• Multispecies Age-Structured Assessment Modeling As A Tool Of Fisheries Management In The Gulf Of Alaska

      Van Kirk, Kray F.; Quinn, Terrance J. II; Collie, Jeremy; Criddle, Keith; Kruse, Gordon; Mueter, Franz (2012)
      A multispecies age-structured assessment model (MSASA) for the Gulf of Alaska (GOA) is developed to examine the effects of integrating predation mortality into stock assessment efforts. Age-specific predation mortality is modeled as a flexible function of predator and prey abundances, constructed from species-preference and size-preference parameters and fitted to stomach-content data. Modeled species include arrowtooth flounder ( Atheresthes stomias), Pacific cod (Gadus macrocephalus), walleye pollock (Theragra chalcogramma), Pacific halibut (Hippoglossus stenolepis) and Steller sea lion ( Eumatopias jubatus). Recruitment, residual natural mortality, full-recruitment fishing mortality, and fishery/survey selectivities are estimated for pollock, cod, and flounder; abundances for apex predators sea lions and halibut are input. Estimated trophic structures and predation links show significant changes as a result of the inclusion of higher trophic level predators, and model results are highly sensitive to assumptions regarding sea lion diet. Simulation exercises suggest that model performance degrades more due to model misspecification and data scarcity than assumptions regarding data weighting and variance. Estimates of predation mortality work in tandem with survey data, constraining predation estimates in the face of incomplete diet data and potentially improving estimates of cohort structure. Exploration of predator functional responses (PFR) shows the default GOA MSASA Holling Type II PFR to be more flexible than initially thought, and that explicitly modeling predator competition for the same prey can improve model fit to stomach-content data. Median parameter estimates and their respective variances from the fitted MSASA model are used to construct management strategy simulations. Reducing fishing pressure on pollock during periods of high predator biomass is less effective at preserving pollock stocks than raising fishing pressure on flounder, and multispecies harvest control rules and biological reference points are shown to be more conservative and more efficient at preserving stock abundance while maintaining catch levels than their single-species counterparts.
    • Nucleic Acid Ratios As An Index Of Growth And Nutritional Ecology In Pacific Cod (Gadus Macrocephalus), Walleye Pollock (Theragra Chalcogramma), And Pacific Herring (Clupea Pallasii )

      Sreenivasan, Ashwin; Smoker, William (2011)
      Pacific cod (Gadus macrocephalus), walleye pollock (Theragra chalcogramma), and Pacific herring (Clupea pallasii) are among the most ecologically and commercially important species in the North Pacific Ocean. In spite of their importance, little is known about larval and juvenile growth strategies in these fish. Since larval and juvenile fish growth may determine future growth, possibly affecting recruitment success, assessments of growth strategies might improve predictive growth models. Nucleic acid ratios (RNA/DNA) can have applications as a sensitive growth index in larval and juvenile Pacific cod, walleye pollock, and Pacific herring, and can potentially be used to determine growth responses and energetic assessments at the cellular level. Determining physiological growth responses in these fish after exposure to different temperatures and nutritional states can help in understanding growth strategies and condition. Nucleic acid ratios from white muscle of juvenile Pacific herring and whole-body Pacific cod and walleye pollock larvae were used as a cellular growth index to provide energetic assessments in these species. Growth responses were studied in these fish across a range of temperatures and nutritional states. Growth was compared between fed, starved/fed and terminally starved Pacific herring cultured at 6.5�C, 8.5�C, and 12.5�C. Relative to fed controls, starved/fed fish showed similar RNA/DNA ratios and soluble protein concentration, but reduced mass. Nucleic acid ratios in starved/fed fish during the starvation phase, and in terminally starved fish, indicated incipient terminal starvation. Also, a seasonal variation of RNA/DNA, protein concentrations and total body lipid concentrations was seen in fed fish, reflecting changes in resource allocation. Early growth was compared in yolk-sac Pacific cod and walleye pollock larvae cultured at 5�C and 8�C, and in yolk-sac Pacific cod larvae cultured in two nutritional states (fed and starved). Growth responses in Pacific cod and walleye pollock larvae were affected by small differences in temperature. Exposure to the lower temperature resulted in higher RNA/DNA in both Pacific cod and walleye pollock larvae. Based on nucleic acid patterns with larval development, it was possible to identify distinct growth stanzas in Pacific cod larvae.
    • Optimal Inseason Management Of Pink Salmon Given Uncertain Run Sizes And Declining Economic Value

