Fine-scale population genetic structure in Alaskan Pacific halibut (<Emphasis Type="Italic">Hippoglossus stenolepis</Emphasis>)

Pacific halibut collected in the Aleutian Islands, Bering Sea and Gulf of Alaska were used to test the hypothesis of genetic panmixia for this species in Alaskan marine waters. Nine microsatellite loci and sequence data from the mitochondrial (mtDNA) control region were analyzed. Eighteen unique mtDNA haplotypes were found with no evidence of geographic population structure. Using nine microsatellite loci, significant heterogeneity was detected between Aleutian Island Pacific halibut and fish from the other two regions (F _ST range = 0.007–0.008). Significant F _ST values represent the first genetic evidence of divergent groups of halibut in the central and western Aleutian Archipelago. No significant genetic differences were found between Pacific halibut in the Gulf of Alaska and the Bering Sea leading to questions about factors contributing to separation of Aleutian halibut. Previous studies have reported Aleutian oceanographic conditions at deep inter-island passes leading to ecological discontinuity and unique community structure east and west of Aleutian passes. Aleutian Pacific halibut genetic structure may result from oceanographic transport mechanisms acting as partial barriers to gene flow with fish from other Alaskan waters.     

Maturation, fecundity, and intertidal spawning of Pacific sand lance in the northern Gulf of Alaska

Pacific sand lance Ammodytes hexapterus in Kachemak Bay, Alaska, showed no sexual dimorphism in length-to-weight (gonad-free) ratio or length-at-age relationship. Most matured in their second year, males earlier in the season than females, but females (31%) attained a higher gonadosomatic index than males (21%). Sand lance spawned intertidally once each year in late September and October on fine gravel or sandy beaches soon after the seasonal peak in water temperatures. Sand lance in Cook Inlet and Prince William Sound displayed similar maturation schedules. Schools were dominated 2: 1 by males as they approached the intertidal zone at a site where spawning has taken place for decades. Sand lance spawned vigorously in dense formations, leaving scoured pits in beach sediments. Fecundity of females (93–199 mm) was proportional to length, ranging from 1468 to 16 081 ova per female. About half of the overall spawning school fecundity was derived from age group 1 females (55% of the school by number). Spawned eggs were 1·02 mm in diameter, demersal, slightly adhesive, and deposited in the intertidal just below the waterline. Sand lance embryos developed over 67 days through periods of intertidal exposure and sub-freezing air temperatures.     

STOCK STRUCTURE OF SEA OTTERS (ENHYDRA LUTRIS KENYONI) IN ALASDA

Sea otters in Alaska are recognized as a single subspecies ( Enhydra lutris kenyoni ) and currently managed as a single, interbreeding population. However, geographic and behavioral mechanisms undoubrably constrain sea otter movements on much smaller scales. This paper applies the phylogeographic method (Dizon et al . 1992) and considers distribution, population response, phenotype and genotype data to identify stocks of sea otters within Alaska. The evidence for separate stock identity is genotypic (all stocks), phenotypic (Southcentral and Southwest stocks), and geographic distribution (Southeast stock), whereas population response data are equivocal (all stocks). Differences in genotype frequencies and the presence of unique genotypes among areas indicate restricted gene flow. Genetic exchange may be limited by little or no movement across proposed stock boundaries and discontinuities in distribution at proposed stock boundaries. Skull size differences (phenotypic) between Southwest and Southcentral Alaska populations further support stock separation. Population response information was equivocal in either supporting or refuting stock identity. On the basis of this review, we suggest the following: (1) a Southeast stock extending from Dixon Entrance to Cape Yakataga; (2) a Southcentral stock extending from Cape Yakataga to Cape Douglas including Prince William Sound and Kenai peninsula coast; and (3) a Southwest stock including Alaska Peninsula coast, the Aleutians to Attu Island, Barren, Kodiak, Pribilof Islands, and Bristol Bay.     

Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet,Southeast Alaska

Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska. In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n = 3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks.     

