The Science Behind Our Regulations

Annica Lyssy
The Science Behind Our Regulations

Figure 1. Lengths of Black Drum caught in bag seines (juveniles), bay trawls (sub adults), and gill nets (adults) from the Upper Laguna Madre 2015 – 2020.

Coming in as a Texas Parks and Wildlife Department (TPWD) intern, I thought I had a decent understanding of what the experience was going to entail. I never knew that I would walk away from the internship with a completely new interpretation of our bay systems and how we maintain the ecosystems along our coast. The Coastal Fisheries Division is responsible for keeping our fisheries healthy. To do this, the Division collects data using different gear types, which is then analyzed and shared to monitor how healthy our bay systems are and if regulations need to be adjusted or instated.

To monitor our fisheries, TPWD has created a system using a combination of three main gear types to collect fisheries data. These gear types are used to collect fish in each life-stage from juvenile to adult (Fig. 1). The gears used for data collection include bag seines for juvenile fish, bay trawls for subadults, and gill nets for adult size fish. In general, each bay system is assigned 20 bag seines and 10 trawls a month and have two ten-week seasons for gill nets. The same general sampling routine, including the collection of water quality data, has been in place for over 40 years so that TPWD can track patterns in the fisheries over time.

Juvenile fish can help predict what the future of our bay ecosystems will look like, and bag seines play a key role when it comes to monitoring recruitment. Bag seines are conducted by dragging the net perpendicular to the shoreline 40 feet out and 50 feet along a given shoreline site. This gear provides TPWD with data on juvenile sportfish, forage fish and any other small-bodied invertebrates swimming along the shorelinef. Bag seine samples can provide data on how successful recruitment is for sportfish such as Spotted Seatrout and Red Drum and for forage species like Pinfish and Mullet. In conjunction with bag seines, habitat data is collected at the sites to look at the association between the species of fish caught and the shoreline vegetation.  

Looking at the different life stages of a fish can provide data not just on survival, but also on environmental changes or community composition. To track these occurrences and the development of fish, TPWD collects data at the subadult stage with bay trawls. Bay trawls are conducted by dragging a trawl net for ten minutes in a large circle. Prior to trawling, hydrological measurements like salinity and temperature are taken and depth is recorded throughout. Bay trawls are different than other gears because they are done in open water. Often, the fish that are caught during trawls are different species that are not present in bag seines and gill nets. These organisms consist of crustaceans like Blue Crabs and benthic species such as Atlantic Croaker and shrimp.

Anglers are most often interested in large sportfish. Coastal Fisheries teams use gill nets to collect data on adult fish in coastal bay systems. Gill nets are stretched 600 feet out from a given shoreline site and consist of four sections of mesh that varies in size from three to six inches. For these samples, teams collect hydrological data, counts and measurements of the fish, and the density and species of vegetation. TPWD gets vital data from gill nets that can be used to determine bag and size limit regulations for anglers. Gill net data are compared throughout the years to determine patterns in abundance. For example, in the Upper Laguna Madre, Red Drum numbers have increased since the 1980s while Southern Flounder populations have decreased.

To get fisheries-dependent data, the Coastal Fisheries Division conducts creel surveys. These surveys consist of a series of questions for anglers that are coming off the water. This fishery-dependent data gives TPWD information about what fish are being harvested from different areas in specific bay systems. Estimates of fishing activity are useful because they help TPWD understand how much fishing pressure certain species are experiencing and how that pressure has changed over time. For example, since the freeze in February 2021, the number of Spotted Seatrout harvested has been below average. However, more anglers seem to be targeting Red Drum instead of Spotted Seatrout since the number of Red Drum harvested in 2021 was slightly above average.

Ultimately, the data that is collected from these three main gear types and creel surveys provides TPWD with the tools to gauge how healthy our coastal ecosystems are and if regulations need to be altered or instated. As we build our database and learn more about our coastal ecosystems, TPWD will be able to maintain and strengthen our bays for many generations to come.