• Marine-entry timing and growth rates of juvenile chum salmon in Alaskan waters of the Chukchi and northern Bering Seas

      Vega, Stacy L.; Sutton, Trent; Adkison, Milo; Murphy, James (2015-08)
      Recent climate change is most pronounced in the Arctic, with many implications for juvenile salmon life-history patterns, such as altered timing of migrations and/or timing and success of life-history stages. The objectives of this study were to determine the timing of marine entry and early marine growth of juvenile Chum Salmon Oncorhynchus keta in the Chukchi and northern Bering seas. Sagittal otoliths were collected from juvenile Chum Salmon in summers 2007, 2012, and 2013 via surface trawls in the southern Chukchi and northern Bering seas. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to discriminate between freshwater and marine environments, and daily growth increments were counted to determine marine-entry dates and growth rates of juvenile Chum Salmon to make temporal and regional comparisons of juvenile characteristics. Marine-entry dates ranged from mid-June to mid-July, with all region and year combinations exhibiting similar characteristics with respect to entry timing, i.e., larger individuals at the time of capture entered the marine environment earlier in the growing season than smaller individuals. Juvenile growth rates were estimated to be, on average, 4.9 % body weight per day in both regions in summers 2007 and 2012, and 6.8% body weight per day in the Chukchi Sea in 2013. This study shows consistent conditions among regions with respect to juvenile Chum Salmon marine-entry timing, with some variation in growth rates. These results provide a novel and more thorough evaluation of juvenile Chum Salmon early life-history characteristics in the Alaskan Arctic and provide a baseline for comparisons with future climate change studies.
    • Maturation of walleye pollock, Theragra chalcogramma, in the eastern Bering Sea in relation to temporal and spatial factors

      Stahl, Jennifer Paige (2004-12)
      Walleye pollock, Theragra chalcogramma, are both ecologically and commercially important in the eastern Bering Sea (EBS). Maturity is a critical parameter in the stock assessment to set annual total allowable catch. Pollock maturity has not been examined in the EBS since 1976, and possible interannual and geographic variation has not been studied to date. Our goal is to estimate correct maturity schedules for EBS pollock. Maturity data, fish lengths and macroscopic maturity stages were collected aboard pollock trawlers during winter 2002 and 2003 across the EBS from 10,197 pollock. Similar data were collected by NMFS scientists during hydroacoustic surveys from 1989-2002. Histological analysis of ovary tissue confirmed the appropriateness of macroscopic staging. However, some pollock classified macroscopically as 'developing' may mature either in the current or following spawning seasons. Therefore, our analysis was performed with two alternative assumptions: fish classified as 'developing' were either considered immature or mature. Maturity rates were estimated by logistic regression. Geographic variability exists; fish mature at the smallest lengths north of the Pribilof Islands. Size at maturity varies interannually, as well. Temporal and spatial variation in maturity may be due to biological or environmental factors, such as pollock density, water temperature, or prey availability.
    • Maturity, fecundity, growth, and sustained yield of coastal cutthroat trout at Florence Lake, Southeast Alaska

      Foster, M. Birch (2003-08)
      The resident coastal cutthroat trout Oncorhynchus clarki clarki population in Florence Lake, Southeast Alaska was sampled from July through October, 1997 to assess its maturity, fecundity, growth and sustained yield. Maturing female cutthroat have significant gonad development between mid September and late October. A gonadosomatic index threshold was established for female cutthroat trout. A logistic model for maturity estimated asymptotic percentages by age and length: 92% and 100% for males and 86% and 80% for females, indicating presence of skip spawning. Male cutthroat trout matured earlier and at smaller length than females, but females matured more rapidly. An allometric model fitted fecundity data well. Schnute's growth model indicated that growth was relatively slow. An ll-inch (279 mm) minimum size limit allows a high proportion of trout at Florence Lake to spawn at least once. Age-based and length-based per recruit analyses performed comparably and established sustainable fishing mortality estimates.
    • Mercury concentrations and feeding ecology of fishes in Alaska