Migration of Pacific Rim Chum Salmon on the High Seas: Insights from Genetic Data

Wild stocks of chum salmon, Oncorhynchus keta, have experienced recent declines in some areas of their range. Also, the release of hatchery chum salmon has escalated to nearly three billion fish annually. The decline of wild stocks and the unknown effects of hatchery fish combined with the uncertainty of future production caused by global climate change have renewed interest in the migratory patterns of chum salmon on the high seas. We studied the composition of high-seas mixtures of maturing and immature individuals using baseline data for 20 allozyme loci from 356 populations from throughout the Pacific Rim. Composition estimates were made from three time series. Two of these time series were from important coastal migratory corridors: the Shumagin Islands south of the Alaska Peninsula and the east coast of the Kamchatka Peninsula. The third was from chum salmon captured incidentally in the Bering Sea trawl fishery for walleye pollock. We also analyzed geographically dispersed collections of chum salmon captured in the month of July. The time series show dynamic changes in stock composition. The Shumagin Island corridor was used primarily by Northwest Alaskan and Asian populations in June; by the end of July stocks from the Alaska Peninsula and southern North America dominated the composition. The composition along the Kamchatka coast changed dramatically from primarily Russian stocks in May to primarily Japanese stocks in August; the previously undocumented presence of stocks from the Alaska Peninsula and Gulf of Alaska was also demonstrated. Immature chum salmon from throughout the Pacific Rim, including large proportions of southern North American stocks, contributed to the Bering Sea bycatch during the months of September and October. The migration routes of North American stocks is far more widespread than previously observed, and the Bering Sea is an important rearing area for maturing and immature chum salmon from throughout the species' range.     

Quantifying food web interactions in the North Pacific – a data-based approach

As part of its annual bottom-trawl survey program, the Alaska Fisheries Science Center (AFSC) has been collecting and analyzing the stomach contents of groundfish predators since 1981. Between 1981 and 2011, a total of 233,451 fish stomachs were collected and analyzed from the eastern Bering Sea, the Gulf of Alaska, and the Aleutian Islands large marine ecosystems; these data are now available online as AFSC’s Groundfish Trophic Interactions Database. Here, we discuss features of the survey and data to aid in the interpretation and use of this extensive dataset for the Alaska region. The primary fish sampled include walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), Pacific halibut (Hippoglossus stenolepis), and arrowtooth flounder (Atheresthes stomias), although 159 predator species have been included in the stomach content analysis. Prey length measurements are included for important commercial prey and can identify age or size classes of prey prior to their recruitment into fisheries and most other surveys. With these data, one can track time trends in growth, mortality, and prey composition as ecosystem indicators, and include food web interactions in fish stock assessments for ecosystem-based fisheries management.     

Mammalian mesopredators on islands directly impact both terrestrial and marine communities

Medium-sized mammalian predators (i.e. mesopredators) on islands are known to have devastating effects on the abundance and diversity of terrestrial vertebrates. Mesopredators are often highly omnivorous, and on islands, may have access not only to terrestrial prey, but to marine prey as well, though impacts of mammalian mesopredators on marine communities have rarely been considered. Large apex predators are likely to be extirpated or absent on islands, implying a lack of top-down control of mesopredators that, in combination with high food availability from terrestrial and marine sources, likely exacerbates their impacts on island prey. We exploited a natural experiment—the presence or absence of raccoons (Procyon lotor) on islands in the Gulf Islands, British Columbia, Canada—to investigate the impacts that this key mesopredator has on both terrestrial and marine prey in an island system from which all native apex predators have been extirpated. Long-term monitoring of song sparrow (Melospiza melodia) nests showed raccoons to be the predominant nest predator in the Gulf Islands. To identify their community-level impacts, we surveyed the distribution of raccoons across 44 Gulf Islands, and then compared terrestrial and marine prey abundances on six raccoon-present and six raccoon-absent islands. Our results demonstrate significant negative effects of raccoons on terrestrial, intertidal, and shallow subtidal prey abundance, and point to additional community-level effects through indirect interactions. Our findings show that mammalian mesopredators not only affect terrestrial prey, but that, on islands, their direct impacts extend to the surrounding marine community.     

