About Our Research

As restoration projects are deliberated, what ecosystems used to look like becomes a very important question. Anadromous fish return to freshwater to reproduce after spending a period of time in the ocean and are therefore impacted by human activities in both places. Historic anadromous fish populations in the St. Croix River were estimated at 7000 to 18,000 salmon and 31,700,000 alewives (1). Both species now have extremely small populations due to freshwater habitat destruction and fisheries. Present-day fisheries are also helping conserve river herring since fish captured at months of river are often transported over dams in order to stock ponds and guarantee sustainability of catches.

The Atlantic cod fishery was one of the earliest and most important fisheries of the United States. Analysis of historic information on Atlantic cod populations, migration patterns and fishing grounds shows a 50% decrease in Gulf of Maine coastal spawning grounds over the last century (2). Studies suggest inshore cod populations historically followed and fed upon large populations of spawning river herring returning to rivers in the spring (2,3,4). We believe that Gulf of Maine cod populations over the past decade have varied between 2-8% of the original carrying capacity.

Gulf of Maine cod and river herring have similar trends of collapse in the past 30 years. Abundance of alewives returning to Maine is correlated with the number of cod produced the following year in the Gulf of Maine, potentially because of energy required for successful reproduction, demonstrates some dependence of cod to river herring. No significant correlations exist when comparing Maine alewife abundance to cod in the Bay of Fundy, Scotian shelf, northern Georges Bank and southern Georges Bank suggesting a dependence on Gulf of Maine alewives as a food source of coastal Gulf of Maine cod.

The objective of our study is to create a timeline that demonstrates how Europeans and indigenous peoples affected coastal ecosystems. Initially we will be valuating the historic abundance of the anadromous river herring, made up of two species: alewives (Alosa pseudoharengus) and blueback herring (Alosa aestivalis). See more information at Maine Department of Marine Resources. Then we will be asking whether these changes are related to the poor condition of cod populations (see illustration below).

Estimates of river herring abundance will be corroborated using fisheries landings data provided by towns over the last century. Historical river herring estimates will then be compared to historical evaluations of cod productivity in the coastal waters, as well as other predators in the Gulf of Maine, to assess the effect of an indirect mechanism - the reduction of river herring spawning habitat and removal of river herring as a prey source - on components of coastal ecosystems.

Two main questions will be addressed: (1) does changing available spawning habitat in the Gulf of Maine river systems due to building of dams on river systems correspond with the abundance of river herring populations? And (2) do historic abundances of river herring populations correspond with the documented decline of historic inshore cod populations in the Gulf of Maine? Photos and Figure by Carolyn Hall

Full description of completed and ongoing research available Final Report (pdf file).

References

  1. Loetze H.K. and Milewski, I. 2004. Two centuries of multiple human impacts and successive changes in a north Atlantic food web. Ecological Applications 14: 1428-1447.
  2. Ames, E.P. 2004. Atlantic Cod stock structure in the Gulf of Maine. Fisheries 29:10-28.
  3. Baird, S. 1874. U.S. Commissioner of Fish and Fisheries Report of the Commissioner for 1872 and 1873. Washington, D.C.
  4. Graham, J., Engle, S. and Recchia, M. 2002. Local knowledge and local stocks: An atlas of groundfish spawning in the Bay of Fundy. The Centre for Community-based Management, Extension Dept., St. Francis Xavier University. Antigonish, Nova Scotia, Canada.