• Otters, sea stars, and glacial melt: top-down and bottom-up factors that influence kelp communities

      Traiger, Sarah B.; Konar, Brenda; Hardy, Sarah; Okkonen, Stephen; Edwards, Matthew; Litaker, Wayne (2017-08)
      Kelp beds are important features of the Alaska coastline and provide habitat, protect coastlines, and support commercial and subsistence harvests. Kelp beds are affected by top-down and bottom-up factors, which are changing due to human and climate-related impacts. The influences of these top-down and bottom-up factors on kelp beds are investigated in three chapters. My first chapter investigated the influence of glacial discharge on recruitment and early community development in subtidal kelp communities by monitoring benthic sessile algae and invertebrates on cleared rocks across a glacial gradient along with various physical and biological parameters in the summers of 2013-2014. It has been predicted that Alaska's glaciers will lose 30-60% of their volume by 2100. The melt from glaciers increases sedimentation and lowers salinity, impacting important habitat-providing kelp. I found that sites upstream from glacial discharge had higher kelp recruitment than downstream sites, and that up to 72% of the variation in community development was related to mobile invertebrates and kelp in the surrounding community. Glacially-influenced environmental factors did not explain any variation that was not already explained by biological factors. My second chapter explored whether patterns in the recruitment of the dominant canopy kelp, Nereocystis luetkeana and the subcanopy kelp, Saccharina latissima were a result of dispersal limitation or failure to grow to macroscopic size. My goals were to determine 1) whether glacial melt conditions affect adult fecundity (spore production) of either species, 2) how sedimentation affects early gametophyte growth and survival in each species, and 3) whether competitive interaction between species at the gametophyte stage is altered by sediments. I found that glacial melt conditions did not affect the fecundity of either species, but sedimentation affected survival and competition. Saccharina latissima was the superior competitor under high sediment conditions. Because glacially-influenced coastal areas often have little exposed hard substrate and predation by sea otters and sea stars on clams can provide hard substrate for kelp colonization, my third chapter examined methods for determining predation on clams by these predators without direct observation. I found that foraging pits of sea otters and sea stars could not be distinguished using quantitative measurements. In contrast, shell litter proved useful in quantifying relative foraging rates. Clam consumption by sea otters and sea stars was equal at all but one site. Collectively, my thesis chapters provide information on the effects of glacial discharge on microscopic and early kelp life stages in Alaska which can be incorporated into management practices.
    • 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.
    • Physical environmental and biological correlates of otolith chemistry of Arctic marine fishes in the Chukchi sea

      Gleason, Christine Marie; Norcross, Brenda; Brown, Randy; Horstmann-Dehn, Larissa; Trefry, John; Christie, David (2012-08)
      Life history movement patterns in marine fishes can be determined by otolith chemistry if environmental variables are reflected in the otoliths. Arctic cod (Boreogadus Saida), Arctic staghorn sculpin (Gymnocanthus tricuspis), and Bering flounder (Hippoglossoides robustus) are abundant Arctic fishes in the Chukchi Sea with overlapping distributions. Physical environmental data, demersal fishes, bottom seawater, and sediment interface seawater samples were collected from the Chukchi Sea Offshore Monitoring in Drilling Area (COMIDA) cruise on July 30, 2009 and the Russian American Long-term Census of the Arctic (RUSALCA) cruise from September 3 to 30, 2009 in the Chukchi Sea. Magnesium (Mg), strontium (Sr), barium (Ba), and calcium (Ca) were measured with an inductively coupled plasma mass spectrometer (ICP-MS) on the most recent growth edge of otoliths and in whole fish blood, as well as Ba in bottom and sediment interface seawater. Environmental variables and fish age correlated with Arctic cod and Arctic staghorn sculpin otolith signatures while only environmental variables correlated with Bering flounder signatures. Elemental correlations were not always consistent for the variables tested among species. The complexity of this multi-element tool suggests otolith chemistry may not be useful to determine life history movement patterns of these demersal Arctic fishes in offshore waters.
    • Quantity and quality of freshwater rearing habitat in relation to juvenile Pacific salmon abundance in the Kulukak River, Alaska