Wild chinook salmon survive better than hatchery salmon in a period of poor production

The population dynamics of chinook salmon (Oncorhynchus tshawytscha) from the Cowichan River on Vancouver Island, British Columbia, Canada are used by the Pacific Salmon Commission as an index of the general state of chinook salmon coast wide. In recent years the production declined to very low levels despite the use of a hatchery that was intended to increase production by improving the number of smolts entering the ocean. In 2008, we carried out an extensive study of the early marine survival of the hatchery and wild juvenile chinook salmon. We found that both rearing types mostly remained within the Gulf Islands study area during the period when most of the marine mortality occurred for the hatchery fish. By mid September, approximately 1.3% of all hatchery fish survived, compared to 7.8%–31.5% for wild fish. This six to 24 times difference in survival could negate an estimated increased egg-to-smolt survival of about 13% that is theorized to result through the use of a hatchery. Estimates of the early marine survival are approximate, but sufficient to show a dramatic difference in the response of the two rearing types to the marine nursery area. If the declining trend in production continues for both rearing types, modifications to the hatchery program are needed to improve survival or an emphasis on improving the abundances of wild stocks is necessary, or both. The discovery that the juvenile Cowichan River chinook salmon remain within a relatively confined area of the Gulf Islands within the Strait of Georgia offers an excellent opportunity to research the mechanisms that cause the early marine mortalities and hopefully contribute to a management that improves the production.     

Inter-island variation in the diet of female northern fur seals (Callorhinus ursinus) in the Bering Sea

The diet of adult female northern fur seals ( Callorhinus ursinus ) is examined through the analysis of faecal material collected during the summer breeding season at three breeding locations in the Bering Sea: St. Paul Island (1988, 1990) and St. George Island (1988, 1990) of the Pribilof Islands Group (USA), and Medny Island (1990) of the Commander Islands Group (Russia). Prey consumption varies annually and accordingly with the physical and biological environment surrounding each island. Juvenile walleye pollock ( Theragra chalcogramma ) is the most common prey of northern fur seals from St. Paul Island; the island is surrounded by a broad neritic environment with widely separated frontal zones and is the greatest distance from the continental shelf-edge. Gonatid squid ( Gonatopsis borealis/Berryteuthis magister and Gonatus madokail Gonatus middendorffi ) were the most common prey of northern fur seals from Medny Island; the island is surrounded by a compressed neritic environment and is adjacent to the continental shelf-edge and the oceanic marine environment. A combination of walleye pollock and gonatid squid is consumed by northern fur seals from St. George Island; the island has a surrounding oceanographic environment intermediate between the other two islands.
Variability in predation on walleye pollock is consistent with fishery information concerning the relative abundance and availability of walleye pollock around St. George and St. Paul Islands. The abundance and availability of these prey resources during the summer breeding season are key factors which influence the health and growth of the northern fur seal populations in the Bering Sea.     

Junk-food in marine ecosystems

The abundance and availability of food are critical determininants of reproductive success and population dynamics of marine top predators. However, recent work has indicated that the quality of the food may also be critically important for some marine predators. The 'junkfood hypothesis' was originally suggested as a potential explanation for a dramatic population decline of Stellers sea lions Eumetopias jubatus in the Gulf of Alaska. According to the hypothesis, a dietary switch to prey of low energy content led to detrimental effects on the population of sea lions. A number of observations indicate that the hypothesis is relevant for several population parameters. Recent work on piscivorous seabirds has provided substantial evidence indicating the relevance of this hypothesis in food webs in e.g. the North Pacific, the North Sea and the Baltic Sea. The emergence of 'junk-food' in these systems may be coupled to large scale changes in climatological and oceanographic forcing, although predation, fishing and competition provide additional plausible hypotheses. It may be possible to predict which kinds of animals will be particularly sensitive to food quality; these seem to be species with limited ability to carry food loads, with energetically-expensive foraging behaviour, and with digestive anatomy evolved to minimize mass at the cost of digestive efficiency. This review suggests that the junk-food hypothesis is a highly relevant factor in relation to sustaining ecosystem resilience, and is an important consideration in ecosystem management. Sustaining healthy populations of marine top-predators requires an understanding of the role of food quality, in addition to food abundance and availability.     

