Sounds of the Spawn
TPWD researchers use hydrophones to locate key spawning areas of speckled trout.
By Larry Bozka
Frenzied seagulls. Tailing redfish. The oily sheen of surface slicks emitted by feeding speckled trout. These and more are the visual cues sought every day by seasoned saltwater anglers.
Rarely, however, do they get to hear the fish they seek.
Biologist Britt Bumguardner has been doing just that for the past three years.
A 22-year veteran of TPWD’s Coastal Fisheries Division, Bumguardner is Laboratory Director at the department’s Perry R. Bass Marine Fisheries Research Station in Palacios. He and his fellow researchers are concluding a program that, through the use of underwater listening devices called “hydrophones,” has allowed observers to monitor the sounds and activity of spawning speckled trout.
“The spotted seatrout hydrophone project was initiated in the spring of 2002 as a Sport Fish Restoration project,” Bumguardner says. “The goal,” he explains, “was to identify spawning areas that would merit priority protection in the event of an oil or chemical spill in the Intracoastal Waterway (ICW). We monitored the sounds made by male spotted seatrout (females don’t make noise) so that we could confirm spawning activity in certain areas.
“We then collected both fish and fish eggs from each area,” Bumguardner continues. “We assessed the female fish to determine how far along they were in the reproductive process and whether or not their eggs were ‘hydrated,’ the final stage of development prior to spawning.”
The free-floating eggs were collected with plankton nets. “We put the eggs in alcohol, and back at the lab, inspected them with a microscope and removed them,” Bumguardner says. “We then took a random sample, and using genetic techniques, distinguished seatrout eggs from the eggs of other species.”
Though a comprehensive report is still underway, some 36 research trips in as many months have yielded some noteworthy observations.
“We’ve determined that spawning concentrations of spotted seatrout are most common in relatively deeper water associated with shallow flats,” Bumguardner says. “The change in water depth may only be 3 to 5 feet in some areas or as much as 15 to 20 feet in others. The ICW itself holds spawning aggregations, as do the cuts connecting the ICW and the bays. We also documented significant spawning activity at larger oil production structures in the open bays, or groupings of smaller structures. Though we’re not sure why, the fish seem to prefer contours and valleys.
“We do know,” Bumguardner concludes, “that spotted seatrout spawn a lot. Estuarine environments are among the most changeable and harsh on the planet, and the high fecundity (egg production) of trout and their versatility in spawning is probably the key to why these fish continue to thrive.”
Web users with Windows Media Player capabilities can hear for themselves the fascinating sounds that researchers have been monitoring since 2002. To eavesdrop on a surprisingly vocal variety of fish species, visit the following Web sites (Bumguardner says his favorite is the toadfish):