      Su, Zhenming; Adkison, Milo (2001)
      This is a comprehensive study on the fishery and management system (including the inseason stock abundance dynamics, the purse seine fleet dynamics and the inseason management) of pink salmon (Oncorhynchus gorbuscha) in the northern Southeast Alaska inside waters (NSE). Firstly, we presented a hierarchical Bayesian modelling approach (HBM) for estimating salmon escapement abundance and timing from stream count data, which improves estimates in years when data are sparse by "borrowing strength" from counts in other years. We presented a model of escapement and of count data, a hierarchical Bayesian statistical framework, a Gibbs sampling estimation approach for posterior distributions, and model determination techniques. We then applied the HBM to estimating historical escapement parameters for pink salmon returns to Kadashan Creek in Southeast Alaska. Secondly, a simulation study was conducted to compare the performance of the HBM to that of separate maximum likelihood estimation of each year's escapement. We found that the HBM was much better able to estimate escapement parameters in years where few or no counts are made after the peak of escapement. Separate estimates for such years could be wildly inaccurate. However, even a single postpeak count could dramatically improve the estimability of escapement parameters. Third, we defined major stocks and their migratory pathways for the NSE pink salmon. We estimated the escapement timing parameters of these stocks by the HBM. A boxcar migration model was then used to reconstruct the catch and abundance histories for these stocks from 1977 to 1998. Finally, we developed a stochastic simulation model that simulates this fishery and management system. Uncertainties in annual stock size and run timing, fleet dynamics and both preseason and inseason forecasts were accounted for explicitly in this simulation. The simulation model was applied to evaluating four kinds of management strategies with different fishing opening schedules and decision rules. When only flesh quality is concerned, the present and a more aggressive strategy, both of which are adaptive to the run strength of the stocks, are able to provide higher quality fish without compromising the escapement objectives.
    • Physical Mechanisms For Variation In Pink Salmon (Oncorhynchus Gorbuscha) Survival Within The Upwelling And Downwelling Domains Of The Northeast Pacific

      Miller, Sara Elizabeth; Adkison, Milo; Criddle, Keith; Cokelet, Edward D. (Ned); Haldorson, Lewis J. (2011)
      Regional coastal conditions have a strong influence on juvenile salmon (genus Oncorhynchus) survival during their critical first months in the marine environment. Salmon survival has been thought to be favored within the downwelling domain if water column stabilities increase, whereas stability may have the opposite effect at lower latitudes. To explore this hypothesis at a local scale, we examined the relationship between stability and the characteristics of growth rate, condition, and marine survival of several stocks of pink salmon (O. gorbuscha) within Prince William Sound (PWS) and two water masses, Alaska Coastal Current and shelf, in the northern coastal Gulf of Alaska (GOA). While slower and weaker development of stratification with a deeper mixed layer depth may be more important for juvenile pink salmon survival in the Sound, earlier and stronger stratification with a shallower mixed layer depth may be more beneficial within the Gulf. As expected, stability within PWS did explain the growth rate of hatchery fish, although stability explained only a small amount of the variability and did not have the same relationship for each hatchery stock. Contrary to expectation, stability just prior to capture did not explain the variability in condition index for either hatchery or wild fish collected from within the Sound or from within either GOA water mass. When stability was below average just prior to capture within PWS, the relationship between condition index and year-class survival was positive; when stability was above-average just prior to capture, the relationship was negative. In a broader scale study, we explored the relationships between regional water column stabilities during early marine residence of pink salmon in both upwelling and downwelling domains of the northeast Pacific Ocean and marine survival rates the following year for hatchery stocks ranging from Vancouver Island, British Columbia, to Kodiak Island, Alaska. Contrary to expectation, our findings were similar between the upwelling and downwelling areas, but differed by the distance offshore. Marine survival rates of hatchery pink salmon from northern and southern stooks increased for salmon that experienced below-average stability on the inner shelf (luring early marine residence while stability effects from the outer shelf showed no consistent relationship to marine survival.
    • Policy And Market Analysis Of World Dogfish Fisheries And An Evaluation Of The Feasibility Of A Dogfish Fishery In Waters Of Alaska, Usa

