• Seasonal and interannual patterns of larvaceans and pteropods in the coastal Gulf of Alaska, and their relationship to pink salmon survival

      Doubleday, Ayla; Hopcroft, Russell; Gradinger, Rolf; Coyle, Kenneth (2013-12)
      Larvacean (=appendicularians) and pteropod (Limacina helicina) composition and abundance were studied with physical variables each May and late summer across 11 years (2001 to 2011), along one transect that crosses the continental shelf of the subarctic Gulf of Alaska and five stations within Prince William Sound (PWS). Collection with 53-µm plankton nets allowed the identification of larvaceans to species: five occurred in the study area. Temperature was the driving variable in determining larvacean community composition, yielding pronounced differences between spring and late summer, while individual species were also affected differentially by salinity and chlorophyll-a concentration. During the spring Oikopleura labradoriensis and Fritillaria borealis were most abundant and present at all stations. Late summer had highest abundances of O. dioica at nearshore stations, while F. borealis dominated numerically at outer stations. The 53-µm plankton nets collected higher abundances of Oikopleura spp., Fritillaria spp., and L. helicina than coarser 150 and 505-µm plankton nets. Limacina helicina abundance had a significant interaction effect among years, seasons and station location. Limacina helicina abundance in nearby PWS explained 30% of the variability in pink salmon survival; however, no significant correlations existed with larvacean or L. helicina abundances from the Gulf of Alaska stations.
    • Seasonal distribution of Steller sea lions (Eumetopias jubatus) in relation to high-quality ephemeral prey species in southeastern Alaska

      Womble, Jamie Neil (2003-08)
      Energetic demands are high for sea lions during spring when females are pregnant and lactating and males are preparing for extended fasting during the breeding season. Therefore, I predicted that the distribution of sea lions in spring would be influenced by the distribution of spring-spawning aggregations of high-energy Pacific herring (Clupeapallasii) and eulachon (Thaleichthys pacificus) in southeastern Alaska. Monthly aerial surveys at 23 Steller sea lions haul outs revealed that haulout use was seasonally dynamic. Some sea lion haulouts were only occupied during spring. Other haulouts exhibited pronounced increases in the number of sea lions during certain seasons. Sea lion haulouts with peak numbers of sea lions in spring were significantly closer to forage fish aggregations than haulouts with peak numbers of sea lions at other times of year. From March through May 2002, I used aerial surveys to monitor the number of Steller sea lions at spring spawning aggregations of Pacific herring and eulachon. The maximal numbers of sea lions observed were 949 at a eulachon-spawning site and 252 at a herring-spawning site. Seasonal pulses of high-energy food resources may be critical to the reproductive success of individual Steller sea lions.
    • 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.
    • Seasonal movement patterns and habitat occupancy of Kotzebue region inconnu

      Smith, Nicholas J.; Sutton, Trent; Seitz, Andrew; Zimmerman, Christian (2013-12)
      Inconnu Stenodus leucichthys are large, long-lived piscivorous whitefish harvested in subsistence and sport fisheries in Alaska. My study was conducted to describe the seasonal movements and habitat occupancy of inconnu in the Selawik and Kobuk River drainages, Alaska, from 2010 through 2012. Methods consisted of surgically implanting acoustic telemetry tags in 80 fish from both rivers in 2010 and 2011 (n = 320), and deploying a fixed array of 20 Vemco VR2W acoustic receiving stations affixed with archival tags throughout Selawik Lake and Hotham Inlet. Tagged inconnu detections revealed that Selawik and Kobuk River inconnu displayed a high degree of spatial and temporal overlap while co-located in the Hotham Inlet/Selawik Lake complex. During the winter period, tagged fish predominately occupied the northern end of Hotham Inlet. In the summer period, fish transitioned from the northern end of Hotham Inlet to Selawik Lake and also the southern end of Hotham Inlet. Average daily displacements for Selawik and Kobuk River inconnu ranged from 2,000 to 10,000 m/day. Water temperature and salinity occupancy ranged from -1.39 to 18.69°C and 0 to 31.3 psu, respectively. No stock-specific or temporal trends in temperature and salinity occupancy by inconnu from the Selawik and Kobuk rivers were detected during my study. In addition to providing a more complete account of the life history of inconnu, these results will aid managers in developing future management strategies.
    • Seasonal movements and habitat use of rainbow trout in the Susitna River basin, southcentral Alaska