Bottom-up effects of a no-take zone on endangered penguin demographics

Marine no-take zones can have positive impacts for target species and are increasingly important management tools. However, whether they indirectly benefit higher order predators remains unclear. The endangered African penguin (Spheniscus demersus) depends on commercially exploited forage fish. We examined how chick survival responded to an experimental 3-year fishery closure around Robben Island, South Africa, controlling for variation in prey biomass and fishery catches. Chick survival increased by 18% when the closure was initiated, which alone led to a predicted 27% higher population compared with continued fishing. However, the modelled population continued to decline, probably because of high adult mortality linked to poor prey availability over larger spatial scales. Our results illustrate that small no-take zones can have bottom-up benefits for highly mobile marine predators, but are only one component of holistic, ecosystem-based management regimes.     

Interannual differences in growth and hatch date distributions of age-0 year walleye pollock Theragra chalcogramma (Pallas) sampled from the Shumagin Islands region of the Gulf of Alaska, 1985 – 2001

Daily increments of age-0 year walleye pollock Theragra chalcogramma otoliths from 1985 to 2001 were examined for interannual variability in growth and hatch dates. Fish were collected in summer and autumn surveys near the Shumagin Islands in the western Gulf of Alaska (GOA). Hatch date distributions of these fish were compared with hatch dates of larvae from spawning aggregations located in Shelikof Strait and the Shumagin Islands based on their spawning times. The hatch date distributions of age-0 year fish captured from the Shumagin Islands area were similar to those observed for larvae from the Shelikof Strait spawning group. Age-0 year fish whose hatch dates corresponded to the Shumagin Islands spawning, which occurred earlier in January and February, were not found. Sea surface temperature was associated with variability in hatch date distribution and growth.     

Seasonal variation in the diet of the king penguin (Aptenodytes patagonicus) at sub-Antarctic Marion Island

King penguins are important consumers of marine resources, throughout the year, at the Prince Edward Islands. Meal size varied from 8.5–12.6% of adult mass, depending on the method of determination. In spite of the biases in the analysis favouring the overestimation of squid, fish and, in particular, myctophid fish accounted for the largest proportion of the stomach samples, 87% by wet mass, 75% by numbers and 69% by reconstituted mass. The relative abundance of fish in the diet dropped markedly in winter followed by a subsequent rise to nearly 100% in summer. This rise coincided with an increase in the chick growth rate and the king penguin population at the island and suggests the rise in relative abundance offish reflects a real increase in the availability of fish around the islands.
Juvenile and adult Krefftichthys anderssoni/Protomyctophum tenisoni and adult Electrona carlsbergi were the most common fish consumed. There was an increase in the modal size of K. anderssoni/P. tenisoni throughout the year which we interpret as growth of a single fish population. Juvenile Kondakoviu longimana was the important squid species taken by king penguins. Crustaceans were only rarely recorded in the diet and may have come from digestion of fish and squid stomachs.
This is the first study of the diet of a Southern Ocean pelagic predator that has identified myctophid fish as a major component of its diet. All three important fish species taken by king penguins at Marion Island have a wide distribution throughout the Southern Ocean and consequently may prove to be important dietary components of other Southern Ocean pelagic predators.     

