Now showing items 1-20 of 91

    • Quality assessment of weathervane scallop (Patinopecten caurinus) and purple-hinge rock scallop (Crassadoma gigantea) from Alaska

      Brenner, Kathryn A.; Oliveira, Alexandra; RaLonde, Ray; Crapo, Charles; Bechtel, Peter (2011-08)
      In Alaska, the Pacific weathervane scallop (Patinopecten caurinus) is the only species commercially harvested. In the Eastern Gulf of Alaska, harvesters report occurrences of poor quality and difficult to market scallops from some fishing areas, designating the product 'weak meat' scallops. The purple-hinge rock scallop (PHRS, Crassadoma gigantea), has aquaculture potential. A recent grow-out study in Alaska was promising, verifying this potential. Our goal was to assess the quality of Alaskan scallops using physical and chemical analyses to understand the perceived differences in meat quality. 'Weak meat' (WS) and standard quality (SS) whole weathervane scallops from Yakutat, two batches of scallop muscle from Kodiak (KS1, KS2) and a group of whole PHRS from Southeast Alaska were sampled. Compared to KS1, KS2 and SS, muscle condition was lower (P<0.05), moisture content was higher (P<0.05) and glycogen content was below the detection limit (<0.62%) in WS. There were no differences (P>0.05) in proximate composition between PHRS and Kodiak scallops, however, PHRS had higher (P<0.05) levels of [omega]-6 fatty acids. Results confirmed anecdotal information from harvesters that WS was inferior in quality when compared to either SS or KS. Furthermore, we concluded that PHRS meat was of high quality, similar to Kodiak scallops.
    • Evaluation of prey composition and nutritional value of diets of free-ranging harbor seals (Phoca vitulina) from Tugidak Island

      Geiger, Gretchen L.; Atkinson, Shannon; Carpenter, James; Horstmann-Dehn, Larissa; Wynne, Kate (2012-12)
      Changes in climate can cause shifts in ecosystem structure that can affect quantity or quality of prey available to predator populations. Due to sex or age-specific behaviors of predators, certain classes within a population may be more severely impacted by changes in their diet. This study evaluated prey composition and nutritional value of summer diets of harbor seals (Phoca vitulina richardii) from Tugidak Island, Alaska from 2001-2009. The MIXIT-WIN program was used to estimate the nutritional value of average harbor seal diets. Changes in relative abundance of certain prey species were correlated to sea surface temperature anomalies. Despite changes in prey composition, the nutritional value of the average harbor seal diet did not change. Fecal corticosteroid metabolite profiles were analyzed to identify age and sex of individual harbor seals from scats. Profiles obtained from a known adult male harbor seal could be differentiated from those of known adult female and juvenile male seals. Similar profiles were observed in unknown age and sex samples. Even though diet diversity differed between these groups, the nutritional quality of consumed diets was not significantly different. Tugidak Island harbor seals have flexible diets allowing them to capitalize on available prey to maintain their nutritional intake.
    • Pacific herring juvenile winter survival and recruitment in Prince William Sound

      Sewall, Fletcher; Norcross, Brenda; Mueter, Franz; Kruse, Gordon; Heintz, Ron; Hopcroft, Russ (2020-05)
      Small pelagic fish abundances can vary widely over space and time making them difficult to forecast, partially due to large changes in the number of individuals that annually recruit to the spawning population. Recruitment fluctuations are largely driven by variable early life stage survival, particularly through the first winter for cold temperate fishes. Winter survival may be influenced by juvenile fish size, energy stores, and other factors that are often poorly documented, which may hamper understanding recruitment processes for economically and ecologically important marine species. The goal of this research was to improve understanding of recruitment of Pacific herring (Clupea pallasii) within Prince William Sound (PWS) through recruitment modeling and by identifying factors influencing winter survival of young-of-the-year (YOY) herring. Towards this end, my dissertation addresses three specific objectives: 1) incorporate oceanographic and biological variables into a herring recruitment model, 2) describe patterns in growth and condition of PWS YOY herring and their relationship to winter mortality risks, and 3) compare the growth, condition, swimming performance, and mortality of YOY herring that experience different winter feeding levels. In the recruitment modeling study, annual mean numbers of PWS herring recruits-per-spawner were positively correlated with YOY walleye pollock (Gadus chalcogrammus) abundance in the Gulf of Alaska, hence including a YOY pollock index within a standard Ricker model improved herring recruitment estimates. Synchrony of juvenile herring and pollock survival persisted through the three-decade study period, including the herring stock collapse in the early 1990s. While the specific mechanism determining survival is speculative, size-based tradeoffs in growth and energy storage in PWS YOY herring indicated herring must reach a critical size before winter, presumably to reduce size-dependent predation. Large herring switched from growth to storing energy, and ate more high-quality euphausiid prey, which would delay the depletion of lipid stores that compelled lean herring to forage. Lipid stores were highest in the coldest year of the seven-year field study, rather than the year with the best diets. With diets controlled in a laboratory setting, spring re-feeding following restricted winter diets promoted maintenance of size and swimming ability, but had little effect on mortality rates compared to fish continued on restricted rations. Declines in gut mass, even among fully fed herring, and low growth potential suggest limited benefits to winter feeding. Mortalities due to food restriction compounded by disease were highest among herring that fasted through winter months, and among small herring regardless of feeding level. Taken together, these findings illustrate the importance of achieving a critical size and high lipid stores in the critical period before winter to promote YOY herring winter survival and ultimately recruitment.
    • Diversity and community structure of eukaryotic phototrophs in the Bering and Chukchi seas