      Cyr, Andrew Philip; López, Juan Andres; O'Hara, Todd; Wooller, Matthew; Seitz, Andrew (2019-05)
      Mercury (Hg) is a ubiquitous contaminant found in nearly every fish species analyzed. Certain forms of Hg accumulate efficiently in fish tissues, sometimes reaching concentrations of concern for human and wildlife health when consumed. This has motivated considerable research and interventions surrounding fish consumption with Hg concentrations as the underlying cause of over 80% of fish consumption advisories in the United States and Canada. The ecological and physiological drivers that influence the concentrations of Hg in fishes are complex and vary among taxa spatially and temporally. Studying these drivers and their respective influences on Hg concentrations can help elucidate observed differences in Hg concentrations across space and time, which can then be used to improve management and consumption strategies. Here I present a series of studies focused on the chemical feeding ecology of Hg by measuring total Hg (THg) concentrations and ratios of nitrogen and carbon stable isotopes in multiple fish species from three regions in Alaska. In Chapter 2 I described foundational field collection efforts to characterize the fish communities from West Creek and the Taiya River in Klondike Gold Rush National Historical Park, and the Indian River in Sitka Historical National Park, Alaska. This chapter and agency report presents a survey of the fish species assemblage of the rivers and laid the framework for the regional analyses I conducted in the study presented in Chapter 3. In Chapter 3 I report inter- and intra-river comparisons of THg concentrations and associated feeding ecology of riparian Dolly Varden, separated by anadromous barriers in each system. I concluded that resident Dolly Varden that co-habit riverine locations with spawning salmon consume more salmon eggs than resident Dolly Varden from other locations of the same river that do not co-habit with spawning salmon. This is reflected in the isotopic composition of their tissues, and subsequently the THg concentrations of these fish are lower relative to Dolly Varden from parts of the same river above anadromous barriers. In Chapter 4, I describe regional patterns of THg concentrations and stable isotope values of carbon and nitrogen in nine species of fish and invertebrates from the Bering Sea and North Pacific Ocean along the Aleutian Islands, using Steller sea lion management zones as a spatial framework. I determine that most species from the Western Aleutian Islands have greater THg concentrations, and more negative δ¹³C values than those from the Central Aleutian Islands, indicating ecosystem-wide differences in THg concentrations and fish feeding ecology. I also determined that Amchitka Pass, a well-documented oceanographic and ecological divide along the Aleutian Island chain, aligns better with differences in THg concentrations than the boundary between Steller sea lion management zones. In Chapter 5, I report THg and methylmercury concentrations in fishes of Kotzebue Sound, including seven species that are important for subsistence users. I determined that fork length influences Hg concentrations within individual species, and that trophic relationships within a food web, a factor associated with biomagnification, influences Hg concentrations across the entire food web. I also observed that muscle tissues from virtually every individual fish had Hg loads below the State of Alaska's criteria for unlimited consumption. Taken together, the work conducted in this dissertation helps us better understand the ecological dynamics of Hg in aquatic food webs and has contributed to Hg monitoring of fish resources across parts of Alaska.
    • Metabolic hormone levels and immunocompetence of neonatal harbor seals (Phoca vitulina) in rehabilitation settings compared to wild harbor seal pups

