• Bioenergetic and economic impacts of humpback whale depredation at salmon hatchery release sites

      Chenoweth, Ellen M.; Atkinson, Shannon; McPhee, Megan; Criddle, Keith; Friedlaender, Ari; Heintz, Ron; Straley, Janice (2018-08)
      Since 2008, humpback whales have been documented depredating hatchery-produced juvenile salmon, a novel prey, at points of their release in Southeast Alaska. The objectives of this dissertation are to determine the spatial distribution, seasonal distribution, and frequency of humpback whale foraging at release sites, determine whether whale presence is affecting the economic productivity of hatchery operations, and compare the bioenergetic benefits for whales feeding on juvenile salmon at hatchery release sites relative to typical prey. Five hatchery release sites were monitored over six years during the spring release season for whale presence/absence, numbers, and behaviors. Linear models were used to determine that for coho salmon, cohorts with frequent humpback whale presence had lower marine survival than cohorts with less or no humpback whale presence, but this was not seen for chum or Chinook salmon. Over six years, these sites lost an estimated 23% of revenue from coho salmon totaling almost a million dollars per year in addition to increased rearing costs to mitigate whale predation. A process model was developed to compare the net energy gain for humpback whales foraging on krill, herring and juvenile salmon. Whales were found to feed profitably on krill and chum salmon where they occurred in dense enough distributions and on herring when large coordinated groups impeded the escape of prey. Coho salmon typically distributed too diffusely for humpback whales to recuperate the full energetic costs of engulfment, indicating that behaviors such as bubble net feeding may be essential for increasing prey aggregation to an energetically profitable level, or humpback whales may be feeding to mitigate energetic losses. As intraspecific competition increases due to recovery and or changes to prey resources, generalist humpback whales may expand feeding to exploit new and less profitable prey resources.
    • Characterizing the diet and population structure of lampreys Lethenteron spp. using molecular techniques

      Shink, Katie G.; López, Andrés; Murphy, James M. (2017-08)
      Lampreys contribute to the health of aquatic ecosystems and are targeted in both subsistence and commercial fisheries. Despite their ecological and commercial importance, the management and conservation of native lampreys have been largely overlooked. The goal of this study was to close current knowledge gaps of lamprey biology through the examination of Lethenteron spp. in Alaska. This study applied two molecular techniques, DNA metabarcoding and microsatellite genotyping, to (1) characterize the diet of marine-phase Arctic lamprey Lethenteron camtschaticum (N = 250) in the eastern Bering Sea and (2) investigate the population structure of larval lampreys Lethenteron spp. (N = 120) within and among three Yukon River tributaries. A combination of visual observations and DNA metabarcoding revealed the presence of diagnostic structures/tissues (i.e., eggs, fin[s], internal organs, otoliths, and vertebrae) and detected DNA sequences of ten ray-finned fishes in the diets of L. camtschaticum. The most frequent prey taxa were Pacific sand lance Ammodytes hexapterus, Pacific herring Clupea pallasii, gadids, and capelin Mallotus villosus. Five of the ten taxa identified in this study were reported for the first time as prey for L. camtschaticum. To investigate the genetic diversity of larval lampreys, a recognized knowledge gap for populations in Alaska, a total of 81 larval lampreys were successfully genotyped at all loci. Global FST of larvae was 0.074 (95% CI: 0.042 - 0.110), while pairwise FST values among the three localities examined ranged from 0.066 - 0.081. Hierarchical model-based Bayesian clustering analyses detected three genetic clusters (K = 3) among all larval lampreys and two genetic clusters (K = 2) among Chena River larvae; no further genetic clustering was identified within the remaining two tributaries. Estimates of contemporary gene flow indicated reciprocal migration among sites. The diet analyses indicated anadromous L. camtschaticum function as flesh-feeding predators that prey upon pelagic fishes in the eastern Bering Sea, while genetic analyses suggested that larval lamprey aggregations within three Yukon River tributaries exhibited higher levels of genetic diversity than are typically found among broad-ranging populations of anadromous lamprey species. Ultimately, this study highlighted the value of molecular techniques to improve our understanding of the biology of a poorly studied fish species in Alaska.
    • Diets of four eelpout species (genus Lycodes) in the U.S. Beaufort Sea based on analyses of stomach contents and stable isotopes of nitrogen and carbon

