Hoffmayer 08-09 Abstract

Title:  Use of passive acoustics to identify and characterize spotted seatrout spawning habitat in two Mississippi estuaries
Project Leader:  Hoffmayer, Eric R.

Spotted seatrout, Cynoscion nebulosus,is the most popular recreational saltwater fish species in Mississippi.  Due to overfishing and coastal habitat loss and degradation, local spotted seatrout population(s) could be in peril. Spotted seatrout spawning habitat in Mississippi coastal waters is unknown. The proposed study will identify, characterize and map spotted seatrout spawning habitat in two Mississippi estuaries, Biloxi Bay (an impacted estuary) and Grand Bay (a pristine estuary). The two estuarine study areas were chosen based on available information on differences in habitat types and quality. Additionally, the study will determine the spatial and temporal variability associated with identified spotted seatrout spawning aggregations within the two study areas, as well as compare identified spawning habitat between the study areas. 

The proposed research will be conducted during April – September, the spawning season for spotted seatrout in Mississippi waters, 2008 and 2009. Passive acoustic technology will be used to locate courtship sounds of spawning male spotted seatrout as a method to identify and map spotted seatrout spawning habitat.

Mobile acoustic surveys will be conducted within each study area at sampling sites chosen based on a stratified-random grid system. Each of the two estuarine study areas will be divided into two zones based on geographic and logistic criteria, and each zone will be further subdivided in to 0.65 nm2 grids. Six grids will be randomly selected for each sampling date with replacement in order to account for seasonal variability. Weekly sampling will ensure that each study area is sampled twice per month, with each of the four zones sampled at least once monthly. Sampling will occur from 1830 hr to roughly 0200 hr, as this is the peak window of male courtship sound production reported for spotted seatrout. 

Because spotted seatrout spawning frequencies have been attributed to lunar influences, the selection of zones to be sampled within the study areas will be rotated monthly so that each will be sampled over the various lunar phases during the course of the spawning season.

Fixed-location data loggers will be moored at identified spawning locations, to determine the temporal variability of spotted seatrout spawning activity. These data loggers will record for 10-second intervals every 10 minutes over the duration of their deployment.  This high-resolution acoustic data will provide insight into diet and seasonal variability in sound production and how to account for this in the mobile acoustic survey.

Identification and characterization of spotted seatrout spawning habitat will enable fishery resource managers to make better informed decisions pertaining to management of spotted seatrout in Mississippi waters. The proposed study will complement a spotted seatrout stock enhancement project currently underway on the Mississippi coast and will have utility in future spotted seatrout investigations in coastal waters of Mississippi and other Gulf states.