Presentation Abstract

The Salish Sea is an important migratory corridor and feeding area for juvenile salmonids yet little is known regarding movement behaviours and survival through this region. We used acoustic telemetry tracking in sockeye and steelhead smolts to: 1) identify marine travel rates and routes, 2) estimate migration survival rates, and 3) identify factors contributing to mortality. Sockeye smolts travelled at 10 km / day in their clear natal river, 200 km / day in the turbid Fraser River mainstem, and 10-15 km / day in the marine environment. Steelhead smolts travelled approximately 2-3 times faster in the same marine segments, potentially owing to their larger size. Both sockeye and steelhead seemed to prefer migrating through western or central routes en-route to the open ocean, rather than more easterly routes when transiting the Discovery Islands chain – and survival to the open ocean, at least for steelhead, was higher if travelling through the most western route. Survival was poorest through the earliest migratory segments for both species and both exhibited less than 10% survival by the final acoustic receiver station near northern Vancouver Island. Several factors were associated with mortality including smolt age, size, tag burden, and fish health as assessed by biomarkers and pathogens. Pathogen-laden sockeye were far more likely to be predated upon (found in the stomachs of bull trout). Sockeye smolts could increase their probability of survival by out-migrating in high densities – survival probability doubled with ~ 2-fold increase in migrating density. This evidence of depensatory mortality indicates that salmonid smolts may survive poorly in years of low marine abundance.

Session Title

The Salish Sea Marine Survival Project: Understanding Salmon Survival

Keywords

Salmon smolts, Telemetry, Salish Sea

Conference Track

SSE11: Species and Food Webs

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE11-385

Start Date

5-4-2018 2:00 PM

End Date

5-4-2018 2:15 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 5th, 2:00 PM Apr 5th, 2:15 PM

Telemetry tracking of salmon smolt migrations through the Salish Sea: examining behaviour, survival and causes of mortality

The Salish Sea is an important migratory corridor and feeding area for juvenile salmonids yet little is known regarding movement behaviours and survival through this region. We used acoustic telemetry tracking in sockeye and steelhead smolts to: 1) identify marine travel rates and routes, 2) estimate migration survival rates, and 3) identify factors contributing to mortality. Sockeye smolts travelled at 10 km / day in their clear natal river, 200 km / day in the turbid Fraser River mainstem, and 10-15 km / day in the marine environment. Steelhead smolts travelled approximately 2-3 times faster in the same marine segments, potentially owing to their larger size. Both sockeye and steelhead seemed to prefer migrating through western or central routes en-route to the open ocean, rather than more easterly routes when transiting the Discovery Islands chain – and survival to the open ocean, at least for steelhead, was higher if travelling through the most western route. Survival was poorest through the earliest migratory segments for both species and both exhibited less than 10% survival by the final acoustic receiver station near northern Vancouver Island. Several factors were associated with mortality including smolt age, size, tag burden, and fish health as assessed by biomarkers and pathogens. Pathogen-laden sockeye were far more likely to be predated upon (found in the stomachs of bull trout). Sockeye smolts could increase their probability of survival by out-migrating in high densities – survival probability doubled with ~ 2-fold increase in migrating density. This evidence of depensatory mortality indicates that salmonid smolts may survive poorly in years of low marine abundance.