RSS 1.0Fisheries
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Early life biology and ecology of king and tanner crabs in the Bering and Chukchi seasPelagic larvae and early benthic juveniles are believed to be the most vulnerable life stages for crabs. Where and when young crab occur and their response to environmental conditions is poorly understood. I present two case studies that demonstrate the importance of monitoring crab early life stages of economically and ecologically important species in the Bering and Chukchi Seas. First, collapsed fisheries and poor juvenile recruitment are recurring issues for many Alaska king crab stocks. Among the most notable examples, Pribilof Islands blue king crab is a federally overfished stock that has failed to rebuild after decades of conservation. Comparison of field assessments from modern and historical periods suggests a current bottleneck in larval supply, severely limiting blue king crab recruitment. Supplementary assessments showed available nursery habitats and fish predation pressure do not appear to be limiting for juvenile king crabs. Blue king crab are unlikely to recover by natural means, therefore juvenile enhancement may be an appropriate tool for possible restoration. Second, larval crab dispersal during the pelagic life phase is relatively unknown across the Pacific Arctic. A multiyear study of larval crab abundance and distribution during late summer months, and their association with environmental covariates, was completed for the north Bering and Chukchi Seas. Larval community structure varied strongly across regions from south to north and many species and stages had specific associations with coastal or offshore water masses. Snow crab larvae were relatively abundant and ubiquitous across the study region and appear to originate from both Pacific and Arctic spawning stocks. Blue king crab larvae were relatively rare in the Chukchi Sea and likely dispersed away from north Bering Sea natal areas. Larvae likely experience increased growth rates and northward dispersal in warm years, which could impact delivery to and survival of settling crabs in nursery habitats. Across analyses, these results improve our understanding of early life dispersal, settlement processes, and possible recruitment bottlenecks for Arctic crab stocks.
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Synergistic effects of climate and invasions: a case study of juvenile Pacific salmon and their introduced freshwater predator (Esox lucius) in a changing Alaska riverClimate change and invasive species are major individual drivers of declines in freshwater productivity and diversity, yet the potential for these factors to interact is poorly understood. I explored the synergistic effects of climate change and invasion to better understand observed changes in a freshwater community comprised of socially valuable salmonid fishes. I modeled daily predation and annual consumption of juvenile salmon by an introduced apex predator, Northern Pike (Esox lucius), as a function of time, streamflow, water temperature, and Northern Pike demography in a rapidly warming system in Southcentral Alaska. I hypothesized that Northern Pike predation would shift from juvenile salmon to alternative prey as a function of progressed invasion and that salmon predation would peak during species-specific out migrations. I also hypothesized that predation on juvenile salmon would be positively correlated with streamflow because high water would cause juvenile salmon to seek refuge in off-channel habitats instigating interaction with Northern Pike. Daily predation and annual consumption of Northern Pike in this system have shifted away from salmon-dominated to dominated by resident fishes over the past decade (2011 to 2022). Streamflow was positively correlated with daily predation on juvenile Chinook Salmon and total Oncorhynchus species in diets. Between 2011-2012 and 2021-2022 the population of Northern Pike shifted to younger individuals with increased growth. Estimates revealed that annual consumption of Chinook Salmon and Coho Salmon by Northern Pike decreased between time periods. Bioenergetic simulations revealed increases of 6 to 12.5% in total per capita consumption of prey by Northern Pike under end of century scenarios. These findings collectively suggest that Northern Pike have switched to alternative fish prey as salmon declined. Seasonal high streamflows and increased water temperature consistent with observed and predicted climate change in Southcentral Alaska appear to increase predation rates on juvenile Chinook Salmon by Northern Pike, while patterns in predation for juvenile Coho Salmon are more uncertain. Predicted future temperatures may increase total consumption of Northern Pike enough to appreciably increase mortality of salmon exacerbating changes in species composition and community structure and further jeopardizing struggling salmon runs. These findings suggest that invasive predators may also become more impactful in other systems undergoing rapid climate change.