      Lekanoff, Rachel M.; Collins, R. Eric; McDonnell, Andrew M.P.; Danielson, Seth L. (2020-05)
      The phytoplankton of the Bering and Chukchi seas support highly productive ecosystems characterized by tight benthic-pelagic coupling. In this study, we focus on the northern Bering and Chukchi seas, considering them as one ecosystem. This community has historically been dominated by diatoms; however, climate change and accompanying warming ocean temperatures may alter primary producer communities. Using metabarcoding, we present the first synoptic, high-throughput molecular phylogenetic investigation of phytoplankton diversity in the Bering and Chukchi seas based on hundreds of samples collected from June to September in 2017. We identify the major and minor taxonomic groups of diatoms and picophytoplankton, relative abundances of genera, exact sequence variants (201 for diatoms and 227 for picophytoplankton), and describe their biogeography. These phylogenetic insights and environmental data are used to characterize preferred temperature ranges, offering insight into which specific phytoplankton (Chaetoceros, Pseudo−nitzschia, Micromonas, Phaeocystis) may be most affected as the region warms. Finally, we investigated the likelihood of using shipboard CTD data alone as predictive variables for which members of phytoplankton communities may be present. We found that the suite of environmental data collected from a shipboard CTD is a poor predictor of community composition, explaining only 12.6% of variability within diatom genera and 14.2% variability within picophytoplankton genera. Clustering these communities by similarity of samples did improve predictability (43.6% for diatoms and 32.5% for picophytoplankton). However, our analyses succeeded in identifying temperature as a key driver for certain taxa found commonly throughout the region, offering a key insight into which common phytoplankton community members may be affected first as the Alaskan Arctic continues to warm.
    • Carbon flux and particle-associated microbial remineralization rates in the northern Bering and southern Chukchi seas

      O'Daly, Stephanie Hicks; McDonnell, Andrew M. P.; Hardy, Sarah M.; Johnson, Mark A. (2019-12)
      It has been hypothesized that climate change will reduce the strength and episodic nature of vernal phytoplankton blooms, increase heterotrophy of microbes and zooplankton, and weaken the tight coupling between pelagic and benthic production that is characteristic of Arctic continental shelves. As a part of the Arctic Shelf Growth, Advection, Respiration, and Deposition rates measurement (ASGARD) project, I quantified sinking particle fluxes and incubated sinking particles to measure the rate of microbial respiration associated with those particles. These measurements were used to characterize the strength of the pelagic-benthic connection. After a record-breaking year of warm temperatures and low-ice conditions in the northern Bering and southern Chukchi Seas, we observed massive vernal fluxes of sinking particulate organic carbon, ranking amongst the highest observed in the global oceans. Moreover, low rates of particle-associated microbial respiration indicate negligible recycling of sinking organic matter within the water column. These results suggest that the strength of the biological carbon pump may be maintained or enhanced in a warming Arctic, supporting strong benthic and upper trophic level productivity and carbon export.
    • Numerical investigations of the hydrography, dynamics, and ice distributions of Chukchi Sea shelf

