Long-term collaborative research commitment to detect groundfish recovery and ecosystem response to conservation efforts in Eastern Gulf of Maine.
Overview
Since their collapse in the 1990s, groundfish such as Atlantic cod stocks in the Gulf of Maine have struggled to recover, with spawning stock densities remaining at historic lows to this day. This is particularly true in the Eastern Gulf of Maine which, despite virtually no directed fishing effort in this area.
The decline in prey species, such as alewives, preceded this collapse and local knowledge firmly connects the fate of the two fisheries. An increase in lobster fishing effort may also play a role in the ecosystem’s declining diversity, and the sluggish recovery of groundfish, in particular cod.
With the ongoing efforts to restore alewife runs along the Maine coast, we continue to look for the response of those species that prey on these fishes, with a long term vision of a thriving ecosystem including a recovered Groundfish fishery.
Atlantic cod fish. Credit: NOAA Fisheries
Updates
The Challenge
Marine surveys are essential for understanding fisheries population trends and reveal that cod prefer hard, rocky bottom to mixed and soft sediments, where harder sediment acts as protective cover from predators. Cod are most frequently caught in shallow water, less than 50 meters. Water in these shallow areas can warm up to temperatures over 20 °C in the summer, but cod are more likely to be caught when surface temperatures are below 15℃. Bottom temperature was also found to be significant and follows a similar pattern to surface temperature, preferring cooler water below 10℃.
These shallow, rocky areas are precisely where state and federal research survey vessels struggle to sample, and yet this is where it is thought cod recovery may be first detected.
The Opportunity
Fisherman’s local ecological knowledge is invaluable to understanding localized patterns of fish behavior and response to changes. A primary question is whether cod population abundance is going up or down in this part of the Gulf of Maine? Is the alewife restoration supporting this as a mediating mechanism?
MCCF, in cooperation with the community and partners, designed and launched a cooperative research program entitled the “Eastern Gulf of Maine Sentinel Survey” with an objective to generate vital data of ecosystem response to alewife restoration and fisheries management. The survey has operated uninterrupted since 2012, as a collaborative between MCCF, the University of Maine, and The Nature Conservancy of Maine, and dozens of commercial fishermen.
Diadromous Watersheds-Ocean Continuum concept - Credit Valerie Ouelette
Robyn Linner (left) works up samples from a long-line haul as Capt. Trundy organizes gear for the next set.
Our Aim & Approach
Each year, graduate students from the University of Maine and MCCF staff accompany almost a dozen fishermen to set baited longlines and jig gear in over 100 locations from June through October. The survey samples over 5,000 square miles of coastal shelf from Port Clyde, Maine to Canada. Sites for survey sampling are randomly selected annually, plus a handful of fishermen’s choice sites. The timing of the research effort in late spring and fall augments the data collected by Federal and State research vessels, by expanding the footprint of suitable habitat where we’re looking for cod recovery significantly.
This long term time series has created actionable data which helps us piece together a more informed picture of how cod stocks and population genetics may influence the recovery trends, and localized factors. Biological samples collected by onboard scientists are studied by partners to investigate stock structure, diet, spawning conditions, and environmental factors that might be playing a role in the recovery of a once iconic fishery in eastern Maine.This data stream also provides today’s commercial fishery with an index of juvenile abundance, as an element of the long-term time streams used in the Gulf of Maine stock assessment.
Examples of biological samples collected are:
Gonads: tell us about reproductive maturity and whether a fish is pre- or post-spawn
• Stomach contents: tell us what a fish is eating
• Otoliths: or ear bones, tell us how old a fish is
• Fin clips: genetic analysis identifies what stock or sub stock population the fish belongs to
• Muscle tissue: tells us about diet patterns
• Photographs: used for morphometric studies
Partners
The Eastern Gulf of Maine sentinel survey also inform a wide array of research questions. Woods Hole Oceanographic Institute analyzes muscle tissue samples of cod for stable isotope signatures indicating diet patterns. The 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 and stomach contents for recent feeding patterns. The University of New Hampshire uses bone samples for genetic stock structure studies. These collaborations have been key to the success of the program, and crucial toward understanding the complexities in the ecosystem. The NOAA Northeast Fishery Science Center uses the long term time series as an index of abundance for juvenile cod, and more recently the data have become an indicator for the Eastern Gulf of Maine cod populations, which may be a unique sub-population and showing promises of recovery since 2022.
Funders
Doree Taylor Charitable Foundation
National Sea Grant
The Nature Conservancy of Maine
Cited Literature & Further Resources
Linner, R. and Y. Chen. 2022. Implications of stock structure in understanding juvenile Atlantic cod (Gadus morhua) habitat suitability in the Gulf of Maine. Reg Stud Mar Sci. Vol. 53.