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Improving species identification, age, and life history information for shortraker rockfish (Sebastes borealis) in Prince William Sound, Alaska, using sagittal otolith analysesShortraker rockfish (Sebastes borealis) are a long-lived species found in the North Pacific Ocean. Limited life history information compels fishery managers to apply conservative estimates of allowable bycatch for this species. To improve the available life history information, we analyzed sagittal otoliths, targeting fish from Prince William Sound, to assess (1) age estimation errors, (2) species misidentification, and (3) relationships between environmental factors and annual growth. To assess errors in age data, otoliths were analyzed for core Δ¹⁴C activity. Those values were compared with bomb radiocarbon reference curves for other North Pacific species (i.e., known age Pacific halibut, Hippoglossus stenolepis, and yelloweye rockfish, S. ruberrimus). Shortraker rockfish Δ¹⁴C activity followed reference curves, partially validating current age estimation techniques. To identify species, otolith shape analyses were performed on putative shortraker and rougheye rockfish (S. aleutianus). Clusters of shortraker, rougheye, and blackspotted rockfish (S. melanostictus) data were identified using random forest algorithms and otolith wavelet estimates. Misidentification rates were examined using out-of-sample error estimates and otoliths from fish whose species was validated using single nucleotide polymorphisms. Model classification errors suggest that historically assigned species were accurate and shortraker rockfish can be identified with 94% success. To investigate potential drivers of fish growth, a chronology of shortraker rockfish otolith increment widths was developed and related to environmental variables using dendrochronology methods. Model comparisons showed significant correlations between annual increment widths (i.e., an indicator of fish somatic growth) and environmental variables, specifically negative correlations with winter temperature at depth, spring surface salinity, and the North Pacific Gyre Oscillation, and positive correlations with spring and winter upwelling and the Pacific Decadal Oscillation 2-years earlier. These three analyses validate and improve data and life history information and support incorporating age and growth data into stock assessment models used to calculate allowable bycatch levels for shortraker rockfish.
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Summer ecology and behavior of the grayling of McManus Creek, AlaskaA study of the summer ecology and behavior of the Arctic Grayling was undertaken on the summer population of McManus Creek, Alaska. An effort to determine the distribution and the patterns of the fish’s movements in the stream was made. The grayling spent the summer months in pools where they established feeding territories. Within each feeding territory a feeding range, where all feeding activities took place, was found. In each pool a hierarchial ordering based on a dominant subordinate relationship existed. This hierarchy was established and maintained by a series of displays. The grayling of McManus Creek were found to feed solely on the surface and at mid-depth. The food items consisted both of flying insects and aquatic insects, the latter making up the largest portion of their diet. It appeared that the fish relied primarily upon benthic drift for nutrition. Being visual feeders, the fish were unable to utilize the large numbers of organisms known to drift during periods of high and muddy water.
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Relative abundance and movement ecology of tiger sharks Galeocerdo cuvier in the waters surrounding Bimini, the BahamasShark populations are under increased anthropogenic pressures around the world. Large-bodied shark species are upper trophic level predators, and therefore there is concern that declining numbers of sharks may have significant implications for ecosystems. In response to these conservation concerns there has been increased focus on the implementation of regulations, fishery management plans, national plans of action, and marine management zones in some nations. However, large sharks are often highly mobile and can move readily across jurisdictional boundaries. Therefore, there is a need to monitor long-term relative abundances within regions and simultaneously examine the duration to which species remain in these areas. The Bahamas was established as a 'Shark Sanctuary' in 2011, but long-term abundance and movement data are lacking for many species. The goal of this study is to determine the relative abundance and movement ecology for tiger sharks Galeocerdo cuvier in the waters around Bimini, The Bahamas. Fishery independent ongline surveys from 1984 to 2019 suggest that the local relative abundance remained stable during this time. Gear selectively prevented direct comparisons of catch rates to other surveys, but for context abundance trend were analyzed from the directed shark fishery in the nearby southeastern USA, which interacts with the same population of tiger sharks. This analysis showed an increasing abundance trend in USA waters during the late 1990s and early 2000s, after which abundances stabilized. Conventional tagging and passive acoustic and satellite telemetry were used to determine residency, regional movements, and long-term philopatry of young-of-the-year to mature tiger sharks. Overall data for juveniles were sparse, likely due to constraints of energetic condition and high natural mortality. Large juvenile and mature tiger sharks displayed seasonal local residency that was negatively correlated with water temperature, but also dispersed widely throughout the region, and spent significant time outside of Bahamas territorial waters. Taken together, these results highlight that localized conservation measures offer some level of protection for tiger sharks, however they do spend time in multiple jurisdictions and regional cooperation on management plans is important.