      Lu, Kofan; Danielson, Seth; Weingartner, Thomas; Hedstrom, Kate; Shimada, Koji; Winsor, Peter (2019-08)
      Warm, moderately salty Bering Sea Water (BSW) carried into the Chukchi Sea through Bering Strait provides an oceanic heat flux for melting sea ice comparable to that of the solar heat flux. Intrusions of BSW transport heat and nutrients via intrapycnocline eddies vertically beneath the sea ice and laterally across structural fronts near the ice edge, setting up hydrographic features important to ice edge communities and the seasonal evolution of the ice melt-back. However, the intrapycnocline eddy dynamics and associated hydrography near the fronts have not previously been well described or characterized. Three numerical models using the Regional Ocean Model System (ROMS) are integrated to systematically investigate the importance of the intrapycnocline eddy field and the factors that affect its dynamics. The models suggest that the heat transported by eddies depends on frontal stratification, which is influenced primarily by the Bering Strait inflow discharge and salinity. The eddy field is also indirectly modified by the sea surface height, which varies with strong winds. Two frontal zones near the ice edge are identified according to the model-derived hydrographic structures and eddy dynamics: the Shelf Water Transition Zone (SWTZ) and the Melt Water Transition Zone (MWTZ). Improved understanding of these frontal zones will benefit future research of the ice edge ecosystem. Our models show a noticeable effect of strong wind events on ice edge displacement and vertical transports, both of which may be important to primary production in the frontal zones. Changing winds associated with increasing sea surface temperatures could alter the manifestation of the processes highlighted in this study.
    • Particles in the Pacific: how productivity and zooplankton relate to particles in the deep sea

      Pretty, Jessica L.; McDonnell, Andrew; Johnson, Mark; Hopcroft, Russ (2019-05)
      The magnitude and spatio-temporal patterns of particulate material flux from the surface ocean through mesopelagic and bathypelagic depths determines sequestration of atmospheric carbon and the food supplied to deep-dwelling ocean life. The factors that influence how and where this organic material is exported from euphotic depths are poorly understood. Zooplankton are thought to play a key role in modulating the transport of surface-produced particles to depths through consumption, fragmentation, active diel vertical migration, and fecal pellet production, thus it is important to study both particulate matter and zooplankton in tandem. In this study, I use an in-situ optical instrument, the Underwater Video Profiler 5 (UVP5), to describe broad scale patterns of large (> 100 μm) particles and zooplankton across a longitudinal transect of the Pacific Ocean during April to June 2015. Satellite-derived surface chlorophyll-a was employed to describe the timescales over which particles arrive in meso- and bathypelagic depths after a productivity peak. High abundances and volumes of particles are noticeable beyond the euphotic zone across the Equator, transition zone, and the sub-arctic Pacific, indicating increased export in these high-nutrient low-chlorophyll (HNLC) areas. In two of these areas, the Equator and transition zone, large abundances and volumes of particles extend into bathypelagic depths. High abundances of zooplankton were seen in all areas where high abundances of particles are seen in bathypelagic waters. Rhizaria were revealed to be pervasive across all biogeographic regions, and appear to play a role in particle attenuation in the sub-arctic Pacific. The insight into patterns between particles, zooplankton, and productivity identify HNLC regions as deserving more detailed examination in future studies of biological pump efficiency.
    • The seasonal dynamics of coastal Arctic lagoons in Northwest Alaska

      Tibbles, Marguerite; Seitz, Andrew C.; Falke, Jeffrey A.; Prakash, Anupma; Robards, Martin D. (2018-12)
      Lagoons are zones of habitat transitions between freshwater and marine ecosystems, providing safe and productive feeding habitats for whitefishes in Northwest Alaska, important to subsistence users in the region. However, many important lagoon processes are not understood. Therefore, the goal of this thesis was to gain a baseline understanding of two important seasonal processes of lagoons in Northwest Alaska. First, I attempted to identify environmental processes correlated with Arctic lagoon breaching for three indicator lagoons that represent a range of environmental characteristics using generalized linear models (GLM) in an information theoretic approach and model averaging. Second, I developed a habitat suitability (HS) model to identify the range of physical conditions that whitefishes may experience if overwintering under ice of these lagoons during the Arctic winter, for the same three lagoons. The GLM model suggested that lagoon breaching day of year was slightly negatively related to day of year of river break-up, but other unconditional confidence intervals for the covariate parameters overlapped zero indicating considerable uncertainty in these estimates. Further data collection and monitoring in the region is needed to improve and verify lagoon breaching modelling results. The HS model indicated that lagoons have reduced suitability as whitefish habitat in winter due to loss of habitat due to the presence of bottomfast ice and a reduction of liquid water quality due to cold temperatures, high salinities and low dissolved oxygen levels. Importantly, small lagoons without freshwater inputs were potential sinks for fish populations. The results from this research will help the National Park Service and the Native Village of Kotzebue in a joint effort to understand and manage these important habitats that are critical for subsistence fisheries as the Arctic faces an uncertain future with climate change, oil spill threats, and increased coastal development.
    • Three-dimensional diving behavior of ringed seals

