Ben Towne ’12 (Bowdoin) – Monitoring the diets of fish in the Gulf of Maine

The research that I was involved over the summer covered many aspects of the Merrymeeting Bay and Kennebec Estuary ecosystem. One part of my research involved directly monitoring the species that comprise major commercial fisheries in the Gulf of Maine. The fish that were of primary importance were cod (Gadus morhua), pollock (Pollachius pollachius), and striped bass (Morone saxatilis).

The once thriving cod-fishery in the Gulf of Maine has been exploited and over-fished since early European colonization. The fishery thrived up until the mid 1900’s when stocks became noticeably downgraded and depleted. This has been a common theme along the north- east coast with the almost complete collapse of the fishery. A native Maine fisherman and scientist, Ted Ames, investigated the collapse of the fishery. He gathered knowledge from fishermen that have been around long enough to still know some of the historic groundfish spawning areas.(Ames 1997) These spawning grounds had been over-fished decades earlier, and had been almost completely forgotten about. To revive the fish populations that once frequented these areas, a sustainable forage base is a necessary prerequisite.

Historically, a main food source for these fish included smaller anadromous fish. Anadromous fish spend most of their lives in salt water but enter fresh water to spawn. The depletion of the some of these fish populations occurred simultaneously to the collapse of the cod fishery. The health of the rivers and lakes that these fish enter, could have been unable to support spawning populations as well as juveniles. Additionally, dams on rivers completely blocked these fish from reaching upstream spawning grounds. One species that is believed to be of utmost importance is the river herring or alewife (Alosa pseudoharengus). Not only are alewives an important commercial resource, but also fish in the Gulf depend on the adult stock and juveniles exiting the rivers as major components within their diet.

To be able to monitor what portion of the diet is comprised of alewives, my colleagues and I would accompany a local fisherman, out of Fort Popham, on fishing trips. Different sites were sampled using bait and lures. The sites consisted of places known to currently have fish such as ledges, eel grass beds (Zostera marina), eddies, and banks. When a fish was caught, it was placed into a water bucket that filtered in oxygenated water. Once the fish was identified, weighed, and measured, the stomach contents were analyzed by placing a tube that ejects pressurized water into the stomach, in order to make the fish regurgitate. Once fish appeared revived, they were released back into the open water. The contents were then placed into a labeled glass jar to be evaluated later in the lab. From this data we were able to directly monitor what forage base was being utilized at different sites and times.

Over the span of five years, we will be able to tell what prey is most predominant in these fish diets and how their prey consumption changes seasonally and annually. Although not all of the regurgitated stomach contents have been analyzed, initial observations revealed that shrimp, alewives, and small crabs make up a large portion of the diet. We hope that over five years, we will see an increase in the ground fish and striper stocks now that the reviving alewife population can provide a large enough forage base for fish stocks to once again be sustainable in the Gulf of Maine.

Faculty Mentor: John Lichter

Funded by Sustainability Solutions Partners

References: Ames, E.P. (1997) Cod and Haddock Spawning Grounds of
the Gulf of Maine;NRAES 118, Ithaca,NY



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