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Estimating relative indices of groundfish abundance from multiple fishery-independent data sources: a comparison of intercalibrating model-based abundance estimatorsStock assessments are critical tools for sustainable fisheries management, and abundance indices estimated from fishery-independent data represent a crucial data source for these assessments. However, financial constraints on these surveys limit the number of samples taken per year, and/or the frequency with which regions are sampled. Additionally, it remains challenging for any individual survey to sample the entire domain of a stock due to contact-selectivity of the sampling gear and the accessibility of specific habitats to specific gear types. Further, the cost of operating fishery-independent surveys can result in surveys conducted on biennial or triennial schedules, resulting in temporal gaps in survey timeseries that may limit their ability to adequately index short lived species. One method by which these challenges might be addressed is through the use of model-based estimators, which estimate relative and/or absolute indices of abundance by intercalibrating data collected by multiple surveys with different spatial, temporal, or habitat footprints. While recent research has explored a number of potential applications of these methods, little to no prior research has assessed the relative performance of these methods in terms of the accuracy or uncertainty of their estimates. In the first chapter of this thesis, I fit Random Walk Timeseries (RWTS) models, Generalized Additive Models (GAM), and Vector Autoregressive Spatiotemporal Models to data collected by three fishery-independent surveys across four species/region case studies, and compare the model-estimated indices to design-based indices estimated by the Alaska Fisheries Science Center (AFSC) Bottom Trawl Survey (BTS) as a reference abundance timeseries. In the second chapter, I then simulate an age-structured and spatially heterogenous population dynamics for the Pacific Cod (Gadus macrocephalus)) stock in the Gulf of Alaska, to explore the reliability of intercalibrated indices of abundance. To do so I generate artificial survey catch data for three fishery-independent surveys, fit GAM and VAST survey intercalibration models, and then assess the accuracy and precision of the model-based indices. Results from the real species-region case studies in Chapter 1 suggest that RWTS, GAM, and VAST models all exhibit comparable performance, but the model structures used in this analysis struggled to estimate indices of abundance consistent with established abundance estimates in the presence of conflicting survey catch-rate signals. Results from the simulation experiment in Chapter 2 also suggest that the accuracy of the model-estimated indices is strongly influenced by the level of contrast in the size-selectivity profiles of the constituent surveys, and the rate at which the size-composition of the surveyed stock changes. I recommend that future work explores forms of these model-based estimators which estimate size-specific changes in abundance, and whether or not the inclusion of those elements improved the accuracy and precision of the estimated indices of abundance.
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When beavers get burned, do fish get fried? The role of beavers to mediate wildfire effects on arctic grayling in boreal AlaskaWildfire is a dominant natural disturbance process throughout boreal North America and fires are increasing in size, frequency, and severity. However, little is known about how wildfire affects boreal fish populations and aquatic habitat despite the substantial impacts of fire on ecosystem processes, and even less is known about how fire effects are mediated by species interactions. For example, North American Beavers (Castor canadensis) are affected by and can influence wildfire dynamics, and their engineering has complex effects on aquatic habitats. North American Beavers therefore have the potential to mediate wildfire effects on aquatic ecosystems and fish populations. Here I investigated relationships between wildfire and the distribution of beavers and a common fish species across a fire-dominated riverscape in Interior Alaska. First, I used satellite imagery to locate and enumerate beaver ponds throughout five large watersheds (total area: 20,711 km²) and modeled the relationship of beaver pond density (ponds per km²) as a function of wildfire history, stream geomorphology, hydrology, and vegetation composition. I then used a simulation to conceptualize the impacts of wildfire and beaver dams on Arctic Grayling (Thymallus arcticus) habitat availability under