      Simpkins, Michael A.; Kelly, Brendan P. (2000)
      The three-dimensional movements of 13 freely diving ringed seals were recorded during the spring of 1990, 1991, 1992, 1996, and 1997 in the Canadian Arctic near Resolute Bay, Nunavut. These data were used to investigate the diving behavior of ringed seals more fully than was possible using previous data, which only recorded the vertical movements of diving animals (time-depth data). During a third of all dives, ringed seals focused much of their effort within a reduced volume, suggesting local search behavior within patches of prey. Local search occurred during descent, ascent, and bottom phases (time spent at depth between the end of descent and the beginning of ascent) of dives, but local search most commonly occurred during bottom phases. Location data from five seals were detailed enough to allow analysis of three-dimensional movements within individual dives. Behaviors were defined for the dives of these five seals based on the character of movements within the dives. Ringed seal dives included horizontally convoluted, travel, and exploration dives, but vertically convoluted, rest, and sit-and-wait foraging dives were not observed. Horizontally convoluted (presumed foraging), travel, and exploration dive behaviors were defined with similar frequency for V-shaped dives (dives with only descent and ascent phases) and U-shaped dives (dives with descent, bottom, and ascent phases). The lack of behavioral differences between dives with distinct time-depth profiles suggested that time-depth profiles were not a reliable means of classifying behavioral dive types for ringed seals.
    • Spatial and temporal patterns in the Gulf of Alaska groundfish community in relation to the environment

      Mueter, Franz Josef; Norcross, Brenda L. (1999)
      The GoA supports a rich demersal fish community dominated by gadids, pleuronectids, sablefish (Anoplopoma fimbria) and rockfishes (Sebastes spp.). This study describes the structure of the juvenile and adult groundfish communities of the Gulf of Alaska (GoA) in relation to their environment and along spatial and temporal gradients. Abundance data were obtained from trawl surveys of juvenile groundfishes in the nearshore areas of Kodiak Island (1991--1996), shrimp-trawl surveys in the same areas (1976--1995), and triennial bottom trawl surveys of adult groundfishes on the GoA shelf and upper slope (1984--1996). Species richness, species diversity, total abundance, and multivariate indices of species composition for each station sampled were statistically related to depth, temperature, salinity, sediment composition, geographic location, and time of sampling to identify spatial and temporal patterns in community structure. The observed patterns were then related to local and large-scale atmospheric and oceanographic trends. Both juvenile and adult groundfish communities were primarily structured along the depth gradient. The abundance of juvenile groundfishes decreased with depth from 0 to 100m, whereas the abundance of adults increased with depth to a peak at 150--200m. Species richness and diversity of the adult community had a significant peak at 200--300m. Spatial patterns suggested higher abundances, lower species richness and diversity, and a different species composition of demersal fishes in the western GoA compared to the eastern GoA. These large-scale spatial patterns appear to be related to differences in upwelling between the eastern and western GoA. A 40% increase in total groundfish biomass on the GoA shelf and upper slope was estimated between 1984 and 1996. Significant changes in species composition occurred in the nearshore areas of Kodiak Island in the early 1980s, from a community dominated by shrimp and small forage fishes to one dominated by large piscivorous gadids and flatfishes. The change in species composition in the nearshore community appeared to be linked to an increase in advection in the Alaska Current. Increased flow around the GoA may enhance the supply of nutrients and plankton on the shelf and upper slope, resulting in an increase in overall productivity of the pelagic and demersal biota.
    • St. Lawrence Island polynya: Ice circulation and dense water production

      Glueck, Mary Frances Milkovich; Weingartner, Thomas J. (1999)
      The St. Lawrence Island polynya (SLIP) opens every winter off the coast of St. Lawrence Island as winds move ice away from the shore. The SLIP is an important site for production of the dense water that flows northward through the Bering Strait to help maintain the Arctic Ocean halocline. Winter 1991/1992 ERS-1 SAR, thermal infrared, and passive microwave imagery are analyzed in combination with regional climate system and analytical simulations to investigate SLIP ice circulation, heat fluxes, and dense water production. Emphasis is on the February 1992 southern SLIP event. Satellite-based measurements show this polynya extended ~165km offshore and ~100km along shore at maximum extent. ERS-1 SAR GPS-derived ice motion indicated maximum ice speeds of ~30km day -1 during polynya expansion. Ice along the polynya boundary drifted parallel to the wind at 3--4% of the wind speed during north/northeasterly winds >7m s-1 Heat fluxes associated with the SLIP varied depending on method of calculation, but indicated increasing trends during polynya development. Associated ice production rates of 4.218.9cm day-1 were computed via different models. Dense water production, derived from ice production rates and polynya size, ranged from 0.011--0.017Sv, suggesting that the SLIP could account for 19--27% of the Bering Sea's contribution and 1--2% of the total Arctic contribution to Arctic Ocean halocline maintenance. Although the regional climate system model generated the SLIP on the same time scales as observed, a larger polynya resulted. The simulated polynya's heat and moisture impact was observed to at least 800mb, reaching 50km downstream. During periods of sustained winds, ice circulation was similar to that observed. Incorporation of a "barotropic" ocean component suggested that ocean circulation may be an important ice circulation forcing mechanism at the SLIP, especially during periods of weak winds, as inclusion greatly improved the simulated ice circulation. The "barotropic" ocean also improved polynya shape and extent. If regional climate changes alter the existence of polynyas like the SLIP, changes in the Arctic Ocean halocline might occur. Additional in situ observations and better fully-coupled atmosphere-ice-ocean models are needed to further ascertain the impact of polynyas on the overall Arctic climate system.
    • Physiology of the endocrine, cardiorespiratory and nervous systems in pinnipeds: Integrative approach and biomedical considerations

