Abstract

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.

Objectives

The goal of this study is to identify and characterize spotted seatrout spawning habitat in two Mississippi estuaries, Grand Bay and Biloxi Bay.  The objectives are to:

1. to compare spotted seatrout spawning habitat between the two Mississippi estuaries, Biloxi Bay (an impacted estuary) and Grand Bay National Estuarine Research Reserve (a pristine estuary)
2. to determine the spatial and temporal variability associated with identified spotted seatrout spawning aggregations
3. to compare the results of this study with a similar study conducted in Tampa Bay, Florida

Methodology

In year 1, we will use passive acoustic technology to locate courtship sounds of male spawning spotted seatrout as a method to identify and map spotted seatrout spawning habitat in Biloxi Bay and Grand Bay, Mississippi.  A mobile acoustic survey will be conducted from May August.  Sampling will be conducted from 1830 hr. to roughly 0200 hr., as this is the peak window of spotted seatrout male courtship sound production.  To ensure representative sampling, stations will be distributed as evenly as possible over the available substrata.  At each station, the hydrophone will be lowered 1 m below the surface and a recording will be made on a Sony Digital Audio Tape (DAT) recorder for 30 seconds.  Depth, salinity, temperature, dissolved oxygen, tidal and lunar stages, and GPS position will be recorded.  Courtship sounds will be categorized as to proximity to listening station and number of individuals producing the sound (individual, several, small group, or aggregation).  In both Mississippi study areas, periodic use of gillnets and hook and line gear will be used to collect adults (as logistics allow) to determine if active spawners are present.

In year 2, we will continue to identify and map spotted seatrout spawning habitat in an effort to investigate inter-annual variation in the spawning habits of spotted seatrout in Mississippi coastal waters.  As in Year 1, a mobile acoustic survey will be conducted from May August.  Sampling will be conducted from 1830 hr. to roughly 0200 hr., as this is the peak window of spotted seatrout male courtship sound production.  To ensure representative sampling, stations will be distributed as evenly as possible over the available substrata.  At each station, the hydrophone will be lowered 1 m below the surface and a recording will be made on a Sony Digital Audio Tape (DAT) recorder for 30 seconds.  Depth, salinity, temperature, dissolved oxygen, tidal and lunar stages, and GPS position will be recorded.  Courtship sounds will be categorized as to proximity to listening station and number of individuals producing the sound (individual, several, small group, or aggregation).  In both Mississippi study areas, periodic use of gillnets and hook and line gear will be used to collect adults (as logistics allow) to determine if active spawners are present.
  
In addition to the mobile acoustic survey, as spawning locations are identified, two 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, which can be programmed to be as long as 70 days.  This high resolution acoustic data will allow us to better understand diel and seasonal variability in sound production and how to account for this in our mobile hydrophone survey.  Data obtained from acoustic surveys and associated survey information will be analyzed to determine spawning habitat preferences based on the use of specific areas, habitat types, and associated environmental parameters by spawning seatrout.

Rationale

Due to overfished spotted seatrout population(s), as well as habitat loss and degradation as a result of post-Katrina coastal development, it is critical to identify and map spotted seatrout spawning habitat in Mississippi coastal waters. The proposed study will provide baseline information on the spatial and temporal variability in spotted seatrout spawning activities in Mississippi coastal waters.  This 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 Mississippi and other Gulf states.  The proposed work will complement a similar study conducted in Tampa Bay, Florida and will expand the knowledge of spotted seatrout spawning habitat in the Gulf of Mexico.  Once spotted seatrout spawning habitat has been identified and characterized in Mississippi, fishery resource managers can use this information for improved management of this species in local coastal waters.

For More Information Contact: the MASGC Research Coordinator, Loretta Leist (Loretta.leist@usm.edu). 
Please reference the project number R/SP-18.