      O'Neil, Danielle Renee (2005-08)
      Health of harbor seal pups in rehabilitation and in the wild were compared using two metabolic hormones (cortisol and total thyroxine, TT4), two cellular immunity components (lymphocytes and eosinophils) and morphometric measurements. Neonatal harbor seals in two rehabilitation facilities were compared to wild harbor seal pups. Permanently captive harbor seals housed at the Alaska SeaLife Center were also studied. High levels of cortisol at weaning suggest changes in the stress response may be due to diet adjustments in pups during rehabilitation. The lower cortisol concentrations post-weaning suggest that pups in rehabilitation had overcome the challenge of pre-weaning diet, handling or environment and avoided chronic stress. TT4 concentrations were higher in wild pups, likely attributed to a more energetically demanding life in a dynamic environment. The rehabilitated pups showed lower lymphocyte counts and higher eosinophil counts compared to wild pups. Wild harbor seal pups were heavier and longer than post-weaned pups in rehabilitation. Animals in rehabilitation are possibly compromised at stranding, but it is also possible that current rehabilitation practices do not mimic what a healthy pup would receive from maternal investment, thus pups undergoing rehabilitation likely remain smaller and possibly immunologically compromised despite repeated and constant care in rehabilitation.
    • Microsatellite variation reveals similar population genetic structure for two species of rockfish (Sebastes borealis and Sebastes paucispinis) with different life histories

      Matala, Andrew Paul (2002-12)
      Rockfish belong to the speciose genus Sebastes (72 species described in the Northeast Pacific). Basic biological and life history information for many rockfish species is limited. Little is known about juvenile recruitment, and identification in early life stages is difficult because the larvae of congeners look similar and often occur in spatial and temporal association. Population genetic structure is an important element for characterization of species or populations, and may provide information on productivity and life history. Eight micro satellite loci were evaluated for variability in analyses of genetic structure for two species of rockfish: the deepwater shelf rockfish bocaccio (S. paucispinis) and the demersal shortraker rockfish (S. borealis) of the continental slope. Tests of homogeneity provided evidence of similar geographically based structure in both species, which is consistent with a neighbor model of gene flow. Structure inferred from this study provides information on the sizes of the basic units of productivity, which may aid in management and conservation efforts.
    • The migration and spawning distribution of sockeye salmon within Lake Clark, Alaska

      Young, Daniel B. (2004-08)
      Recent declines in the number of sockeye salmon Onchorynchus nerka returning to Lake Clark, Alaska have caused economic hardship in the region and raised resource concerns among local subsistence users and Federal managers. A lack of information regarding the distribution of spawning habitats in the glacially turbid Lake Clark watershed instigated this research. Radio telemetry was used to 1) determine the in-lake movement patterns of adult sockeye salmon and 2) identify sockeye salmon spawning locations. Sockeye salmon were radio tagged at they entered Lake Clark and tracked to spawning locations. After entering Lake Clark, sockeye salmon usually migrated to a region of the lake that was within 15 km of their spawning location. Tagged fish migrated faster and more directly to spawning locations in tributary rivers and lakes than to Lake Clark beaches. Thirty three spawning locations were identified in the Lake Clark watershed including 18 new spawning locations compared to previous scientific research and ten compared to traditional local knowledge. Most radio tagged sockeye salmon (65%) returned to spawning locations in glacially turbid waters and most spawning locations (75%) were adjacent to privately owned lands. Proactive measures should be taken to conserve both migration corridors and spawning habitats.
    • Migration patterns and energetics of adult chinook salmon Oncorhynchus tshawystcha in Alaska rivers