      Zenteno-Savin, Tania; Castellini, Michael A. (1997)
      This thesis explored several aspects of the hormonal and cardiovascular physiology in pinnipeds (seals and sea lions). Plasma concentrations of the vasoactive hormones angiotensin II (Ang II), arginine vasopressin (AVP, the antidiuretic hormone) and atrial natriuretic peptide (ANP) were studied in six species of seals and sea lions. Resting levels of AVP, ANP and Ang II in these pinnipeds were similar to those reported for other vertebrate species, including humans. Age-related differences were found in the concentrations of these hormones in seals and sea lions. Geographic differences in hormone concentrations were found in Steller sea lions and harbor seals. To address the endocrine and cardiovascular responses to breath-holding (apnea) in marine mammals, heart rates and plasma levels of Ang II, AVP and ANP were studied in Weddell seal (Leptonychotes weddellii) and northern elephant seal (Mirounga angustirostris) pups during periods of spontaneous breathing (eupnea) and apnea. Ang II, AVP, and ANP, as well as the autonomic nervous system, were found to contribute differently to the control of heart rate in seal pups, depending whether the respiratory system was in eupnea or apnea. Because of changes in seals of different ages, it appeared that the integration of cardiorespiratory and hormonal function is not fully mature at birth, but develops post-natally, probably simultaneously to the development of diving behavior. These studies also suggested that the factors affecting cardiorespiratory function, including hormones, may differ by species. Plasma concentrations of AVP, ANP and Ang II were measured during food limitation and fasting in captive Steller sea lions (Eumetopias jubatus) and compared to levels in free-ranging conspecifics. The results suggest that Steller sea lions have a remarkable capacity to maintain hydrosmotic and endocrine balance during short-term food limitation and fasting. Hormonal studies did not provide conclusive evidence that Steller sea lions in Alaskan waters are currently affected by long-term food limitation.
    • Biological impacts and recovery from marine disposal of metal mining waste

      Kline, Edward R. (1998)
      Waste from coastal, metal mining operations may be disposed of in the ocean. Studies were conducted using tailings and wastewater (effluent) from a proposed gold mine that is located near Juneau, Alaska, USA. The ability of invertebrates to colonize tailings after obliteration by submarine tailings disposal (STD) was assessed through a field experiment. Trays of tailings and reference sediment were placed on the sea floor and retrieved over a 22 month period. The taxonomic composition, abundance, and biomass of invertebrates that colonized tailings and reference sediment were similar. Therefore, recolonization of invertebrates after obliteration by STD should not be inhibited by the presence of these tailings as a bottom substrate. In a laboratory study, the toxicity of effluent from the milling process was compared for early life stage fish and crustaceans. Common reference species and species that are indigenous to southern Alaska were exposed to effluent. The relationship between effluent concentration and organism response was established for immobilization, paralysis, and death. For each response, the sensitivity of the reference species bracketed that of the indigenous species. An overall ranking of species sensitivity could not be made because it depended on the response that was compared. The source of effluent toxicity was determined for one of the reference species, a crustacean. A simulated effluent was created to duplicate the ionic composition of the actual effluent. Toxicity was compared in effluent, effluent with increased salinity, simulated effluent, and solutions with adjusted concentrations of ions. Calcium was in excess in the effluent, relative to seawater, and was isolated as the source of toxicity. Sodium deficiency in the effluent, relative to seawater, reduced calcium toxicity.
    • Investigations of health status and body condition of harbor seals (Phoca vitulina) in the Gulf of Alaska