      Fraley, Kevin Marshall; Falke, Jeffrey; McPhee, Megan; Prakash, Anupma (2015-12)
      Potamodromous Rainbow Trout are an important ecological and recreational resource in freshwater systems of Alaska, and increased human development, hydroelectric projects, declining Pacific salmon stocks, and climate change may threaten their populations. We used aerial and on-the-ground telemetry tracking, field-measured and remotely-sensed aquatic habitat characteristics, snorkel surveys, and resource selection and occupancy models to characterize seasonal movements and habitat use of adult Rainbow Trout (>400 mm FL) at multiple spatial and temporal scales across the large (31,221 km²) and complex Susitna River basin of southcentral Alaska during 2003-2004 and 2013-2014. We found that trout overwintered in mainstem habitats near tributary mouths from November to April. After ice-out in May, trout ascended tributaries up to 51 km to spawn, and afterward moved downstream to lower tributary reaches to intercept egg and flesh subsidies provided by spawning salmon in July and August. Trout transitioned back to mainstem overwintering habitats at the onset of autumn when salmon spawning activity waned. Fidelity to tributary of capture varied across seasons, but was high in three out of four drainages. Different habitat characteristics influenced Rainbow Trout habitat use during each season, including stream gradient and sinuosity in the winter, substrate suitability and sinuosity during spawning, mean annual flow during the pre-salmon feeding season, and Chinook salmon spawning potential after the arrival of adult salmon in freshwater. We found that during the ice-free feeding season trout responded to fine-scale (channel unit) characteristics rather than more coarse-scale (stream reach) variables. Weekly movements were significantly longer when spawning salmon were present compared to pre-arrival. We found no difference in movements and habitat use for a subset of fish for which sex was identified using genetic analysis. However, the observed sex ratio was heavily female-biased, which contrasts with what has been observed in other non-anadromous salmonid populations. As most trout undertake extensive movements within and among tributaries and make use of a variety of seasonal habitats to complete their life histories, it will be critical to take a broad and multiscale approach to their management in light of anticipated future land use and climate change.
    • Seasonal movements of arctic grayling in a small stream on the Arctic Coastal Plain, Alaska

      Heim, Kurt C.; Wipfli, Mark; Seitz, Andrew; Falke, Jeffrey (2014-08)
      In watersheds of the Arctic Coastal Plain (ACP) of Alaska, Arctic Grayling adopt a migratory life history strategy to persist in a landscape with long (~ 8 month), cold winters that cause shallow aquatic habitats to freeze solid. We investigated movement patterns of adult and juvenile Arctic Grayling in a shallow beaded stream (Crea Creek), a dominant headwater stream type on the ACP. From 2012–2013 Arctic Grayling (N = 1035) were tagged with passive integrated transponder tags and monitored using an array of stream-wide antennae. Migration into Crea Creek peaked immediately after ice break-up in the main channel of the study area. Fish caught within the stream in June were in relatively poor body condition compared to fish captured later in summer. In both years, fish entering the stream during high flow and colder temperatures swam farther upstream than those entering during low flow and warmer temperatures. Migration of adult fish out of the stream was most strongly correlated with decreasing stream discharge, whereas juvenile downstream migration occurred in two peaks and was negatively correlated to minimum stream temperature and discharge. Among juveniles, fish of larger size and higher body condition tended to emigrate earlier. These results indicate that the population level migratory response is strongly tied to seasonal changes in hydrology, though heterogeneity among individuals also influences the response to seasonal change. This work demonstrates the importance of environmental cues, and surface-water flow mediated connectivity during the open-water period, and provides information needed to identify susceptibilities of migratory fishes to climate change and petroleum development on the ACP.
    • Seasonal movements of northern pike in Minto Flats, Alaska