      Neuneker, Kristin R.; Falke, Jeffrey; Seitz, Andrew; Nichols, Jeff; Cox, M. Keith (2017-12)
      Adult Chinook Salmon Oncorhynchus tshawytscha undertake extensive and energetically costly migrations between food resources in the ocean and their freshwater spawning habitats, requiring them to adapt behavioral and physiological traits that allow them to successfully reach their spawning streams and reproduce. Such adaptations may be shaped by physical factors in the environment and individual- and population-specific biological characteristics. Chinook Salmon in North America are important resources for both United States and Canadian stakeholders, but relatively little is known about their freshwater migration patterns and energetic status in many rivers across their range. This research explored variation in migration timing and migration rates of Chinook Salmon in two Southeast Alaska transboundary rivers (Taku River, Stikine River), examined energetic status at multiple sampling locations in Alaska, and created and tested a predictive model for energetic status using bioelectrical impedance analysis (BIA). Migration timing was earlier for fish that spawned in more distant tributaries in both transboundary systems and the Taku River was earlier compared to the Stikine River. Migration rates decreased during periods of high flows, were slower for fish in the Taku River, and were slower in both systems in 2016 compared to 2015. Migration rates were faster for fish with spawning sites farther upstream when compared to those that spawned closer to the river mouth, but these rates decreased over time as fish swam farther upriver. Chinook Salmon (N = 129) sampled for energetic status at the beginning of their freshwater spawning migration had higher total percent lipid than those near the spawning grounds (ANOVA: F = 202.1, df = 3, P < 0.001), and total percent lipid and water were precisely predicted based on BIA measurements (R² = 0.82, RMSE = 5.33; R² = 0.78, RMSE = 2.43 respectively). The BIA model was tested to determine if it could be generalized between similar species, but this was found to be less precise than species-specific models. The BIA measurement technique was also easily implemented into an existing study on a remote Chinook Salmon population. Given threats from climate change and mining activities, this information will be useful for fisheries researchers as a benchmark for understanding migration behaviors in these Chinook Salmon populations, and indicates that integration of BIA into population monitoring may be a useful tool for creating management practices targeted at facilitating successful migration behaviors and increasing or maintaining energetic status for these fish.
    • Migratory patterns of Yukon River inconnu as determined with otolith microchemistry and radio telemetry

      Brown, Randy J. (2000-05)
      Migratory patterns of Yukon River inconnu Stenodus leucichthys were evaluated using otolith aging and microchemical techniques and radio telemetry. Research was conducted each fall between 1997 and 1999, on inconnu captured at a study site 1,200 river km from the Bering Sea. Biological data were collected to establish maturity and spawning condition. Sagital otoliths were analyzed optically to determine age distribution, and microchemically to determine amphidromy. Inconnu were tagged with radio transmitters and located in upstream spawning destinations. Inconnu captured at the study site were uniformly large, mature fish preparing to spawn. Age estimates ranged from 7 to 28 years. Microchemical analyses suggested that the population was amphidromous rather than freshwater only. Preliminary testing of radio transmitter attachment methods showed that the internal method (pushed through the esophagus into the stomach) was superior to the external method (attached behind the dorsal fin) for use with migrating inconnu. Most radio-tagged inconnu were located during their spawning time in a common region of the Yukon River. Inconnu captured at the study site each fall were mature fish engaged in a spawning migration that originated in the lower Yukon River or associated estuary regions, and continued towards a common spawning destination in the Yukon River, approximately 1,700 river km from the sea.
    • Milk fatty acid composition of perinatal and foraging Steller sea lions: examination from pup stomachs

      Miller, Carlene Nicole; Polasek, Lori K.; Oliveira, Alexandra C. M.; Horstmann-Dehn, Larissa A. (2014-08)
      To investigate the relationship of milk fatty acid composition between perinatal and foraging Steller sea lions and within each maternal state (i.e., perinatal or foraging), milk samples were collected in 2010 and 2011 via gastric intubation from Steller sea lion pups on a small rookery in the central Gulf of Alaska. Subsamples of initial milk samples were taken over four hours post-collection to examine changes of fatty acids within milk over time. Maternal states of lactating females of sampled pups were determined via remotely operated video cameras on the rookery. Fatty acid composition within milk, collected from Steller sea lion pup stomachs, did not change over the four hour post-collection period, and thus milk fatty acids were not modified within milk over time. Milk fatty acid composition between Steller sea lion maternal states was different, and thus can be utilized to distinguish between perinatal and foraging Steller sea lions of the same geographic region. In the absence of direct observations, this study demonstrated the use of a viable method to determine maternal state. Milk fatty acid composition remained relatively constant within perinatal Steller sea lions, suggesting steady mobilization of fatty acids from blubber to milk, and within foraging Steller sea lions, implying females forage in the vicinity of the rookery and on similar prey species. Differences in milk fatty acid composition between maternal states, including differences in the relative percentages of polyunsaturated fatty acids, may have implications for growth and development of offspring. For lactating Steller sea lions, foraging after the perinatal period is important for continued delivery of fatty acids needed by young pups.
    • Mitochondrial DNA haplotype genealogies and population histories in the late Pleistocene: contrasts of pink salmon broodyears

