Dolphins and herring of the Salish Sea: understanding responses of a top predator to fluctuating prey and human disturbance
Presentation Abstract
Pacific white-sided dolphins (Sagmatias obliquidens) are found reliably in inshore waters of British Columbia, including the northern extent of the Salish Sea. A long-term (>25 year) ecological study on this species provided an opportunity to develop a generalizable framework to predict population consequences of varying prey levels and acoustic disturbance to a top predator in the northeastern Pacific. Dolphin survival and reproductive rates were estimated from a large, long-term photo-ID dataset. We modelled non-calf survival as time-varying functions of two prey species as candidate covariates: Pacific herring (Clupea pallasii) and pink salmon (Oncorhynchus gorbuscha). Pacific herring are critical to food webs in the Salish Sea and for a healthy ecosystem. Herring support seabirds, fish, and marine mammals and are of vital cultural significance, but many stocks, including in the Salish Sea, have declined and failed to recover. We found that Pacific white-sided dolphin apparent survival declined significantly during years of low herring abundance, but did not vary with pink salmon abundance. Our field experiments revealed that dolphins decreased their time feeding in the presence of low-amplitude (126 dB) boat noise. During experimental treatments, the altered activity budgets resulted in a mean proportional reduction in foraging of 0.289 (95% bootstrap CI: 0.163, 0.408) between control and treatment conditions. We constructed a PCoD-like model that allowed us to predict demographic consequences of disturbance by perturbing this prey-demography link. The result is a flexible, generalizable PCoD framework that can be applied to model responses of a marine top predator to naturally varying levels of forage fish abundance, as well as noise-mediated disruption of foraging. We welcome opportunities to derive prey-demography links for similar species and apply the tool to the Salish Sea ecosystem more broadly.
Session Title
Session 1.2 A: Trophic energy flow in the Salish Sea: Part IV (Marine Mammals)
Conference Track
Trophic Interactions - Zooplankton, Phytoplankton, Salmon, Forage Fish & Invasive Species
Conference Name
Salish Sea Ecosystem Conference (2020 : Online)
Document Type
Event
SSEC Identifier
2020_abstractID_5798
Start Date
21-4-2020 12:30 PM
End Date
21-4-2020 2:00 PM
Genre/Form
conference proceedings; presentations (communicative events)
Subjects – Topical (LCSH)
Dolphins--Food--Salish Sea (B.C. and Wash.); Pacific herring--Predators of--Salish Sea (B.C. and Wash.)
Geographic Coverage
Salish Sea (B.C. and 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
application/pdf
Dolphins and herring of the Salish Sea: understanding responses of a top predator to fluctuating prey and human disturbance
Pacific white-sided dolphins (Sagmatias obliquidens) are found reliably in inshore waters of British Columbia, including the northern extent of the Salish Sea. A long-term (>25 year) ecological study on this species provided an opportunity to develop a generalizable framework to predict population consequences of varying prey levels and acoustic disturbance to a top predator in the northeastern Pacific. Dolphin survival and reproductive rates were estimated from a large, long-term photo-ID dataset. We modelled non-calf survival as time-varying functions of two prey species as candidate covariates: Pacific herring (Clupea pallasii) and pink salmon (Oncorhynchus gorbuscha). Pacific herring are critical to food webs in the Salish Sea and for a healthy ecosystem. Herring support seabirds, fish, and marine mammals and are of vital cultural significance, but many stocks, including in the Salish Sea, have declined and failed to recover. We found that Pacific white-sided dolphin apparent survival declined significantly during years of low herring abundance, but did not vary with pink salmon abundance. Our field experiments revealed that dolphins decreased their time feeding in the presence of low-amplitude (126 dB) boat noise. During experimental treatments, the altered activity budgets resulted in a mean proportional reduction in foraging of 0.289 (95% bootstrap CI: 0.163, 0.408) between control and treatment conditions. We constructed a PCoD-like model that allowed us to predict demographic consequences of disturbance by perturbing this prey-demography link. The result is a flexible, generalizable PCoD framework that can be applied to model responses of a marine top predator to naturally varying levels of forage fish abundance, as well as noise-mediated disruption of foraging. We welcome opportunities to derive prey-demography links for similar species and apply the tool to the Salish Sea ecosystem more broadly.
