Abstract
River herring (alewife, Alosa pseudoharengus, and blueback herring, Alosa aestivalis) are anadromous alosines that play important ecological roles and comprised major US fisheries in the past. Stocks are at historically low levels Atlantic coast-wide and river herring are being considered for listing as threatened species under the Endangered Species Act. A comprehensive, linked freshwater and marine approach to restoring these important species is proposed, informed by a “life cycle” strategy for the recovery of an Endangered Pacific salmon species. The California coho salmon strategy entails identifying core populations stratified by biological units, assessing threats and developing site-specific and range-wide recovery actions to restore habitat and abate threats to all life stages. Protecting and strengthening core populations, combined with marine strategies, is likely key to the recovery of the species at scale. A case study is presented from the Taunton River, a ∼1300-km2 watershed in Massachusetts (USA) that hosts one of the largest river herring runs in New England. This watershed and its river herring populations possess multiple characteristics that indicate resilience and thus it could be an example of a river herring core habitat, critical for the recovery of the species at scale. A watershed-wide protection and restoration initiative is underway. Site-based strategies including dam removal, low impact development retrofits, and land protection are linked to policy efforts such as establishing streamflow standards and easing permitting of restoration projects to protect and improve connectivity, flow, and water quality. These watershed-based strategies are linked to regional scale research and fisheries management to set sustainable directed harvest targets and reduce the bycatch of river herring in ocean fisheries. Core habitats for river herring need to be identified range-wide and investments in those places prioritized to secure resilient source populations.
Introduction
River herring are anadromous, plankton-feeding fish that spend most of their adult lives at sea, returning to freshwater by age 4 to spawn (Collette and Klein-Macphee, 2002). Adults quickly return to the sea and young rear in freshwater until fall. An individual may complete five or more spawning migrations in a lifespan up to 10 years. Historical accounts suggest river herring occurred in extraordinary abundance, which made them important from economic and cultural, as well as ecological, perspectives. These species supported native Americans and European colonists as a reliable food source in early spring when other foods were scarce. Harvest records in Massachusetts date back to the 17th century. Their cultural significance is illustrated by works such as Henry David Thoreau's (1849) lament of the loss of herring runs due to dam construction on the Concord River. They are also important forage fish for freshwater and marine predators (Loesch, 1987) and transfer nutrients in both directions between freshwater and marine realms (Mullen et al., 1986). Unfortunately, the 2012 Atlantic States Marine Fisheries Commission (ASMFC) stock assessment of river herring determined that the status of these species is depleted, and National Oceanic and Atmospheric Administration (NOAA) is investigating whether river herring should be listed under the Endangered Species Act in all or some portion of their range. Depletion of river herring stocks has resulted in the closures of fisheries for these species and impacts on other coastal fisheries dependent on these forage fish. Obstructed access for alewives to just nine watersheds in Maine is estimated to have resulted in lost production of 11 billion fish from 1750 to 1900 (Hall et al., 2012).
Loss of access to spawning habitats, overfishing, and pollution all played roles in historical declines and extirpations of diadromous species such as river herring around the North Atlantic basin (Limburg and Waldman, 2009). Anadromous fish are subject to habitat impacts and pollution in freshwater from dams and urbanization, in addition to environmental and harvest pressures at sea (Moring, 2005). Recent high mortality of river herring is attributed to a combination of factors including fishing (in-river directed and ocean bycatch), inadequate access to habitats, impaired water quality, excessive predation, and climate change (ASMFC, 2012). Shifts in environmental conditions may differentially affect river herring populations. Weather patterns can impact river herring in several ways—changing food production and thus growth in nursery areas, influencing cues and success of fall outmigration (Nelson et al., 2011), and indirect effects such as closure of fishways when spring flows exceed tolerances (Brown et al., 2013). Because of their complex life cycles, the management of multiple factors in rivers and at sea is necessary for species recovery. Given the species' importance and status, it is vital to identify which investments in conservation, management, and research are most likely to recover populations that will be resilient to future threats including impacts of climate change. It is equally important to set realistic benchmarks, measure population responses, and actively use data to inform management decisions.
The “life cycle conservation” strategy outlined in Canada's Policy for Conservation of Wild Pacific Salmon (Fisheries and Oceans Canada, 2005) and recently in the United States in a detailed recovery plan for endangered Central California Coast coho salmon (NMFS, 2012a) is a useful model to consider applying to river herring on the East Coast. The goal of this approach is to align conservation actions around the needs of salmon at each life stage and link them across the salmon's entire migratory path from freshwater to estuary to open ocean. The coho recovery plan identified “core” populations stratified by biological units, assessed threats, and developed site-specific and range-wide recovery actions designed to restore conditions and abate threats. Spawner abundance targets were established at each scale (focus populations, diversity strata, whole ecologically significant unit). This approach focuses recovery actions in areas considered critical for species survival.
