Atlantic bluefin tuna
BIOLOGICAL SAMPLING
Globally, commercial tuna fisheries account for more than $33 billion and conservative estimates including their recreational component exceed $45 billion. While their value is high, our understanding of their life history is not. We conduct research on a variety of tunas, but our primary focus is on Atlantic bluefin tuna in the Gulf of Maine.
Every season, the Pelagic Fisheries Lab collects over 1500 Atlantic bluefin tuna samples including heads, stomachs, and livers. These samples come from various sources including commercial dealers, local Atlantic bluefin tuna tournaments, commercial fishermen, recreational fishermen, and more.
Once we collect Atlantic bluefin tuna heads, we make sure they are iced down to preserve freshness. We remove muscle tissue samples for genetic testing as well as an archive sample to save for later projects. We also extract otoliths, small calcified structures located in the brain cavity of Atlantic bluefin tuna, which are used to estimate the age of the fish when it was caught and where the fish was spawned (stock of origin).
We would like to acknowledge that the research we conduct in the Pelagic Fisheries Lab would not be possible if it were not for industry involvement and collaboration. We thank every individual who helps us obtain these samples every field season.
A fully polished Atlantic bluefin tuna otolith displayed on a monitor ready to be aged.
A sectioned and polished Atlantic bluefin tuna otolith that is being imaged for aging.
Atlantic Bluefin Tuna otolith aging
After extracting otoliths from the Atlantic bluefin tuna head, there are several different processes needed to prepare otoliths for aging and micro-milling.
For aging, tuna otoliths form annuli, which resemble 鈥渢ree rings鈥. These rings represent fast & slow growth zones that are identifiable by dark and light shades when observed with transmitted light. By counting the fast growth bands, we can get an estimate for the number of annual feeding seasons the fish has lived through which represents the age of the fish, similar to aging a tree by counting the rings presented by growing seasons.
Atlantic Bluefin Tuna Otolith Microchemistry
For determining stock of origin, the otoliths are milled using a machine called a micro-mill. At the center of each otolith are chemical markers composed of material deposited while individuals are on their spawning grounds. Based on these chemical signatures, we can estimate if the Atlantic bluefin tuna was spawned in the Gulf of Mexico (Western stock) or in the Mediterranean (Eastern stock). This information is extremely important because, although the stocks are managed separately, there is evidence of some mixing between the two stocks 鈥 particularly here in the Gulf of Maine.
The micro-mill work is conducted by the Kerr Lab of the University of Maine for their project on 鈥淓valuating Age Structure, Aging Bias and Mixed Stock Composition of Atlantic bluefin tuna in the Northwest Atlantic鈥.
The otolith of an Atlantic bluefin tuna.
Atlantic bluefin tuna otoliths arranged in resin bars in preparation to be cut into smaller sections.
An Atlantic bluefin tuna otolith ready to be sectioned using an IsoMet precision saw.
Atlantic Bluefin Tuna Foraging Ecology
As part of an ongoing research effort, the Pelagic Fisheries Lab initiated a long-term study on Atlantic bluefin tuna foraging ecology to see what they eat in the Gulf of Maine and how that may change over time. This project has grown into a collaborative research effort with the Maine Department of Marine Resources.
Atlantic Bluefin tuna best handling practices
The Pelagic Fisheries Lab presents the “Best Handling Practices” for commercial Atlantic bluefin tuna. Special thanks to NOAA Fisheries and the Saltonstall-Kennedy Program, who provided us with essential funding to complete this project. This video was shot, produced, and edited by Nick Jones of Jones Media Co.
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Questions?
pelagicfisherieslab@gmail.com