      Albert, Matthew L.; Sutton, Trent M.; Evenson, Matthew J.; Margraf, F. Joseph; Verbyla, David (2016-08)
      Northern pike (Esox lucius) is a large, long-lived piscivorous species that are harvested in sport and subsistence fisheries in Alaska. My study described the seasonal movements of northern pike that inhabit the Minto Lakes portion (Goldstream Creek drainage) of the Minto Flats wetland complex, Alaska, from May 2008 through January 2010. Very high frequency (VHF) radio tags (n = 220) were surgically implanted in northern pike in Minto Flats in May 2007, 2008, and 2009, and fish were relocated with fixed telemetry stations and aerial- and boat-based telemetry surveys. Radio-tagged northern pike displayed a distinct spring pre-spawning migration into the Minto Lakes study area, where they remained for the duration of the open-water season. A protracted out-migration occurred between late September and early December, with downstream movements peaking in November and October of 2008 and 2009, respectively. Radio-tagged fish present in the Minto Lakes study area during the open-water season overwintered exclusively in a 26-km reach of the Chatanika River from its confluence with Goldstream Creek upstream to the Murphy Dome Road access point. Daily movement rates were greatest during May and August. In addition to providing a better understanding of northern pike life history in Minto Flats, these results will aid managers and researchers by identifying critical habitats and providing information to better design future population assessment experiments.
    • Seasonal oceanographic influences on Pacific herring and walleye pollock distribution and abundance in nearshore embayments of Kodiak Island, Alaska

      Loewen, Mary E. (2007-08)
      The importance of Alaskan embayments as adult walleye pollock and Pacific herring habitat is unknown. Seasonal hydroacoustic and trawl surveys were conducted in three oceanographically distinct bays to correlate abiotic and biotic habitat factors with nearshore fish distributions around Kodiak Island. Relationships between fish densities and sea surface temperature and salinity, bottom depth, zooplankton density and diversity, bottom temperature and salinity, and water column stratification were analyzed through General Additive Models (GAMs). Bathymetry and temperature were consistently included as important habitat variables. Relationships between fish density and habitat variables differed by season and location, suggesting factors defining preferred habitat vary seasonally. Herring appear to prefer warmer, fresher surface waters associated with the Alaska Coastal Current. Mean pollock density increased between February and August, indicating the nearshore area is important summer habitat, while it is less important for herring after winter spawning. Pollock and herring utilize different horizontal and vertical areas of the bays, with pollock in deeper waters. Pollock separated vertically by size class, but no vertical separation was found for herring of different size classes. The range of size classes and high densities of both species suggest these previously unsurveyed areas are important pelagic fish habitat.
    • Seasonal reproductive endocrinology and anatomy of Steller sea lions (Eumetopia jubatus)

      Harmon, Heather Louise (2001-08)
      The decline of western Alaskan Steller sea lions (SSLs) may be related to changes in reproductive rates. However, our understanding of SSL reproductive biology is poor. My objectives were to determine if saliva samples are a valid alternative to plasma samples for measurements of peripheral progesterone and testosterone, to describe annual cycles of steroid concentrations, and to provide anatomical verification of reproductive endocrinology. Samples were collected from adult, captive and wild SSLs. Progesterone and testosterone concentrations in paired plasma and saliva samples were highly correlated (96% and 84%, respectively). Captive SSLs had seasonal variations in these steroids that did not follow typical pinniped patterns, suggesting that reproductive activity may be sensitive to social cues. The wwild SSLs exhibited steroid patterns similar to other seasonal breeders. Vaginal cytology could not be evaluated for detecting estrus because no samples were obtained during estrus. Testes volume was correlated to plasma testosterone concentrations (71%).
    • Seasonal thermal habitat use and bathymetric distribution of burbot in Tanada and Copper Lakes, Alaska

