Contrasting fishing effort reduction and habitat connectivity as management strategies to promote alewife (Alosa pseudoharengus) recovery using an ecosystem model

Abstract

Small pelagics, or forage fish, link lower and higher trophic levels in marine food webs. Recently, attention has been given to the management of forage fish, including anadromous river herring (Alewife Alosa pseudoharengus, blueback herring A. aestivalis) and American shad (A. sapidissima) due to their current depleted status and historically important ecological and economic roles. Little is known about the impact of changes in their biomass on marine food webs and what management practices will promote their recovery. Estimated historical riverine productivity was utilized to evaluate potential ecosystem impacts of the increasing river to ocean connectivity to resemble 19th-century conditions. The Ecopath with Ecosim modeling framework was used to simulate management strategies, focused on anadromous forage fish, by creating scenarios of fisheries reduction (mixed fishery effort reduction) and river to ocean habitat connectivity (75% of historical connectivity achieved). Sixty-year simulations covered the entire time series including a 36-year forecast period to evaluate the ecosystem impacts of management strategies. Results suggest nonlinear relationships and large changes in biomass flows from forage fish to upper trophic levels in the Gulf of Maine ecosystem. Increases in biomass were observed for pelagic sharks, demersal piscivores, and species of conservation concern such as pinnipeds and seabirds, although overall results were strongly influenced by indirect trophic effects. Promoting anadromous forage fish recovery through increased connectivity resulted in the redundancy of marine ecosystem niches that would increase resilience to climate, fisheries, and other perturbations. This study highlights the value of employing ecosystem models for testing management scenarios to contrast different approaches to recover anadromous forage fish towards its former ecological prominence.

Nonlinear dynamics, resilience, and regime shifts in aquatic communities and ecosystems: an overview

“…Disturbances and subsequent recovery of marine and inland water populations, communities, and ecosystems are illustrated in studies of tidal salt marsh creeks subjected to erosion (Wu et al 2022), oceanic food webs affected by a major oil spill (Lewis et al 2022), picoplankton communities disturbed by episodic physical forcings in the upper ocean (Rii et al 2022), and small pelagic fish populations in relation to changing fisheries management (Dias et al 2022). While disturbances are often obvious, these studies document the recovery process through the use of numerous metrics.…”

Early detection and recovery of river herring spawning habitat use in response to a mainstem dam removal

“…This is especially true for river herring, as forage species populations remain vulnerable to high natural mortality pressures as prey [ 5 , 8 , 23 ]. Modeled changes in New England alosine biomass show minimal responses to reduced fishing effort, whereas combining reduced fishing effort and substantial increases in freshwater-marine connectivity could increase biomass to early 1900’s baselines [ 24 ]. Dam removal thus likely plays an important role in restoring depleted river herring populations given the species’ ecology and life history.…”

Managing Small Fish at Large Scales: The Emergence of Regional Policies for River Herring in the Eastern United States

“…The large number of stressors and the interactions among them calls for a diverse portfolio of management responses (Nelson et al 2020; Dias et al. 2021; Panel 1). Historically, two of the most abundant diadromous species in the Eastern United States were the anadromous Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis , collectively known as “river herring.” These species are ecologically important in freshwater, estuarine, and marine systems, especially as prey for a wide variety of predators including larger fishes (Buckel et al 1999; Moring and Mink 2002; Ames and Lichter 2012), birds (Viverette et al 2007), and mammals (Browne and Terhune 2003).…”

“…These barriers also exacerbate effects of other stressors, including invasive species, thermal pollution, contaminants, sedimentation, and altered hydrology (Bednarek 2001). The large number of stressors and the interactions among them calls for a diverse portfolio of management responses (Nelson et al 2020;Dias et al 2021; Panel 1). Historically, two of the most abundant diadromous species in the Eastern United States were the anadromous Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis, collectively known as "river herring."…”