Quantifying the influence of environmental conditions on potential trophic interactions and growth of juvenile sockeye salmon and threespine stickleback within Iliamna Lake
Investigators
University of Alaska Fairbanks
University of Washington
Student
- Elena Eberhardt, program
Overview
The issue
Our short-term objective is to examine how threespine stickleback and juvenile sockeye salmon in Iliamna Lake of Bristol Bay’s Kvichak River system are responding to climate change, and the potential trophic interactions between these species. Specifically, we will: 1) Develop an Iliamna Lake ice-off Index through the intercalibration of new gridded satellite data for sea ice with long-term community observations (Iliamna, Kokhanok, Pedro Bay) compiled by UW-ASP/FRI, to create a comprehensive tool to aid in understanding lake condition and growing season. 2) Explore whether growth in stickleback and juvenile sockeye exhibit coherent or uncorrelated growth trends among years, based on long term UW-ASP/FRI fall surface trawl data (1963+). 3) Combine developed ice-off Index and growth trends from parts 1 & 2 with long-term climate and temperature observations from UW-ASP/FRI and regional airports to understand how climate change is affecting growth, relative abundance, and competition between juvenile sockeye and threespine stickleback. Long-term project goals fulfill actions in the focus areas of Environmental Literacy & Workforce Development, Healthy Coastal Ecosystems, and Sustainable Fisheries and Aquaculture. The overarching goals are: 1) Continue and expand the decades-long tradition of collaboration with Iliamna Lake community menbers in Pedro Bay and Iliamna Village, through outreach, discussion of community environmental and fish observations, and direct involvement of local high school or undergraduate students in field data collection. 2) Continue long-term data collection (water temperature, ice-off, zooplankton, and relative abundance and growth of sockeye salmon and stickleback) as part of workforce development, involving graduate and undergraduate students and local interns. 3) Improve understanding how how future climate change may impact the growth potential for juvenile sockeye salmon and interspecific competition in large freshwater lake systems.
Objectives
Development of our Iliamna Lake satellite ice-off index will involve comparison of new satellite ice coverage data with community observations recorded by UW-ASP/FRI. Community observations extend to the mid 1950’s, while satellite data are available for the last 20 years. Satellite data will be assessed identify a standardized set of grid cells representing Iliamna Lake. Next, observations from the standarized grid will be used to find the dates representing 15%, 30%, 50% of ice left on the lake in spring (Feb-May). We will then regress these satellite-derived percent ice-off dates against community observations to determine which satellite percentage date best aligns with the community-based dates recorded, for comparability with past observations. The development of this intercalibrated ice-off index for Iliamna Lake will provide a consistent basis for further analysis of climate-driven changes. For examination of juvenile sockeye and stickleback growth, we will use length and mass data from fall UW-ASP/FRI surface trawl and beach seine sampling (1962-2022) to evaluate how the length, condition (length-weight residuals), and the relative abundance (catch ratio) of juvenile sockeye and stickleback have varied over time. Based on these historical data and new data collected as part of this project, we will quantify the extent to which growth patterns for these species are correlated among years. We will then utilize the new ice-off index as well as UW-FRI lake temperature data to quantify how species-specific growth and catch ratios vary as a function of environmental conditions. This analysis will identify which years and climate conditions support the greatest scope for sockeye and stickleback growth, and whether optimal growth conditions differ between these species. Non-linear mixed effects models will be used to estimate the effect of temperature and ice-off date on quantities of interest, while controlling for sample date and among sample site variation.
How will researchers conduct their study?
We propose to examine how environmental changes are influencing juvenile sockeye salmon and threespine stickleback growth, and potential interspecific trophic interactions within Lake Iliamna. Lake Iliamna is an important nursery habitat for juvenile Bristol Bay sockeye salmon, and has been warming in recent years. It has also begun thawing earlier, with some years not even achieving a full freeze in the winter. The date at which Iliamna Lake ice goes out in the spring is considered the “ice off” date and impacts the duration of the growing season of juvenile fish, the abundance of key zooplankton forage species, and other lake processes. Threespine stickleback complete their life cycle in Iliamna Lake, and can adjust quickly to changes in environmental conditions, reach sexual maturity quickly, and rapidly colonize habitats, making them strong competitors. Under a warming climate, threespine stickleback may be experiencing increased growth and abundance, which could affect juvenile sockeye salmon growth and survival because their optimal scope for growth is at higher temperatures than that of sockeye salmon. By utilizing historical surface trawl and environmental datasets, community ice-off observations, and newly available satellite products we will explore how the changing lake ecosystem and freeze patterns are impacting the growth of juvenile sockeye salmon as well as their major competitors for zooplankton resources, threespine stickleback. Understanding shifts in the freshwater conditions and how they influence sockeye growth dynamics is crucial to sustainable fishery management in a changing climate. Our project responds to the goals of sustainable fisheries and healthy coastal ecosystems directly by creating new tools and information to increase our ability to interpret how climate systems are changing and inform and prepare the Bristol Bay commercial fishery and Iliamna Lake communities for future impacts.
