PORT O’CONNOR, Texas—The life of a coastal fisheries biologist isn’t all Jacques Cousteau glamour.

But the biologists at the Texas Parks and Wildlife Coastal Fisheries Department office in Port O’Connor track fish population trends and, ultimately, the health of San Antonio Bay.

The biologists end their gill netting surveys in mid-June, which they conduct twice a year—spring and fall—for 10 weeks each time. The results during each period represent a speck in the spectrum of data collected for the past 30 years.

One recent morning, the biologists entered the water between Port O’Connor and Seadrift by Lane Road to see what fish were tangled in the gill nets they left overnight.

“It gets pretty morbid this time of year,” Norman Boyd, ecosystem leader of the San Antonio Bay system, warned about the warm June waters.

The Parks and Wildlife boat bounced atop the water to reach the first net between Turnstake and Steamboat Pass. Upon reaching the buoy-marked destination, Boyd measured the temperature, salinity and turbidity of the water, putting a sample in a small container.

The next step was to reel in the 600-foot-long net, removing the tangled fish along the way.

Boyd and Jeremy Helms readied their gloves while Theresa Krenek readied her pencil, clipboard and measuring station.

The first 20 minutes yields plenty of juvenile bull shark, mostly dead, and Boyd wondered where the game fish went the night before. Boyd untangles a bonnethead shark, named for its bonnet-shaped head, and shows how many tiny spots cover its body. He throws it toward Krenek, who measures its length.

If the biologists spot a problem, they may also conduct fishery-independent sampling and try to determine if a population decline is caused by nature or humans.