This is a hot button topic in several New England states, eliciting citations of contradictory research and a lot of emotion, depending on one’s priorities for lake management. The fundamental issue is that alewife (usually Alosa pseudoharengus, but other related herring species are sometimes involved) feed by straining water through gill rakers for plankton, much like baleen whales filter out krill and larger plankton in the ocean, leaving very low biomasses of zooplankton for other fish to eat. Where adult alewife enter lakes from the ocean as anadromous fish, spawn, and leave, the juveniles remain during summer and decimate the zooplankton, but those lakes tend to evolve ecologically, with zooplankton reaching winter maxima and managing to support the food web. But where a landlocked alewife population is established, zooplankton density may be depressed all year long, severely limiting food for small fish that feed visually on large zooplankton. Alewife may provide a valuable food base for some gamefish, but do so at the expense of the rest of the fish community.
Restoring a historic alewife run is therefore a very different policy decision than stocking alewife into a lake where they will be landlocked. For fishing enthusiasts, the potential for trophy gamefish is attractive when a landlocked alewife population is established. But for those interested in clear water, the alewife will promote the greatest amount of algae possible for whatever level of fertility is present. In a lake with enough phosphorus to support algae blooms, the presence of alewife all year is almost a guarantee of blooms, whereas a different fish assemblage might minimize bloom potential by favoring zooplankton control of algae.
If stocking of alewife was accompanied by a nutrient control program to limit the potential for algae blooms, it might be more palatable, but fishery agencies that are the normal advocates for such stocking have never been in the business of overall lake management, and are not known to be advocates for nutrient control. This lack of a more holistic approach to lake management has led some to refer to fishery agencies as government of the fish, by the fish, and for the fish. At the same time, those focused on water clarity have been called Secchi disk worshipers and such a narrow focus is also not holistic. Those promoting anadromous alewife runs are on pretty sound ground, but the debate goes well inland from coastal areas.
Alewife, Alosa pseudoharengus