      Gasper, Jason R.; Kruse, Gordon; Greenberg, Joshua; Fong, Quentin; Miller, Marc (2011)
      Spiny dogfish is a valuable commodity on the world market and has a global capture distribution. There are three chapters evaluating dogfish markets and fisheries in this dissertation; Chapter 2 evaluates the spatial distribution of dogfish in the Gulf of Alaska; Chapter 3 provides an overview of world markets and evaluates conditions that have led to a decline in dogfish product demand in Europe; and Chapter 4 uses the information from the previous 2 chapters to provide and policy and market overview of dogfish fisheries in Alaska. Results from this study provide a comprehensive world overview of the modern dogfish fisheries and market segmentation using an evaluation of trade and price statistics. These results indicate that the dogfish market is adulterated, supplied by both sustainable and non-sustainable dogfish sources. Media attention resulting from overfishing has reduced demand for dogfish products in Europe due to the adulterated market. Overcoming the loss of market share will require eco-labeling to inform consumers about sustainable dogfish stocks. The impact of eco-labeling in Asian countries is less clear due to unknown inter-Asian market channels for fins and meat and little information on consumer attitudes towards labels. Alaska products could leverage either Asian or European consumers, but a profitable fishery will likely require regulatory changes and improved stock assessment to allow a directed fishery. In addition, pending regulatory changes, establishing robust market channels between Alaska and Europe will likely require some form of eco-labeling; especially given current eco-labeling efforts in Canada and the Atlantic US.
    • Population Structure And Behavior Of Pacific Halibut

      Seitz, Andrew C.; Norcross, Brenda (2006)
      Pacific halibut (Hippoglossus stenolepis) is not managed on regional scales with separate population dynamics, but rather as a single, fully mixed population extending from California through the Bering Sea. However, some of the evidence from which this paradigm was established is questionable and I hypothesize that there are separate spawning populations of Pacific halibut in three regions, the Gulf of Alaska, Bering Sea and Aleutian Islands, because these regions are geographically separated by land masses and/or deep water passes that may prevent movement by adults. Pop-up Archival Transmitting (PAT) tags were attached to Pacific halibut in each region to examine their movement and behavior. First, geolocation by ambient light was able to discern basin-scale movements of demersal fishes in high latitudes and therefore this technique provided a feasible method for providing scientific inference on large-scale population structure in Pacific halibut. Second, because seasonally low ambient light levels and inhabitation of deep water (>200 m) restricted geolocation by light during winter, an alternative method, a minimum distance dispersal model, was developed for identifying migration pathways of demersal fish in the Gulf of Alaska based on daily maximum depth. Third, the PAT tags provided no evidence that Pacific halibut in the southeastern Bering Sea and Aleutian Islands moved among regions during the mid-winter spawning season, supporting my hypothesis of separate populations. Fourth, geographic landforms and discontinuities in the continental shelf appeared to limit the interchange of Pacific halibut among areas and possibly delineate the boundaries of potential populations in the Gulf of Alaska and eastern Bering Sea, with apparent smaller, localized populations along the Aleutian Islands. This possible population structure may be reinforced by regional behavioral variation in response to the environment. Future research should be directed at quantifying the exchange of individual fish among regions for possible local area management plans that more accurately reflect population structure.
    • Reproductive Potential Of Pacific Cod (Gadus Macrocephalus) In Alaska