      Scannell, Heather L.; Sutton, Trent; Margraf, F. Joseph; Wuttig, Klaus (2016-12)
      Burbot Lota lota are a cold water, benthic, primarily piscivorous species that inhabits lakes and rivers throughout their Holarctic distribution. Habitat requirements for Burbot are still poorly understood, in part due to the disregard this species has received in fisheries management plans. From June 2009 through September 2011, I investigated the seasonal movements and bathymetric distribution of Burbot in Tanada and Copper lakes, Alaska, using archival tags programmed to record water depth and temperature. One hundred and forty Burbot (70 in each lake) were surgically implanted with archival tags, and 1 year later fish were recaptured to retrieve the archived data (Tanada Lake: 15 fish; Copper Lake: 9 fish). During the ice-out period in spring (mid-May through June), Burbot initiated a migration to the littoral zone (mean depth = 10.72 m; mean internal temperature = 9.4°C). In the summer months (July and August) when lakes were stratified and photoperiod was nearly constant, Burbot occupied the thermocline (mean depth = 7.28 m; mean internal temperature = 12.1°C). During fall months prior to the ice-up period (September and October), occupancy depth shifted to the profundal zone (mean depth = 22.09 m; mean internal temperature = 6.3°C). Under the ice, Burbot remained in the profundal zone and a putative spawning period was observed during February and March when Burbot from both lakes migrated from the profundal zone to ≤ 5 m in depth (mean internal temperature = 2.1°C). Throughout the year Burbot displayed a pattern of diel vertical movements with activity levels peaking during crepuscular hours. However, during the summer when photoperiod was nearly constant, Burbot were relatively sedentary, with only 22% of depth records indicating movement (changes in depth ≥ 1 m). Results from this study indicate that photoperiod and water temperature were highly correlated with seasonal depth occupancy and activity levels in Burbot.
    • 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.
    • Sensitivity to hydrocarbons and cytochrome P4501A enzyme activity in Arctic marine birds and waterfowl

      Riddle-Berntsen, Ann E.; Hollmén, Tuula; Buck, C. Loren; Aguilar-Islas, Ana (2017-12)
      The Arctic is host to a taxonomically diverse group of birds, including species of conservation and subsistence importance that spend many months of their annual cycle in the region. With prospects for oil and gas resource development and increases in vessel traffic in the Beaufort and Chukchi Seas, arctic birds could be valuable bioindicators to monitor contaminants and specifically hydrocarbons from crude oil. Using liver cytochrome P4501A (CYP1A) activity, I measured levels of hydrocarbon exposure in three bird species of subsistence importance: king eiders (Somateria spectabilis), common eiders (Somateria mollissima), and greater white-fronted geese (Anser albifrons). Over the course of three years, I collected liver samples during spring and fall hunts near Utqiaġvik (formally Barrow) and validated methods for both direct-take and opportunistic liver sampling. Enzyme activity results show significant differences in CYP1A activity levels among species, seasons, and years. Except birds collected during fall 2014, when significantly high enzyme activity was observed in all sampled species, all other collections resulted in median activity levels similar to those reported in other sea duck species in Alaska from un-oiled or non-industrialized habitats. I also used species-specific hepatocyte culture in a broader selection of arctic marine birds and waterfowl candidate bioindicators to assess and compare species CYP1A activity responses as a measure of sensitivity to hydrocarbons. Cytochrome P4501A results from hepatocyte cultures dosed with positive control reference reagents and Alaska North Slope crude oil showed differences in species responses. Based on sensitivity results, I recommend the common eider and common murre (Uria aalge) as bioindicators for use in CYP1A monitoring due to their consistent and measureable responses in our experiments. However, additional species are promising candidates (e.g., tufted puffin; Fratercula cirrhata) but further testing is needed. This is the first study of reference hydrocarbon exposure and comparative laboratory assessment of CYP1A inducing compounds for arctic marine birds and waterfowl and these results form the basis for hydrocarbon monitoring programs and risk assessments.
    • Six Thousand Years Of Change In The Northeast Pacific: An Interdisciplinary View Of Maritime Ecosystems

