State agencies including the Oregon and Washington Departments of Fish and Wildlife are tasked with managing mixed-stock fisheries on fall-run Chinook and coho salmon as they enter the Columbia River and undergo upriver spawning migrations. Multiple Chinook salmon stocks are listed as Threatened under the Endangered Species Act and protected accordingly. In addition to controlling harvest on these stocks, managers strive to maintain fishing access to recreational anglers. This entails maintaining a balance between avoiding overharvest of listed stocks while allowing optimal catch of unlisted fish. Anglers provide large economic contributions to communities neighboring mainstem fisheries, with estimated benefits from some fisheries exceeding hundreds of thousands of dollars per day.

The colloquially named Buoy 10 fishery is a particularly high angling effort fishery at the mouth of the Columbia River. Here, tens of thousands of angling trips occur in just over a month and harvest thousands of Chinook salmon. Management agencies manage harvest by setting expected season lengths and daily bag limits and monitor harvest with creel surveys. Sampling for coded wire tags (i.e., encoded short pieces of wire embedded in the nasal cavity) provides estimates of stock-specific contributions to harvest. On occasion, unexpected trends in stock-specific harvest require in-season adjustments to regulations, which include early season closures.

Limited sample sizes of coded wire tag recoveries can produce high uncertainty in estimates of stock-specific harvest and prompt unnecessary or incorrect management actions. Additionally, high variability in angling effort can produce unexpected surges in harvest. In response to these challenges, state agencies have sought to develop new methods for monitoring harvest, novel regulatory options, and improved fishery insights.

To develop new stock identification methods and corresponding monitoring tools, researchers at ORCFWRU conducted biological sampling of landed Chinook salmon from the Buoy 10 fishery in 2017, 2018, and 2019. Samplers collected tissue samples and observations of phenotype, including color, morphometrics (i.e., body shape), spotting, and fat content in muscle tissue. Tissue samples allowed researchers to conduct genetic stock identification, in which individual fish were assigned to stock groupings using DNA markers.

Researchers showed genetic stock identification can reliably assign salmon to stock groupings and generate reasonable estimates of group-specific harvest for the Buoy 10 fishery. Genetic stock identification also allowed researchers to develop classification tools using observations of phenotype and user-friendly visual guides. These classification tools allow rapid and reliable on-site stock identifications by ODFW creel clerks and potentially by anglers. Both genetic and visual methods of stock identification offer alternative monitoring methods to the existing use of coded wire tags. Visual stock identification also allows agencies to provide stock-specific release recommendations to anglers. This management option has the potential to shift stock composition of retained catch and prolong fishing access without overharvesting protected stocks.

Researchers also developed novel quantitative models for estimating stock-specific harvest and predictive fishery angling effort. New Bayesian models produce harvest estimates with similar accuracy to existing models in addition to novel estimates of uncertainty. Results also suggest incorporating prior information in models can improve estimation of in-season harvest. Furthermore, angling effort models accurately predict trends in angling effort (71 percent variation explained) and identified the influence of annual and daily factors. For example, researchers observed angling effort is positively related to pre-season forecasts of Chinook salmon run sizes, previous catch rates, and occurrence of weekends. Predictions of expected angling effort fluctuations can guide pre-season fishery planning and inform in-season fishery adjustments.

The diversity of insights obtained from ORCFWRU research efforts, in addition to their utility to decision-making, underscores the value of fisheries research that captures the dynamics of fish, anglers, and management. An improved understanding of angler behavior, for instance, allows for more accurate predictions of future harvest. Advances in monitoring methods and estimation models also can reduce uncertainty in estimates of past harvest and improve decision-making. Basic biological insights, like the observation of visual differences among stock groupings, can lead to new management actions capable of meeting multiple fishery objectives.

New advances in fishery insights and decision-making methods still await for the Buoy 10 fishery. Researchers are working to conduct decision analyses capable of identifying optimal management strategies both before and during each fishery season. Building on work with harvest models, researchers also are using simulations to evaluate the impacts of competing management actions on uncertainty in stock-specific harvest estimates.

Collaborations between USGS, OSU, and ODFW, as well as angler willingness to participate in sampling, have proven effective in addressing management challenges for the Buoy 10 mixed-stock fishery and should continue providing new insights and management tools in the future.

The ONB features articles from U.S. Geological Survey Cooperative Fish and Wildlife Research Units across the country. The Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This story was written by Alex Jensen, PhD Candidate Department of Fisheries and Wildlife Oregon State University at the USGS Oregon Cooperative Fish and Wildlife Research Unit.