variable hydrologic conditions. Next, I sampled 62 streams for Arctic Grayling environmental DNA (eDNA) and sampled 10 of those streams for Arctic Grayling abundance. I used a generalized linear model (GLM) and N-mixture model to understand the relationship between eDNA concentration and Arctic Grayling abundance and distribution throughout the study area. I found that wildfire metrics explained most variation in beaver pond density (pseudo R² = 0.75) across the landscape and were positively associated with beaver pond density, although geomorphological and hydrological parameters were also important. My simulations indicated that beaver dams can create substantial barriers to fish dispersal during low water conditions (up to 20% reduced habitat availability in some river basins) and can severely reduce (up to 65%) habitat availability in some tributary streams. I found that eDNA concentration was moderately correlated with Arctic Grayling abundance (GLM: pseudo R² = 0.45) and unexplained variation was likely due to the spatial mismatch between fish sampling and scale of eDNA representation. However, I estimated eDNA residence time of about 6.7 hours in one stream, and eDNA appeared to accumulate longitudinally throughout the tributary, indicating that an eDNA sample near the downstream end was likely a good relative representation of Arctic Grayling abundance in a tributary. Results from the N-mixture model indicated that stream geomorphology and hydrology were the most important predictors for Arctic Grayling abundance (eDNA concentration), wildfires had a negative effect, and beaver dam density had a mixed effect on Arctic Grayling abundance. Overall, this study illustrated that beaver densities can increase after wildfires in Interior Alaska stream networks, which could result in negative impacts on Arctic Grayling habitat availability if beavers impair fish passage; however, these effects are dependent on the environmental context and suggest beaver-fish interactions may be best managed on a case-by-case basis.
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Model-based estimation of juvenile salmon spatial ecology in the eastern Bering Sea, AlaskaQuantitative descriptions of juvenile salmon spatial ecology during the marine phase of their lifecycle are needed to help direct conservation efforts and uncover latent relationships between juvenile salmon and their environment. The NOAA Fisheries Essential Fish Habitat (EFH) program contributes to the conservation of species in the marine waters off of the coast of Alaska by identifying areas of particular importance to reproduction and growth. Salmon EFH definitions have not yet been updated using the species distribution modeling approach taken most recently in defining Alaska groundfish and crab EFH. Current EFH definitions for Alaskan salmon are geographically broad, do not quantitatively describe relationships between marine conditions and salmon, and lack estimates of uncertainty. This research estimated static (time-averaged) and dynamic (time-varying) juvenile salmon distributions in the eastern Bering Sea (EBS) by fitting species distribution models (SDMs) to fishery-independent survey data and environmental indices spanning the years 2002-2019. Following model selection, species distribution maps were generated using predictions based upon the best-performing static and dynamic models to inform EFH definitions for the juvenile life stage. In Chapter 1, roughly parallel nested model structures were fit within two SDM frameworks: generalized additive models (GAMs) and Vector Autoregressive Spatio-temporal (VAST) models. Results from Chapter 1 indicate that while there was evidence for spatial variation in juvenile salmon distributions through time, this variation was encompassed by the EFH boundaries predicted by static models. In terms of performance, GAM and VAST frameworks were largely comparable, although VAST models appeared to be more robust to issues associated with spatial imbalance in survey data. In Chapter 2, nested GAM model structures tested the influence of environmental covariates on variability in the abundance and/or distribution of five species of juvenile Pacific salmon in the EBS. Model selection results and mapping indicated that in-situ environmental covariates significantly influenced abundance of juvenile salmon, while annual covariates significantly influenced the distributions of juvenile salmon. Center of gravity estimates found some evidence for species distribution shifts inshore/offshore and to the north/south in response to specific hindcast environmental conditions. This work might be leveraged to update current salmon EFH definitions and inform future model-based conservation efforts.
