On Aug. 25, 2017, Hurricane Harvey made landfall about 5 miles east of Rockport, Tex. The category 4 storm had an eye wider than the length of Manhattan, wind gusts up to 145 miles per hour and a 10 foot storm surge. The catastrophic storm resulted in at least 103 deaths in the United States.
But amid this destruction, one thing seemed to weather the storm quite well — spotted seatrout, which were busy making babies as the eye of the hurricane passed over their spawning grounds.
“Their urge to reproduce, or that inclination, is so strong that not even a hurricane can stop them,” Christopher Biggs, a graduate student at The University of Texas at Austin and first author of the study, said.
Mr. Biggs and his colleagues reported their discovery, which was based on underwater audio recordings, last week in Biology Letters. The resilience of these fish suggests that they and their relatives, popular for recreational fishing in the Gulf of Mexico, may cope surprisingly well with increases in human activity and other temporary disturbances.
To see if the species could reproduce well enough to keep up with recreational fishers, Mr. Biggs and Brad Erisman, a marine biologist and lead author of the study, have been monitoring spotted seatrout reproduction.
Their team has been looking at spawning: when fish cast eggs and sperm into the water that meet, fertilize and develop into a new population, if all goes well. The team wants to know when the fish start, how long they go and how temperature and saltiness, which fluctuate in the estuary near Port Aransas, Tex., might affect their behavior in different locations.
But because the water is murky, they can’t just dive in and look. Instead, they rely on these fish’s unusual audible mating calls. In this species, as well as other drum fish named for their sounds, the males cry out in grunts and pulses during spawning. An individual sounds like a panther standing behind a trickling stream of water. And when many call together, they can evoke a chorus of chain saws.
Mr. Biggs and his colleagues had deployed underwater microphones in April 2017 at 15 popular spawning grounds. These programmable recording devices are protected inside waterproof casing and strapped to a PVC pipe. To install and remove them, Mr. Biggs had to dive down six or 12 feet and hammer them into the sandy sea bottom.
When news of Harvey’s strength and direction was announced, Mr. Biggs was at a conference in Florida. He raced home to Texas and took a boat out to retrieve his recorders. He recovered about half before he had to evacuate, and the storm took most of the rest.
Audio analysis of the six months of rescued recordings revealed some surprises. First, despite previous work suggesting spawning coincided with changes in the moon, their survey showed the fish population spawned daily.
And then the two recorders that survived the hurricane yielded another unexpected finding.
At first, the researchers thought the storm’s noise was too loud to hear anything. But when it calmed, they heard the fish spawning — the day before the storm, in its eye and the day after.
“That was completely surprising when you consider the total destruction on land,” he said.
Following the hurricane, the fish began spawning earlier in the day, possibly cued in part by temperature changes in the water.
“You would think if they felt their environment getting that disrupted, they would just go somewhere else, but yet they were still hunkered down right in the same spots that they had been before,” Mr. Biggs said.
Whether they stopped during the worst of it and restarted in the calm, however, we may never know.
This year the team has deployed another set of hydrophones to find out why the fish make sounds when they spawn. Is the call more of a social cue to sync spawning after they’ve already gathered? Or is it more like a dinner bell calling out “Hey, it’s spawning time in the estuary, come and get it?”