      Fadely, Brian Scott; Castellini, Michael A. (1997)
      Harbor seal (Phoca vitulina) declines during the past 20 years in the Kodiak Island and Prince William Sound regions contrast with stable or slightly increasing populations in southeastern areas of Alaska. Aspects of health status and body condition were investigated to test the hypothesis that these declines were driven by nutritional limitation, and to determine whether recent differential population trajectories among Kodiak Island, Prince William Sound, and southeast Alaska could have health-related components. For comparisons between 1992-96, three aspects of health status were examined; blood chemistry, blubber distribution and quantity; and blubber quality. Clinical ranges of plasma chemistries and hematologies were established for free-ranging seals in the Gulf of Alaska. Significant handling, individual, and seasonal effects were found on many blood parameters that could bias interannual and interregional comparisons if not incorporated in models. Based on statistical modeling, some seals showed more clinically aberrant values than expected by chance, but these were not clumped among regions or years. Differences existed in interannual blood chemistry and hematology patterns between juveniles and adults. Likewise, there were regional differences in blood chemistries of unknown significance. Morphometric indices were poor indicators of condition defined as size-at-age or blubber content. This was related to patterns of blubber distribution and variability, which differed between males and females. Blubber quality, measured as lipid content, did not substantially vary seasonally or between geographic regions, but blubber from Prince William Sound was less hydrated than blubber from non-declining areas. There were no detectable differences in body condition of seals from the Gulf of Alaska sampled during 1963/64 (pre-decline), 1976-78 (during decline) and 1995-96. However, sample sizes were small and patchily distributed throughout locations and years. Thus, the likelihood of detecting body condition changes in response to environmental conditions was poor. Body condition was not substantially different among seals from Prince William Sound, Kodiak Island and southeast Alaska measured during 1993-96. However, interannual blood chemistry and body condition patterns were evident among Prince William Sound seals that may have been associated with environmental conditions.
    • Structure and growth of Pacific halibut otoliths: Identifying spatial and temporal variation

      Hagen, Peter Thomas (1997)
      Otoliths are polycrystals of calcium carbonate and protein that grow through the process of biomineralization within the otic capsule of teleost fish. Otoliths of Pacific halibut (Hippoglossus stenolepis) are routinely collected to provide age information, but other information has not been examined in detail. The purpose of this study was to investigate whether otolith structural patterns reveal information about otolith growth, and by inference, about fish growth and habitat during its early life. Variation in the increment widths of the first five annuli of adult halibut otoliths over a 26 year period were partitioned in two ways: the year the growth took place and the year-class to which the fish belonged. The year of growth explained temporal variation in the youngest ages and was attributed to changes in temperature which may influence recruitment success, while the year-class of growth explained temporal variation in older juveniles, but could reflect sampling bias. An analysis of microstructure increments indicated that relative otolith growth rate was an indicator of larval somatic growth. Young halibut from the Gulf of Alaska exhibited similar larval growth histories, though individual and nursery area differences were apparent. Specimens from the Bering Sea had slower larval growth rates than halibut from the Gulf of Alaska. Trace levels of strontium within otoliths were associated with ontogenetic changes of larvae and winter annuli formation of adults. Levels of potassium and sodium varied by nursery area of capture suggesting some utility for stock separation, though there was indication of significant interannual variation. The shape of the larval crystal within the otolith microstructure of young halibut was found not to be associated with nursery area of capture, and thus is not a good candidate as a stock separation tool. The high variation within individuals suggests that the shape of the crystal is not determined by external events. Overall, several patterns preserved in otoliths can provide insight into processes that influence the growth of halibut and distribution of individuals and these patterns can be recovered from adult fish. However careful interpretation is still required to separate meaningful information from spurious data.
    • Screw configuration effects during twin-screw extrusion of starchy and proteinaceous materials

      Gautam, Akhilesh; Choudhury, Gour S.; Hansen, Conly S.; Das, Debendra K; Kramer, Donald E.; Kelley, John K.; Smiley, Scott T. (1998)
      This study investigated the effects of screw configuration and feed composition during extrusion of starchy and proteinaceous materials. All experiments were carried out in a twin-screw extruder with a length/diameter ratio of 32:1. The screw speed, feed flow rate, and moisture content were 400 rpm, 12 kg/h, and 15%, respectively. Kneading block (KB) and reverse screw elements (RSE) were placed at different locations in the 200 mm experimental zone near the die, where the temperature was maintained at $\rm 150\sp\circ C.$ An on-line method for measurement of residence time distribution (RTD) in a food extruder was developed, tested, and validated. The technique was based on the electrical conductivity of the material in the die, which was altered by addition of an electrolyte tracer at the feed inlet. The change in current flow was measured as a proportional voltage response across a resistor. The on-line method correlated well with the established erythrosine dye method and precisely determined the effects of screw speed, feed flow rate, screw configuration on RTD. The effects of type, length and position of mixing elements and spacing between two elements on energy inputs, RTD, molecular changes of starch, and macroscopic extrudate characteristics were compared. The results showed that the specific mechanical energy (SME), mean residence time, and extent of starch breakdown were higher for screw profiles with RSE than that with KB. These parameters also increased with longer mixing elements, increased distance of the elements from the die, and with increased spacing between two elements. Specific thermal energy (STE) input showed opposite trend to that of SME. Die temperature was highest when the elements were placed at 0 mm from the die. Such a screw profile produced an extrudate with highest overall expansion and lowest apparent density. Radial expansion was highest with KB in the screw profile than with RSE. KB seemed to be the element of choice for maximizing radial expansion. Increasing mixing element length or spacing between two elements decreased product expansion. Hardness of the product decreased linearly with increasing radial expansion as shown by the breaking strength data. Changing feed composition by adding Arrowtooth flounder muscle decreased the SME input, increased STE and mean residence time. Hydrolysis changed the properties of Arrowtooth flounder muscle so much that it enhanced the expansion characteristics of starch in rice flour and improved extrudate texture.
    • Distribution of large calanoid copepods in relation to physical oceanographic conditions and foraging auklets in the western Aleutian Islands

