Not the alewife you're used to: The politics of trophic interactions between sea-run alewife and naturalized smallmouth bass in the St. Croix River, Maine

Background/Question/Methods

In 1981, fishway improvements to the first dam on the St. Croix River, New Brunswick –Maine led to resurgence in the St. Croix’s anadromous (searun) alewife population. This marked the beginning of a struggle between local economic interests and state, national, and international conservation interests over alewife access to the river. The State of Maine Legislature voted in favor of local economic interests in 1995 by legislating that alewives be excluded from 99% of their spawning habitat in the St. Croix River to preserve smallmouth bass populations in the upper watershed. A central question in the debate over alewife was how alewives affected the trophic dynamics of their freshwater spawning habitat. In particular, the concern expressed by the anti-alewife lobby was that a size structured interaction contributed to poor smallmouth bass growth and year class failures. This paper summarizes a project implemented in 2005 to summarize the data and positions of alewife opponents and proponents, and collect new data on anadromous alewife – smallmouth bass interactions in eastern Maine lakes. Diet and zooplankton standing stock data were collected from four lakes with sympatric smallmouth bass and anadromous alewife populations.
Results/Conclusions

Young-of-year (YOY) alewives and smallmouth bass were caught in mixed schools by beach seine in 1.2m of water or less. YOY of both species ate zooplankton, especially in earlier samples. Alewives collected later in the season had changed little in diet preference; smallmouth bass diversified their diets to include fish and more benthic invertebrates. Zooplankton size structure decreased over time but less than might be expected given results for landlocked alewives. One reservoir with intermittent populations of landlocked alewives never had large zooplankton. The study concluded that alewives did not negatively affect smallmouth bass in lakes in the region. Growth did not decline in the presence of anadromous alewives, YOY smallmouth bass condition did not decline when alewives were present, and diet overlap between the two species was low in three of four lakes. Ramifications of this study to the ongoing political process surrounding the St. Croix River will also be discussed.