      Ormseth, Olav Aleksander; Norcross, Brenda L. (2007)
      The reproductive potential of female fishes, which results from the number of eggs they produce and the quality of individual eggs, is a critical factor in fisheries biology. Reproductive potential is important to individuals because maternal fitness is the product of the number of offspring produced and how many offspring survive. The growth rate of populations and their capacity for supporting commercial fisheries also depend on the number of viable offspring that females produce. I studied the reproductive potential of female Pacific cod (Gadus macrocephalus) in the North Pacific Ocean. Pacific cod is an important ecological and economic resource, yet much of its reproductive biology remains unexplored. I used several different approaches to investigate whether egg number or egg size are more important in determining reproductive potential, and to evaluate factors that influence reproduction. An analysis of life history variation among Pacific cod in Canada and Alaska demonstrated that despite differences in life history strategies, females from different populations had similar lifetime reproductive success (a proxy for individual fitness). I also collected Pacific cod in the Gulf of Alaska, eastern Bering Sea, and western Aleutian Islands from 2002 to 2005. Biochemical analyses of Pacific cod eggs revealed that Pacific cod produce low-energy eggs that are adapted for rapid development on the seafloor. Larger females produce eggs with less arachidonic acid (a fatty acid that has been linked to egg quality) than smaller females, suggesting that they may sacrifice egg quality to maintain fecundity. Determination of fecundity and egg size in 590 females from different areas and years revealed that maternal length and weight are excellent predictors of fecundity, but that variability in egg size is not related to the age or size of females, The greatest difference in reproductive potential among years and areas was reduced egg size in the eastern Bering Sea in 2003, which may have been due to changes in ocean temperature or prey availability that impacted the ability of females to store energy. These results suggest that female Pacific cod maximize their fitness through increased egg production, not egg quality, and that their reproductive success is under strong environmental control.
    • Seasonal Variability Of Pristane In Mussels (Mytilus Trossulus) In Prince William Sound, Alaska

      Short, Jeffrey W.; Shirley, Thomas (2005)
      Pristane (2,6,10,14-tetramethylpentadecane) concentrations in mussels (Mytilus trossulus) increase abruptly during spring in Prince William Sound (PWS), Alaska. This increase is mainly due to ingestion by mussels of pristane-laden feces produced by nearshore zooplanktivores, especially juvenile pink salmon (Oncorhynchus gorbuscha), and I evaluate whether the increase may be used as an index of foraging success, and hence early marine survival, of pink salmon. Pristane is biosynthesized by Neocalanus copepods. Examination of the trophic and temporal distribution of pristane found in 3,007 samples implicates Neocalanus copepods as the source of pristane in PWS. Neocalanus copepods often dominate the zooplankton biomass during spring in PWS. Juvenile pink salmon, preying on Neocalanus , produce pristane-laden feces that are accumulated by mussels 52 times more efficiently than is dissolved pristane. Releases en masse of ~100,000,000 juvenile pink salmon from a hatchery at the peak of the Neocalanus bloom were immediately followed by increases in pristane concentrations of nearby mussels monitored during 1996 and 1998. Accumulation of dissolved pristane, or of fecal pellets produced by Neocalanus copepods, were substantially less important pathways of pristane transfer to mussels. The transfer pathway to mussels via feces produced by zooplanktivores preying on Neocalanus is the basis for a potential linkage between pristane accumulation by mussels and survival of juvenile pink salmon, because it reflects indirectly the magnitude of Neocalanus prey consumed. Annual survival values of hatchery pink salmon were weakly correlated (P = 0.10) with pristane concentrations monitored in mussels at 25 stations distributed throughout PWS from 1995 through 2001. Although Neocalanus copepods are considered important forage for juvenile pink salmon, feeding experiments reported herein confirm previous studies implicating growth inhibition by pristane. Hence, the forage value of Neocalanus copepods may be considerably lower than is usually assumed.
    • Stock Structure And Environmental Effects On Year Class Formation And Population Trends Of Pacific Herring, Clupea Pallasi, In Prince William Sound, Alaska

