Rains bring flood of freshwater into bays
Runoff lowers system’s salinity, redistributes fish, delivers nutrients
Right now and for a while to come, Sabine Lake is appropriately named; it’s more a freshwater lake than the bay system straddling the Texas Louisiana border. Trinity Bay seems more an extension of Lake Livingston than a lobe of the state’s largest estuarine system. And the Colorado River, where the flood gates on the Mansfield Dam creating Lake Travis were opened this week for the first time since 2007, is pumping more freshwater into the Matagorda Bay system than it has seen in years.
Runoff from unusually heavy rains through much of winter and spring have poured down the Sabine, Neches, Trinity, San Jacinto, San Bernard and Colorado rivers, swamping the bay systems into which they flow with a wall of muddy freshwater, diluting the bay’s saline waters, displacing or at least redistributing aquatic life.
The short-term effects of the bays being overwhelmed by freshwater are a mix of mostly negatives and a few positives, both for the marine aquatic species scrambling to find habitat in which they can best survive and for many anglers who, like the fish, have been forced from their normal haunts.
“Everything’s been zapped by all of this flooding,” said Jerry Mambretti, upper coast regional director for Texas Parks and Wildlife Department’s coastal fisheries division. “When you get this much water, it’s going to have an impact.” And it has. Anglers have seen it, with the freshwater slug quite literally muddying the water. The most sought-after inshore fish — speckled trout, redfish, flounder, black drum — have been all but impossible to find or catch in portions of upper-coast bays where freshwater has displaced the saline waters the marine fish require. Knowing where to look
But for some anglers, the flooding has proved a blessing. Fish forced from portions of the bay too fresh to support them have concentrated in the relatively few areas holding water with suitable salinity levels — places such as the Galveston and Sabine jetties and pockets of East Galveston Bay, West Galveston Bay and West Matagorda Bay, spots far enough from the freshwater plume, benefited by currents that keep the freshwater at bay or deep enough that they hold a layer of heavier salty water beneath a layer of lighter freshwater. Find those places and fishing can be extremely productive.
Anglers aren’t the only ones seeing the impacts of the massive amounts of freshwater surging into upper-coast bay systems. State coastal fisheries staffers are seeing it, too.
The surge of freshwater into bays along the upper coast coincided with the start of the annual spring gill net sampling season for Texas coastal fisheries staffers. Over a 10-week period beginning the second full week or April, TPWD coastal fisheries crews in each bay system take a total of 45 samplings of the bay’s finfish population. Those samplings are done by setting 600-foot gill nets at randomly selected sites throughout the bay system.
The nets, which have three 200-foot panels of 6-inch, 5-inch and 3-inch webbing, are set in the early evening and picked up the next morning. Crews identify, count, measure and collect other information on the fish captured in the nets and temperature and salinity levels of the water.
The gill net sampling, conducted each spring and fall since 1975, gives fisheries managers insight into relative abundance of the bay’s fish populations, the age structure of species’ populations and, most important, data on long-term population trends.
By setting the nets at sites picked randomly by computer, data produced are a statistically valid reflection of the bay’s fishery. Variety of species
This year, the spring gill net sampling began April 11. And the results from the first couple of weeks show the effects of the freshwater pouring into the bays.
“It’s kind of nuts what we’re seeing in some of our nets,” said Glen Sutton, Galveston Bay ecosystem leader for TPWD’s coastal fisheries division.
A net set this past week in the upper reaches of Trinity Bay, near the mouth of the Trinity River, produced a mix of freshwater and saltwater species. But that’s what you’d expect in water with a salinity level of 0.1 parts-per-thousand. (“Normal” salinity levels in Galveston Bay during spring usually range from 5-20 ppt, with lower levels in the upper bay and higher in the lower reaches less influenced by runoff.)
That net near the Trinity held a few redfish and bull sharks, two marine species with a considerable tolerance for freshwater. But, Sutton said, it also held good numbers of blue catfish and buffalo, two freshwater species. And hardhead catfish — lots of hardheads.
Another net set near Houston Point in water with a salinity level of 1 ppt also held buffalo and blue cats, plus redfish and, surprisingly, a few speckled trout, a species that has little tolerance for low salinity levels. And lots of hardheads.
Two net sets in East Galveston Bay, where salinity levels were about 7.5 ppt and 7.3 ppt, produced speckled trout, redfish and, Sutton said, “a ton of big gafftop.”
In both bays, the nets also produced several alligator gar.
“There are gar all over the place, right now,” Sutton said of the freshwater gar that often move into bays when salinity levels are low.
Coastal fisheries crews in Sabine Lake also have encountered good numbers of alligator gar in their gill net sets, especially in the marshy estuaries of the bay system, said Carey Gelpi, TPWD’s Sabine Lake ecosystem leader.
“We had the biggest alligator gar we’ve ever caught in the history of gill net sampling in Sabine Lake,” Gelpi said. That fish, measuring 6 feet, 7 inches and weighing more than 100 pounds, was one of many crews have found in their nets set in the bay system fed by the Neches and Sabine rivers.
Not surprising, considering the Sabine River saw record-setting flooding during March and salinity levels throughout Sabine Lake are extremely low.
“The highest salinity we’ve seen has been 1.9 ppt,” Gelpi said. But even in that low salinity environment, the bay is holding a fair number of marine fish. Nets have collected bull sharks (including fish measuring as much as 5 feet), good numbers of redfish and fair numbers of speckled trout, Gelpi said.
“We even had a jack crevalle in one net,” he said. “That was a kind of surprise because they’re a fish that really prefers a highsalinity environment.”
While the freshwater resulted in many — most — marine fish relocating to areas with more comfortable salinity levels, it’s not that unusual to find some saltwater fish in the areas that are too fresh for their physiology, Sutton said. And he believes food draws them.
Some juvenile fish and forage species are more tolerant of freshwater and will move into fresher areas because they offer protection from predator species that prefer higher salinity water, Sutton said. And that abundance of potential meals can override predatory marine fishes’ aversion to freshwater.
“If the energy they get from the food they find there is higher than the energy it takes to maintain themselves in freshwater, they’ll certainly spend time in low-salinity water,” Sutton said. Fish food
Over coming weeks and months, even as freshwater inflows slow and salinity increases, that food supply is likely to improve across entire the bay system. Sutton and Gelpi said the flooding almost certainly will have a longterm benefit to the fisheries through higher production of forage species.
“All that water coming down the rivers brings with it a huge flush of nutrients,” Gelpi said. Those nutrients fuel a massive bloom of phytoplankton that, in turn, serves as food for forage species such as menhaden. And those vegetarian menhaden — “pogies” or “bumpers” to most anglers — are a major food source for speckled trout, redfish, flounder and many other inshore fish anglers target.
Last year, spring flooding helped produce a bumper crop of bumpers in Galveston Bay, Sutton said. And that greatly benefitted the fishery and anglers.
“That certainly could happen again this year,” he said.
It’s something anglers along the upper coast can look forward to while waiting for all this freshwater to go away.