Maine Groundfish Research

Since the 1990s, the groundfish fishery in the eastern Gulf of Maine has been considered to be commercially collapsed. There are several leading hypotheses about the sources of the continued depletion of groundfish stocks: 1) extirpation of local stocks, which has impeded recovery; 2) a lack of  adequate forage base – including Atlantic herring and alewives, 3) lack of groundfish protection during critical life stages, including for juvenile and spawning fish; and 4) lack of protection of critical habitat. Now, though, there are signs that the fish are rebuilding.

Groundfish has been managed by the federal agency on a large scale: one abundance estimate is done for each species from Cape Cod to the Canadian border. The quality of the data from eastern Gulf of Maine is also poor, since the federal survey has few sampling sites there because of the rocky bottom and the prevalence of lobster traps. As a result, it is not possible to monitor or manage the sub-populations of fish distinct to particular bays or shoals.

Our groundfish research has been motivated by wanting to monitor the sub-populations distinct to the eastern Gulf of Maine. Groundfish in the area collapsed in the 1990s, long before they collapsed in the rest of the Gulf of Maine. We have enlisted coastal fishermen who work locally, observing local ecological dynamics. If we are able to assess and understand the behavior of these local stocks, then if – we think when – they rebuild, we will be in a better position to manage them sustainably.

Sentinel Survey

In 2010, Maine Center for Coastal Fisheries, Dr. Yong Chen at the University of Maine and local fisherman teamed up to start the Sentinel Survey. This collaborative research program uses both longline and jig hook gear to gather local, fine-scale information about groundfish populations in areas that are not well sampled by existing monitoring programs. Through partnerships with the Northeast Fisheries Science Center and The Nature Conservancy, data from the Sentinel Survey is evaluated to produce robust information for groundfish species such as Atlantic cod and Atlantic halibut.


The Sentinel Survey is a monitoring tool that helps build a scientific framework to understand groundfish stocks at a finer scale than that of federal management. Initially the survey has provided documentation of the collapse and is positioned to capture a potential restoration. Vested fishermen involvement in the program ensures that local knowledge is embedded in the research design. Additionally, the Sentinel Survey is used as a collaborative platform by various research groups to collect biological information on many different species. Woods Hole Oceanographic Institute analyzes muscle tissue samples of cod and pollock for stable isotope signatures indicating diet patterns. Gulf of Maine Research Institute uses photos of cod for morphometric studies on population structure. The University of Maine examines cod otoliths for age structure information. These collaborations have been key to the success of the program, and crucial toward understanding the complexities in the ecosystem.
Read the 2016 Sentinel Survey.

The Sentinel Survey has more sampling sites than any other monitoring program: its hook gear design is effective even fishing in dense lobster gear. Significantly, the survey is thus able to determine the relative abundance of cod in this ecologically distinct region. The colored station markers indicate depth strata and jig and longline stations.

BACI Survey

River restoration and dam removal is resulting in a rebound of prey species such as river herring, including alewives, which are prey for predators such as cod. Using Sentinel Survey sampling methods, the BACI (Before-After-Control-Impact) study evaluates the potential predatory response of Atlantic cod to increased prey availability at the mouth of the Penobscot River where historic restoration efforts have removed dams and opened 1000 miles of habitat for species such as river herring.  The BACI data is collected during the spring migration of adult groundfish into the estuary, and in the fall when juveniles are headed out to sea. We compare data collected at three Penobscot Bay sampling stations with data collected at three adjacent areas considered distinct from the Penobscot River restoration.

Data collected through the BACI study will provide insight on the coupled interaction between a predator and its prey, as well as track a shift in the dynamics of Atlantic cod in response to the river herring’s return to Penobscot Bay. Given the enormity of the Penobscot River system and the unprecedented, 10-fold increase in alewives in the system in the first three years, the framework of this study will inform future restoration projects around the world, and have significant implications for the entire New England groundfish fishery.
Read the BACI Survey.