6. Native Alewife Restoration and Lake Water Quality
All-Day Session (Augusta Room, North Wing, 2nd Floor)
Concerns have been raised that restoration of native alewife runs to eutrophic lakes may exacerbate algae blooms and reduce water clarity. Two supposed mechanisms are offered. First, juvenile alewives are efficient consumers of the largest zooplankton which are themselves efficient consumers of suspended algae. A depleted zooplankton population may temporarily leave more nuisance algae in the water column, which reduces water clarity. Second, there are fears that spawning adult alewives may introduce more marine-derived nutrients to already overly fertile ponds than out-migrating juveniles can carry away in their bodies. Data from various Maine lakes show no clear relationship between the presence of native alewives and water clarity. Phosphorus budget studies suggest that low escapement may mitigate or reverse phosphorus loading impacts. In the absence of scientific consensus, public natural resource agencies have staked out opposing positions which may stall efforts to reconnect fragmented ecosystems.
Public discussion among researchers and resource managers will clarify research goals to determine optimum escapements and management strategies for restoring extinguished alewife runs while mitigating unwanted water quality impacts.
- 8:30AM – 8:55AM: Assessing the Impacts of Reintroducing Alewives: Lessons from ecological theory and existing research, William G. McDowell
- 9:00AM – 9:25AM: Top down vs. bottom up effects of searun alewife on lake phytoplankton dynamics: a case study of Highland Lake, Maine, Karen Wilson
- 9:30AM – 9:55AM: Exploring how a range of management objectives could affect alewife population recovery, Betsy Barber
- 10:00AM – 10:25AM: Factors affecting the density and growth of juvenile river herring: insights from 32 coastal New England freshwater lakes, Matthew T. Devine (student)
- 1:30PM – 1:55PM: River Herring Ecology and select Maine Lakes, Mike Brown, Gail Wippelhauser, Nate Gray
Maine Department of Marine Resources, Augusta, Maine
- 2:00PM – 2:25PM: Effect of anadromous alewives (Alosa pseudoharengus) on water quality of some Maine lakes, Barry Mower
- 3:00PM – 4:00PM: Panel Discussion
* Presenters are indicated in bold font.
8:30AM – 8:55AM
Assessing the Impacts of Reintroducing Alewives: Lessons from ecological theory and existing research
William G. McDowell
Department of Biology, Merrimack College, Andover, MA
Alewives, (Alosa pseudoharengus), are an anadromous fish native to the eastern seaboard of the United States. As adults, they return from the ocean in late spring and early summer in order to reproduce in freshwater lakes, and juveniles remain in freshwater until late summer when they return to the ocean. Alewives were once abundant throughout Maine, though dams and other human impacts have led to dramatic declines and the extirpation of many populations, causing the species to be listed as a species of concern by the US National Marine Fisheries Service. Anadromous alewives have been restored to many lakes throughout Maine, however there have been concerns about the impacts of alewives on water quality, as ecological theory indicates that alewives could lead to more algae via top down control of the food web, and bottom up impacts via the introduction of marine derived nitrogen and phosphorus. However, research on Maine lakes has shown that the reintroduction of alewives has not led to negative impacts on water quality. Here, we explore exactly what is meant by top down and bottom up control of algae growth, provide background on our current knowledge of the impacts of alewife reintroductions, and compare and contrast alewives to lessons from other trophic cascades and anadromous species such as salmon.
Top down vs. bottom up effects of searun alewife on lake phytoplankton dynamics: a case study of Highland Lake, Maine
Karen Wilson1, Jeff Dennis2, Linda Bacon2, Meg Thurrell3, Keith Williams4
1 Dept. of Environmental Science and Policy, University of Southern Maine
2 Lakes Division, Maine Department of Environmental Protection, Augusta, ME
3 Dept. of Biology, University of Southern Maine
4 Highland Lake Association Water Quality Monitoring Team
A PowerPoint presentation is not available for this talk. Please contact the speaker if you need more information.
Searun alewife (Alosa pseudoharengus) are strong interactors in lake ecosystems through the import and export of nutrients, and through efficient consumption of zooplankton. In 2015-2018, mesotrophic Highland Lake (Windam & Falmouth, Maine) experienced significant drops in water clarity during July and August (Secchi depth ≤ 2 m) in years in which alewife numbers ranged from ~14 – 100 spawning adults/acre. Continuing development of housing subdivisions in the watershed spurred the Lake Association to instigate an intensive study of the lake to determine the cause(s) of the algal bloom responsible for reduced water clarity. Results from 2018, during which the bloom did not fully materialize, showed a strong, spatially distinct spike in total phosphorus associated with a persistent metalimnetic dissolved oxygen minima after water clarity began to recover. This spike in TP had been observed in epilimnetic composite samples in previous years after the bloom had occurred. Adult alewife reached a high of ~100 spawning fish/acre, and juvenile alewife were present in the lake as late as mid-October. Processing of zooplankton and phytoplankton samples for species abundance and composition is in progress, although the lake exhibited a strong reduction in larger zooplankton after the spring clearwater phase. Results from this case study highlight the complexity of alewife-lake ecosystem interactions and the productivity of strong collaborations between lake associations and limnologists.
