Study Shows Sharks Recovering in Southeast
Every year, biologists across the Southeast take to the ocean to catch, study, and release thousands of sharks ranging from 3-foot bonnetheads to 13-foot tiger sharks. The surveys provide scientific snapshots of these apex predators, which play an important role in keeping oceans healthy but saw rapid declines starting in the mid-1970s.
Now, a study analyzing data from these projects suggests good news: after two decades of conservation and management measures, many of the region’s most common shark species show signs of bouncing back from overexploitation.
Published recently in Fish & Fisheries, the paper analyzed data for seven shark species between 1975 and 2014: four large coastal sharks (sandbar, blacktip, spinner, and tiger sharks) and three small coastal sharks (Atlantic sharpnose, blacknose, and bonnethead sharks). By the end of the study period, all but one of the species (Gulf of Mexico blacknose shark) showed an increase in abundance.
First author Cassidy Peterson, a graduate student at the Virginia Institute of Marine Science, amassed the study data from six state-, federal-, and university-run surveys across the Southeast, including two conducted by SCDNR biologists: the coastal longline survey and SEAMAP survey.
“What's great about this analysis is that it brings together different survey data and produces robust estimates of population trends,” said marine biologist Bryan Frazier, who oversees SCDNR’s coastal longline survey and is a contributing author on the study. “Using traditional stock assessment methods, it may take a year or more to determine the status of a single species. This tool will allow for more real-time monitoring of multiple species.”
In late summer and fall, Frazier and crew set out aboard the R/V Silver Crescent to study mature red drum and sharks off the coast of four major South Carolina estuaries. At thirty randomly selected locations in each estuary, the team drops a long fishing line into the water, its forty hooks baited with Atlantic mackerel or striped mullet. The gear soaks for half an hour, and the pungent bait attracts red drum and sharks in the area. As they reel the line in, the biologists aboard the Silver Crescent work rapidly to measure, tag, and release any hooked animals.
SCDNR staff also conduct the federally funded Southeast Area Monitoring and Assessment Program South Atlantic (SEAMAP-SA) Coastal Trawl Survey, which collects long-term data on not just sharks and their habitats, but also crustaceans, bony fish, cephalopods, and horseshoe crabs. In spring, summer, and fall, the Coastal Trawl Survey crew surveys shallow nearshore areas from Cape Hatteras to Cape Canaveral aboard the R/V Lady Lisa, a shrimp trawler retrofitted for marine research.
Over time, the data collected on these trips have helped SCDNR researchers track fluctuations in South Carolina’s shark populations. The challenge, of course, is that large coastal shark species don’t respect state lines. Sandbar sharks, for example, may travel from the estuaries of North Carolina as far as the Gulf of Mexico as they mature. Studies combining regional data are thus necessary for the most accurate account of how shark populations are faring.
Because sharks were poorly studied before commercial and recreational shark fishing began in earnest in the 1970s, biologists remain uncertain what historic shark populations looked like – and therefore what might constitute full recovery for each species.
Overall, though, Frazier says the study’s results should be cause for optimism and encouragement that shark management measures are working – not cause for alarm.
“While an increasing number of sharks in the water may frighten beachgoers, there’s little to be concerned about,” Frazier said. “Shark bites remain an exceedingly rare occurrence in SC waters.”
Peterson CD, Belcher CN, Bethea DM, Driggers III WB, Frazier BS, Latour RJ. Preliminary recovery of coastal sharks in the south-east United States. Fish Fish. 2017;00:1–15. http://onlinelibrary.wiley.com/doi/10.1111/faf.12210/abstract.