      Churikov, Dmitri Yurievich (2000-12)
      Seven segments of mtDNA, comprising 97% of the mitochondrial genome, were PCR-amplified and examined for restriction site variation using 13 restriction endonucleases in three Oncorhynchus species: pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon. Multiple haplotypes, but shallow mtDNA trees were observed for each species. 'Star-like' structures indicating historical population explosions were observed in haplotype genealogies. Given reasonable rates of mtDNA sequence evolution, this may reflect recolonization of vast areas in Alaska after the last (Wisconsinian) or preceding (Illinoian) glacier retreats. The phylogeographic survey of 18 Alaskan and Eastern Asian pink salmon populations revealed a distinct phylogeographic break between Alaska and Asia in even-year, but continuous distributions of the mtDNA lineages throughout the same range in the odd-year broodline. A nested cladistic analysis of geographical distances indicates that spatial distribution of mtDNA lineages in both broodlines resulted from interplay between historical range expansions and isolation by distance.
    • Molecules to marinescapes: the characterization of microbial life in the Arctic Ocean

      Hassett, Brandon T.; Gradinger, Rolf; Collins, R. Eric; Leigh, Mary Beth; McBeath, Jenifer; Lopez, J. Andres (2016-05)
      Microbes are the base of all marine food webs and comprise >90% of all living biomass in the world’s oceans. Microbial life and functioning in high-latitude seas is characterized by the predominance of unknown species that encode uncharacterized genes, replenish nutrients, and modulate ecosystem health by interfacing with disease processes. This research elucidates eukaryotic microbial diversity and functionality in Arctic and sub-Arctic marine environments by describing the culturable and genetic diversity of eukaryotic microbes and the life histories of marine fungi belonging to the Chytridiomycota. This work includes the description of two new mesomycetozoean species, the assembled and annotated genome of Sphaeroforma sirkka, the first description of a cryptic carbon cycle (the mycoloop) mediated by fungi from any marine environment, and the description of large-scale eukaryotic microbial diversity patterns driven by temperature and latitude in the eastern Bering Sea. These results help establish a valuable baseline of microbial diversity in high latitude seas.
    • Monitoring stress hormones in rehabilitated and captive otariids

      Petrauskas, Lisa (2005-08)
      Cortisol and corticosterone are the primary mammalian stress hormones released in response to a perceived stressor. Cortisol is rapidly metabolized in the blood, while corticosterone is the dominant product in fecal material. Radioimmunoassay procedures to measure fecal corticosterone and serum cortisol in California sea lions were validated, and adrenal response to surgical and non-surgical procedures was assessed. Other objectives included seasonal and behavioral variability in fecal corticosterone concentrations in captive Steller sea lions, as well as adrenal response to various stressors of a rehabilitated Steller sea lion. There was a significant (P ... 0.05) adrenal response for rehabilitated California sea lions that underwent minor invasive surgical procedures. The small sample size in this study allowed the identification of a correlation of season and behavior in three captive Steller sea lions. This study found that peak fecal corticosterone values reflected responses to acute stressors during rehabilitation for a Steller sea lion pup. Overall, fecal corticosterone was an adequate tool for monitoring stress non-invasive1y in California and Steller sea lions. In turn, the results indicate that California sea lions may be a suitable surrogate species to study the adrenal response to more invasive procedures that may be used in Steller sea lions.
    • Movement and habitat utilization by golden king crab Lithodes aequispinus benedict 1895 in southeastern Alaska

