Date of Completion

12-15-2016

Embargo Period

6-13-2017

Keywords

predation, ecosystem modeling, river herring, striped bass, fisheries management, ecology, Connecticut River, blueback herring, alewife

Major Advisor

Eric Schultz

Associate Advisor

Jason Vokoun

Associate Advisor

Chris Elphick

Associate Advisor

Peter Turchin

Associate Advisor

Richard Jacobson

Field of Study

Ecology and Evolutionary Biology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Case studies of the ramifications of predator management for prey population dynamics can play a valuable role in developing ecosystem fisheries management. My dissertation focuses on the predator-prey interaction between Striped Bass (Morone saxatilis), an abundant predatory finfish, and an imperiled prey population of anadromous Blueback Herring (Alosa aestivalis). Annual returns of Blueback Herring to the Holyoke Dam on the Connecticut River in southern New England collapsed during the 1980-2000s, coincident with Striped Bass recovery. I studied the abundance and demography of both species in the Connecticut River during 2005-08, measured predation levels, and surveyed the in-river recreational Striped Bass fishery. Herring in 2005-08 were on average younger, smaller, and less likely to be repeat spawners than during the 1960s. These findings suggest elevated mortality operating on adult herring, consistent with other contemporary studies of river herring runs. I estimated that approximately 125,000 Striped Bass were present in the upper 64 km of the river stretch below the Holyoke Dam in spring 2008, and that this predator contingent was capable of consuming 200,000-800,000 adult herring annually. I also estimated that increased in-river recreational Striped Bass harvests might reduce annual predatory losses by 4-10%. I constructed a stage-structured model of the Blueback Herring population spawning above the Holyoke Dam, and used it to a) assess whether Striped Bass predation could explain the collapse of the herring run to the Holyoke Dam, and b) whether reductions in adult herring mortality effected through increased Striped Bass harvest could substantially improve recovery prospects. Model simulations suggested that Striped Bass predation made a substantial contribution to the collapse of the Holyoke herring run: over 50% of model simulations predicted a run crash, and metrics of population resilience and reproductive potential were greatly reduced in the presence of Striped Bass predation. Increased in-river harvests of Striped Bass offer potential to conserve Blueback Herring under some scenarios; however, the requisite harvest levels appear improbable given the observed intensity of the fishery. This study will inform future efforts to conserve river herring and manage Striped Bass populations, and illustrates the trade-offs inherent to ecosystem-based management.

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