      Brown, Evelyn Dale; Norcross, Brenda L. (2003)
      Fluctuating forage fish populations trigger large ecosystem responses in the North Pacific. A representative species, Pacific herring, Clupea pallasi, was chosen to model environmental effects on population fluctuations and recruitment with a case example in Prince William Sound (PWS), Alaska. A unique approach was used to (1) develop a spatially-explicit, life history-based conceptual stock model, (2) quantify population level effects of climatic trends, and (3) model key environmental factors affecting recruitment. Framed as a simulation model, the stock model was compartmentalized by life-history stages based on shared habitats and environmental forcing. Initial model conditions impacting year-class formation were adult size-at-age, spawn timing, location and spawner density, and conditions during egg incubation, all impacting a two-stage larval mortality rate. Larval survival probably dictates the extremes in year-class strength. Age1 abundance should reflect recruitment levels 2--3 yrs later, unless a predator pit exists. A metapopulation structure was proposed with at least two local population groupings with spatial complexity required to maintain stock levels. Herring abundance correlated with long-term climate trends supporting hypotheses of bottom up environmental forcing. Adult growth was oscillatory over a 13 yr period in phase with zooplankton production and climatic trends. Spawn timing occurred progressively earlier over the last 30 yr period with a concurrent regional spawn allocation shift and decrease in recruits per spawner. Incorporating local stock structure and local environmental variables into nonlinear herring recruitment models improved explanatory power over traditional models. Best-fit variables were eastern PWS SST, salinity, SST variance, and salinity variance from spring to fall. Eight critical life stage periods were defined based on the season and lag of the best-fitting varibles. Examining other variables in these critical periods led to defining potential key processes affecting year class formation. Allocation of spawn and age-3 recruits to metapopulation regions also impacted recruitment to PWS as a whole and these results supported the metapopulation theory. The results led to formulation of a new theory, entitled "opposing response", explaining the mechanism producing the observed pattern of alternating strong and week year class strengths in northern Pacific herring.
    • The Colonization Mechanism Of Pink Salmon Populations In Glacier Bay, Alaska, Based On Genetic Data

      Kondzela, Christine M.; Gharrett, A. J.; Wilmot, Richard; Pella, Jerry; Smoker, William; Finney, Bruce (2010)
      Following retreat of the last glacial advance in the early 1700s, pink salmon Oncorhynchus gorbuscha colonized many watersheds in Glacier Bay, Alaska. Streams in the lower Bay were populated first, and colonization proceeded up the Bay during the last 200 years. The objective of this study was to use analyses of genetic data---microsatellite and allozyme loci, and mitochondrial DNA haplotypes---to elucidate the colonization mechanism. The even- and odd-year broodlines served as replicate experiments; the mechanisms of colonization for the two broodlines were similar in most respects. The population genetic structure, based on allele/haplotype frequencies and genetic diversity (FST), suggested that in general, deglaciated streams were populated by colonists from nearby locations. The populations in lower Glacier Bay were likely established by colonists from populations outside Glacier Bay. In turn, the lower Bay populations contributed colonists to populations farther up the Bay, which subsequently provided colonists to the most recently deglaciated locations in the upper Bay, although in the even-year there appeared to be some contribution to the youngest populations from older populations, outside of or in lower Glacier Bay. Few genetically divergent donor sources contributed colonists based on the limited linkage disequilibrium, higher relatedness, and lower allelic diversity within Glacier Bay populations. The number of fish involved in initial colonization was not large, based on slightly reduced genetic diversity within Glacier Bay, but minimal founder effect signals precluded very small numbers of fish as well. Most of the genetic variation appeared early in the formation of populations and effective population size estimates were >100 fish in every population. Some gene flow after initial colonization is supported by the increased allelic diversity and decline in relatedness with population age, but heterogeneity within Glacier Bay suggested that gene flow must be limited among some populations. Colonization of the youngest streams coincided with the historically high abundance of pink salmon in Southeast Alaska during the 1990s; I speculate that the rapid expansion in the size of these populations subsequent to this study was the result of high survival rather than extensive gene flow.
    • The Influence Of Estuarine Habitats On Expression On Life History Characteristics Of Coho Salmon Smolts In South-Central Alaska