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Uncovering patterns and mechanisms of paralytic shellfish toxicity in Alaska's geoduck clam fisheryThis dissertation explores the patterns and mechanisms of paralytic shellfish toxicity in commercially harvested geoduck clams caused by the toxin-producing dinoflagellate Alexandrium catenella in Southeast Alaska. Alaska's commercial fishery for geoduck clams (Panopea generosa) is a small but lucrative fishery, with annual ex-vessel values averaging US $3.9 million (2010-2022). In recent years, the presence of paralytic shellfish toxins (PSTs) in clam tissue resulted in declines in fishery openings and harvest. PSTs can bioaccumulate in the tissues of filter feeders when A. catenella blooms in the spring and summer seasons. However, high levels of toxicity in geoduck clams occur sporadically during the fishery in the fall and winter months long after toxic blooms have subsided. Levels of PSTs in geoduck clams vary substantially from week-to-week, and elevated PSTs are increasingly causing economic loss to the fishery through sampling costs from repeated testing and by delaying or closing harvests. In the past decade (2011-2021), about 60% of geoduck clams tested for PST failed regulatory screenings, up from a 36% failure rate in the decade prior (2001-2010). Knowledge about patterns and distributions of this harmful algal species and its toxins will help improve management of geoduck dive fisheries and provide information to reduce impacts of PSTs on this fishery. In Chapter 1, Patterns in geoduck clam paralytic shellfish toxicity from two decades of shellfish testing in southeast Alaska, we show that geoduck clams are increasingly failing biotoxin screening tests in some areas and these patterns are most closely correlated with regional air temperatures. In Chapter 2, Alexandrium catenella benthic cyst distribution, sediment characteristics, and geoduck clam (Panopea generosa) toxicity in Southeast Alaska, we provide the first A. catenella cyst distribution map for this region and found that cyst counts declined over the three-year study, but patterns were not related to geoduck PST levels or sediment characteristics. Lastly in Chapter 3, Geoduck clam (Panopea generosa) toxicity dynamics across harvest areas, time, age, and cyst gut content in Alaska's commercial fishery, we confirmed the ability for geoduck clams to ingest dormant A. catenella cysts but revealed that neither this process, nor the age of a clam, is directly related to patterns of paralytic shellfish toxicity in this clam species. All together, these findings lead to a better understanding of the variability of PSTs in geoduck clams and are informative to future fishery management and the protection of human health.
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The role of apex predators, habitat, and seascape complexity on nearshore fish assemblages in Southeast, AlaskaNearshore marine ecosystems contain dynamic and complex submerged vegetated habitats that offer shelter and prey for juvenile, migratory, and residential species, including many commercial, subsistence, and recreationally important species. The efficacy of the nursery role, shelter, and source of prey of the nearshore is influenced by various abiotic and biotic forces and in this dissertation, we examine the influence of submerged vegetation type, presence of apex predators, and the seascape context on patterns of nearshore fish assemblages in southern Southeast Alaska. We found species-specific responses by juvenile salmon in the nearshore, with seasonality overwhelmingly driving juvenile salmon abundance in eelgrass meadows and Chum Salmon present in greater abundance in understory kelp beds compared to eelgrass meadows, whereas Pink Salmon exhibited no difference. As a known apex predator, the reintroduction of sea otters likewise altered the nearshore fish assemblage with increased richness in eelgrass meadows and assemblage-wide shifts in understory kelps. Finally, in addition to habitat type and apex predators, spatial patterning and presence of adjacent vegetation can affect the nursery role of nearshore habitats. We observed differences in the fish assemblage in eelgrass meadows sampled in homogeneous seascapes with continuous eelgrass meadows and heterogeneous seascapes that included adjacent habitats, including more abundant commercial and forage species in heterogeneous seascapes. This research reinforces the importance of nearshore ecosystems in supporting robust fisheries and highlights the structuring role that submerged vegetation, apex predators, and complex seascapes have in sustaining diverse fish populations. Considering the greater ecological dynamics in the nearshore is vital for decision making in habitat conservation and management and for evaluating its role for fisheries, particularly in the context of increased threats to nearshore ecosystems.
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Aquatic habitat of the Tiekel River, southcentral Alaska, and its utilization by resident Dolly Varden (Salvelinus malma)The Tiekel River is a third order stream in southcentral Alaska and contains stream-resident Dolly Varden (Salvelinus malma) that are small in size. The purpose of this project was to compile baseline aquatic habitat data, determine which habitats were the most important to the Dolly Varden and should be protected from future development, and develop management recommendations. Habitat data suggested that the Tiekel River drainage contained a wide variety of habitats that could fulfill the life requirements for a number of fish species. Habitat suitability index graphs were constructed for the important habitat variables and should be used in the planning of future habitat alterations to assure that habitat quality does not suffer. The beaver ponds were found to have a greater probability of producing large fish than the stream habitats. Fish size was positively correlated with August water temperatures and chlorophyll a concentrations.
