A survey started nearly 25 years ago in the U.S. East Coast waters is helping scientists and fishery resource managers to monitor shark populations and their role in marine ecosystems.
Researchers caught 1,675 sharks from 19 different species and tagged 1,352 individuals during the 2009 survey in April and May. They recorded the length, sex and location of each animal caught before the fish was tagged and released, although it wasn’t weighed. Most of the animals caught and tagged were sandbar sharks, a common species in the western Atlantic.
Any dead fish are carefully dissected at sea, with researchers looking for parasites, collecting DNA and blood samples, and obtaining samples for studies of age and growth, reproductive biology and food habits.
Nancy Kohler, head of the Apex Predators Program at the NEFSC Narragansett Lab said:
“During the survey, we often catch 19 or more species, many of which are highly migratory, and we still have a lot to learn about them. We do not know how large certain species are when they mature, for example. It is important that we obtain basic biological information from the fish we catch so that we can learn as much as possible about their life histories, or the changes that the animals undergo from birth to death.”
She explained the survey is conducted in the spring because coastal shark species distributions are concentrated during this time of year since the waters north of Delaware are too cold, thus making it easier to survey the whole population.
In addition to numerous sandbar sharks, the researchers also caught one great white, many tiger and dusky sharks, and some Atlantic sharpnose. The current data are part of just one of several long-term data sets that are used to determine the health of shark populations.
The survey, which has been conducted every 2-3 years along the last 25, takes six weeks to complete and is divided into three legs, each approximately two weeks long. Eight scientists are on board mostly NOAA’s ship Delaware II for each leg, and fishing is conducted around the clock. Environmental information, such as water temperature and ocean chemistry, is obtained at each station.
The survey data are then provided to the fishery managers who monitor populations in the Atlantic and Gulf of Mexico. NOAA Fisheries Services manages the commercial and recreational shark fisheries in U.S. waters. The United States began regulating shark fisheries in 1993 and currently manages 39 species. A fishery management plan that includes sharks, swordfish, and tunas went into effect in 1999, regulating sharks under a catch limit and quota system.
Copyright © 2009 by Marine Science Today, a publication of OceanLines LLC