SEA 



SCIENCE 



Striped Bass Predation 

 of River Herring Explored 



By Ann Green • Photos by Michael H aim in ski 



w. 



' ith an almost full moon glowing in 

 the dark sky, North Carolina Sea Grant research- 

 ers are engaged in a tug of war deep in the 

 Albemarle Sound. 



Standing near the edge of a boat railing, 

 four men pull in a line on a purse seine net — 



Joe Hightower heads out along the Chowan River to 

 collect striped bass. 



which closes up at the bottom like a drawstring 

 on a woman's purse — in rhythmic motion. 



Then the researchers examine a large catch 

 of juvenile herring that have an iridescent glow in 

 the dark. 



"The density of juvenile river herring is higher 

 than I expected based on recent data," says North 

 Carolina State University zoologist Jeff Buckel. 

 "We expected juvenile herring catches to be 

 extremely low in the Albemarle Sound." 



The purse seine net is just one type of gear 



used in a Sea Grant study that focuses on the 

 mortality of two species of herring — alewife and 

 blueback herring — in the Chowan River and 

 Albemarle Sound prior to outward migration to 

 the ocean. 



Over the past year, researchers also have 

 used beach seines, gill nets and 

 bottom trawling to collect juvenile 

 river herring and their predators. In 

 recent years, both adult landings 

 and juvenile recruitment of river 

 herring have declined in North 

 Carolina. 



There has been much public 

 concern about the negative impact 

 of striped bass on economically 

 important species, including river 

 herring, Buckel says. 



Striped bass populations along 

 the Atlantic coast have grown 

 dramatically in the last 1 5 years, says 

 Buckel. In North Carolina, the 

 number of striped bass that are 

 more than four years old has 

 increased eight-fold, according to a 

 study byjohn Carmichael, a 

 biologist with the N.C. Division of 

 Marine Fisheries (DMF). 



"The population of striped 

 bass is larger than we have ever 

 seen," says the Sea Grant project's co-investiga- 

 tor, Joe Hightower, a biologist with the U.S. 

 Geological Survey. "We are looking to see if the 

 ecosystem is out of balance." 



Alternative Way of Collecting Fish 



To determine the impact of striped bass 

 predation on juvenile river herring, the researchers 

 collect striped bass on the Chowan River by 

 electroshocking — a process that uses a generator 

 to send an electric current through the water, 



temporarily stunning the fish. 



Electroshocking can be used in locations 

 where large nets are not applicable, says 

 Hightower. "The fish are attracted to the electric 

 field and swim toward the boat. You can adjust 

 the setting for different species," he adds. 



After collecting the samples, scientists 

 looked at the stomach contents of striped bass. 



"Preliminary results show that the amount 

 of river herring found in the stomachs of small 

 striped bass is higher than what is found in larger 

 striped bass," says Buckel. "However, small 

 striped bass also feed on menhaden, silversides 

 and bay anchovy. High densities of these 

 alternative prey may provide juvenile river herring a 

 refuge from predation." 



Sea Grant researchers also looked at the 

 growth and feeding rates of striped bass 

 throughout the summer. 



"Preliminary results from 2002 suggest that 

 the growth and feeding rates of small striped bass 

 were low in May and June, but increased in July," 

 says Buckel. "This result was surprising and could 

 mean that the impact of these small predators in 

 early summer is minimal." 



Researchers also found that large striped 

 bass had a higher percentage of empty stomachs 

 in August compared to other months. "This 

 confirms earlier research that found large striped 

 bass lose weight when the water temperatures are 

 warm," says Buckel. 



In North Carolina, striped bass as well as 

 river herring are important for commercial 

 fisheries. 



After striped bass are caught, they go to 

 packing houses and restaurants for consumer use. 

 Some bluebacks and alewives go to fish-packing 

 plants for transformation into herring with cream 

 sauce or other delicacies, but most become 

 fertilizer, fishmeal or bait. 



Continue d 



COASTWATCH 21 



