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Forage Fish and Gulf of Maine Cod

May 28, 2012
Spring 2012

In early April NOAA Fisheries announced interim management measures for Gulf of Maine (GOM) cod. These new catch limits allocate to fishermen a total of 6,700 metric tons of GOM cod for the 2012 fishing year. NOAA has announced its intention to update the 2011 GOM cod assessment in time to set catch limits for 2013. Short of new findings, the catch limit for GOM cod in 2013 is likely to be much lower than in 2012.

Among the most perplexing questions facing fisheries ecologists studying cod is: Why haven't cod populations in eastern Maine rebounded over the past thirty years? Despite virtually no fishing pressure, cod continue to be very scarce east of Pemaquid. If cod in eastern Maine are indeed their own sub-population, it seems logical that their numbers would increase in an era free of fishing. Yet they remain very low.

Oceanographic conditions likely prevent larvae from cod spawning in the western GOM from traveling east. Likewise, tagging data suggest that adult cod from the western GOM rarely travel east. This might help explain why relatively more abundant stocks in the western GOM have not repopulated he eastern GOM. Regardless, there must be something other than fishing pressure that is keeping cod stocks in eastern Maine from rebounding.

That something might be food.

Ted Ames of Penobscot East Resource Center speculates that the decline of forage fish in coastal Maine waters, both Atlantic herring and river herring, may be suppressing cod recovery. Once abundant, these high quality prey species are favored food for cod. Ames' thinking reflects work done in Canada to understand the collapse, and muted rebound of cod off Newfoundland in recent years. Despite two decades of fishing bans in this region, cod have not fully recovered, and forage fish shortages are thought to be involved (Sherwood et al. 2007) -- in this case shortages of capelin (a herring-like fish).

If Ames is correct, and the situation is anything like that in Newfoundland, cod is unlikely to return in any significant numbers to eastern Maine until its favored food returns as well. Habitat restoration efforts along the coast, most notably the Penobscot River Restoration Project, could make critical spawning habitat available to river herring once again. Ecologists predict that the planned removals and bypasses on three major dams along the main stem of the Penobscot River will lead to increases in river herring (a term used to include both alewives and blueback herring) runs. With backing from The Nature Conservancy and the Penobscot River Restoration Trust, scientists from the University of Southern Maine and GMRI are conducting baseline ecological surveys of the Penobscot River, its bay, and estuary to monitor those predicted changes.

Fishermen and managers alike hope that river restoration projects will increase alewife populations, and improved Atlantic herring assessments will result in a clearer picture of the dynamics between Atlantic herring and cod. Both could ease a constraint on cod recovery -- their food.

Additional Links & Resources

Penobscot East Resource Center

Penobscot River Restoration Project

NOAA Fisheries Gulf of Maine Cod Hot News

Northeast Cod Tagging Program

Canada News: Newfoundland cod fishery sees glimmer of hope. May 21, 2012

Waypoints Winter 2012: Gulf of Maine Cod Faces Tumultuous Times

Publications

Ames, E.P. 2004. Stock Structure of Atlantic Cod in the Gulf of Maine. Fisheries, 29:10-28, 2004

Ames, E.P. 2010. Multispecies Coastal Shelf Recovery Plan. Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem 
Science, 2:217-231, 2010

Sherwood, G.D., Rideout, R.M., Fudge, S.B., and Rose, G.A. 2007. Influence of diet on growth, condition and reproductive capacity in Newfoundland and Labrador cod (Gadus morhua): insights from stable carbon isotopes. Deep-Sea Research II 54: 2794-2809.