Coral in Alaska: distribution,abundance, and species associations

To help identify fishery management actions that minimize the adverse impacts of fishing activities on corals in Alaska, the distribution and abundance of corals were analyzed based on trawl survey data collected during 1975–1998. We also examined the species of commercially managed fish that are associated with coral. Soft corals, primarily Gersemia sp. (=Eunephthya sp.), were the most frequently encountered corals in the Bering Sea. In the Aleutian Islands gorgonian corals, primarily in the genera Callogorgia, Primnoa, Paragorgia, Thouarella, and Arthrogorgia were the most common corals. In the Gulf of Alaska, gorgonian corals, primarily in the genera Callogorgia and Primnoa, and cup corals, primarily `Scleractinia unidentified', occurred most frequently. The Aleutian Islands area appears to have the highest abundance and diversity of corals. Some fish groups are associated with particular types of coral. Rockfish (Sebastes spp. and Sebastolobus alascanus) and Atka mackerel (Pleurogrammus monopterygius) were the most common fish captured with gorgonian, cup, and hydrocorals, whereas flatfish and gadids were the most common fish captured with soft corals.     

The Long-Term Dynamics of Sablefish (Anoplopoma fimbria) Stocks in the Western Bering Sea and Prospects for their Commercial Exploitation

Russian Journal of Marine Biology - The dynamics of sablefish stocks and fishery in the Bering Sea, the Gulf of Alaska, and off the Aleutian Islands are considered based on the data of bottom and...     

Oceanographic characteristics of the habitat of benthic fish and invertebrates in the Beaufort Sea

We relate the spatial variability in the distribution of benthic taxa of the Beaufort Sea to oceanographic characteristics of their habitat with the goal of illustrating potential mechanisms linking climate change to Arctic marine communities. Offshore fish of the Beaufort Sea have not been surveyed since 1977 and no synchronous measures of fish distribution and the oceanographic characteristics of their habitat have been made previously. A survey was conducted during August 2008 in the western Beaufort Sea, Alaska. The distribution and abundance of benthic fish and invertebrates were assessed with standard bottom trawl survey methods. Oceanographic data were collected at each trawl station and at several locations between stations. The dominant benthic taxa, Polar cod (Boreogadus saida), eelpouts (Lycodes sp.), and snow crab (Chionoecetes opilio) were associated with cold (<?1.5°C), high salinity (>33) water found offshore of the shelf break, derived from the Chukchi Sea. These waters are expected to be high in secondary productivity, such that we hypothesize that the distribution of fish and crab was driven by conditions favorable for successful foraging. Predictions of the impacts of climate change require an understanding of the mechanisms linking the distribution and abundance of marine organisms to their oceanographic habitat. Our study documents the association of dominant benthic fish and invertebrates of the Beaufort Sea with specific water mass types and is thus a step toward this understanding.     

Predicting population consequences of ocean climate change for an ecosystem sentinel,the seabird Cassin's auklet

Forecasting the ecological effects of climate change on marine species is critical for informing greenhouse gas mitigation targets and developing marine conservation strategies that remain effective and increase species' resilience under changing climate conditions. Highly productive coastal upwelling systems are predicted to experience substantial effects from climate change, making them priorities for ecological forecasting. We used a population modeling approach to examine the consequences of ocean climate change in the California Current upwelling ecosystem on the population growth rate of the planktivorous seabird Cassin's auklet (Ptychoramphus aleuticus), a demographically sensitive indicator of marine climate change. We use future climate projections for sea surface temperature and upwelling intensity from a regional climate model to forecast changes in the population growth rate of the auklet population at the important Farallon Island colony in central California. Our study projected that the auklet population growth rate will experience an absolute decline of 11–45% by the end of the century, placing this population on a trajectory toward extinction. In addition, future changes in upwelling intensity and timing of peak upwelling are likely to vary across auklet foraging regions in the California Current Ecosystem (CCE), producing a mosaic of climate conditions and ecological impacts across the auklet range. Overall, the Farallon Island Cassin's auklet population has been declining during recent decades, and ocean climate change in this century under a mid‐level emissions scenario is projected to accelerate this decline, leading toward population extinction. Because our study species has proven to be a sensitive indicator of oceanographic conditions in the CCE and a powerful predictor of the abundance of other important predators (i.e. salmon), the significant impacts we predicted for the Cassin's auklet provide insights into the consequences that ocean climate change may have for other plankton predators in this system.     

