Menhaden, a type of fish, are about one-half of the U.S. Atlantic and Gulf of Mexico fish harvest and have become smaller over the last 65 years in the U.S. Atlantic and Gulf Coast as ocean temperatures climb, according to Oceanography and Coastal Sciences Professor R. Eugene Turner.
Turner recently published a study about how Menhaden are shrinking due to rising ocean temperatures.
“The younger ones haven’t shrunk as much as the larger ones,” Turner said. “It depends on the interval, so for roughly 25 years, the one or two-year-old fish have shrunk about 10 percent, and the 4-year-old fish have shrunk about 24 percent, and that’s for Louisiana, for Atlantic, it’s slightly different.”
Menhaden had a dockside value of about $129 million in 2013. They are a coastal species that spawn offshore and move to estuaries where juveniles grow to be 1- and 2-year-old fish. The air and sea surface temperature off the Atlantic coast and the Gulf of Mexico has steadily increased, especially in estuaries, where heat exchange occurs efficiently between air and sea. Adult Menhaden return offshore where they are harvested with purse seine nets, according to a news release.
Scientists have been measuring Menhaden for about 60 years, primarily in North Carolina.
Menhaden in the Atlantic and the Gulf of Mexico are about one-half of the fisheries’ catch by volume. They are not so important dollar-wise, but they are used for chicken feed, cosmetics, bird food and oil is a major component of it, Turner said.
Data collected by the National Marine Fisheries Service shows a decline in annual weight and length among 3-, 4- and 5-year-old fish. For example, a 4-year-old fish captured in 2010 weighed 11 percent less than a 4-year-old fish captured in 1987.
Consequences of this change extend throughout the food web because many other species rely on Menhaden as their food source.
“There’s a physiological constant in a way, not true for everything, but larger you are, the colder it is because oxygen has to get to the internal organs,” Turner said. “If it’s a larger organism, it takes a while to get oxygen in there. If it’s thinner, there’s more diffusion of oxygen through the outside of the membrane through the organisms.”