Exploring how a range of management objectives could affect alewife population recovery
Betsy Barber1, Jamie Gibson2, Andrew O’Malley1, Joseph Zydlewski1,3
1 University of Maine, Department of Wildlife, Fisheries, and Conservation Biology, Orono, ME
2 Fisheries and Oceans Canada, Science Branch, Maritimes Region
3 U.S. Geological Survey, Maine Cooperative Fish and Wildlife Research Unit, University of Maine, Orono, ME
Many alewife populations in Maine have experienced recent increases in spawner abundance. We developed a population model using best available regional data to explore the theoretical influence of management actions in the St. Croix River. Specifically, we explored the influences of fish passage improvements, stocking of adult spawners, and commercial harvest. We conducted simulations for a range of adult passage rates (upstream and downstream) and juvenile downstream passage. The relative location of dams to spawning habitat within this watershed affected the scope of population recovery because of the multiplicative effects of dam passage. Low passage efficacy also reduced both the overall abundance expected in the run as well as truncating the age structure of the population (reduction of older age classes). Interestingly, the theoretical effect of a commercial fishery on population recovery was strongly dependent on its location in the watershed relative to spawning habitat. We present this model as a tool that can be readily applied to other systems to inform local decision making by stakeholders.
Factors affecting the density and growth of juvenile river herring: insights from 32 coastal New England freshwater lakes
Matthew T. Devine (student)
University of Massachusetts Amherst, Department of Environmental Conservation
Current management objectives for anadromous (searun) alewife, Alosa pseudoharengus include restoring the species to historic spawning habitats, yet favorable conditions are not well described. Additionally, although it is assumed that adult run size reflects juvenile productivity and vice versa, these relationships have not been formally tested. Without knowledge of the adult-juvenile relationship and an understanding of what constitutes ideal spawning and nursery habitats in lakes, prioritization of habitat restoration is limited. In this study, we investigate the influence of adult density on juvenile density and explore the extent to which landscape characteristics (lake size, land cover) and lake nutrients (nitrogen, phosphorous, dissolved organic carbon) influence juvenile growth. Using a newly developed lake sampling protocol for juveniles, and laboratory analysis of otoliths to determine age and growth rates, we observed large differences in density and growth both within and among lakes. Adult density explained 60% of the variation in juvenile density and this relationship was nonlinear. Dissolved organic carbon (DOC) explained additional variation in juvenile densities, with lower herring densities in lakes with elevated concentrations of DOC. Surprisingly, growth rates were not influenced by nutrient levels. Instead, the density of juveniles best predicted growth where low density (stocked) lakes exhibited higher growth rates (mean ±SE = 1.04 mm/day ±0.020) than higher density lakes (0.891 mm/day ±0.017), suggesting density dependent growth as a key mechanism. Incorporating these relationships into population models will improve predictions of recruitment and assist management decisions and habitat prioritization for this economically and ecologically important species.
River Herring Ecology and select Maine Lakes
River herring (alewives and blueback herring) have direct and large impacts on regional ecologies in the freshwater (and marine) environment. The “Keystone species” aspect of their presence/absence will be discussed. A trophic cascade will be shown in which river herring are the keystone species. Several examples will be cited.
Effect of anadromous alewives (Alosa pseudoharengus) on water quality of some Maine lakes
Maine Department of Environmental Protection, Augusta, Maine
Maine’s water quality standards require that surface waters be suitable as habitat for fish and other aquatic life. Spawning areas are a critical part of habitat necessary to sustain fish populations. Anadromous alewives (Alosa pseudoharengus) are indigenous to many coastal aquatic systems with historic access to spawning grounds in lakes and ponds. In last 100 years or so, many dams have been constructed that have eliminated access of alewives to their spawning grounds. Human development of lakes and pond shorelines and watersheds has caused an increase in the input of phosphorus and resulting algal blooms. Knowing that in a simple food chain, juvenile alewives consume zooplankton, which in turn consume algae, some lakeshore residents fear that the Department of Marine Resources program for reintroduction of alewives to their original spawning lakes and ponds will cause or exacerbate algal blooms. But lake and pond food webs are much more complex than theoretical simple food chains. The Department of Environmental Protection has conducted two extensive studies and has examined water quality data from several other lakes or ponds with alewives. While no two lakes or ponds are exactly alike, to date there are no data documenting an increase in algal blooms in lakes with alewives. To the contrary, if water levels allow emigration of adults and juveniles from lakes and ponds, there may be a net export of phosphorus to the extent that blooms or their potential are reduced. A current study of Highland Lake in Falmouth may further inform these issues
2:30PM – 3:00PM
Afternoon Break (Main Auditorum)
Panelists: Bill McDowell, Karen Wilson, Betsy Barber, Matthew Devine, Mike Brown, Gail Wippelhauser, Nate Gray, Barry Mower