      Hoem Neher, Tammy D.; Rosenberger, Amanda; McPhee, Megan; Mueter, Franz; Zimmerman, Christian (2012)
      Expression of traits that lead to life history diversity in salmonids may provide population-level resilience and stability in dynamic environments. I examined habitat use and variability in life history trait expression in juvenile coho salmon Oncorhynchus kisutch occupying two contrasting estuary environments in south-central Alaska. My goal was two-fold: first, to determine if salmon were using estuaries as rearing environments and were therefore potentially vulnerable to selection pressures within; and second, to compare traits of salmon that reared in contrasting estuary environments to explore the potential for differential trait expression related to estuary size and habitat complexity differences. Juvenile coho salmon reared in estuaries for extended periods of time and patterns of use corresponded to environmental conditions within the estuaries. Populations using adjacent but contrasting estuary environments exhibited differential trait expression and were genetically distinct. My work highlights how pristine, functioning estuary habitats contribute to resilience of salmon populations to environmental changes in two ways: first, by providing habitats for individuals to increase in size and condition prior to ocean entry; and second, by providing for alternative life history tactics (providing quality habitat to delay marine entry times and increase body size). Management approaches for resilient salmon runs must therefore maintain both watershed and estuary function.
    • The Influence Of Water Velocity And Depth On Prey Detection And Capture By Juvenile Coho Salmon And Steelhead: Implications For Habitat Selection And Segregation

      Piccolo, John J.; Hughes, Nicholas F. (2005)
      I studied the effects of water velocity and depth on drift-foraging by juvenile coho salmon and steelhead to assess how these influence their reported habitat segregation into pools and riffles, respectively. I used three-dimensional video analysis of stream-tank foraging experiments to test how velocity and depth influence prey capture probabilities, and the geometry and dynamics of prey detection and capture. I used the experimental results to develop net energy intake models to predict optimal foraging velocities for coho and steelhead. Prey capture probabilities for both coho and steelhead declined from $65% to 10% with an increase in velocity from 0.29 to 0.61 m · sec -1, with little difference between the species. Capture maneuver characteristics were similar for both species, including reduced prey detection distance and capture probabilities within the capture area, constant prey interception speed, and increasing return speed. I conclude that faster velocity reduces prey capture success by coho and steelhead, but that differences in capture abilities are not responsible for habitat segregation. Prey capture probabilities for both species were constant at ~40% at depths from 0.15 to 0.60 m, with little difference between the species. Capture maneuver characteristics were similar for both species, including increased prey detection distance and interception speed, and constant return speed. I predict that prey capture rate increases proportionally to water depth for coho and steelhead, but that differences in capture probabilities are not responsible for habitat segregation. I used the experimental results to develop net energy intake models that predicted optimum foraging velocities of 0.29 m · s-1 for coho and 0.30 m · s-1 steelhead. Modeled 10% and 25% increases in swimming costs for coho reduced optimum velocity by 0 and 0.01 m · s-1, respectively. These results, coupled with those from the depth experiments, suggest that habitat segregation may be due to factors other than short-term foraging considerations. I propose that these are largely selective mechanisms such as size-based habitat selection, differences in growth trajectories, or prey specialization. I do not discount the possibility that interactive mechanisms are also important, especially at periods of high fish density or limited prey availability.
    • The Role Of Copepods In The Distribution Of Hydrocarbons: An Experimental Approach

