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Size of Prey Matters Most.

Bluefin tuna are going hungry in a sea full of fish because their foraging habits are most efficient with larger--not necessarily more abundant --prey, according to a study led by Walter Golet, assistant research professor in the School of Marine Sciences at the University of Maine, Orono.

The Gulf of Maine is an important foraging ground for bluefin tuna (Thun-nus thynnus). Their preferred prey is Atlantic herring (Clupea harengus). Tuna spend up to six months in the Gulf consuming high-energy prey such as the herring and, in doing so, accumulate as much as 200 pounds in fat. Energy acquired in the Gulf of Maine is vital to support bluefin tuna migration and reproduction.

The population of Atlantic herring has increased over the past two decades, suggesting that foraging conditions should have been favorable for bluefin tuna. A decline in bluefin tuna despite abundant prey resources was puzzling, so the researchers tested hypotheses related to the energetic payoff of eating herring of various sizes, comparing this across different regions of the northwest Atlantic.

Researchers identified a correlation between bluefin tuna body condition, the relative abundance of large Atlantic herring, and the energetic payoff resulting from consuming different sizes of herring. The correlation is consistent with the optimal foraging theory, a model used to predict how an animal behaves when it is searching for food.

These correlations could explain why the condition of bluefin tuna suffers even when prey is abundant. According to the researchers, this also may explain a shift in distribution of bluefin tuna to offshore banks and locations further north on the northwest Atlantic shelf where herring (and their corresponding energetic payoff) are larger.

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Title Annotation:BLUEFIN TUNA; Atlantic herring
Publication:USA Today (Magazine)
Article Type:Brief article
Geographic Code:0ATLA
Date:Jun 1, 2018
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