Modelling nearshore intertidal habitat use of young-of-the-year Pacific sand lance (Ammodytes hexapterus) in Barkley Sound, British Columbia, Canada

The Pacific sand lance (Ammodytes hexapterus) is an ecologically important prey species for many vertebrate marine predators in the Pacific Northwest. In this study, we examined the use of intertidal habitat by young of the year (YOY) sand lance in Barkley Sound, British Columbia. We selected 14 of the original 29 independent environmental variables for modelling based on univariate analysis for variable selection. These were then used to model sand lance presence-absence using a classification tree approach. Based on our models we found that sand lance avoided mud and intertidal eelgrass. For sites that had very little mud and no intertidal eelgrass, sand lance preferred sediment size mean ≥1,918 μm or sites with sediment size mean ≤1,918 μm but with relatively well sorted sediment (sorting values ≤2.56 SDs, used as a heterogeneity index of the substrate grain size). Adjacent subtidal characteristics were not found to be important at this scale of study. This suggests intertidal substrate characteristics and presence-absence of intertidal eelgrass are the main influences on occurrence of YOY in the intertidal. Our results support the hypothesis that sand lance are associated with particular sediment types, however intertidal sediment types used by sand lance in our study differ from known preferences of sand lance for subtidal sediment types. This difference may be due to unique habitat constraints for intertidal versus subtidal regions. Although it is unknown if the results of this study are widely applicable, the results begin to identify intertidal habitat features that are important for Pacific sand lance.     

The effect of herbivores and humans on the Sand Forest species of Maputaland,northern KwaZulu-Natal,South Africa

Sand Forest in the Maputaland region of KwaZulu-Natal in South Africa is deemed the most valuable, but also probably the most complex vegetation type of this part of the Maputaland–Pondoland–Albany hotspot of biodiversity. However, Sand Forest is under threat from the current human population growth in that region as well as from uncontrolled increases in wild herbivore numbers in conservation areas. The present study compares the impacts of herbivores and humans on the state of woody resources between two sites under differing utilisation regimes. Sand Forest was found to be a complex association of tree assemblages defined by different canopy and subcanopy properties. Although marked differences in the abundance of selected species were noted at the two sites, the Sand Forest remained dominated by fine-grained species under both utilisation regimes. The fine-grained nature of Sand Forest implies that regeneration depends on the creation of small canopy gaps either by natural processes, humans or elephants, while the creation of large gaps could transform it into woodland. Management of conservation areas where Sand Forest occurs should therefore concentrate efforts on regulating animal populations to levels that provide gap properties that favour forest regeneration.     

Recreational Fish-Finders—An Inexpensive Alternative to Scientific Echo-Sounders for Unravelling the Links between Marine Top Predators and Their Prey

Studies investigating how mobile marine predators respond to their prey are limited due to the challenging nature of the environment. While marine top predators are increasingly easy to study thanks to developments in bio-logging technology, typically there is scant information on the distribution and abundance of their prey, largely due to the specialised nature of acquiring this information. We explore the potential of using single-beam recreational fish-finders (RFF) to quantify relative forage fish abundance and draw inferences of the prey distribution at a fine spatial scale. We compared fish school characteristics as inferred from the RFF with that of a calibrated scientific split-beam echo-sounder (SES) by simultaneously operating both systems from the same vessel in Algoa Bay, South Africa. Customized open-source software was developed to extract fish school information from the echo returns of the RFF. For schools insonified by both systems, there was close correspondence between estimates of mean school depth (R² = 0.98) and school area (R² = 0.70). Estimates of relative school density (mean volume backscattering strength; S_v) measured by the RFF were negatively biased through saturation of this system given its smaller dynamic range. A correction factor applied to the RFF-derived density estimates improved the comparability between the two systems. Relative abundance estimates using all schools from both systems were congruent at scales from 0.5 km to 18 km with a strong positive linear trend in model fit estimates with increasing scale. Although absolute estimates of fish abundance cannot be derived from these systems, they are effective at describing prey school characteristics and have good potential for mapping forage fish distribution and relative abundance. Using such relatively inexpensive systems could greatly enhance our understanding of predator-prey interactions.