      Apsens, Sarah J.; Norcross, Brenda; Iken, Katrin; Mueter, Franz; López, Andres (2017-12)
      Eelpouts of the genus Lycodes are an abundant group of demersal fishes in the U.S. Beaufort Sea. Currently eelpout diet and the exact role of eelpouts in the Arctic food web are poorly understood. Additionally, if and how eelpouts avoid intra- and interspecific competition for resources is unknown. In this study, diets of four common Beaufort Sea eelpout species were analyzed with respect to along-shelf (longitude) gradients, across-shelf (depth) gradients, and ontogeny (fish body length) to determine diet composition and patterns of resource partitioning. Diets of the four most numerous eelpout species were analyzed using a combination of stomach contents and nitrogen and carbon stable isotope analyses: Adolf's Eelpout Lycodes adolfi, Canadian Eelpout L. polaris, Archers Eelpout L. sagittarius, and Longear Eelpout L. seminudus. Nitrogen stable isotopes of fish tissue were analyzed to determine trophic level and carbon stable isotopes to determine if origin sources of carbon in food web pathways of eelpout diets differed among species. Fishes were collected in the central (2012) and eastern (2013 and 2014) Beaufort Sea in August and September as part of the U.S.-Canada Transboundary program. Prey groups Polychaeta, Amphipoda, Isopoda, Ophiuroidea, and Copepoda composed a large proportion of the diet by percent weight for all four species of Lycodes, but their relative contributions differed among the species examined. This study indicated that eelpouts feed almost exclusively on benthic prey and avoid interspecific competition by occupying different habitat space and having different diets. Intraspecific similarity in diet composition was low suggesting these fish have diverse diets even among individuals of the same species. Fish length was associated with changes in diet composition for L. adolfi and L. sagittarius, but not L. polaris and L. seminudus. Longitude and depth were correlated with shifts in diet composition for L. sagittarius, but not the other three species. Lycodes polaris occupied a lower trophic level than the other three eelpout species based on nitrogen stable isotope values. Despite differences in the across-shelf distribution between L. polaris and the three deep-water eelpout species, carbon sources of diet were indistinguishable among the four eelpout species. Ecological information on abundant Arctic fish species like eelpouts is needed for long-term ecosystem monitoring, which is especially important in light of pronounced climate changes and increased human activities in the Arctic.
    • Estimating sizes of fish consumed by ice seals using otolith length-fish length relationships

      Walker, Kelly; Norcross, Brenda L.; Brown, Randy; Lopez, Andres; Quakenbush, Lori (2017-12)
      Arctic fishes and ice seals are key components of the Alaskan Arctic ecosystem. Bearded (Erignathus barbatus), spotted (Phoca largha) and ringed (Pusa hispida) seals are consumers of Arctic marine fishes. Little is known about the sizes of fish that ice seals consume because prey items are digested quickly once exposed to stomach acids. Otoliths, fish ear bones, are often the only parts of a fish that remain in a seal stomach. Otolith length relates directly to fish length, making size estimations of consumed fish possible for piscivore diet studies. Otoliths were measured from fishes collected from cruises in the Beaufort and Chukchi seas during 2009 - 2014. Otolith length - fish length and fish length - fish weight relationships were developed for 11 Arctic marine fish species that are commonly consumed by ice seals in Alaska. Otoliths from seal stomachs provided by subsistence hunters to the Alaska Department of Fish and Game were identified to species level and measured for total length. A mixed effects model was used to determine how the variables of seal species, harvest location, seal age class and sex influenced the sizes of fish consumed. Harvest location and seal age class were the primary factors that affected fish size in ice seal stomachs. Estimating length and weights of fishes consumed by ice seals will help further diet and energetics studies that have not previously been possible in the Alaskan Arctic.
    • Feeding ecology of larval and juvenile walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) in the Southeastern Bering Sea