      Misarti, Nicole; Finney, Bruce (2007)
      The goal of this thesis is to develop long-term records of North Pacific ecosystems and explore relationships between change in marine ecosystems and prehistoric Aleut culture through soil chemistry, isotope analyses of lake cores, and isotope analyses of bone from archaeological middens. Chemical analysis of soils yielded differences in soils of various archaeological features as well as middens of varying composition. Sites that had no middens were chemically distinguishable from sites that did have middens helping to define resource consumption in the local region. An important result of this study is that no single ecosystem (nearshore benthic, coastal pelagic or deep-ocean pelagic) experienced the same changes in delta13C and delta 15N over the past 4,500 years. This suggests that changes in climate affected different ecosystems in unique ways. Only one change spans all species studied, the decrease in modern delta13C in comparison to delta13C of prehistoric specimens. According to these comparisons, the modern Gulf of Alaska may not be in the highly productive state that it was for the past 4,500 years, with the possible exception of the Medieval Warm Period. Lake core sediment analysis suggests an increase in salmon stocks in the Gulf of Alaska beginning ∼6,000 years ago, with a decrease during the Medieval Warm Period. In fact, salmon stocks in the Gulf of Alaska appear to be healthiest during periods of atmospheric cooler and wetter climate over the past 4,500 years. In comparing my paleoecological records to the archaeological record of the area it appears that humans were affected by changes in their environment but, even in relatively small numbers, humans also influenced local ecosystems for the past 6,000 years. By building on our understanding of long-term climate change and long-term fluctuations in ecosystems and trophic dynamics of species in the North Pacific, and through considering humans in the ecological context, we can better understand present conditions in marine ecosystems.
    • Small-scale variability in benthic food webs in the Northeastern Chukchi Sea

      Tu, Kelley Lannon; Blanchard, Arny; Horstmann-Dehn, Larissa; Iken, Katrin (2013-08)
      Benthic food web structure can differ over large scales across Arctic shelves in relation to hydrographic conditions, but little is known if such differences also may occur on smaller scales in hydrographically complex areas. The length, food sources, trophic composition, and energy distribution of benthic food webs in three study areas in the northeastern Chukchi Sea (i.e., Klondike, Burger, and Statoil, as part of the Chukchi Sea Environmental Studies Program) were compared using stable isotope analysis and bomb calorimetry. Food web length (four trophic levels), food sources, and linear models of food webs were comparable among areas. Marked differences in food web structure were observed when trophic levels were quantified by benthic biomass and abundance. High proportions of biomass and abundance of trophic level 3 taxa at Burger were attributed to high deposition of refractory material. High proportions of trophic level 1 and 2 taxa at Klondike and Statoil reflected availability of fresh material. Burger could potentially present a rich foraging ground for some benthic predators due to especially high benthic prey energy densities. Findings emphasize that marine food webs can vary on small spatial scales in accordance with hydrographic conditions, particularly when quantitative trophic level distribution is considered.
    • Sound and human impacts on beluga whales in Cook Inlet, Alaska