      Duesterloh, Switgard; Shirley, Thomas C. (2002)
      Copepods may provide a significant pathway for the concentration and transfer of polyaromatic compounds (PAC) to higher trophic level consumers. PAC dissolved from weathered crude oil are more persistent in the environment and have much higher toxicity than the lighter, more volatile fractions of crude oil. Because of their polarity, PAC tend to accumulate in bio-lipids. Subarctic copepod species can contain up to 80% of their body dry weight in lipids and have a high surface area to volume ratio. Thus, PAC accumulation is rapid and bioaccumulation factors are in the order of 500--8000, depending upon species and lipid content. While direct toxic effects of oil on copepods have been reported in the order of 10 mg/L, toxicity increases substantially in the presence of natural ultraviolet (UV) radiation. Phototoxic effects to the copepods Calanus marshallae and Metridia okhotensis were observed at concentrations of ~2mug/L total dissolved PAC followed by 4--8 hours of exposure to ambient daylight. Responses included mortality, immobilization and discoloration of lipid sacs. Further experiments were conducted to test the interaction effects of various concentrations of PAC dissolved from weathered Alaska North Slope crude oil and subsequent exposure to sunlight with and without the UVB component to the copepods Neocalanus flemingeri and N. plumchrus. Phototoxicity was found to be a linear function of the product of light intensity and PAC concentration. High natural variability in egg production rates precluded significant results of the toxicity of oil to copepod reproduction. This work has shown that copepods could potentially provide a mechanism for the concentration of dissolved PAC from the water and its transfer into pelagic and benthic food chains.
    • Thyroid hormone binding to brain nuclear extracts during smoltification in coho salmon

      Cheek, L. Michael (1991)
      Salmon complete a metamorphosis called smoltification prior to entering salt water. Increased thyroid activity, olfactory imprinting, and chemical and structural changes in the brain are known to occur at this time. This study was undertaken to determine if triiodothyronine (T$\sb3$) binding to brain nuclear extracts changes during smoltification. During this investigation serum thyroxine (T$\sb4$) concentrations increased three fold during smoltification coincident with changes in coloration and morphology and surged again during downstream migration to six times presmolt concentrations. Using ultrafiltration assays, homologous displacement experiments of KCl extracts of recovered brain cell nuclei indicated that maximal binding capacity increased during smoltification and down-stream migration. The increase in receptor concentration lagged the increase in serum thyroxine by one week. Dissociation constants increased during smolt transformation but declined abruptly during down-stream migration. However, dissociation constants did not change during smoltification if nuclear extracts had been previously incubated at room temperature to remove endogenous ligand. Dissociation rate increased significantly, coincident with the increase in receptor concentration measured by homologous displacement. The maximal probable percent occupancy of available receptors increased from 60% before to greater than 95% during the smolt transformation climax. These results provide evidence that thyroid hormone receptors participate in brain development and olfactory imprinting in smolting salmon.
    • Utilizing Multi-Source Abundance Estimation And Climate Variability To Forecast Pacific Salmon Populations

