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The relationship between oyster farms and their environment, a sea otter’s perspective

Investigators

Brenda KonarCollege of Fisheries and Ocean Sciences
University of Alaska Fairbanks
Weatherly BatesAlaska Shellfish Farms

Synopsis

This project will examine sea otter interactions with oyster farms and the relationship of these interactions with environmental parameters. Sea otter behavioral observations (activity and foraging) in and around oyster farms will be compared with observations where oyster farms do not exist or are not active. Environmental parameters that may influence sea otter behavior will also be examined as part of this study and will include benthic community structure, benthic habitat structure (substrate type, rugosity, and slope), static attributes (such as protection from storms, and water depth) and hydrographic attributes (turbidity, conductivity, salinity, temperature, and dissolved oxygen). Fouling organisms on the oyster cages themselves may also influence sea otter interactions with farms. This project will be tightly linked with the long-term monitoring Gulf Watch Alaska Program and the pending Mariculture Research and Restoration Consortium Program. Data collected in this proposed Sea Grant project will contribute data to these other programs and data collected by the other programs will contribute to the data needs of this project.

Overview

The issue

Sea otters are often considered keystone species and are very abundant in Kachemak Bay, an area with the highest density of oyster farms in the state of Alaska. While sea otters and oyster farms have been co-existing in this area since 1989, the natural increase in the sea otter population post fur-trade and Exxon Valdez oil spill and the growing interest in expanding mariculture has warranted new interest in potential interactions.

Why is this an Alaska Sea Grant project?

This project addresses two focus areas from Alaska Sea Grant’s 2018–2023 Strategic Plan: Sustainable Fisheries and Aquaculture, and Healthy Coastal Ecosystems.

How will researchers conduct their study?

Field surveys will be conducted in at least three different bays in Kachemak Bay (Bear Cove, Halibut Cove and Peterson Bay). Within each bay, three aquaculture sites and three control, non-aquaculture sites will be selected and monitored between June and August 2022 (site selection and preliminary surveys will occur in May). If there are sites with old unused structures, they will also be monitored. Additionally, we will monitor three sites in three different bays where oyster farming is currently not being conducted (Mallard Bay, Sadie Cove, and China Poot Bay). At each site (a minimum of n=27 sites), sea otter scan surveys to determine occupancy and behavior (resting, foraging, etc…) in addition to standardized sea otter foraging observations (dive time, success, prey, size of prey obtained, etc...) will be completed twice a month for three months. At each site, substrate type, rugosity, slope, exposure, and water depth will be determined in addition to benthic community structure (percent cover and abundance of available organisms). As part of this study, the general similarity of bays (with and without oyster farms) and sites (with and without oyster farms) will be measured through comparisons of these characteristics along with turbidity, conductivity, salinity, temperature, and dissolved oxygen. We will also work with farmers to determine what fouling organisms are associated with mariculture farm structures (bags, cages, and lines) to determine if sea otters are feeding on these organisms. We will then correlate all biological and physical parameters among bays and sites using various multivariate statistics to determine correlations between physical characteristics, biological communities, and sea otter occupancy and behavior. We will also compare sea otter activity and diet observations around oyster farm and non-farm sites and control bays with sea otter data being collected in other parts of Kachemak Bay by the Gulf Watch Alaska nearshore component.