Goal: To monitoring delphinids during mid- and deep-water net trawls in order to mitigate accidental captures or injuries to marine mammals.
Our Role: To use a towed hydrophone array system to monitor dolphins in the vicinity of nets before and during net tows.
Time Period: Summer 2011
The Deepwater Horizon oil spill disaster of 2010 created an immediate need to monitor the effects of the spill on marine life in potentially affected areas of the Gulf of Mexico. In 2011 NOAA deployed their research vessel, Pisces, to sample mid-and deep water species of marine life (i.e. fish and crustaceans). Net trawls were conducted to examine the meso- and bathypelagic fauna. The net tows were conducted both during the day and night, at stations located both inside and outside of the oil spill zone. Unfortunately during one of the earlier research cruises, three spotted dolphins (Stenella attenuata) were incidentally caught and drowned in one of the net deployments. At night, a potentially hazardous situation existed for delphinid species (which often were attracted to nets because of concentration of prey inside), but could not be seen by the tow operators because of light conditions. Because of this, NOAA requested Bio-Waves to provide a passive acoustic system to mitigate the possibility of catching dolphins both during the day and night while net tows where being conducted. During the night, when visual observations were not possible, passive acoustic monitoring was the only effective method to detect dolphins in the area. During this research cruises, Bio-Waves acousticians monitored a towed hydrophone array for 30 minutes prior to deployment of nets, and if any dolphins were detected, the deployment of the net was delayed. If dolphins were not detected, the array was retrieved and the trawl net was deployed. During four 10-day cruises in which Bio-Waves conducted passive acoustic monitoring and mitigation, no additional dolphins incidentally caught in nets. This demonstrated the success of passive acoustic monitoring and mitigation for this activity, with limited impact on the success of the overall research objective.
Sponsor: National Oceanic and Atmospheric Administration (NOAA)