      Shotwell, Stacey Anne Kaleinauialoha; Adkison, Milo D. (2004)
      Data limitation is a common property of many fisheries. Some Pacific salmon populations are a typical example of this situation because the monitoring of numerous tributaries within an area becomes logistically intractable. Fishery management often responds to this scenario with qualitative stock assessments in the form of harvest projections In some cases, fishery data, although limited, exists in a variety of sources and may be integrated to develop quantitative population estimates. The first objective of this investigation is to generate a modeling process that combines multiple data sources to estimate abundance and escapement estimates for data-limited salmon populations. Second, we consider the reliability of these estimates by testing for robustness to various simulated levels of measurement error in the data. Finally, we perform rigorous development and selection on an age structured spawner-recruit model that incorporates abundance and escapement estimates and identifies potential environment-recruit relationships. We demonstrate our technique with a case study on summer chum salmon from the Kuskokwim and Yukon Rivers, Alaska. Recent declines of summer chum returns to this salmon-dependent region have created hardships for the local area residents. We developed a maximum likelihood statistical framework that synchronously combined all available data sources from this management region to estimate abundance and escapement. Successful estimation was dependent on an independent estimate of abundance for a least a few years. We provide error estimates of the modeling process through bootstrap methods. Simulations showed that measurement error had negligible effect on abundance estimates, whereas performance for escapement estimation was tied to the sequence of abundance years. High explanatory power was attained by including environmental variables in the spawner-recruit relationship developed from these population estimates. We used a three-stage modeling process to maintain biological realism in the predictor variables. Recent changes in variables chosen for the best model were consistent with poor environmental conditions and estimates of forecasting error were much lower than models using no environmental information. Based on our findings, we recommend that managers consider the utility of multiple source estimation and environmental variability with our modeling approach for future regulatory decisions of Pacific salmon fisheries in data-limited regions.
    • Variability Of Pink Salmon Family Size Has Implications For Conservation And Management Models

      Geiger, Harold Joseph, Iii; Gharrett, A. J. (2002)
      In several populations of pink salmon, the short-term dynamics population size was related to both the mean and variance of individual family sizes, because not all families were equally productive. In the marine lifestage, population increases came disproportionately from the most productive families, especially in populations with the highest average marine survival. Moreover, the trait of marine survival itself had a statistically detectable genetic component. This implies that the most favored phenotypes change from generation to generation, and that the marine environment is unpredictable and changing. These results, together with laboratory studies of freshwater survival and measurements of wild pink salmon in Prince William Sound, Alaska, seemed to indicate that family-specific variation in marine survival and variation in egg retention within the redd were the most important potential influences on variation of pink salmon family size in the studied populations, when density was controlled to intermediate levels. These results provide more justification for maintaining stock sizes at intermediate or high levels, and for protecting metapopulation structure. These results also show the importance of variation and instability in the recruitment process of Pacific salmon, and highlight the inadequacy of current models of salmon recruitment, which emphasize stability and long-term averages.
    • Walleye Pollock (Theragra Chalcogramma) Distribution In The Eastern Bering Sea Related To Fishery And Environmental Factors

      Shen, Haixue (2009)
      Walleye pollock (Theragra chalcogramma) in the eastern Bering Sea (EBS) support the largest single-species fishery in the world. Pollock also play an important role in the EBS ecosystem as an important prey species. The decline of the western population of Steller sea lions during the 1980s and 1990s raised concerns about the potential competition between the pollock fishery and the sea lion population. My research focused on pollock distribution related to the fishery and physical environment at different temporal and spatial scales using fisheries acoustic data and observer data in the winter fishing season during 2002-2006. Temperature and wind played important roles in determining the pollock distribution in winter, especially from late February to March. The changes in spatial structure during the fishing season suggested that the fishery probably influenced pollock distribution by removing some portion of the local population and perhaps even smoothing out the aggregated distribution of pollock. At a small scale, pollock schools became smaller and denser. At the meso-scale, the distances between schools increased. At a larger scale, range estimates from variography increased which indicated that the spatial correlation among pollock extended to greater distances after fishing. Fishing behavior was also studied using Levy flight theory and its relation to pollock distribution in the EBS. Fishing behavior was significantly correlated to the fractal dimension of fish which measures the degree of pollock clustering, rather than to pollock spatial concentration or density in the EBS. The observer data were also included to analyze the effect of fish distribution on fishing behavior at the school scale. The results indicated that school density rather than the school size played an important role in fishing behavior. Finally, catch depletion analysis was used to examine the potential local depletion. While frequentist and Bayesian methods confirmed that the fishery caused slight local depletion in some areas in the EBS, the magnitude was less than that before sea lion protection measures were put into place in 1999 to spread out the fishery in space and time.