      Coyle, Kenneth Orval (1997)
      Acoustic measurements and net sampling were used to estimate zooplankton abundance and biomass relative to water mass types and flow fields in the western Aleutian Islands during June and July, 1992 and 1993. Observations are interpreted relative to the distribution and abundance of least auklets (Aethia pusilla), which forage on zooplankton. Highest zooplankton biomass (up to 7 g m$\sp{-3}$) occurred during June 1992, in the pycnocline separating the upper mixed layer from the cold intermediate layer north of a front separating Bering Sea and Alaska Stream water. The large calanoid Neocalanus flemingeri had highest abundance but the larger Neocalanus cristatus accounted for most of the biomass. N. cristatus and N. flemingeri were absent south of the Bering Sea front, where the community was dominated by Neocalanus plumchrus and Eucalanus bungii. Auklets were foraging almost exclusively north of the Bering Sea front. Neocalanus spp. abundance in the upper mixed layer was much lower in July 1993, than in June 1992. Neocalanus occurred primarily in scattered aggregates near the pycnocline over Bering Sea Intermediate water and at the surface in Pacific water. Auklets shifted their foraging activities to passes and shelf areas among the islands, where tidally generated divergences and convergences upwelled and concentrated prey into patches in the mixed layer. Elevated densities of Neocalanus were observed in convergence zones in Delarov Pass and over a ridge south of Kiska Island. Convergence zones were identified by intense sound scattering from entrained bubbles and by deceleration of the horizontal velocity components in acoustic doppler current data, a record of current speed and direction beneath the vessel. Densities of auklet prey in the study area during June were apparently influenced by the position of the front between Bering Sea and Pacific water masses. The position of the front was influenced by Alaska Stream flow anomalies lasting for several years. Prey densities on the shelves and in the passes during July were influenced by tidal currents at spatial scales of tens of meters to ten kilometers and lasting one tidal cycle.
    • The development of diving behavior and physiology in juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica

      Burns, Jennifer Moss; Castellini, Michael (1997)
      The development of diving behavior and physiology in juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica was studied in order to determine the effects of age, body size, and condition on diving ability. During the austral summers of 1992, 1993, and 1994, the diving behavior of 39 pups and 15 yearlings was monitored using time depth recorders (TDRs). In addition, 26 pups were equipped with satellite-linked time depth recorders (SLTDRs) to track fall and winter diving behavior. Blood samples and morphological measurements were taken at each handling. Pups began to dive within two weeks of birth, and the mean dive depth, duration, and number of dives per day increased significantly over the next 10 weeks. During this period, the ability of pups to regulate physiological processes related to diving increased, as did their aerobic dive limit (ADL). Whereas diving behavior was determined primarily by age rather than mass in young pups, age had little effect on the diving behavior of pups older than 2 months (as determined from SLTDR records). Because seals were not handled after SLTDR deployment, the effects of mass could not be directly modeled in these pups. However, in yearlings, the ADL, and approximately 50% of the variation in dive behavior could be explained by differences in body size. Most dive parameters differed by time of day, and deeper and longer dives were more frequent in the afternoon period. The diel pattern was consistent with the hypothesis that pups were foraging throughout the day on vertically migrating prey species. In yearlings, dive patterns suggested that large individuals foraged primarily on shallow water prey, while smaller animals concentrated on deeper prey such as Antarctic silverfish. Tracking studies revealed that juveniles were capable of long distance movements, but suggested that they remained closer to the coastline than adults. The absence of obvious differences in dive behavior between regions suggested that juveniles were foraging on similar prey throughout the Ross Sea. While scat analyses confirmed this hypothesis, tissue stable isotope ratios suggested that some juveniles were feeding on different prey, or in different areas than adults.
    • The red king crab fishery: handling effects, bait efficiency, and pot behavior