      Hoyt, Zachary N. (2003-12)
      Movements and habitat use of golden king crabs (GKC), Lithodes aequispinus, were investigated with a manned submersible and ultrasonic telemetry in Frederick Sound, Alaska. Crabs were collected with commercial crab pots and ultrasonic transmitters were attached to the carapaces of 26 crabs; movements and depth distribution of male and female crabs were monitored bi- monthly from May 11, 2000 to April 12, 2001. Crabs preferred steep, complex habitat with hard substrate; few were on flat, soft substrate. Male and female GKC were not segregated by depth in mid-May. Seventeen pairs of courting crabs were observed during dives; 14 of these pairs were associated with either intermittent or continuous boulder fields and 3 with wall substrates. Crabs did not have seasonal site fidelity. Crabs had seasonal changes in depth distribution, moving to deeper water during late fall and winter and returning to shallower depths during spring. Crabs moved as far as 39 km over one year. No evidence of spatial fidelity was observed; golden king crabs may be moving greater distances or site fidelity maybe on a longer temporal scale than our study, or golden king crabs may be nomadic in nature.
    • Movement of the giant red sea cucumber Parastichopus californicus in Southeastern Alaska

      Cieciel, Kristin (2004-08)
      This thesis provides information on sea cucumber movement that could inform management of the growing fishery for the sea cucumber, Parastichopus californicus, in Southeast Alaska. Daily movement of individual P. californicus was quantified at six sites to assess spatial variation in movement, at three-month intervals over one year at one site to assess seasonal changes in movement, and densities were measured monthly at three depths over one year. Movements varied among seasons and sites ranging from 0 to 34.5 m·24 h⁻¹, and were highest in summer (mean ± SE = 4.6 ± 0.5 m) and lowest in fall (mean ± SE = 1.9 ± 0.3 m). Densities were highest in spring and summer and lowest in fall and winter. Recently tagged animals move, on average, 2 m more than animals tagged 72 h earlier, indicating that movement is best assessed 48 h after tagging. Stock assessments should be conducted in spring and summer to coincide with increased animal densities, with the fishery occurring in fall and winter to provide a possible refuge for a portion of the population. Overall, P. californicus demonstrate limited adult movement, indicating that populations are geographically limited with little possibility of animal migration or repopulation of adults in harvested areas.
    • A multi-proxy approach to determine paleoecological change of mangroves, during the holocene, in Belize, Central America

      Monacci, Natalie Marie (2007-12)
      This thesis presents multiple analyses of mangrove peat cores from Spanish Lookout Cay (BT - 79) and from along the banks of the Sibun River (SR-63), Belize to examine ecosystem responses to environmental change during the Holocene. Radiocarbon measurements showed these sites were colonized by mangroves ~8,000 cal. yrs BP and have decreased sedimentation rates from ~6,000 to ~1,000 cal. yrs BP, which is attributed to a decrease in sea-level inundation. Core SR-63 has a change in lithology from primarily mangrove peat to fluvial material at 2,500 cal. yrs BP, which is attributed to erosion inputs of the drainage basin. Changes in the pollen assemblage, such greater input from non-mangrove pollen, are coeval with changes in sedimentation rates at both sites. Subfossil mangrove leaves, from core BT-79, are used for stable isotope ([delta]¹⁵N, [delta]¹³C, and [delta]¹⁸O) analyses to illustrate past physiology and seawater inundation. The composition of organic material in core SR-63 changes from autochthonous to allochthonous sources, which is coeval with the change in lithology. A decrease in the rate of sea-level rise is assumed to be the cause of the significant changes seen in these mangroves, which counters existing sea-level curves.
    • Multi-scale movement of demersal fishes in Alaska

