Streaming Media
Presentation Abstract
Efforts by people to restrain tidal inundation to promote agriculture and development has led to large amounts of tidal wetland habitat loss in large river deltas across the Pacific coast. Concomitant declines in these populations have raised questions about the extent to which juvenile Chinook salmon compete for limited estuary habitat and how estuary restoration will help recover populations. To examine the potential for habitat limitation, we used a cross-system approach to combine outmigrant and population density data in four large river deltas of Puget Sound. By adjusting outmigration abundance to natural-origin outmigrants/ha of delta channel, we were able to develop a statistical stock-recruit model that standardized outmigrations across all four estuaries. Our analysis revealed evidence for negative density dependence throughout the range of observed outmigration sizes. We were able to estimate a density at which capacity was likely exceeded at an instantaneous (daily) time scale, and this estimate was within the range of other independently observed density-dependent processes like diet selectivity and reduced growth. While density dependence was observed within most years in all deltas, certain systems were much more likely to exceed capacity than others. We also observed both total lack of use of some locations even when capacity had been exceeded elsewhere, as well as local densities at over 10x estimated capacity. Our findings call into question simplifications of deltas gradually filling as they near capacity and “spilling over” into other habitats upon exceeding capacity. Nevertheless, in those systems that surpass estimated capacity, estuary restoration is likely to have immediate, consistent, and widespread benefits. For systems that do not regularly surpass capacity, careful consideration of the desired future population state (i.e., meeting recovery plans) in the context of other possible recovery strategies will help practitioners determine the long-term efficacy of estuary restoration.
Session Title
Salmon Management & Marine Survival
Conference Track
SSE4: Fish Science and Policy
Conference Name
Salish Sea Ecosystem Conference (2022 : Online)
Document Type
Event
SSEC Identifier
SSE-traditionals-444
Start Date
27-4-2022 9:45 AM
End Date
27-4-2022 11:15 AM
Type of Presentation
Oral
Genre/Form
conference proceedings; presentations (communicative events)
Subjects – Topical (LCSH)
Chinook salmon--Habitat--Washington (State)--Puget Sound; Salmon--Habitat--Washington (State)--Puget Sound; Deltas--Washington (State)--Puget Sound; Fish populations--Washington (State)--Puget Sound; Animal population density--Washington (State)--Puget Sound
Geographic Coverage
Puget Sound (Wash.)
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Type
Text
Language
English
Format
vnd.ms-powerpoint
Included in
Fresh Water Studies Commons, Marine Biology Commons, Natural Resources and Conservation Commons
Density-dependent habitat limitations for juvenile Chinook salmon in large river deltas of Puget Sound
Efforts by people to restrain tidal inundation to promote agriculture and development has led to large amounts of tidal wetland habitat loss in large river deltas across the Pacific coast. Concomitant declines in these populations have raised questions about the extent to which juvenile Chinook salmon compete for limited estuary habitat and how estuary restoration will help recover populations. To examine the potential for habitat limitation, we used a cross-system approach to combine outmigrant and population density data in four large river deltas of Puget Sound. By adjusting outmigration abundance to natural-origin outmigrants/ha of delta channel, we were able to develop a statistical stock-recruit model that standardized outmigrations across all four estuaries. Our analysis revealed evidence for negative density dependence throughout the range of observed outmigration sizes. We were able to estimate a density at which capacity was likely exceeded at an instantaneous (daily) time scale, and this estimate was within the range of other independently observed density-dependent processes like diet selectivity and reduced growth. While density dependence was observed within most years in all deltas, certain systems were much more likely to exceed capacity than others. We also observed both total lack of use of some locations even when capacity had been exceeded elsewhere, as well as local densities at over 10x estimated capacity. Our findings call into question simplifications of deltas gradually filling as they near capacity and “spilling over” into other habitats upon exceeding capacity. Nevertheless, in those systems that surpass estimated capacity, estuary restoration is likely to have immediate, consistent, and widespread benefits. For systems that do not regularly surpass capacity, careful consideration of the desired future population state (i.e., meeting recovery plans) in the context of other possible recovery strategies will help practitioners determine the long-term efficacy of estuary restoration.