River herring could benefit from a holistic, range-wide strategy linking key freshwater systems with coastal and marine habitat needs for all life stages. Identification of a network of core populations, stratified by biologically relevant units, could help focus resources such as technical assistance and funding on places likely to be important for viability. Expert input is vital to develop sound criteria for selecting cores.
Resilience (ability to persist through and recover from disturbance) of diadromous species has been a key theme of recent Diadromous Species Restoration Research Network workshops. Waldman (2013) elaborated on factors that test resilience such as barriers and watershed modifications; and extrinsic and intrinsic factors that contribute to resilience such as habitat heterogeneity, riparian zone condition, spawning habitat quality, meta-population structure, and life-history variation.
Maintenance of genetic, spatial, and phenotypic diversity of species and populations has been identified as a significant factor for both species conservation and provision of ecosystem services. Schindler et al. (2010) found that population diversity combined with life-history diversity significantly reduces interannual variability in adult returns of sockeye salmon, which supports ecosystem services by minimizing fisheries closures.
Significantly less is known about river herring stock structure compared with Pacific or Atlantic salmon. Life-history information reviewed in ASMFC (2012) identified that stock structure for river herring could occur either at the river or regional scale (>100 km). Genetic (Palkovacs et al., 2008, 2012) and morphometric (Cronin-Fine et al., 2013) results to date seem to support the regional scale. However, these analyses are ongoing, and stock structure along with extinction risk and climate change are key topics on which NOAA is gathering information to make a listing determination (NMFS, 2012b). Genetic differences were detectable between most rivers tested. This is consistent with observation in the stock assessment that nearby rivers could exhibit differences in trends in abundance, age structure, species composition, and other metrics, indicating that there are localized factors affecting the population dynamics of both species.
Whether river herring in the ocean cluster with their river or regional stocks or whether the river stocks mix completely at sea has not been determined yet. ASMFC (2012) also noted that many genotypes are probably extirpated.
There is strong evidence that river herring home to natal rivers. However, some individuals will colonize new areas; using otolith microchemistry, Gahagan et al. (2012) estimated straying rates in Connecticut streams at ∼20% for both species, higher than rates reported for salmon species and American shad. Some subpopulations tend to act as sources, whereas others are considered sinks, having a greater propensity for extirpation (Pulliam, 1988). Within various meta-populations, source populations must be identified and monitored to ensure their persistence and the possibility of future recolonizations of sink sites.
One example of a watershed that may function as habitat for one or more relatively resilient, core populations for river herring is the Taunton River (Figure 1), the longest free-flowing coastal river in New England. The Taunton was designated by Congress as a National Wild and Scenic River in 2009 in the recognition of “outstandingly remarkable” features including fisheries and biodiversity.
Map of the Northwest Atlantic coast indicating the Taunton River watershed and generalized areas where significant river herring bycatch events in the directed Atlantic herring fishery were reported between 2005 and 2011 (Cieri et al., 2008; Cournane and Correia, 2010; Bethoney et al., 2012; Cournane et al., 2012).
One of the largest river herring runs in New England spawns in the headwater lakes of a single one of the Taunton's tributaries, the Nemasket River. Surveys indicate that river herring are present in several other tributaries and spawning likely occurs in the mainstem as well, but detailed counts and demographic information are available only for Nemasket alewife. Only two male blueback herring have been sampled since 2004 (Nelson et al., 2011), but the sample location is upstream of the majority of suitable spawning habitat for blueback herring.
Belding (1920) outlines the decline in alewife habitat and fisheries in the Taunton River in the early 1900s, blaming poor management and fishway neglect. The Nemasket run persisted, but was seriously depleted by the mid-1960s, when renewed interest in the fishery led to fishway renovations and stricter harvest controls. With improved management, when visual counts began in 1996, the run had rebounded to over 1 million fish. In the early 2000s, the Nemasket run dropped, but less dramatically than others in the region, and increased quickly. Following the peak of 1.9 million fish in 2003, numbers declined through 2005 to 401 000 fish. Since 2008, numbers have increased to 791 150 fish on average (Nelson et al., 2011) and rebounded to ∼1.5 million by 2012 (J. Sheppard, unpubl. data).
Nemasket River alewife grow faster, include more age classes and older fish, and grow larger (up to 270 mm) than others in Massachusetts (NMFS, 2012b), suggesting that they may be more resilient. The habitat in this area also shows resilient characteristics. For example, the 2000-ha Assawompsett Pond Complex, the Nemasket's headwater lakes are vigorously protected as public water supplies. Most of its course runs through natural floodplains and riparian zones that buffer the effects of non-point source pollutants. There has been no legal harvest since 2005, when a state moratorium was enacted in response to poor condition of runs state-wide. The relatively pristine nature of the habitats in this area likely contributes to the population's apparent resilience.