      Nielsen, Julie K.; Seitz, Andrew C.; Loher, Timothy; McDermott, Susanne F.; Mueter, Franz J.; Adkison, Milo D. (2019-05)
      Information on the movement of migratory demersal fishes such as Pacific halibut, Pacific cod, and sablefish is needed for management of these valuable fisheries in Alaska, yet available methods such as conventional tagging are too coarse to provide detailed information on migration characteristics. In this dissertation, I present methods for characterizing seasonal and annual demersal fish movement at multiple scales in space and time using electronic archival and acoustic tags. In Chapter 1, acoustic telemetry and the Net Squared Displacement statistic were used to identify and characterize small-scale movement of adult female Pacific halibut during summer foraging in a Marine Protected Area (MPA). The dominant movement pattern was home range behavior at spatial scales of less than 1 km, but a more dispersive behavioral state was also observed. In Chapter 2, Pop-up Satellite Archival Tags (PSATs) and acoustic tags were deployed on adult female Pacific halibut to determine annual movement patterns relative to MPA boundaries. Based on observations of summer home range behavior, high rates of year-round MPA residency, migration timing that largely coincided with winter commercial fisheries closures, and the demonstrated ability of migratory fish to return to previously occupied summer foraging areas, the MPA is likely to be effective for protecting both resident and migrant Pacific halibut brood stock year-round. In Chapter 3, I adapted a Hidden Markov Model (HMM) originally developed for geolocation of Atlantic cod in the North Sea for use on demersal fishes in Alaska, where maximum daily depth is the most informative and reliable geolocation variable. Because depth is considerably more heterogeneous in many regions of Alaska compared to the North Sea, I used simulated trajectories to determine that the degree of bathymetry heterogeneity affected model performance for different combinations of likelihood specification methods and model grid sizes. In Chapter 4, I added a new geolocation variable, geomagnetic data, to the HMM in a small-scale case study. The results suggest that the addition of geomagnetic data could increase model performance over depth alone, but more research is needed to continue validation of the method over larger areas in Alaska. In general, the HMM is a flexible tool for characterizing movement at multiple spatial scales and its use is likely to enrich our knowledge about migratory demersal fish movement in Alaska. The methods developed in this dissertation can provide valuable insights into demersal fish spatial dynamics that will benefit fisheries management activities such as stock delineation, stock assessment, and design of space-time closures.
    • Multiple stable isotopic analyses ([delta]¹³C, [delta]¹⁵N, [delta]¹⁸O, and [delta]D) of the Boulder Patch, a high arctic kelp community: trophic and temporal perspectives

      Debenham, Casey William Jones (2005-12)
      The Boulder Patch, a high Arctic kelp community, is a rarity in the Alaskan Beaufort Sea. Considered a biodiversity oasis, this area provides habitat for many organisms. Trophic relationships, spatial patterns, and isotopic changes over time were examined within the Boulder Patch using stable carbon and nitrogen isotopes. 394 samples, representing over 55 species were analyzed. Isotope values showed considerable variability in the food web base, particularly for the kelp Laminaria solidungula. Isotopic values for most animals fit their known feeding strategies. Little spatial variation was observed in isotope values, however temporal differences were found in L. solidungula isotope values between 2002 and 2004, and between archived samples collected during the 1980's. To better understand patterns in stable oxygen and hydrogen isotopes, values were assessed and applied in an ecological context. Sixty-four samples were analyzed, encompassing 29 species. Results indicated distinct differences between primary producers and animals, offering insights into a possible application of [delta]¹⁸O and [delta]D in ecological studies. By defining trophic structure and elucidating feeding strategies of organisms, this study enhanced the biological knowledge in the Boulder Patch, providing ecological information on a high arctic kelp community.
    • Multispecies Age-Structured Assessment Modeling As A Tool Of Fisheries Management In The Gulf Of Alaska

