for tagged hatchery-reared juvenile salmon. Model simulations also suggested the importance of salmon density and predator size as important factors modifying the predation process. [source] Site fidelity and the demographic implications of winter movements by a migratory bird, the harlequin duck Histrionicus histrionicusJOURNAL OF AVIAN BIOLOGY, Issue 3 2006Samuel A. Iverson Understanding the degree of demographic connectivity among population segments is increasingly recognized as central to the fields of population ecology and conservation biology. However, delineating discrete population units has proven challenging, particularly for migratory birds as they move through their annual cycle. In this study, radio telemetry was used to assess movement rates among habitats by harlequin ducks Histrionicus histrionicus during the non-breeding season in Prince William Sound, Alaska. A total of 434 females were outfitted with radio transmitters over six years of data collection, and their signals tracked by aircraft. Using a spatially nested design, it was determined that 75% of radioed females remained in the bay or coastline area where they were originally trapped, 94% remained on the same island or mainland region of Prince William Sound where they began the winter period, and 98% remained within the 4500 km2 study area as a whole. Home range analyses corroborated these findings, indicating that the scale of individual movements was small, with 95% kernel home range estimates averaging only 11.5±2.2 km2. A simple demographic model, which incorporated estimates for population size, survival, and movement rates, was used to infer the degree of independence among population segments. Immigrant females were found to contribute little to population numbers in most areas, accounting for only 4% of the adult female population at a scale of approximately 100 km2. These results have important implications for the scale of conservation action for the species and demonstrate that winter movements can have a strong influence local population dynamics. [source] Seasonal foraging movements and migratory patterns of female Lamna ditropis tagged in Prince William Sound, AlaskaJOURNAL OF FISH BIOLOGY, Issue 2 2005L. B. Hulbert Conventional and electronic tags were used to investigate social segregation, distribution, movements and migrations of salmon sharks Lamna ditropis in Prince William Sound, Alaska. Sixteen salmon sharks were tagged with satellite transmitters and 246 with conventional tags following capture, and were then released in Prince William Sound during summer 1999 to 2001. Most salmon sharks sexed during the study were female (95%), suggesting a high degree of sexual segregation in the region. Salmon sharks congregated at adult Pacific salmon Oncorhynchus spp. migration routes and in bays near Pacific salmon spawning grounds in Prince William Sound during July and August. Adult Pacific salmon were the principal prey in 51 salmon shark stomachs collected during summer months in Prince William Sound, but the fish appeared to be opportunistic predators and consumed sablefish Anoplopoma fimbria, gadids, Pacific herring Clupea pallasi, rockfish Sebastes spp. and squid (Teuthoidea) even when adult Pacific salmon were locally abundant. As Pacific salmon migrations declined in late summer, the salmon sharks dispersed; some continued to forage in Prince William Sound and the Gulf of Alaska into autumn and winter months, while others rapidly moved south-east thousands of kilometres toward the west coasts of Canada and the U.S. Three movement modes are proposed to explain the movement patterns observed in the Gulf of Alaska and eastern North Pacific Ocean: ,focal foraging' movements, ,foraging dispersals' and ,direct migrations'. Patterns of salmon shark movement are possibly explained by spatio-temporal changes in prey quality and density, an energetic trade-off between prey availability and water temperature, intra-specific competition for food and reproductive success. Transmissions from the electronic tags also provided data on depth and water temperatures experienced by the salmon sharks. The fish ranged from the surface to a depth of 668 m, encountered water temperatures from 4·0 to 16·8° C and generally spent the most time above 40 m depth and between 6 and 14° C (60 and 73%, respectively). [source] LENGTH-MASS AND TOTAL BODY LENGTH OF ADULT FEMALE SEA OTTERS IN PRINCE WILLIAM SOUND BEFORE AND AFTER THE EXXON VALDEZ OIL SPILLMARINE MAMMAL SCIENCE, Issue 4 2002Lisa Mignon Rotterman Abstract After the 1989 T/V Exxon Valdez oil spill (EVOS), the body condition of non-pregnant female sea otters (Enhydra lutris) ages 4 yr and older in the EVOS-affected region of western Prince William Sound, Alaska (WPWS), was significantly poorer than that of individuals captured in the same or adjacent habitat in WPWS approximately a decade earlier, and than that of individuals inhabiting unoiled habitat in eastern PWS (EPWS) between 1984 and 1990. However, the body condition of females of this age category captured in WPWS prior to EVOS was not significantly different from that of pre-and postspill EPWS females. The mean total body length (TBL) of non-pregnant females captured prespill in WPWS was significantly less than that of pre-and postspill EPWS and postspill WPWS females. Evidence from this and other studies suggests that the body condition of at least some classes of sea otters was negatively affected by one or more EVOS-related factors. [source] Characteristics of sex-biased dispersal and gene flow in coastal river otters: implications for natural recolonization of extirpated populationsMOLECULAR ECOLOGY, Issue 3 2002G. M. Blundell Abstract River otters (Lontra canadensis) were extirpated from much of their historic distribution because of exposure to pollution and urbanization, resulting in expansive reintroduction programmes that continue today for this and other species of otters worldwide. Bioaccumulation of toxins negatively affects fecundity among mustelids, but high vagility and different dispersal distances between genders may permit otter populations to recover from extirpation caused by localized environmental pollution. Without understanding the influence of factors such as social structure and sex-biased dispersal on genetic variation and gene flow among populations, effects of local extirpation and the potential for natural recolonization (i.e. the need for translocations) cannot be assessed. We studied gene flow among seven study areas for river otters (n = 110 otters) inhabiting marine environments in Prince William Sound, Alaska, USA. Using nine DNA microsatellite markers and assignment tests, we calculated immigration rates and dispersal distances and tested for isolation by distance. In addition, we radiotracked 55 individuals in three areas to determine characteristics of dispersal. Gender differences in sociality and spatial relationships resulted in different dispersal distances. Male river otters had greater gene flow among close populations (within 16,30 km) mostly via breeding dispersal, but both genders exhibited an equal, low probability of natal dispersal; and some females dispersed 60,90 km. These data, obtained in a coastal environment without anthropogenic barriers to dispersal (e.g. habitat fragmentation or urbanization), may serve as baseline data for predicting dispersal under optimal conditions. Our data may indicate that natural recolonization of coastal river otters following local extirpation could be a slow process because of low dispersal among females, and recolonization may be substantially delayed unless viable populations occurred nearby. Because of significant isolation by distance for male otters and low gene flow for females, translocations should be undertaken with caution to help preserve genetic diversity in this species. 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