Better Estimating Size of Bluefin Tuna Populations

Written by on December 15, 2014 in Fish, Marine Life

New research suggests that western Atlantic bluefin tuna mature at a much younger age than currently assumed, which could have an impact on the way fisheries scientists estimate population sizes.

School of bluefin tuna. Photo credit: NOAA.

School of bluefin tuna. Photo credit: NOAA.

“Whether a bluefin tuna or cod, for realistic fish stock assessments it’s important to know at what age, where, when and how often fish spawn. Here in Gloucester and New England, it’s painfully clear from the groundfish management crisis that fisheries scientists and managers must get these basics right,” Molly Lutcavage, one of the lead researchers from the University of Massachusetts Amherst, explained in a news release.

The researchers used a new endocrine-based approach for determining age at sexual maturity. Previously, the age was determined by observing fish sizes at known spawning grounds during the spawning season, because bluefin tuna are known to gather roughly by size during reproduction. However, this leaves the potential of overlooking bluefin tuna that use other spawning locations, which could lead to an underestimate of population size and reproductive potential.

“We needed to analyze sexual maturity in bluefin of different sizes where they mix, on their feeding grounds such as the Gulf of Maine. But since this is not a breeding location, fish lack the obvious characteristics of those in spawning condition,” Lutcavage said. “We had to come up with a novel approach to determine maturity. Endocrine tools, recently developed in Israel for bluefin aquaculture, were just what we were looking for.”

To try this new method, they sampled 110 Atlantic bluefin tuna, taking size, weight, and hormone level measurements. They found that “maturity schedules” for eastern and western Atlantic bluefin tuna are not what we had previously thought and that they reach sexually maturity at 134-185 cm CFL (curved fork length).

The authors conclude that maturity and reproduction markers currently used for western Atlantic bluefin tuna need to be revised, “which would contribute to more accurate stock assessments and estimates of spawning stock biomass.”

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Copyright © 2014 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .


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