      Blevins, Rachael E.; Atkinson, Shannon; Quinn, Terrance II; Murray, Maribeth; Lammers, Marc; Dahl, Peter (2015-12)
      Cook Inlet beluga whales (CIBs) are a geographically and genetically isolated population residing in Cook Inlet, Alaska year round. The population declined by approximately 50% between 1994 and 1998 and was listed as endangered under the Endangered Species Act in 2008. The original decline was attributed to overharvest; however, the population has failed to rebound despite the virtual absence of harvest since 1998. This suggests that other factors, such as declining prey availability, increased predation, contaminants, disease, climate change, catastrophic events, habitat loss, unauthorized take, and underwater noise pollution, may be limiting the population's recovery. The goal of this dissertation research was to study the potential impacts of underwater noise on the CIB population. The objective of Chapter 1 was to study CIB acoustic behavior to gain a greater understanding of how CIBs utilize sound. The objective of Chapter 2 was to measure underwater sound levels in Cook Inlet to understand the background noise levels with which CIBs must cope. The objective of Chapter 3 was to document reactions of CIBs to noise disturbance utilizing local ecological knowledge to allow insight into the potential impacts of noise on beluga behavior. The results of Chapter 1 showed that belugas exhibit significant seasonal and spatial variation in calling behavior which suggested differences in habitat usage or differences in the surrounding environment, including background noise levels. The results of Chapter 2 showed that root mean square sound pressure levels exhibited high variation with the highest levels recorded in the 100 Hz frequency band. The seasonal differences in sound levels observed in this study were likely due to greater small vessel traffic and oil and gas development activities in the summer than the winter. In Chapter 3, participants reported observations of CIBs exhibiting avoidance reactions to noise sources including boats, planes, explosions, pile driving, construction, and cars. The results of this chapter showed that noise is perceived to alter beluga behavior and possibly beluga distribution in Cook Inlet. This dissertation research showed that underwater noise has the potential to affect CIBs, however the cost of this impact remains unclear and warrants further study. In light of the lack of support for many of the proposed factors limiting the population and the need for further research for many of these factors, it would be valuable to consider the cumulative effects of these multiple stressors. While their potential impact may be small individually, when combined, these factors may have a synergistic and significant impact on individual whales and, in turn, on the CIB population. Management of cumulative effects may be necessary to ensure the recovery of this endangered population.
    • Spatial and temporal availability of Pacific salmon mediate compensatory growth in coastrange sculpin and sex-age specific spatial habitat use in brown bears

      Godin, Michael Joel; Tallmon, David; McPhee, Megan; Pyare, Sanjay (2017-05)
      Pacific salmon bring marine nutrients into freshwater ecosystems and provide food for countless species. Two major consumers of salmon along the Pacific coast are Coastrange Sculpin Cottus aleuticus and brown bears Ursus arctos. I examined the effects of salmon temporal availability on the growth rate of sculpin and the spatial use of habitat by brown bears. In a study on Coastrange Sculpin I found that treatment groups denied food, in the form of salmon eggs, for two or three weeks exhibited compensatory growth following resumption of feeding in the laboratory and field respectively. The compensatory growth response was mediated by stream of origin and temperature, controlled in the laboratory. Sculpin groups from different streams of origin had different overall growth rates in the laboratory despite being housed under identical conditions. At the end of the food-deprivation period, sculpin housed at 20°C exhibited a 5% greater weight loss compared to sculpin housed at 10°C. High temperatures (20°C) prevented compensatory growth in one treatment group and lengthened the catch up period for other treatment groups compared to those housed at moderate temperatures (10°C). In a study on brown bear spatial and temporal use of habitat in Berners Bay, Alaska, I found that brown bears use salmon when they are available and reproductive status of adult female bears affects use of this resource. Brown bears used space within 250 meters of salmon spawning reaches 50% more when salmon were present (69%) than when salmon were not present (19%) at spawning reaches. However, sex, age, and reproductive status all affected the use of space near spawning reaches. When salmon were available, adult females without cubs used space similarly to dominant adult males, while females with cubs used space similarly to subdominant juveniles. Adult females without cubs used space within 100 meters of spawning reaches 13% more than females accompanied by cubs. Salmon runs in Southeast Alaska are exhibiting reduced duration and earlier arrival of migration timing, reducing their temporal availability to consumers. Additionally, climate change is projected to increase temperatures throughout Southeast Alaska. Warmer temperatures resulting from climate change may improve digestion and growth for sculpin in colder streams, but could negatively affect the ability of sculpin to exhibit compensatory growth. Reduced salmon availability and increased human activity might lead to changes in behavior and dominance among brown bears feeding on salmon.
    • Spatial and temporal patterns of epibenthic community and food web structures in the Chukchi sea between 2004-2012

