New Technique Estimates Sexual Maturity of Rare Bluefin Tuna

First Posted: Dec 03, 2014 08:28 AM EST
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Do you like eating bluefin tuna? You may want to watch what you eat. These large fish have been overexploited for years. Now, though, scientists are making efforts for determining the age at sexual maturity for wild stocks of western Atlantic bluefin tuna, which could help officials better manage fish stocks.

"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," said Molly Lutcavage, one of the researchers, in a news release. "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."

In order to assess bluefin tuna, the scientists introduced a new endocrine-based approach. This allowed the researchers to determine the timing of sexual maturation in one of the most important commercial tuna species in the Atlantic.

In the past, sexual maturity for bluefin tuna was determined by observing fish sizes on the known spawning grounds during the known spawning season. Since bluefin tuna aggregate roughly by size for reproduction, this is a bit like searching for expectant mothers only in hospital delivery rooms. Spawning bluefin using locations and times other than those observed in the northern Gulf of Mexico were largely overlooked, which lead to underestimating the spawning stock biomass.

"We needed to analyze sexual maturity in bluefin of different sizes where they mix, on their feeding grounds such as the Gulf of Maine," said Lutcavage. "But since this is not a breeding location, fish lack the obvious characteristics of those in spawning condition. 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."

So what did they find? It turns out that Atlantic bluefin tuna of sizes 134 to 185 cm CFL sampled in the northwest Atlantic are sexually mature. This means that alternative reproductive behavior scenarios for spawning locations and times should be considered.

These findings should help officials to estimate more accurate stock assessments. This, in turn, should help bolster tuna populations.

The findings are published in the journal Scientific Reports.

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