Sustainability and resilience are strengthened by the presence of multiple subpopulations in different tributaries within the watershed (Waldman, 2013). The most recent survey of the Taunton watershed indicates that river herring are present in 15 other tributaries, and the system may support relatively high genetic diversity. One of these systems, the Town River/Lake Nippenicket, has supported runs up to 300 000 adults since 2000. Replicating protection and restoration efforts to as many tributaries as possible will enhance the core function of the Taunton River, offering river herring more options of habitat types and greater geographic diversity.
American eel, American shad, rainbow smelt, white perch, Atlantic tomcod, sea lamprey, and Atlantic sturgeon are also documented as present in the watershed, but current information on status is limited. Factors that could increase the watershed's value as a core for multiple diadromous species, such as the absence of mainstem dams (or hydroelectric dams anywhere in the watershed), also mean that some key drivers for diadromous fish survey efforts in other watersheds are not present. An updated survey would be valuable to inform whether the watershed is or could be a core for other species, based on criteria developed for them.
Strategies
The Nature Conservancy (TNC) is among several local, state, and federal partners, including MA Division of Marine Fisheries (DMF), MA Division of Ecological Restoration, NOAA, Taunton River Wild and Scenic Stewardship Council, and Middleboro–Lakeville Herring Commission working to maintain the river herring core of the Taunton River and restore conditions throughout the watershed to support the broad recovery of these species.
By taking a holistic approach, our goal is to enhance the resilience of watershed functions and ecosystem services in the face of climate change and predicted future development, so that benefits to the river herring and other species can continue into the future. Goals include improving connectivity, flow, and water quality in spawning/rearing watersheds and addressing excessive mortality at sea. Strategies include removing migration barriers, retrofitting existing development to increase groundwater recharge and reduce pollution and protecting key lands. These site-based strategies are linked to state-wide policy efforts such as establishing streamflow standards and easing permitting of restoration projects and regional scale research and fisheries management to reduce the bycatch of river herring in ocean fisheries.
Connectivity restoration
Barriers such as dams and undersized culverts not only block the passage of migratory fish; they also impair natural river and stream processes and pose safety hazards for the surrounding communities. There are over 100 dams within the Taunton River watershed, mostly unused remnants of defunct mills. About 25% of these block access to significant habitats for river herring and have been prioritized for removal or retrofit with new or updated fishways. For example, when complete, the Mill River restoration's removal of three dams and placement of a fishway on a fourth will provide access to 160 ha lacustrine and 48 km of riverine habitat. Estimates of potential river herring run size range from 50 000 to 600 000, based on recent adult returns to the Monument River (Nelson et al., 2011), a nearby system with similar habitat. Post-restoration monitoring of river herring began in 2013 and will continue until at least 2020. The focus of restoration is maximizing the restoration of river processes in an attempt to re-establish self-sustaining complex habitat, thus dam removal is strongly preferred. In all, 8–10 dams are proposed for removal by 2017, while efforts continue to assess feasibility of dam removal vs. fish passage at the remaining priority structures.
In addition to implementing dam removal projects, reforms in related regulations are also important. Changes in the state permitting process have been proposed to reduce costs and timelines for aquatic restoration projects like dam removal, culvert replacement, and coastal restoration. In 2012, new legislation established a $20 million state fund to remove and repair dams, giving incentives for owners to remove unneeded dams and properly maintain useful dams.
Water quantity and quality
The success of the anadromous reproductive strategy depends on elevated spring flows to cue migration in to rivers and suitable water and habitat quality after the spring freshet to support juvenile development (Chase, 2010). An observed correlation between the abundance of returning river herring and the flow that occurred 3 years prior suggests that flow during the fall outmigration period may be a primary driver of year-class strength for these fish (Nelson et al., 2011). A detailed study of water use and water transfer throughout the Taunton watershed found that 78 of 108 subwatersheds have water deficits compared with natural conditions, and in aggregate, there is a 6.2% water deficit caused by water use and run-off from impervious surfaces (Horsley Witten Group, Inc., 2008). Portions of several tributaries, including the Nemasket, often run extremely low in summer.
Although streams in much of the watershed are in relatively good condition, impairments including algal blooms, low dissolved oxygen, sediments, and pathogens have been observed (Rojko et al., 2005). The most common pollutant pathway noted in the report is stormwater run-off from roadways. A key recommendation of the watershed plan (Horsley Witten Group, Inc., 2011) is retrofitting existing development to increase groundwater recharge and improve water quality. For example, at Bridgewater State University, a rain garden installed in a reconstructed parking lot was designed to treat pollutants, reduce peak flows, and restore recharge to natural conditions. Students are monitoring water chemistry and hydrology.