      Coleman, Jesse M.; Sutton, Trent; Zimmerman, Christian; Adkison, Milo (2012-12)
      Monitoring of freshwater habitat and its influence on stream-rearing fish is essential for recognizing and mitigating the impacts of human- and climate-induced changes. For the purposes of developing a monitoring program in the U.S. Fish and Wildlife Service Togiak National Wildlife Refuge, densities and habitat relationships of juvenile coho salmon Oncorhynchus kisutch and sockeye salmon O. nerka were estimated in two tributaries of the Kulukak River, Alaska, in July 2010. Multiple-pass depletion electrofishing was used to estimate density in a random sample of habitat units belonging to one of four categorical habitat classes. Regression methods were also used to quantify the physical habitat associations of juvenile coho and sockeye salmon density in the study areas. Densities of juvenile coho and sockeye salmon ranged from 0.22 fish-m⁻² in West Fork riffles and 0.05 fish·m⁻² East Fork riffles to 2.22 fish M⁻² and 1.32 fish-m⁻² in East Fork eddy drop zones (EDZ), respectively. The largest proportions of freshwater habitat were comprised of run (71 %) and EDZ habitats (44%) in the East Fork and West Fork, respectively. Regression coefficients for coho and sockeye salmon densities were positive with respect to proportional areas of in-stream overhanging vegetation (0.78 and 0.74, respectively), large wood (0.99 and 0.97, respectively), and undercut banks (0.99 and 0.02, respectively). Conversely, coho and sockeye salmon density was negatively related to depth ( -1.45 and -0.52, respectively) and velocity ( -2.45 and -1.67, respectively). Although substrate size was negatively related to sockeye salmon density ( -0.40), this variable had a weak positive relationship with coho salmon density (0.08). These findings suggest that EDZ habitats are important for juvenile coho and sockeye salmon during summer rearing and in-stream cover is an essential component of these rearing habitats.
    • Using multispectral aerial imagery and GIS-based approaches to quantify juvenile salmon rearing habitat in the Kulukak River, Alaska

      Woll, Christine; Sutton, Trent; Prakash, Anupma; McPhee, Megan (2012-05)
      Monitoring the quality and quantity of freshwater rearing habitat for Pacific salmon Oncorhynchus spp. is essential for maintaining stocks of these species. Because field-based habitat monitoring in remote areas can be expensive, time-consuming, and/or subjective, new methods are desired. The objectives of this study were (1) to develop methods for using multispectral aerial imagery to classify juvenile rearing habitat and determine the accuracy of these methods and (2) to use these methods to quantify and map juvenile salmon habitat characteristics in two study areas in the Kulukak River, Alaska. I demonstrated that a decision-based fusion approach using images acquired in the visible, near-infrared, and thermal-infrared regions classified habitat classes important for juvenile salmon with accuracies of 82.5% and 67.5% in the respective study areas. In addition, I quantified and mapped habitat variables often used in juvenile salmon studies on several scales and created habitat-suitability maps for coho salmon O. kisutch, demonstrating that both my study areas differed in habitat quantity and quality and are most likely low-quality rearing areas. This study demonstrates that airborne images can be used to determine the quality and quantity of juvenile Pacific salmon rearing habitat in small streams and thus decision support in fisheries management.
    • Using remote sensing, occupancy estimation, and fine-scale habitat characterization to evaluate fall chum salmon (Oncorhynchus keta) spawning habitat usage in Arctic Alaska

      Clawson, Chelsea M.; Falke, Jeffrey; Westley, Peter; Prakash, Anupma; Martin, Aaron (2017-08)
      Groundwater upwellings provide stable temperatures for overwinter salmon embryo development and this process may be particularly important in cold, braided, gravel-bed Arctic rivers where rivers may freeze solid in the absence of upwellings. Aerial counts and remote sensing were used during 2013-2015 to estimate fall chum salmon (Oncorhynchus keta) spawner abundance states (e.g., low or high), classify river segments by geomorphic channel type (primary, flood, and spring), and map thermal variability along a 25.4 km stretch of the Chandalar River in interior Alaska. Additionally, I used on-the-ground examination of fine scale variation in physical habitat characteristics at 11 representative sites to characterize habitat variability, placed temperature loggers to assess overwinter thermal conditions in redds, and used a developmental model to predict hatching and emergence timing given known spawning dates and incubation temperatures. I delineated 330 unique river segments (mean length = 536 m) and used a multi-season multistate occupancy model to estimate detectability, occupancy, and local colonization and extinction rates. Triplicate surveys performed in 2014 allowed me to estimate detectability and the influence of observer bias. I found that detectability did not vary by observer, channel type, or segment length, but was better for high abundance (0.717 ± 0.06 SE) relative to low abundance (0.367 ± 0.07 SE) aggregations. After correcting for imperfect detection, the proportion of segments occupied by spawning fall chum salmon was highest in 2014 (0.41 ± 0.04 SE), relative to 2013 (0.23 ± 0.04) and 2015 (0.23 ± 0.04). Transition probabilities indicated unoccupied segments were likely to remain so from year to year (2013→2014 = 0.67; 2014→2015 = 0.90), but low abundance spawning segments were dynamic and rarely remained in that state. One-third of high abundance sites remained so, indicating the presence of high quality spawning habitat. Mean segment temperatures ranged from -0.5 to 4.4°C, and occupancy varied positively with temperature. I predicted a 50% probability of occupancy in segments with temperatures of 3°C. With my on-the-ground work, I found that habitat characteristics varied among the three channel types, with most significant differences between main channel and off-channel habitats. Dissolved oxygen and pH decreased with increasing temperature, and conductivity increased with temperature. Predicted hatching and emergence timing ranged from 78 and 176 days (December 11th and March 18th) to 288 and 317 days (July 8th and August 6th), respectively, post-spawning, and were highly variable within sites and among channel types owing to high habitat thermal heterogeneity. Because the Chandalar River supports 30% of the fall chum salmon run in the Yukon River Basin, information such as provided by this study will be critical to allow resource managers to better understand the effects of future climate and anthropogenic change in the region.