Importance of near-bottom oceanographic data in modeling the distribution of eulachon bycatch in the U.S. West Coast shrimp trawl fishery

Identification Information

Citation

Originator: Leif K. Rasmuson, Scott D. Groth, Christopher A. Edwards, Eric S. Anderson, Matthrew T.O. Blume, Kendall R. Smith

Publish Date: 12/1/2025

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Leif Rasmuson

Job Position: Marine Fisheries Research Project Leader

Telephone: 541-270-4741

E-Mail Address: leif.k.rasmuson@odfw.oregon.gov

Description

Abstract: Species distribution models (SDMs) are increasingly used in fisheries science to understand species’ spatial patterns and improve stock assessments. This study developed SDMs for eulachon smelt (Thaleichthys pacificus), a threatened, demersal forage fish often caught as bycatch in the United States West Coast ocean shrimp trawl fishery. Using ten years of observer data (2012–2021, n=19,749 with 25.4% being zeros), the study assessed the influence of static (e.g., substrate) and dynamic (e.g., ocean temperature, currents) environmental variables on eulachon abundance. The best-performing SDM included near-bottom temperature and current data, outperforming SDMs using only surface variables. Eulachon abundance peaked at ~150 m depth, especially over gravel substrates, and during nighttime. Although none of the SDM-based abundance indices significantly correlated with the Columbia River stock assessment index, bottom-based SDMs showed stronger alignment with the stock assessment (R=0.61, p=0.08 & R=0.62, p=0.07). Management implications are significant. Gravel habitats were associated with higher eulachon bycatch, and vessels can use bottom-typing tools to avoid them. Also, delaying the season opener could reduce bycatch, as eulachon catch was reduced by 0.0109 mt per trawl over the interquartile range of day of the year. These findings can inform Best Management Practices (BMPs), which have historically led to regulatory changes such as the adoption of excluder grates and LED lights. Overall, incorporating near-bottom oceanographic data greatly enhanced predictive performance, especially for demersal species like eulachon. These mechanistic SDMs can be projected forward, aiding future management amid changing ocean conditions. While some discrepancies remain, this approach offers promising insights for adaptive fishery management and conservation of imperiled species like eulachon.

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Time Period of Content:

Geographic Extent: California Current

Status: Final

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Format: .R, .m, .pdf

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No data information was supplied.

Entity and Attribute Information

Attributes Description: The code used to develop this manuscript are presented here. Data area available on request as they contain confidential information. The "gray literature" cited are all collated here for ease.

Is a physical copy maintained for reference at Headquarters? Unknown