Food webs are challenging to describe, particularly for generalist predators whose diet consists largely of taxonomically diverse invertebrates. To better understand predator-prey relationships for fish belonging to Salmonidae and Cottidae, I compared traditional morphological identification of prey with sequencing of individual items and next generation sequencing of fish stomach homogenates. I also used next generation sequencing to assess invertebrate biodiversity from environmental DNA samples – stream water, ethanol preservative from Surber samples and fish stomach homogenates. Morphological identification was often limited to the Order level but allowed for quantitative data. Genetic analysis provided substantially greater taxonomic resolution, with sequencing of stomach homogenates revealing a much more diverse diet in fish. Water samples detected terrestrial and aquatic invertebrate species and Surber ethanol revealed a similar invertebrate diversity as fish stomach homogenates. Fish, however, appeared to be generalist feeders and collectively accounted for the greatest number of unique taxa.
Salmon smolts undergo physiological changes in the spring that are important for successful migration to seawater. Species that are widely distributed may differ in timing of physiological changes associated with smelting. In my first study, I compared indices of smolt characteristics among populations that differ in migration distance to the ocean. Fraser River sockeye salmon from four regions in the watershed were intercepted at different times during migration to characterize the parr-smolt transformation. Gill Na⁺/K⁺-ATPase (NKA) activity was highly variable at the start of migration, and was not explained by the distance from the ocean. Gill NKA activity changes with migration were also highly variable, but consistently smolts in the ocean had the highest gill NKA activities. The nature of smelting appears to be dynamic and variation was not based on the region of origin, timing during migration, or on the year of migration. The duration of time when anadromous salmon are able to survive in seawater – the smolt window – is influenced by temperature. In my second study, I found that warm water temperature abbreviated the smolt window. Additionally, isoforms of the gill NKA enzyme and endocrine signals suggest that the stimulus for smelting occurred prior emigration from the natal lake. Modeling the thermal experience that smolts encountered as they migrated downstream to the ocean in 2012 suggested Chilko fish did not experience temperatures as warm as the temperatures that abbreviated the smolt window in my study. Furthermore, climate change projections for temperature may not limit successful emigration of Chilko sockeye salmon smolts from central British Columbia to the ocean – but changes in other abiotic and biotic factors may confound this prediction.
Coastal cutthroat trout (O. clarkii clarkii, CCT) are arguably the most poorly understood species of salmonid and little is known of their seasonal patterns of movement, particularly in British Columbia. My study was conducted to assess the overwintering and spawning behaviours of migratory CCT in the Kitimat River watershed and to evaluate how behaviours were influenced by a suite of biotic and abiotic metrics. Radio transmitters were surgically implanted into mature CCT in the late summer and fall of 2012 (Year 1; n = 41) and 2013 (Year 2; n = 68). In the late fall, CCT aggregated within deep, slow moving pools. During the winter, CCT either remained stationary within a single overwintering habitat, or were mobile, moving among 2 to 5 habitats. Spawning occurred in first to third order tributaries throughout the watershed, from April 14 to May 15. Spawning mortality was high, and 57% of radio tagged CCT did not survive spawning. ...
The influence of environmental variables on larval development of coho salmon (Oncorhynchus kisutch), with specific focus on the influence of near-freezing incubation temperatures, was examined across populations within British Columbia. A survey across the geographical distribution within British Columbia was conducted to determine the range and variability of incubation temperatures experience by incubating coho salmon. Temperatures throughout incubation differed significantly among locations, averaging approximately 1 °C in colder interior locations and approximately 5 °C in warmer coastal locations. Environmental variables influenced egg size, fecundity, female size and gonadal somatic index, such that higher latitude of spawning grounds increased, larger systems decreased, and increased temperatures experienced by a population increased the four life-history traits. Suggesting significant effects of latitude of spawning grounds, size of spawning system and temperatures experienced by a population on shaping patterns of reproductive investment. ...
Smolting is an important time in the life of anadromous salmon when juveniles undergo changes that prepare them for life in the ocean. Widely distributed salmon populations have evolved based on the selective pressures of their local environments. I examined population differences in the development, duration (smolt window) and loss of seawater tolerance, how temperature influenced development among populations, and temperature preference throughout smolting in coho salmon (Oncorhynchus kisutch). For my first objective, I compared smolt development among three populations in British Columbia, Canada that each had different migration distances to the ocean. In year one, fish appeared to undergo an incomplete smoltification based on the biochemical marker Na+/K+-ATPase (NKA). Additionally, molecular markers (mRNA expression of gill NKA α1a, NKA α1b, as well as growth hormone (GHR), prolactin (PrlR) and glucocorticoid (GR1) receptors) suggest that fish also did fully develop physiological changes associated with smolting. In year two, the smolt window (approximately 300 accumulated thermal units – ATU) did not differ by population as evident by elevated NKA activity. Molecular markers (gill NKA α1a, NKA α1b, GHR, and PrlR) for smolting also did not show a population difference – indicating that distinct populations do not differ in their development, duration, or loss of seawater tolerance. For my second objective, I examined temperature preference in short- and long-distance migrating populations of coho salmon juveniles. Mean temperature preference did not differ between the two populations (15.9 °C and 16.1 °C) and did not change throughout smolting. Based on the observed temperature preferences, smolts do not prefer temperatures that are advantageous for prolonging the smolt window. Additionally, the disparity between temperature preference and what is likely available in the environment at the time of smolting demonstrates that temperature is not a selective pressure for juveniles to behaviourally regulate the development of seawater tolerance.
Wild Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) from the Horsefly River in central British Columbia vary in adult migration timing, but often rear sympatrically as juveniles. These species provide an interesting opportunity to investigate adaptations to the environment in the juvenile life-history stage, which may differ from adaptations at the adult stage. Temperature preference did not differ significantly between Chinook salmon and coho salmon. Aerobic scope (difference between maximum and routine metabolic rates) was also similar between the two species, and neither showed a distinct temperature optimum for peak physiological performance. Coho salmon had a significantly higher upper thermal limit compared to Chinook salmon, although differences were small and may not be biologically meaningful. Thus, these two populations appear to be well adapted for their current environmental conditions rather than show any tendencies to be differentially suited to selective pressures they will experience as adults.