      Strasburger, Wesley Wayne; Hillgruber, Nicola; Pinchuk, Alexei; Mueter, Franz (2012-08)
      Poor recruitment success during warm years (e.g., 2001-2005) was hypothesized to lead to reduced gadid recruitment in the southeastern Bering Sea. These groundfishes are of particular importance, both commercially and ecologically in the southeastern Bering Sea. The spatial and temporal overlap of early life stages of walleye pollock and Pacific cod may explain their strongly correlated recruitment trends in the southeastern Bering Sea. The goal of this study was to compare feeding patterns of larval and juvenile walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea, and to assess the possibility of prey resource competition. Larvae and juveniles from both species collected between May and September 2008, an exceptionally cold year, were used to analyze stomach contents. Fish body size was most consistently related to diet composition within species, however, spatial and depth factors also had an influence. Feeding success and diet composition of these two gadid species were consistently different throughout the spring, summer, and especially fall seasons. Pacific cod larvae and juveniles consistently consumed larger prey items in every season and progressively fewer prey items, especially in the fall. This data suggests that competition for prey resources was unlikely during cold 2008.
    • Fifty years of Cook Inlet beluga whale ecology recorded as isotopes in bone and teeth

      Nelson, Mark A.; Wooller, Matthew J.; Iken, Katrin; Quakenbush, Lori T. (2017-12)
      Beluga whales (Delphinapterus leucas) are found across the Arctic and Subarctic in seasonally ice covered waters. Five stocks of beluga whales are associated with the waters near Alaska for at least part of the year and four of those five stocks are abundant and commonly hunted by Alaskan Natives. The belugas resident in Cook Inlet are also an important cultural and subsistence resource to Alaskan Natives in the area, but a ~50% decline in abundance in the 1990's led to the stock being designated as depleted under the Marine Mammal Protection Act in 2000 and listed as endangered under the Endangered Species Act in 2008. Numerous studies of beluga whales in relation to stranding events, predation (killer whales), parasitism, disease, contaminants, and other potential population threats have not identified the reason for their inability to recover. Changes in diet have been considered, but are difficult to study because observations of feeding in muddy water and beluga stomachs are difficult to obtain. To investigate the past feeding ecology of beluga whales from Cook Inlet I sampled bone and teeth for isotopic analyses. I sampled bone from 20 individuals that died between 1964 and 2007 for stable carbon and nitrogen isotope analysis (values expressed as δ¹³C and δ¹⁵N values). I also micro-sampled annual growth layer groups in the teeth of 26 individuals representing the years from 1962 to 2007. Bone and tooth data showed a general decrease in δ¹³C and δ¹⁵N values over time. The δ¹³C values from analyses of growth layer groups declined from -13.4‰ to -16.2‰ and δ¹⁵N values declined from 17.2‰ to 15.4‰. Although these values are consistent with a change in feeding ecology over time, the magnitude of the decrease in δ¹⁵N values (~2‰) is insufficient for a full trophic level shift (~3‰).The relatively large decrease in the δ¹³C values over the same time period (~3‰), however, is much greater than a full trophic level shift (~1‰) and suggests an increase in prey associated with freshwater, which typically have lower δ¹³C values than prey associated with marine water. To test this hypothesis I analyzed the strontium isotope composition (⁸⁷Sr/⁸⁶Sr ratios) of growth layer groups in teeth from a sub-set of individuals. The resulting ⁸⁷Sr/⁸⁶Sr ratios trended away from the global marine signature (0.70918) over time and toward the more freshwater signatures measured in rivers flowing into the upper reaches of Cook Inlet. These results indicate that the diet of Cook Inlet beluga whales has changed over time. This could be from feeding on different, more freshwater derived prey species, or from feeding on the same species, but on individuals from locations with a more freshwater influence. Both of these interpretations are consistent with population survey data indicating a retraction in beluga range into the upper reaches of Cook Inlet. This study presents the first evidence of a long term (~50 years) change in Cook Inlet beluga whale feeding ecology. The consequences of this change toward more freshwater-influenced prey, and how this change relates to Cook Inlet beluga whales' decline or recovery remains unknown. However, to better examine this change in feeding ecology a follow-up study will; 1) develop a strontium isoscape for the Cook Inlet watershed; 2) analyze more teeth to better analyze changes in feeding ecology by demographic group (sex, age); and 3) analyze growth layer groups from Bristol Bay beluga teeth for a comparison with Cook Inlet belugas to determine if the changes represent an ecosystem change within Cook Inlet or a broader scale change affecting another region. This study builds towards a better understanding of the changes in Cook Inlet beluga feeding ecology and will help to determine if changes in diet could be a factor in their recovery.
    • Insight into the diet history of ice seals using isotopic signatures of muscle tissue and claws

