Bay systems adapt to freshwater runoff
Texas coastal fisheries staffers who pulled up to a stretch of shoreline in St. Charles Bay on the state’s midcoast earlier this month to conduct a bag seine sampling had a good idea of what they likely would collect. After all, it is something they do 90 times a year as part of the longest-running standardized coastal fisheries monitoring program in the nation.
The 60-foot, fine-mesh seine they pull for 50 feet along the shoreline at a spot randomly selected by a computer program typically collects a smorgasbord of smallish marine life — shrimp, juvenile fish and crabs and other representatives of coastal life that give fisheries scientists insight into the relative abundance of some species and, in the case of juvenile fish, the recent reproductive success of others.
But what the fisheries crew found when it hauled the seine onto the bank to begin sorting, counting and recording their catch was not typical. Instead of the net holding the normal assortment of killifish and bay anchovies, juvenile speckled trout, croaker, redfish and blue crabs, it yielded surprises.
“They had a couple of fingerling largemouth bass and some sunfish,” said Mark Fisher, science director for Texas Parks and Wildlife Department’s coastal fisheries division. “That tells you how much freshwater runoff we’ve seen. Largemouth bass in St. Charles Bay …”
Effects wide-ranging
The aberration of freshwater species such as bass and sunfish showing up in areas usually far too salty for them to survive is one of the effects an unusually long stretch of extremely wet conditions across much of Texas has had on the fisheries in the state’s coastal waters. And those effects have played a large role in what Texas coastal fisheries managers have seen over the last few months as they conducted the monitoring programs that they have done each spring for, in most cases, more than 40 years.
Those effects have been particularly pronounced on the upper coast, where the Galveston Bay and Sabine Lake systems, both fed by rivers that have been swelled with runoff almost continuously since autumn, has been swamped with freshwater. Results of those monitoring efforts, especially the just-concluded 10-week gill-net sampling programs, suggest that, while marine fish populations in the bays are generally good or even great in most instances, the siege of freshwater runoff has shuffled distribution of some salinity-sensitive species such as speckled trout. Some less salinity-sensitive species — redfish and black drum — appear relatively unaffected. Others — blue crabs in Galveston Bay and forage species such as menhaden — appear to be benefitting.
“The amount of freshwater in the bay has been the thing that’s really stood out,” Carey Gelpi, Sabine Lake ecosystem leader for TPWD’s coastal fisheries division, said of what the coastal fisheries team saw on the state’s easternmost bay system.
Most inshore marine finfish species such as speckled trout, redfish and black drum prefer water with a salinity of 10 to 20 parts per thousand. For months, water this salty has been rare in much of the Galveston Bay complex and nonexistent in Sabine Lake.
“In most of the bay, we’ve had salinities of less than 1 ppt for the past couple of months,” Gelpi said. “It’s been 1-2 ppt for what seems like the past six months.”
Wedges of heavier, salty water have pushed into the bay, with some areas of Sabine Lake’s southern end seeing short periods during which salinity levels climb as high as 9 ppt but mostly in the range of 4-5 ppt.
Going with the flow
Parts of Galveston Bay have seen similar freshwater swampings.
The results of freshwater overwhelming the bay have been seen in much of Galveston Bay, but especially in Trinity Bay, where the Trinity River has been above or near flood stage since autumn.
“It’s been below 1 ppt for a very extended period,” Glen Sutton, TPWD’s Galveston Bay ecosystem leader, said. “And it’s not been a short-term thing; it has been persistent.”
The gill nets that TPWD coastal fisheries teams set during their spring sampling season showed some of the effects of this freshwater flushing. In each bay system on the coast, teams set 600-foot gill nets perpendicular to the shoreline at sites randomly selected by computer. A total of 45 sets are made over the 10-week period, with nets set at sunset and picked up soon after dawn. All fish in the nets are identified, counted, measured and recorded. TPWD has been conducting this sampling using the same protocols since the 1970s, giving managers insight to longterm trends of marine fish populations.
During sampling this spring, Sabine Lake teams encountered “a lot” of freshwater species, Gelpi said, including largemouth bass, bluegills and other sunfish, freshwater drum, crappie and freshwater catfish.
“We saw freshwater fish in places we’d never seen them before,” he said.
