Harvey runoff churns up a few surprises
Tadpoles and sunfish, alligators and alligator gar, largemouth bass, channel and blue catfish, gizzard shad and smallmouth buffalo are aquatic creatures Texas freshwater fisheries biologists pretty much expect to encounter in the course of their work.
They are not what biologists and technicians monitoring Texas’ coastal fisheries reckon to come upon as they monitor the state’s marine ecosystems.
“It’s not very often that we see more than a handful of freshwater species,” said Carey Gelpi, Sabine Lake ecosystem leader for Texas Parks and Wildlife Department’s coastal fisheries division.“But when your bay turns into what’s essentially a freshwater lake for several weeks, you can expect some surprises. We’ve had our share, for sure.”
So have coastal fisheries staffs in the Galveston and Matagorda bay systems, the other Texas marine ecosystems most directly and heavily impacted by the injection of unprecedented amounts of freshwater runoff associated with Hurricane Harvey’s record-setting flooding.
Harvey’s flooding rains hit the final week of August and first week of September, with runoff swamping the bays just as TPWD coastal fisheries staff were preparing to begin their fall gill net surveys of the bays.
Twice a year, in early summer and early autumn for almost four decades, TPWD coastal fisheries crews conduct research involving setting 600-foot gill nets at random locations (picked by computer) throughout each bay system. The effort is spread over a 10-week period with a total of 45 net sets made. The nets are set perpendicular to the shoreline at dusk and retrieved the next morning. All aquatic organisms captured by the nets are removed, each creature’s species and length recorded, with some of the catch kept for further research. Crews also record environmental data such as water temperature and salinity.
The gill net sampling is designed as part of the agency’s monitoring of the relative abundance, size distribution and other demographics of the bay’s fisheries, with special focus on species such as speckled trout, redfish, drum, flounder and others that carry huge economic and recreational value. The data collected give fisheries scientists and managers insights into long-term trends in the fisheries.
The fall gill net sampling season begins in mid-September. This year, that timing hit as bays on the upper half of the Texas coast were swamped with runoff from Harvey’s record-setting rains, and as TPWD coastal fisheries staff were dealing with the damage the storm did to their personal property and the boats, buildings, equipment and other gear.
“Every coastal field station except the one in the lower Laguna Madre suffered at least some damage,” said Mark Fisher, Rockport-based science director for TPWD’s coastal fisheries division. “Several staff were personally affected. We had co-workers who lost their homes. But, to their credit, the staff was able to start the gill net season on time.”
What those crews encountered was quite different from what they usually see.
“For the first couple of weeks after the storm, there were no usable boat ramps on Sabine Lake,” Gelpi said. “They were under water. Freshwater.”
That surge of runoff flushed freshwater species into what normally are saltwater environments, or allowed freshwater species to range into areas where they normally could not survive.
That freshwater inundation was biblical, with areas of bays that in a normal September and October would hold salinity levels of 15-20 part-per-thousand dropping to 0 ppt. The flood of freshwater went far beyond the bay systems, with the plume of “sweet” water pushing miles into the Gulf of Mexico. TPWD teams conducting their regular monthly trawl samplings in Texas waters of the open Gulf found salinity levels as far as 9 nautical miles offshore to be half or less than the normal 35-40 ppt.
“We saw salinities in the low 20’s in the Gulf offshore of Galveston during September, and in the low 20’s and upper teens off of Sabine Pass,” Fisher said. But that doesn’t tell the whole story, he said. Those salinity measurements were taken just off bottom, where the most saline water would be found — freshwater is much less dense than saltwater and rides in a layer over the heavier, saltier water. Surface water as far as 10 miles off the coast was almost wholly fresh. “That’s just unheard of.” Coastal fisheries crews working the gill net sampling saw the effects of the freshwater slug.
“We actually were catching tadpoles in some of our bag seines,” Gelpi said of Sabine Lake samplings. Gill nets produced freshwater largemouth bass, buffalo, channel and blue catfish and sunfish along with saltwater redfish. Lots of alligator gar
The gill nets in Sabine Lake also have caught alligator gar, Gelpi said. A lot of alligator gar.
Sabine Lake crews were not the only ones.
“We’re seeing alligator gar in almost every net,” Glen Sutton, Galveston Bay ecosystem leader, said of fall gill net sets in the state’s largest bay system. “Just tremendous numbers of them — more than we’ve ever seen. We’ve even caught alligator gar in West (Galveston) Bay, where we’ve never caught them before.”
It’s been the same in the Matagorda Bay system.
“So many alligator gar!” said Leslie Hartman, Matagorda Bay ecosystem leader. “We’ve had some nets with dozens in them.”
Alligator gar are a freshwater species found in the river feeding the bays. The primitive fish, which can grown to more than 300 pounds, can easily tolerate modest salinity levels and are commonly found in brackish areas of bays. But not in anything near the numbers or in the areas seen this autumn.
“It’s pretty certain that all that freshwater pushed those gar into the bays,” Sutton said.
It pushed other freshwater-loving creatures into the bays, too.
“We’ve been seeing a lot of gizzard shad, which are a freshwater species,” Sutton said.
Then there have been the alligators.
“We’ve had a couple of instances where alligators have ended up in our gill nets,” Sutton said.
The most “interesting” such encounter was when a crew checking a gill net in the Drum Bay area were retrieving a net that had fewer fish in it than the crew expected. They discovered why when they came upon an 11-foot gator entangled in the net. The “very much alive and not happy” gator had been using the gill net as a buffet, snacking on trapped fish.
The gator was able to disengage itself from the net, much to the relief of the reptile and the TPWD crew.
There have been other surprises — ones not easily directly attributable to the freshwater swamping.
Snook, a highly soughtafter tropical marine sport fish native to much of the Texas coast but for decades relegated almost solely to the lower coast, have shown up in sampling nets in all three bay systems.
A juvenile snook captured in a TPWD gill net set in the upper reaches of Sabine Lake during this sampling effort is the first snook taken in the history of such samplings in the border-straddling bay system, Gelpi said. Two snook, both in the 2022-inch range, have been taken over past weeks in the Galveston Bay system, Sutton said. One was taken in Drum bay, the other in Bastrop Bay.
Mild winters a factor?
Matagorda Bay has seen a surge in snook encounters during this gill net sampling season, Hartman said.
“We usually see one or two or so snook over a whole gill net season,” she said. “This year has been a real surprise. We’ve had several snook. We had six in one net in East Matagorda Bay. Just this week, we had four more.”
Perhaps temperaturesensitive snook, like gray snapper, are extending their range as Texas winters continue their long warmer-than-normal string.
Anecdotally, the bay system biologists said, the bays’ redfish and speckled trout appear to be doing pretty well, considering the freshwater drenching. Redfish numbers in all bays appear to be continuing strong. Reds can tolerate lower salinity levels than many other bay species. Speckled trout abundance has been spotty, but improving as salinity levels in the bays moderate. Through six weeks of the fall gill net survey, Sabine Lake catches of trout appear down a bit, Gelpi said.
Trout catches in the Matagorda complex are “decent,” Hartman said, with some very large trout showing up especially in East Matagorda Bay.
In Galveston Bay, where salinities are climbing but generally still lagging behind what are considered “normal” levels for October, speckled trout catches in this fall’s gill net survey are actually a bit ahead of what they were this time a year ago, Sutton said. But that may be because the fish are concentrated in areas holding favorable salinities, he added.