      Zhou, Shijie (1996)
      Red king crabs (Paralithodes camtschaticus) are caught by pots in a male-only fishery in Alaska. The objectives of this research were: (1) to examine impacts of the commercial fishery on discarded female and sublegal male crabs; (2) to examine bait efficiency; (3) to document crab behavior to pots; and (4) to develop a model describing catch versus soak time. I estimated from observer data that 64.6% of crabs in the Bering Sea fishery were females and sublegal males; I simulated commercial crab handling procedures in the laboratory to test effects on discarded crabs. Although body damage increased significantly with increased handling, there were no significant effects on righting time, feeding rate, weight gain, carapace length increment, or survival. I examined the efficiency of five potential baits (squid, herring, mussel, king crab muscle, and king crab ovary) by observing chemoreception and feeding behavior of the crabs. Chemosensory threshold varied between $10\sp{-4}$ to $10\sp{-6}$ g.L$\sp{-1}$, and feeding threshold ranged from $10\sp{-2}$ to $10\sp{-3}$ g.L$\sp{-1}.$ Crabs were most sensitive to the extract of conspecific muscle, while herring was most effective in arousing feeding behavior. Little difference existed between males and females in chemoreception and feeding behavior. Behavioral responses of the crabs to crab pots were observed by time-lapse video. Crabs approached the pot from downstream, and 78.3% of crabs searched less than 90$\sp\circ$ before leaving or entering the pot. The entry success rate was 8.1%. Only large males could begin escape from the bottom panel. Crabs had difficulties in accessing the pot and in escaping from inside the pot. The standard pot appeared inefficient in catching legal males, while it retained many non-legal crabs. I constructed a general model to describe the relationship between catch and soak time for trap fisheries. The model is expressed as $C\sb{t}=ab+a(t-b)\ e\sp{-ct},$ where $C\sb{t}$ is the catch per trap haul at soak time t, and a, b, and c are parameters to be estimated. This model is suitable for both short and long soak times.
    • Seasonal sea ice, the cold pool and gadid distribution on the Bering Sea shelf

      Wyllie-Echeverria, Tina; Norcross, Brenda L.; Wooster, Warren S. (1995)
      The variability in winter seasonal sea ice cover, its impact on the summer hydrography of the Bering Sea shelf, and the consequences to the demersal distributional patterns of walleye pollock (Theragra chalcogramma) and Arctic cod (Boreogadus saida) were investigated. Winter ice conditions acquired by remote sensing techniques were compared to the following summer's hydrographic conditions and fish distributions acquired from fisheries surveys between 1972-1993. Linkages among atmospheric, oceanic, and biological interactions occurred on two scales, an interannual mode of warm or cold conditions and multi-annual regimes of warm, cold or mixed conditions. The southernmost extent of sea ice as measured along meridian 169$\sp\circ$W (P$\sb{\rm S}$) can be used to identify warm or cold conditions on the shelf. Warm conditions occurred when P$\sb{\rm S}$ extended southward, between 60$\sp\circ$-$57\sp\circ30\sp\prime$N, bottom temperatures were 3.8$\sp\circ$-4.6$\sp\circ$C and the subsurface cold pool of water extended eastward, between meridians 170$\sp\circ$-166$\sp\circ$W. Cold conditions occurred when P$\sb{\rm S}$ extended southward, between $57\sp\circ30\sp\prime$-56$\sp\circ$N, bottom temperatures were 1.2$\sp\circ$-3.0$\sp\circ$C and the subsurface cold pool of water extended eastward, between meridians 163$\sp\circ$-158$\sp\circ$W. During the 20 year time series of climatic conditions, three regimes occurred: a cold regime prevailed from 1972-1977, a warm regime from 1978-1984, and a mixed regime from 1985-1991. Age-1 and age-2 and older walleye pollock were primarily in the outer domain during cold conditions and in the middle and inner domain during warmer conditions. Arctic cod were present during cold conditions. Shifts in distribution of these species have ecosystem-wide consequences and can occur on either interannual scales or on the time-scale of regime shifts. Changes in the level of piscivorous predation on age-1 pollock, including cannibalism, occurred on the annual scale while prey species of seabirds and marine mammals fluctuated on the regime scale. Warm or cold summertime conditions were predictable from the previous winter's ice extent, which provides basic information on the level of environmental variability that affects biological systems and can be utilized in modeling this system. The results predict that older pollock will be concentrated in the outer domain following winters with extensive ice, information which could be useful to the fishing industry.