On the morning of March 22, I joined a crew of three Texas Parks and Wildlife Department fisheries biologists as they pulled in gillnets which had been set out the day before on Belton Lake.
The biologists were from the TPWD Inland Fisheries District 2B which is headquartered in Waco.
This office has responsibility for several bodies of water, including Alvarado Park, Lake Aquilla, Belton, Pat Cleburne Reservoir, Fort Parker State Park, Lake Granbury, Lake Limestone, Lake Mexia, Stillhouse Hollow Reservoir, Tradinghouse Creek Reservoir, Lake Waco and Lake Whitney.
On that morning, John Tibbs, Michael Baird, and John Provine pulled in five nets which would be the first five of a total of 20 or more nets to be set out over the next few weeks. Each net is allowed to set for approximately 24 hours before being collected and its content analyzed.
Each gillnet is approximately 125 feet long, consisting of five 25-foot-long panels. The nets are 8 feet high, with a mesh size of 1 to 3 inches, and are constructed of monofilament of roughly 30-pound test.
When the gillnets are deployed, they are weighted down in such a way that the bottom edge of the net lies near the bottom and the 8-foot height of the net extends upward from the bottom toward the surface. Colored floating buoys mark the ends of the net so boaters can avoid entanglement and so the nets can be easily found for collection the following day.
According to Tibbs, the Waco District Supervisor, “Fisheries biologists monitor the fisheries of all of the reservoirs statewide using netting and electrofishing. These efforts help inform them on the status of the fishery and guide their reservoir plan moving forward. Habitat, stocking, regulations — all of these things require the data obtained by our sampling efforts.
“We gillnet Belton every two years as an ongoing effort to monitor the hybrid striper population as well as blue and channel catfish. Other reservoirs’ frequency ranges from every two years to every four years.”
Over the past two decades TPWD has studied the stocking of fewer, but larger, fingerling-sized hybrid striped bass versus the stocking of more, but smaller, fry-sized hybrid striped bass.
Concerning TPWD’s findings, Tibbs said, “Gill netting is absolutely essential to ongoing refinement of our hybrid striper stocking approach. Information obtained over the past 20 years has shown impressive returns from our fry stockings compared to our fingerling stockings.
“This has allowed us to modify our stocking approach to a fry-only approach, which has resulted in impressive gains in hybrid striper numbers and more consistent availability of hybrids to stock. Currently we are assessing the effects of two fry stocking densities to further refine our approach.”
As this “two fry stocking densities” approach plays out in real life on Belton Lake, the reservoir typically sees approximately 600,000 fry stocked on even years, and approximately 1.2 million stocked on odd years.
I asked Tibbs how many nets typically get set out, and for how many nights, in order to complete a sampling.
“Statewide it varies, as fisheries biologists are tasked with answering specific questions with their sampling. For example, if the goal is to compare catch rate with previous years, netting would continue until statistical variability is reduced to a pre-determined level. In the case of Belton, we are looking to collect a certain number of hybrid stripers for age analysis so netting will continue until we catch them.”
As I watched the gillnets being taken in, I witnessed fish of many different sizes and species
being collected including blue catfish, channel catfish, crappie, redear sunfish, smallmouth buffalo, white bass, longnose gar, freshwater drum and hybrid striped bass.
As the three-man crew efficiently worked to process each net’s contents, I noted some fish got more attention than others. For example, hybrid striped bass were collected and retained in onboard coolers, whereas catfish were only measured and weighed, while yet others were essentially disregarded.
I asked why that was.
Tibbs explained, “Species that aren’t traditionally caught with gill nets and are sampled with electrofishing are not measured, because we already have a better, more unbiased sample.
“‘Rough fish’ such as smallmouth buffalo are also not counted unless there is a significant fishery for them. There is no need to sacrifice the catfish in the sample because we aren’t collecting age data on them as we are doing with the hybrids.
“We likely will (keep catfish) in the future, and then the focus of the collection will change.”
The hybrid striped bass which were retained will be dissected and have the otoliths removed from their skulls. This bone-like mass allows for accurate aging of each fish sampled.
Tibbs explained that the net placement locations are randomly assigned using ArcView software and a GPS device. If there is heavy timber or the water depth exceeds the target maximum, the nets may be moved elsewhere nearby, or, in some cases, to a different random location.
Shallower nets are oriented perpendicular to the shoreline, whereas directionality does not come into play on nets set in deeper, more open water.
I also asked Tibbs about how the field data gets woven into a report, and then what is done in terms of decision-making with that reported data.
“The reports are finalized on July 31 every year and are placed on our website soon thereafter at the following link: https://tpwd.texas.gov/publications/pwdpubs/lake_survey/index.phtml.”
Concerning the data collected on Belton Lake, Tibbs added, “We are looking specifically at hybrid striper stocking as well as the blue catfish fishery that is continuing to expand. Other species data will also be reviewed and results made public.”
Tibbs appreciates input from the angling public and invites inquiries to his email account at John.firstname.lastname@example.org.