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Growth patterns of juvenile sockeye salmon in different thermal environments of Alaskan lakesRearing conditions imposed on juvenile salmonids in lakes are important determinants of freshwater growth patterns. In Alaska, sockeye salmon (Oncorhynchus nerka) nursery lakes exhibit a wide range in thermal characteristics. Compared to clear lakes, stained lakes are warmer and have longer growing seasons, whereas glacial lakes are colder and have shorter growing seasons. In stained lakes, a shallow thermocline restricts most of the heat to the surface layers. Deep mixing in glacial lakes, concomitant with meltwater intrusion, keep much of the water column near 4 °C. Mean depth accounts for 77% of the among-lake variation in the seasonal average water temperature (TS). Length of growing season is dependent on latitude and altitude; however, water temperature is not. Taken together, the factors TS, zooplankton biomass, and sockeye fry density accounted for 70% of the variation in age-1 sockeye smolt size. This limnological information can be included in stock-recruit models of sockeye salmon to improve assessments for management.
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Dynamics of a super-population of dolly varden in the Chiniak Bay system, Kodiak Island, AlaskaA weir was operated at Buskin Lake, Kodiak Island, Alaska in the spring of 1990, 1991 and 1992 to study the stock structure of a superpopulation of Dolly Varden (Salvelinus malma) in Chiniak Bay. In 1991, Jolly-Seber estimates of abundance (60,585) and survival (29.3%) were higher than the weir estimates of 30,725 and 6.3%. Growth parameter estimates were 0.23 for the Brody coefficient and 522 mm as the largest fish in the population. Age 4-7 fish dominated the spring emigration from Buskin Lake. Dolly Varden found in the fall at the American and Olds rivers and Buskin Lake constitute the main spawning stocks for the Chiniak Bay super-population at 3,375, 2,669 and 3,711 fish respectively in 1991. A dynamic pool model used in conjunction with Relative Stock Density was effective in detecting increases in length-specific exploitation of larger fish, but not for detecting increasing fishing mortality in the mature stock.
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Evaluation of Arctic grayling enhancement: a cost per survivor analysisAge-O Arctic grayling Thymallus arcticus were stocked as sac fry and fingerlings in lakes in interior and south central Alaska to evaluate cost per survivor at age 1. When sac fry, 4-g, and 6-g fingerlings were stocked in the same lakes in 1986, estimates of the mean rate of survival at age 1 were 0.08, 0.63, and 0.75. The differences were significant. The mean costs per survivor at age 1 were $1.58, $0.24, and $0.21. The differences were significant between sac fry and both sizes of fingerlings. However, the difference was not significant between 4-g and 6-g fingerlings. When sac fry and 4-g fingerlings were stocked in different lakes in 1986 and again in 1987, estimates of the mean rate of survival to age 1 were 0.11 and 0.34. The difference was significant. The mean costs per survivor at age 1 were $0.82 and $0.70. The difference was not significant. I recommend stocking 4-g fingerlings because they require less rearing in a hatchery than 6-g fingerlings and the cost per survivor is usually less than that for sac fry.
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Effects of placer mining sedimentation on Arctic graying of interior AlaskaDuring summer 1982 and 1983, I assessed the effects of placer mining sedimentation on Arctic grayling, Thymallus arcticus, in the headwaters of the Birch Creek and Chatanika River drainages, northeast of Fairbanks, Alaska. In each drainage I compared the differences between two streams near their confluence, one that was undisturbed and one with mining activity upstream. Although many age-0 and adult grayling used unmined streams for summer habitat, I found no grayling in the mined streams except during periods of migration. Apparently, grayling consistently chose clearwater streams for summer residence. Caged fish studies demonstrated that if grayling could not escape from streams carrying mining sediments, they would suffer direct, chronic effects, including gill damage, dietary deficiencies, and slowed maturation. The indirect effects of sedimentation on grayling populations, through loss of summer habitat for feeding and reproduction, are more severe than the direct ones.