Water withdrawals are permitted through the 1986 MA Water Management Act. Regulations under the Act are currently being revised through the Massachusetts Sustainable Water Management Initiative, which aims to improve the implementation of existing water management legislation through proposed policy changes that follow the Ecological Limits of Hydrological Alteration framework. The policies would provide a legal and scientific basis for establishing streamflow standards that ensure adequate flows for people and nature (Kendy et al., 2012).
Although the Taunton River watershed is in relatively good condition (improved from the past), several measures indicate that it may be susceptible to future degradation. Located between the cities of Boston, MA, and Providence, RI, with relatively affordable land, the region's human population is growing rapidly. Riparian lands provide for filtering of run-off as it flows from upland areas towards streams but, 56% of all sub-basins are comprised of less than 10% conservation lands or open space (Horsely Witten Group, Inc., 2008). The amount of developed land in the watershed increased 62% from 1971 to 1999. Several large contiguous habitat areas remain, typically anchored by large wetlands such as 7000 ha Hockomock Swamp. These large areas and streamside lands are the focus of land acquisition efforts for conservation. This work can have multiple benefits; as can be seen at Assawompsett Ponds, where over 300 contiguous protected hectares maintain clean drinking water for 150 000 people in six communities and maintain the integrity of spawning/rearing habitat for river herring.
Linking to marine habitat
Protection and restoration of river herring must go beyond the preservation of freshwater and estuarine habitats. Because river herring spend the majority of their life at sea, they are vulnerable to sources of mortality that occur beyond their natal river system (Figure 1). Management agencies have worked to address these concerns by highlighting the importance of mortality at sea, restricting harvest both in state and in federal waters. In state waters, directed fisheries for river herring were restricted by Amendment 2 to the ASMFC Shad and River Herring Fishery Management Plan, which imposed a coast-wide moratorium in 2012, with exceptions for states with approved sustainable fisheries plans. Amendment 2 also enacted new requirements for fisheries-independent and -dependent monitoring and reporting that should make future stock assessment both easier and more robust. In federal waters, the New England and Mid Atlantic Fishery Management Councils have voted to adopt bycatch caps for river herring and to increase the monitoring of catches.
Available evidence suggests that incidental catches of river herring are substantial, with unintentional yearly catches of ∼435 000 kg from 2006 to 2010 (MAFMC, 2012). However, because the 2012 stock assessment did not determine an overall population estimate with which to set a bycatch cap or overfishing/overfished status of river herring, the relationship between a river herring bycatch cap and river herring fishing mortality remains poorly understood (Cournane et al., 2012). Efforts are underway to create peer-reviewed coast-wide population/biomass models that can be used to set biologically based catch limits. In the interim, cap options are being developed using recent catch data.
A voluntary bycatch avoidance project, led by MA DMF and the University of Massachusetts at Dartmouth, involves increasing portside sampling of Atlantic herring and mackerel landings, a near real-time information system on the location of river herring and shad bycatch events, and testing if oceanographic features can be used to indicate areas with a high probability of bycatch. Cooperation by industry members and the appearance of distinct bycatch patterns within the avoidance areas suggests that these systems may be resulting in reduced alosine bycatch (Bethoney et al., 2012); the work is ongoing. This system potentially offers a method to keep river herring mortality within a regulatory cap, but that hypothesis will need to be tested.
Biological samples from the port sampling are provided to cooperators for analysis of genetics and otolith microchemistry. These data should shed light on the important question of whether certain runs are disproportionately impacted by bycatch. The results of this work can inform management actions likely to increase the abundance of river herring, helping to bolster spawning runs in core watersheds such as the Taunton River.
Conclusion
The resiliency of the Taunton River watershed's river herring population and its ecosystems provides a unique opportunity to aid river herring recovery. Because of the complex life cycle of the fish, habitat protection and restoration must occur in many different ecosystems across freshwater and marine realms and also consider both the aquatic systems and the land use in the surrounding watershed. A holistic approach to the protection and restoration of this core, and others range-wide, is important in the effort to recover larger river herring populations. Ongoing investments in surveys and stock assessments are necessary to evaluate the success of recovery strategies and support timely adaptive management. Recovery of these forage fish will benefit the river and marine ecosystems, as well as support sustainable fisheries for social and economic benefits.
Acknowledgements
This manuscript was improved by comments from Mike Bednarski, Daniel Bessette, Cathy Bozek, Erika Feller, Bill Hoffman, Jake Kritzer, and two anonymous reviewers.
References
Author notes
Handling Editor: Rochelle Seitz