      Carroll, Sara Shanae; Norcross, Brenda; Horstmann-Dehn, Larissa; Quakenbush, Lori; Wooller, Matthew (2012-05)
      Climate change and sea ice reduction in the Arctic may impact foraging of ice-associated predators. The goal of my thesis work was to examine interannual differences in the diet of ringed, bearded, spotted, and ribbon seals as described by stable nitrogen and carbon isotope ratios of muscle tissue and claws to assess foraging plasticity. Isotopic mixing models from muscle data were used to describe the proportional contribution of prey groups during 2003, 2008-2010. Results showed a higher proportional contribution of smelt (Osmeridae) and benthic prey to ringed and bearded seal diets in 2003 compared to 2008-2010. Seasonal keratin layers deposited in claws can document trophic history up to about 10 years. During 2007 (record ice minimum), proportionally more ringed seals fed at a lower trophic level, while spotted seal adults and young-of-the-year fed at a lower trophic level during 2006. Bearded seals may have been foraging more pelagically from 2008 to 2010. Ice seals may be taking advantage of more abundant pelagic crustaceans as the Arctic ecosystem changes to a pelagic-dominated food web. Interannual variations and high variability among species and individual diets illustrate the opportunistic nature and flexibility of ice seals to changes in prey composition.
    • Pacific sleeper sharks in the Northeast Pacific Ocean: relative abundance, plausible incidental exploitation rates, trophic ecology, and habitat use

      Courtney, Dean Louis; Adkison, Milo D.; Foy, Robert; Sigler, Mike; Criddle, Keith R.; DiNardo, Gerard (2017-12)
      Pacific sleeper shark relative abundance indices in the eastern Bering Sea and Gulf of Alaska were developed from sablefish longline surveys and the sustainability of a plausible range in Pacific sleeper shark incidental exploitation rates in the Gulf of Alaska was evaluated with a risk analysis using Monte Carlo simulation for use in fisheries management. A significant increase in Pacific sleeper shark relative abundance was identified in the Gulf of Alaska during the years 1989-2003. The aggregate risk of ending in an overfished condition in the Gulf of Alaska increased from 0% under a low exploitation rate scenario to 59% under a high exploitation rate scenario. Baseline information about Pacific sleeper shark trophic ecology and habitat utilization in the eastern Bering Sea and Gulf of Alaska was developed for use in ecosystem-based fishery management. Analysis of stable isotope ratios of nitrogen (δ¹⁵N) and lipid normalized carbon (δ¹³C′) identified significant geographic and ontogenetic variability in the trophic ecology of Pacific sleeper sharks in the eastern Bering Sea and Gulf of Alaska and revealed wider variability in the feeding ecology of Pacific sleeper sharks than previously obtained from diet data based on stomach contents alone. Time series analysis of Pacific sleeper shark electronic tag data from the Gulf of Alaska identified a simple autoregressive relationship governing short-term movements (hours) throughout the time series which included substantial variation in longer time period movement patterns (months) and demonstrated that statistical inference about habitat utilization could be drawn from simultaneous analysis of an entire time series depth profile (six months of data) stored on an electronic archival tag.