But they also saw good numbers of some important marine fish. Catch rates of speckled trout were slightly below the long-term mean, he said. But the fish often were concentrated in the rare pockets of saltier water.
Results were similar for redfish, with the mean catch rate in the nets slightly below the long term.
In Galveston Bay, the speckled trout catch rate in this spring’s gill-net sampling was significantly lower than the previous year, Sutton said.
“This year, (the catch rate) was about half what it was last year,” Sutton said.
That decline, while important, should be seen in context, he said.
“Last year was a really good year,” Sutton said. And, he added, the flush of freshwater could have triggered the salinity-sensitive trout to move into deeper areas of the bay — mid-bay reefs, channels and other areas — holding saltier water. Those areas are not included in the gill-net sampling.
Also, portions of the bay system farthest removed from runoff-gushing waterways held good, salty habitat and plenty of fish.
“The south shoreline of West (Galveston) Bay was in really good shape,” Sutton said. “Lots of fish and lots of blue crabs.
Even lots of seagrass, and the water was clear and salty. Fish were doing great.”
The gill-net survey indicated Galveston Bay’s redfish were not nearly as affected by the freshwater as speckled trout. The bay’s booming redfish population, which, like its speckled trout numbers, have been at or near record levels in recent years, continued showing their numbers in the gill-net survey. Redfish catch rates were up this spring, he said.
A reason for this spring’s disparity between gill-net catch rates for redfish and speckled trout almost certainly is tied to redfishes’ ability to tolerate low salinity.
“They don’t care about salinity,” Sutton said of redfish. “As long as there’s food available, they’ll put up with low or even no salinity.”
Smorgasbord of food
And there is a lot of food in the bays. Upper coast waters are holding a wealth of forage, recent sampling indicates.
“There’s a tremendous amount of menhaden — pogies — out there,” Sutton said. This year’s crop of menhaden, a major forage fish for inshore sportfish such as trout and redfish, in upper coast waters looks to be outstanding based on recent samplings. During bag seine samplings in Galveston Bay, TPWD coastal fisheries teams set a bay system record when they collected an estimated 46,000 young menhaden in a single 50-foot drag of the net along an East Galveston Bay shoreline.
That abundance of forage was seen in the Sabine Lake system and adjacent waters, Gelpi said. And all that freshwater runoff could be playing an important role in fueling it, he said. All that runoff pouring into the bays and into the nearshore Gulf carries a cargo of suspended nutrients. Those nutrients feed phytoplankton, the microscopic plants on which menhaden feed.
Sampling in the nearshore Gulf water off Sabine Pass showed the plume of nutrient-rich runoff pushing a considerable distance into the open ocean, Gelpi said. (Salinity levels of surface water as far as 9 miles offshore have been as low as 6 ppt; they normally run 15-20 ppt or higher there.)
That supercharger of nutrients has fueled a burst of productivity in this “extended estuary.”
“We’ve seen a real surge in production in the nearshore Gulf,” Gelpi said. “Menhaden, croaker, silver trout and other fish. It’s been a real benefit there.”
The volume and persistence of freshwater inflows into the bays also appears to have helped Galveston Bay’s blue crab population, Sutton said.
“We’re seeing some really good numbers of blue crabs,” Sutton said. “They seem to be having a great year.”
Blue crabs can benefit from extended low salinity because they can use those areas as refuge as well as larder. The crabs can do just fine in very low salinity water, but many of the marine fish that prey on them can’t, Sutton said.
This siege of heavy freshwater runoff into Texas upper coast waters is proving a mixed blessing to the bay’s fisheries and fishers. It certainly has made fishing tougher for most anglers. And it has forced some marine fish to move from areas they normally haunt. But it also has injected considerable nutrients into the fishery, fueling the food chain that supports the fisheries.
All’s not lost
Despite the setbacks and frustrations many upper coast anglers have endured during these months of muddy, fresh bays, the future appears bright.
“All this freshwater is unusual, especially so much for so long in some areas,” Texas’ coastal fisheries science director Fisher said. “But coastwide, our trout and redfish numbers have been at or near records.”
That is something for upper coast anglers to hold onto as they head into the heart of summer fishing season that most hope holds no more wet surprises.