      Van Kirk, Kray F.; Quinn, Terrance J. II; Collie, Jeremy; Criddle, Keith; Kruse, Gordon; Mueter, Franz (2012)
      A multispecies age-structured assessment model (MSASA) for the Gulf of Alaska (GOA) is developed to examine the effects of integrating predation mortality into stock assessment efforts. Age-specific predation mortality is modeled as a flexible function of predator and prey abundances, constructed from species-preference and size-preference parameters and fitted to stomach-content data. Modeled species include arrowtooth flounder ( Atheresthes stomias), Pacific cod (Gadus macrocephalus), walleye pollock (Theragra chalcogramma), Pacific halibut (Hippoglossus stenolepis) and Steller sea lion ( Eumatopias jubatus). Recruitment, residual natural mortality, full-recruitment fishing mortality, and fishery/survey selectivities are estimated for pollock, cod, and flounder; abundances for apex predators sea lions and halibut are input. Estimated trophic structures and predation links show significant changes as a result of the inclusion of higher trophic level predators, and model results are highly sensitive to assumptions regarding sea lion diet. Simulation exercises suggest that model performance degrades more due to model misspecification and data scarcity than assumptions regarding data weighting and variance. Estimates of predation mortality work in tandem with survey data, constraining predation estimates in the face of incomplete diet data and potentially improving estimates of cohort structure. Exploration of predator functional responses (PFR) shows the default GOA MSASA Holling Type II PFR to be more flexible than initially thought, and that explicitly modeling predator competition for the same prey can improve model fit to stomach-content data. Median parameter estimates and their respective variances from the fitted MSASA model are used to construct management strategy simulations. Reducing fishing pressure on pollock during periods of high predator biomass is less effective at preserving pollock stocks than raising fishing pressure on flounder, and multispecies harvest control rules and biological reference points are shown to be more conservative and more efficient at preserving stock abundance while maintaining catch levels than their single-species counterparts.
    • Natural abundance of nitrogen(15) in a subarctic lake and biogeochemical implications to nitrogen cycling

      Gu, Binhe (1993)
      Stable isotope ratios of nitrogen ($\delta\sp{15}$N) were employed to track the origin and fate of nitrogen in a subarctic lake, Alaska. The annual planktonic nitrogen cycle was dominated by N$\sb2$ fixation in spring and NH$\sb4\sp+$ assimilation in summer. In winter, microbial nitrification was the major sink for NH$\sb4\sp+$ and denitrification was accounted for most of the loss of NO$\sb3\sp-.$ The small isotope fractionation in nitrification is proposed as a result of substrate (NH$\sb4\sp+)$ limitation. The temporal and spatial homogeneity of the $\delta\sp{15}$N of dissolved organic nitrogen may be related to its large pool size and refractory nature. A stable isotope mass balance suggests that the winter phytoplankton was only composed of 10 to 20% of the suspended organic matter in water column due to low primary productivity during the ice cover period. A close correlation between $\delta\sp{15}$N of phytoplankton and $\delta\sp{15}$N of dissolved pools indicates that NH$\sb4\sp+$ was the predominant nitrogen source for non-N$\sb2$-fixing algae. The similarity of $\delta\sp{15}$N between a spring blue-green bloom and N$\sb2$ suggests an atmospheric origin for nitrogen. A mixing model estimated that the blue-green algal bloom derived approximately 70% of its nitrogen from molecular nitrogen. This fixed nitrogen was further transferred to higher trophic levels via the food chain and to other primary producers following mineralization. The $\delta\sp{15}$N of aquatic macrophytes indicates that non-rooted species obtained their nitrogen from the water column while rooted species obtained their nitrogen largely from the sediment. Evidence from dual isotope tracers ($\delta\sp{15}$N and $\delta\sp{13}$C) suggests that the zooplankton were supported by phytoplankton throughout the growing season despite an apparent abundance of detritus in the water column. Benthic fauna relied on either phytoplankton detritus or other organic matter in the sediment. The $\delta\sp{15}$N data exhibit only two to three trophic levels in both planktonic and the benthic communities in Smith Lake.