      Serratos, Carlos; Iken, Katrin; Bluhm, Bodil; Danielson, Seth (2015-12)
      The Chukchi Sea shelf, an area undergoing rapid environmental change and concurrently increasing human activity, supports communities of epibenthic organisms and food webs that are sustained by high primary productivity in the overlying water column and are influenced by physical environmental conditions. The goal of this study was to characterize these epibenthic communities (using trawl hauls) and benthic food webs (using carbon and nitrogen stables isotopes) in 2009 and 2012 and to identify persisting or changing patterns between 2004, 2009 and 2012 as part of NOAA's Russian-American long-term Census of the Arctic (RUSALCA) program. Fifteen stations each were sampled in August to September of 2009 and 2012 in the Chukchi Sea, of which eight repeat stations in the southern Chukchi were sampled in 2004, 2009 and 2012 for temporal comparisons. Epibenthic communities differed in structure between the northern and the southern study regions, with somewhat variable subgroupings within each of those larger regions between years. Overall biomass (mean 49680 ± 45510 g wet weight 1000 m⁻²) was dominated by echinoderms in particular at northern stations, followed by crustaceans. Repeat stations retained relatively consistent epibenthic community composition across sampling years, despite the at times drastic temporal variability in abundance and biomass. Point in time measurements of water column environmental variables (e.g., salinity, oxygen, temperature) were less strongly correlated to the epifaunal community structure than comparatively stable environmental measures (e.g., substrate type, depth, latitude). Benthic food web structure in the southern Chukchi Sea varied significantly and consistently between water masses in all study years, while δ¹⁵N and δ¹³C of pelagic particulate organic matter (PPOM) did not. This indicates that benthic consumers integrate the highly variable POM isotopic signatures and reflect long-term conditions. A persistent gap in δ¹⁵N values between PPOM and epibenthic consumers in nutrient-poor Alaska Coastal Water indicated that the majority of consumers in that water mass did not directly consume POM, which may undergo an additional trophic step of microbial processing before entering the benthic food web. In contrast, shorter food webs without this gap in the nutrient-rich Bering Sea Anadyr Water reflected tight pelagicbenthic coupling. The mostly consistent temporal patterns in epibenthic and food web structure compared to variable standing stock stress the importance of selecting multiple metrics for ecosystem monitoring. The data from this study may serve as a benchmark by which to measure a biological response to climate change and human impacts.
    • Spatial patterns, environmental correlates, and potential seasonal migration triangle of Arctic cod (Boreogadus saida) distribution in the Chukchi and Beaufort seas

