SEA 



SCIENCE 



TOP: A mother and her calf swim nearthe Proteus. BOTTOM LEFT: Andy Read and 

 Ari Fried laender spot a dolphin in the distance as Kim Urian records its location. 

 BOTTOM RIGHT A leftover fish head in a gill net is a telltale sign of dolphin depredation. 



consuming to attach the devices; he can't afford 

 to experiment during the height of Spanish 

 mackerel season. Leaving Save Waves on the 

 nets also is out of the question, as the powerful 

 net reel would shatter them. 



"They're not very robust," says Read. Save 

 Waves are designed for European fisheries, 

 which typically haul in nets by hand. If Save 

 Waves were ever to be used in the United States, 

 they would have to be redesigned to withstand 

 hydraulic equipment, he adds. 



The Blame Game 



Soon, researchers on the Proteus spot a 

 group of dolphins heading for Swanner's boat. 

 Read and Urian quickly record the dolphins' 

 position using an onboard Global Positioning 

 System (GPS) unit, and Williams, the group's 

 acoustic expert, drops a hydrophone in the water 

 to record the dolphins' echolocation clicks. 



As each dolphin surfaces, Friedlaender 

 photographs its dorsal fin for later identification. 



"Knowing who's who is important in our 

 work," says Read. 



The team is fairly sure these dolphins 

 mostly live in estuarine areas, traveling from inlet 

 to inlet. 



Read suspects the animals are not trying 

 to grab a free meal from Swanner's nets, 

 however. Data from past observations and photo 

 identification indicate dolphins living primarily in 

 the open ocean are more likely to depredate than 

 their estuarine counterparts. 



Even so, the team must wait until Swanner 

 pulls in his nets to be sure the estuarine dolphins 

 weren't snacking. 



"You'll know there was depredation 

 because there will just be mackerel heads in the 

 net," says Burke. 



"Dolphins get blamed for most of the 

 depredation because they're very visible," 

 explains Read. Sea turtles, sharks and crabs are 

 other likely suspects, but dolphins usually take 

 the fall because of their highly visible, high- 

 energy behavior. 



Yet the dolphins' speed and gymnastics 

 don't seem to increase their risk of entanglement, 



says Read. In a previous study, he and Urian 

 observed a group of dolphins swim alongside 

 as many as 10 gill nets without getting tangled. 



"How are they figuring out the nets are 

 there?" Urian wonders rhetorically. 



To try and answer that question, Swanner 

 designed a fake gill net — a corkline with floats 

 but no actual netting. The dolphins aren't quite 

 sure what to make of it, says Urian. 



"A couple go under, but most of them go 

 around," says Read. "It really does seem like 

 they are confused by it — they expect to see a 

 net there." 



Navigational Nuances 



Eventually, the dolphins investigating 

 Swanner's nets lose interest and swim away. 



Williams' hydrophone didn't pick up 

 any echolocation clicks. Many of the estuarine 

 dolphins don't seem to use their powerful sonar 

 ability while transiting the Hatteras shoreline, 

 she says. 



The team has recorded the same dolphins in 

 both Hatteras and Beaufort, and they echolocate 

 more in Beaufort, she says. 



The reason for this variation isn't entirely 

 clear, but water clarity may be a factor, adds 

 Read. 



If the water is turbid, dolphins may be 

 forced to echolocate more frequently, he says. 

 Read suggests that dolphins use a range of senses 

 to navigate their environment, including vision 

 and passive listening. 



"If the net isn't visible, and it doesn't 

 produce any sound, they might run into it," he 

 reasons. 



Without a clear understanding of how 

 dolphins detect nets, it is difficult to develop 



new fishing gear or methods to reduce 

 entanglements. In addition to acoustic alarms, 

 Read hopes to study whether altering net design 

 would affect entanglement rates. 



"Nets with larger mesh [holes] tend to be 

 more dangerous to dolphins because they are 

 designed to catch larger animals," he explains. 

 Mesh with smaller holes and made of thicker 

 material would be stiffer, possibly making it 

 easier for dolphins to escape. 



But Read cautiously balances what is 

 good for the ocean versus what is good for those 

 who depend on it: "The bigger question is how 

 would thicker nets with smaller holes affect the 

 catch?" 



More than an hour after his first set, 

 Swanner pulls in the nets and finds only four 

 mackerel, three bluefish and one blue crab. 

 Dunn and Waples report similar luck from the 

 Shannon D. 



Bad weather and unusually low fish 

 catches last summer made it difficult to gather 

 enough data to draw conclusions about dolphin 

 response to Save Waves, says Read. However, 

 data from Burke's observations show that the 

 devices did not affect fish catches. 



Read and his team plan to return to 

 Hatteras this summer to continue researching 

 the devices, produced by Save Wave Dolphin 

 Savers. 



"We'd rather not be introducing all that 

 sound into the environment," he admits. "But 

 I also don't think it is fair to provide fishermen 

 with a potential means of reducing depredation 

 and then not assess whether it works." □ 



26 SPRING 2005 



