MONITORING FISH SPAWNING LOCATIONS AND MARINE MAMMAL SOUNDS WITH PASSIVE ACOUSTIC RECORDER ON A WAVE GLIDER

Abstract

Remote observations of marine animal behavior have one distinct advantage over direct observations: the observer is not present to disturb the animals. There are no vessel noises, no diver’s bubbles, no people present that could alter the behavior of the animals being observed. Because fishes and marine mammals are known sound producers, these animals’ location while producing sounds during a mobile survey can be recorded, and their species identity determined; in some cases, their behavior can be associated with specific sounds. We used Blackbeard the Acoustic Wave Glider (AWG) to conduct affordable, mobile, long-term passive acoustic monitoring of marine animals and the coastal ocean acoustic environment off North Carolina. (Luczkovich et al., in press). Passive acoustic methods from fixed recording platforms have been used previously to document spawning locations of weakfish, Cynoscion regalis, and other fishes in the drum family Sciaenidae in estuarine environments (Luczkovich et al. 2008). Others have demonstrated that sciaenid fishes make spawning “drumming” calls outside the inlets on the continental shelf (Conaughton and Taylor, 1995; Holt, 2008). However, “chattering” sounds that were reported offshore by Conaughton and Taylor (1995) were actually later shown to be due to striped cusk-eels, Ophidion marginatum. Here we report that choruses and individual calls of many fish (weakfish, striped cusk-eels, red drum, Sciaenops ocellatus, spotted sea trout, Cynoscion nebulosus, sea robins Prionotus sp., oyster toadfish Opsanus tau and an unknown grouper Epinephelus sp.) were recorded during wave glider transects running along the 20 and 30 m depth isobaths along the continental shelf of North Carolina coast. Marine mammal sounds (humpback whales Megaptera novaeangliae and bottlenose dolphins Tursiops truncatus) were also recorded during these excursions. The estuarine-dependent weakfish spotted seatrout, and red drum fishes (Sciaenidae) were more common in shallow areas (~20 m) near inlets and by artificial reefs, whereas the grouper calls were recorded in deeper water (~30 m) on live bottom reefs. These fishes’ sounds are likely to be associated with spawning, suggesting spatial separation of their spawning areas, and extending the known spawning habitats for these species beyond estuaries. The AWG can be used to map critical spawning habitat in offshore areas where anthropogenic vessel noises occur, and where energy development has been planned.