      Forster, Caitlin; Norcross, Brenda; Mueter, Franz; Seitz, Andrew; Longerwell, Elizabeth (2019-05)
      Arctic Cod (Boreogadus saida) is a key forage fish species in the Arctic marine ecosystem and provides a critical energetic link between lower and upper trophic levels. Despite its ecological importance, spatially explicit studies synthesizing Arctic Cod distribution across a multitude of research efforts previously have not been conducted in the western portion of its range. I used spatial generalized additive models (GAM) to map the distribution of Arctic Cod by size class and relative to environmental variables. I compiled demersal trawl data from 21 research cruises conducted from 2004 to 2017 in the Chukchi and Beaufort seas, and investigated size-specific patterns in distribution to infer movement ecology of Arctic Cod as it develops from juvenile to adult life stages. High abundances of small, juvenile Arctic Cod (<70 mm total length) in the northeastern Chukchi Sea and western Beaufort Sea were separated from another region of high abundances in the eastern Beaufort Sea, near the US and Canadian border, suggesting possible population structure in the Pacific Arctic. In both the Chukchi and Beaufort seas, large, adult Arctic Cod (>130 mm total length) were found offshore and spatially segregated from small and medium (71-130 mm total length) fish, indicating an ontogenetic offshore movement of Arctic Cod as it matures. Relating environmental correlates to Arctic Cod abundance demonstrated that temperature and salinity were related to juvenile distribution patterns, while depth was the primary correlate of adult distribution. Furthermore, a comparison of spring and summer 2017 abundances of Arctic Cod in the southern Chukchi Sea, from the Bering Strait to Cape Lisburne found low abundance in the spring when compared to the summer. Differences in Arctic Cod abundance at different times of year suggest that Arctic Cod migrate seasonally, potentially following patterns of biological production in the Chukchi Sea. Arctic Cod migration may follow a classical 'migration triangle' route between nursery grounds as juveniles, feeding grounds as subadults, and spawning grounds as adults, in relation to ice cover and seasonal production in the Chukchi Sea. The analysis presented here is necessary to address federally mandated research requirements, which include improving understanding of stock structure and resolving essential fish habitat (EFH) for different life stages, as well as to gain better general understanding of the role of Arctic Cod in the Pacific Arctic.
    • Spatial trends and environmental drivers of epibenthic shelf community structure across the Aleutian Islands

      Bland, Aaron; Konar, Brenda; Iken, Katrin; Johnson, Mark; Zimmermann, Mark (2018-12)
      The continental shelf around the Aleutian Islands supports important commercial and subsistence fisheries as well as multiple seabird and marine mammal populations. To sustainably manage these populations, more information is needed on the distribution of the benthic communities that support some of the top level consumers. Given the vast size and highly variable physical environment of the Aleutian Islands, it is likely that epibenthic community structure on the continental shelf will vary by geographic area and physical and oceanographic conditions. This project examined spatial patterns in Aleutian epibenthic shelf communities among oceanographic regions (island groups separated by major oceanographic passes) and islands within these regions and identified environmental drivers responsible for important community divisions. Benthic trawls were conducted at 12 Aleutian islands across four oceanographic regions to characterize epibenthic shelf community structure along the island chain. It was tested whether the spatial variability in shelf community structure among regions and islands was correlated to multiple environmental variables including bottom water temperature, water depth, distance from shore, exposure, bottom rugosity, sediment grain size, sediment chlorophyll content, and drift algal food subsidies. Overall, communities differed both among regions and among islands within regions. Communities in the Far Western region (Near Strait to Buldir Strait) differed from communities in other regions, largely due to a high density of sand dollars in the Far West. However, none of the measured environmental characteristics explained this difference. Additionally, there was no evidence for a break in epibenthic shelf community structure across Samalga Pass between the East and the Central regions, even though Samalga represents a biogeographic break for many other Aleutian community types, including zooplankton, fish, and kelp forest communities. Within the Central region, a characteristic soft-sediment community (including the flatfish Atheresthes spp. and the crabs Labidochirus splendescens and Chionoecetes bairdi) distinguished Adak Island from other Central islands. Compared with groundfish trawl surveys conducted by the Alaska Fisheries Science Center (AFSC), this study captured less fish but more invertebrates by biomass, which is likely related to different gear selectivity used by the two studies. These findings provide information on the distribution of Aleutian shelf communities that complement existing information from AFSC surveys. In particular, it is shown that there is potentially an important division in epibenthic shelf communities across Buldir Strait, in agreement with the literature identifying this pass as an important biogeographic break. Furthermore, it is suggested that future assessments of Aleutian epibenthic communities should employ a combination of sampling gear types to better represent various epibenthic taxa.