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Estimation of angler harvest, catch and effort in the Swanson River canoe trails system, Kenai National Wildlife Refuge, AlaskaMethods of estimating harvest, catch, angler effort and quality of catch were tested during the summer of 1988 on the Swanson River Canoe Trails System, Kenai National Wildlife Refuge, Alaska. Angler interviews at Trails System access points provided the best estimates of these sport fishing variables. Rainbow trout dominated the catch (95%); about three-fourths were less than 254 mm long and most were released. Total estimated catch of trout was 18,448 (10,221-26,675; ρ=0.95); estimated harvest was 25 percent of the catch: 4,651 (2,722-6,580; p=0.95). Aerial surveys (counts of cars and boats) and the trail head registers provided seasonal use trends for the Trails System, but there was no relationship between these indices and the variables of the fishery. Anglers must be personally interviewed in order to acquire data to evaluate the fishery.
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Injury and survival of northern pike captured by electrofishingI exposed 240 northern pike Esox lucius to four levels of pulsed direct current (PDC). Incidence of spinal injury for 30 Hz was 5.0% at 100 V and 10.0% at 400 V; and for 60 Hz was 8.3% at 100 V and 11.7% at 400 V. Injury rates were not significantly different among treatments (P=0, 58) . I also electroshocked 140 fish with 120-Hz PDC at 300-600 V; spinal injury increased to 29% (P<0.01). These fish were held for 1 month in ponds to compare survival with 70 unshocked fish; survival was 91-92% for both groups (P=0.57). During field trials I captured about three northern pike with 60-Hz PDC for every one caught with DC and 30-Hz PDC (P=0.08). Conventional electrofishing (i.e., 60-Hz PDC at 100-400 V) did not cause significant injury in adult northern pike but did capture them efficiently. PDC at frequencies above 60 Hz should be avoided.
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Seasonal allocation of energy in four tissues of northern pike from Minto Flats, AlaskaThe seasonal changes in energy content of the gastrointestinal tract, gonad, liver, and muscle of 120 mature northern pike (Esox lucius Linnaeus) from Minto Flats, Alaska were estimated (bomb calorimetry) during winter, early spring (prespawning), late spring (postspawning), and fall 1988. Increases in the specific energy contnet of testes was completed by September, and did not change from September to March. Ovarian specific energy content remained unchanged between the postspawning (21.78 kJ/g) and fall (21.89 kJ/g) periods, then accumulated during the winter (24.80 kJ/g). Gastrointestinal tract specific energy content decreased in fish of both sexes during spawning, and increased during winter. Liver specific energy content occurred in females during summer, and in males during winter. Winter is a critical period for males and females; gonadal energy requirements in females must be met to assure reproductive success the following spring, and, important energy reserves necessary for survival are accumulated in males.
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Stock assessment of arctic grayling at Ugashik Lakes, AlaskaArctic grayling (Thymallus arcticus) stocks were assessed at Ugashik Narrows and Outlet in Southwest Alaska during the open-water periods of 1987, 1988, and 1989. Abundance, size, and age data were collected, which were then compared with historical data for 1968-1984. The Narrows is the stream between Upper Ugashik Lake and Lower Ugashik Lake, and the Outlet is the source of the Ugashik River from Lower Ugashik Lake.
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Habitat utilization by fishes in the Tanana River near Fairbanks, AlaskaThis study evaluated summer habitat utilization of fishes and the effects of floodplain developments on fish and aquatic habitat in the glacially-fed Tanana River near Fairbanks, Alaska. Aquatic habitats were quantitatively described on the basis of water velocity, depth, and clarity, and substrate, cover and vegetation. Lake chub and longnose sucker were abundant in all habitats. Whitefishes, juvenile salmon, and northern pike were captured most frequently in areas with high water clarity. Burbot preferred deeper, turbid waters. Young-of-the-year of lake chub and longnose sucker preferred shallow, silty backwaters; juvenile lake chub demonstrated no habitat preferences; and adult lake chub, juvenile longnose sucker, and juvenile/adult slimy sculpin preferred gravel riffles. Bank stabilization activities have significantly modified aquatic habitat and fish communities of Tanana River backwaters. In general, free-flowing sidechannels have become blocked-off sloughs resulting in reduced turbidities and lower flows.
