• Diet and movement of depredating male sperm whales (Physeter macrocephalus) in the Gulf of Alaska

      Wild, Lauren A.; Mueter, Franz; Straley, Janice; Sigler, Michael; Witteveen, Briana; Andrews, Russ (2020-05)
      Sperm whales (Physeter macrocephalus) remove fish from commercial fishing gear in high latitude foraging grounds. This behavior, known as depredation, occurs in the Gulf of Alaska (GOA) sablefish longline fishery and has increased in frequency and severity since the mid-1990s. Sperm whale foraging ecology and movements in the GOA are poorly understood but are important considerations to how depredation impacts fishery resources and whale behavior. The goals of this dissertation were to use stable isotope analysis to evaluate trophic connections between sperm whales and their prey, estimate the proportional contribution of various prey items to sperm whale diets, and use satellite tag data to evaluate movement and diving behavior of sperm whales in the GOA. Understanding isotopic variability in cetacean skin is important to evaluating dietary information from this tissue; thus, in chapter 1, I first analyzed the stable isotope ratios among layers of cetacean skin to determine how much variability there was within and across layers of cetacean skin. Results showed horizontal layers of cetacean skin to be significantly different isotopically, suggesting evidence of a dietary time series in layers of cetacean skin, where the innermost skin layer represents the most recent diet. These results were used in my second chapter to isolate the most recent diet of sperm whales from the inner layer of skin, and then to estimate proportional contributions of different prey to sperm whale diets. Results showed that the sperm whales sampled prefer sablefish, dogfish, skates, and rockfish, and that the proportional contribution of sablefish to sperm whale diets has increased over the past 15 years as depredation has increased in severity. Chapter three presented an analysis of twenty-nine satellite tags placed on depredating sperm whales in the GOA between 2007 and 2016 to explore movement and diving behavior and how these behaviors may be linked to prey preferences found in chapter 2. Tagged sperm whales in the GOA preferred the continental slope habitat and made long migrations along the slope toward Mexico and the Gulf of California, speeding up and switching behaviors from foraging to transiting when they left the GOA. Dive depths and durations exhibited individual variability and were significantly correlated to light levels, lunar cycles, sablefish fishery catch-per-unit-effort, and seafloor depth. Results suggest diving behavior tracks that of primary groundfish prey items, and dive depths become shallower in areas of high sablefish densities, as inferred from fishery catches, potentially reflecting depredation behavior. Together these results provide a much-improved understanding of the impact of depredation on sperm whale dietary preference, and show insights into the importance of the GOA as a foraging ground for endangered sperm whales.
    • Examination of saffron cod (Eleginus gracilis) population genetic structure

      Smé, Noël A.; Gharrett, Anthony; Mueter, Franz; Heifetz, Jonathan (2019-05)
      The Saffron Cod (Eleginus gracilis) is an abundant forage fish that inhabits the coastlines of the north Pacific and Arctic oceans. We examined Saffron Cod population genetic structure to provide a reference baseline in anticipation of human and climate-change alterations of the Arctic environment. Nine microsatellites were designed to describe the genetic compositions of and variation among 40 collections of Saffron Cod from four regions (northwestern Alaska, Gulf of Alaska, Sea of Okhotsk, and Gulf of Anadyr). The northwestern Alaska collections (Bering Sea, Norton Sound, and Chukchi Sea) exhibited little genetic divergence. The Gulf of Anadyr collection differed from other regions but was most similar to those of the northwestern Alaska region. The two collections within the Sea of Okhotsk (Sakhalin Island and Hokkaido Island) differed genetically, but not to the extent they did from other regions. The collections from the Gulf of Alaska (Kodiak Island and Prince William Sound) comprised a lineage that was distinct from all of the other collections, including the geographically adjacent northwestern Alaska collections. The absence of genetic structure among northwestern Alaska collections probably reflects their recent expansion into previously unavailable habitat that became available after the Last Glacial Maximum (~16,000 years ago). The divergence of the Gulf of Alaska lineage may have resulted from recurrent episodes of isolation from previous glaciations.
    • Paleoceanographic shifts in the Gulf of Alaska over the past 2000 years: A Multi-proxy perspective

      Boughan, Molly McCall; Finney, Bruce; Naidu, Sathy; Whitledge, Terry E. (2008-12)
      The Gulf of Alaska (GOA) is a dynamic region influenced by climate variability on time scales ranging from days to millennia. Recent regime shifts suggest interdecadal GOA primary productivity patterns, yet it is unclear whether such fluctuations extend beyond the instrumental record. This thesis examined the nature of prevalent climatic and oceanographic patterns before the twentieth century using several marine sediment core proxies for paleoproductivity and paleoceanography. Sediment cores were from two locations: Bay of Pillars, Kuiu Island, in southeast Alaska (56.63 ̊N, 134.35 ̊W), and a central midshelf location (GAK4) along the Global Ecosystem Dynamics (GLOBEC) Seward Line (59.25 ̊N, 148.82 ̊ W). Proxy data from these cores include: percentages of organic carbon, nitrogen and biogenic opal; organic carbon-to-nitrogen ratios; stable isotope ratios from sediment organic matter (δ13C and δ15N) and foraminifera tests (δ13C and δ18O); and foraminifera faunal analysis. Bay of Pillars proxy data suggest that the onset of the Little Ice Age (LIA) ca. 1200 AD coincides with pulses of decreased salinity and increased productivity. GAK4 proxy data indicate increased productivity and decreased terrestrial input over the past century; as well as fresher surface water was during the latter portion of the LIA (1716 – 1894) and positive Pacific Decadal Oscillation phases.
    • The reproductive biology and management of walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska

      Williams, Benjamin C.; Kruse, Gordon; Criddle, Keith; Dorn, Martin; Quinn, Terrance II (2018-08)
      Ecosystem-based fishery management (EBFM) entails treating resource allocation and management as elements of a comprehensive framework that accounts for ecological linkages. The goal of EBFM is to maintain ecosystem resiliency in a manner that provides for the services desired e.g., fishery catch, species abundance, economic viability. Historically fisheries have been managed on a per species basis with a general focus on increasing or decreasing harvest rates. This management strategy often excludes meaningful processes such as interactions with other species, environmental changes, and economic effects of management changes. One feasible path for implementation of EBFM is through enhancement of existing single-species fishery management models. Contemporary age-structured stock assessment models generally use an estimate of spawning stock biomass (SSB), i.e., the biomass of female spawning fish, to approximate stock reproductive potential (RP). This approximation inherently assumes a proportional relationship between SSB and RP. Maturity at age or at length is a key aspect of reproductive biology that is central to estimating both RP and SSB. As a sequential augmentation to a single species management model the relationships among body condition, population abundance, the probability of being mature, relative fecundity, and environmental correlates were examined for female walleye pollock Gadus chalcogrammus in the Gulf of Alaska. Maturity data were corrected for spatial sampling bias using a mixed-effects generalized additive model. Once corrected for spatial bias, relationships between maturity, ocean temperature, body condition, ocean productivity (in the form of chlrophyll-a), and population abundance were explored. Estimates of fecundity were updated through the processing of archived samples and were also examined with mixed-effects generalized additive models to explore relationships between the previously listed covariates. Multiple measures of RP were examined to explore differences between methods currently incorporated into the stock assessment and updated measures of total egg production and time varying maturity. Walleye pollock body condition is density-dependent, declining with population abundance. However, after accounting for the effects of length, age, location, year, chlorophyll-a concentrations, summer ocean temperature and sample haul, condition has a positive effect on the probability of a fish being mature. Similarly, condition has a positive effect on relative fecundity, after accounting for length, age, egg diameter, chlorophyll-a concentrations, winter ocean temperature and sample haul. A positive relationship is observed between depth-integrated summer ocean temperature and maturity and depth-integrated winter ocean temperature and fecundity. Chlorophyll-a concentrations have a dome shaped relationship with maturity, peaking at 2.3 mg/m⁻³, and a negative relationship with fecundity. Variations in body condition have a direct influence on the estimated RP of the fish stock through both differences in the maturation schedule and total egg production. Over some periods these updated estimates of RP differ from estimates of female SSB from the annual stock assessment. Alternative estimates of annual RP, particularly total egg production, may provide better estimates of annual reproductive output than spawning stock biomass. In addition, relationships to density-dependent and density-independent factors provide informative predictions that can be incorporated into stock assessment analyses. Inclusion of spatially explicit information for walleye pollock maturity has implications for understanding stock reproductive biology and thus the setting of sustainable harvest rates used to manage this valuable fishery. Additionally, because management decisions have economic as well as biological consequences a suite of management strategies were simulated to examine the economic viability of a proposed small-vessel walleye pollock fishery in Alaska state waters in the Gulf of Alaska. As a case-study for straddling stocks, an agent-based model was developed to examine a suite of available federal and state management strategies as they relate to the economic viability of a nascent Alaska state-waters trawl fishery for walleye pollock that may develop after a long history of parallel state and federal waters management. Results of alternative strategies were compared in terms of indicators, such as variance of catch and quasi-rent value. Given the input characteristics of these simulations, the management strategy that produces the best overall improvements relative to status quo involved a federal-waters management strategy that allows for community-based cooperatives and an open access strategy in state-waters. Agent-based models may be used to inform managers of the underlying dynamics of catches and revenues in order to avoid unintended consequences of management decisions and to improve the likelihood of attaining fishery management objectives. This dissertation provides incremental additions to our knowledge of walleye pollock reproductive biology its spatial and temporal dynamics, and environmental correlates that may serve as ecological indices. These indices, coupled with an improved understanding of the socio-economic examinations of fishery management changes through agent-based modeling, may assist in producing more holistic management strategies, such as EBFM.
    • Wasting disease and environmental variables drive sea star assemblages in the northern Gulf of Alaska

      Mitchell, Timothy James; Konar, Brenda; Iken, Katrin; Kelley, Amanda (2019-05)
      Sea stars are ecologically important in rocky intertidal habitats. The recent (starting 2013) sea star die-off attributed to sea star wasting disease throughout the eastern Pacific, presumably triggered by unusually warm waters in recent years, has caused an increased interest in spatial and temporal patterns of sea star assemblages and the environmental drivers that structure these assemblages. This study assessed the role of seven potential static environmental variables (distance to freshwater, tidewater glacial presence, wave exposure, fetch, beach slope, substrate composition, and tidal range) influencing northern Gulf of Alaska sea star assemblages before and after regional sea star declines. For this, intertidal surveys were conducted annually from 2005 to 2018 at five sites in each of four regions that were between 100 and 420 km apart. In the years leading up to the regional mortality events, assemblages were different among regions and were structured mainly by tidewater glacier presence, wave fetch, and tidal range. The assemblages after wasting disease were different from those before the event, and there was a partial change in the environmental variables that correlated with sea star structure. In these recent years, the environmental variables most highly correlated with sea star assemblages were slope, wave fetch, and tidal range, all of which relate to desiccation, attachment, and wave action. This indicates that the change in sea star density and structure by wasting disease left an assemblage that is responding to different environmental variables. Understanding the delicate interplay of some of the environmental variables that influence sea star assemblages could expand knowledge of the habitat preferences and tolerance ranges of important and relatively unstudied species within the northern Gulf of Alaska.