Abstract
Spotted seatrout (Cynoscion nebulosus) is an ecologically and economically important species in Texas and Louisiana estuaries. Information regarding the movement patterns and habitat usage of spotted seatrout remains limited. This study utilized acoustic telemetry to investigate how spotted seatrout utilize Sabine Lake, an estuary located along the Texas-Louisiana border. A network of 32 receivers was deployed in December 2020 to assess residency duration and potential emigration from the estuary. A total of 27 spotted seatrout were implanted with acoustic transmitters and 18 individuals were detected throughout the array. Of the 18 individuals detected, 11 individuals showed a high residency index (18.96% to 33.62%) and 4 individuals showed low residency index (0.46% to 0.93%). Nine of the spotted seatrout tagged were deemed either dead or had shed their tag. Keith Lake emerged as a key area of importance for spotted seatrout, as indicated by both spatial maps and detection analyses. During the study period, all but two of the tagged individuals stayed within Sabine Lake or had their final detection in the main body of Sabine Lake. The lack of detections at the edge of the array, in the Sabine and Neches rivers or the ship channel into the Gulf of Mexico may suggest predation events or removal by recreational fishers. These findings provide valuable insights for fisheries management strategies employed by both Texas and Louisiana, emphasizing the need for targeted conservation efforts in key habitats within Sabine Lake.
Introduction
Estuaries, where freshwater and saltwater mix, are vital habitats that support diverse marine life and serve as nursery grounds for species like the spotted seatrout (Cynoscion nebulosus). These environments provide essential resources such as food, shelter, and spawning areas. Understanding how spotted seatrout move within estuaries is key to effective conservation and fisheries management, as their movement is influenced by environmental conditions, habitat structure, and human activity. Sabine Lake, located on the Texas-Louisiana border, offers a unique setting for such research due to its mix of industrial and protected habitats as well as slim passage ways to the Gulf, inter coastal waterway, and the Sabine and Neches Rivers. This study utilized acoustic telemetry to track individual spotted seatrout and examine patterns of site fidelity, habitat use, and emigration. The findings aim to identify critical habitats and inform targeted management strategies that support sustainable seatrout populations across the region.
Methods
To study the movement patterns of spotted seatrout in Sabine Lake, researchers used an acoustic telemetry array alongside environmental data. twenty-seven seatrout were captured using gill nets and rod-and-reel methods, then surgically implanted with Vemco V9 transmitters. Fish were released near their capture sites after recovery. Receivers were placed across key habitats to monitor movements continuously. Environmental data—such as temperature, salinity, and dissolved oxygen—were collected from TABS stations and research partners. ArcGIS Pro was used to map fish presence, and RStudio generated abacus plots to highlight seasonal trends. Residency Index (RI) was determined using the following formula: RI (%)= (number of days detected/tag length) *100. This metric helps quantify how long an individual fish remained within the study area.
Figure 1: Illustration of a receiver mounted on a stationary structure in the water, detecting signals from transmitters placed internally in spotted seatrout. Red pinging represents the communication between transmitter and receiver.
Results
Across the study period, the array recorded 74,066 detections of the 27 tagged individuals. All fish remained within the boundaries of the estuary throughout the monitoring period. Of the 27 transmitters deployed, 18 were determined to be active, representing 66% of the tagged fish. The remaining 33% were inactive, which may be due to transmitter failure, predation, or other loss. Most fish (55.56%) were released at Keith Lake, with other release sites including Texaco Island and the Channel (11.11% each), and single releases at Garrison’s Ridge, Johnson Lake, the Sabine Channel, and the Sabine River (5.55% each). Detection patterns indicated variation in individual residency. On average, tagged fish were detected on 9% of the days between their first and last detection (Residency Index: 8.96% ± SE 10.08%), with individual indices ranging from 0.46% to 33.64%. Transmitters 6, 25, 26, and 4 had the highest residency values, ranging from 18% to 33%, suggesting these individuals remained in the estuary for prolonged periods. In contrast, fish with transmitters 12, 7, 1, and 21 were detected only briefly, with residency indices below 1%, indicating limited presence or rapid departure following tagging. Spatial visualizations of detection data reveal that the highest concentrations of tagged spotted seatrout were located around Keith Lake, Texaco Island, and near the Channel, as shown by the larger bubble size (figure 2 & 3). Moderate detections were also observed in the Sabine River and Coffee Ground Cove. In contrast, detection frequency was notably low in the channel leading toward the Gulf of Mexico, and no detections were recorded in the open Gulf. Additionally, none of the tagged individuals were detected in neighboring estuarine systems, such as Galveston Bay or Calcasieu Lake, suggesting a strong site fidelity to the Sabine Lake Estuary.
Figure 2: Map of receivers (R1-R32) and release locations indicated by a trigangle. Size of bubble indicates number of individual spotted seatrout detections and gray ‘o’ marks for receivers with no detections. Color corresponds to unique receivers that detected spotted seatrout.
| Transmitter number | Number of receiver detections | Number of days detected | Dectable days | Residency index (%) | Tag length | Ratio of days detected |
|---|---|---|---|---|---|---|
| Transmitter 11 | 3 | 145 | 143 | 33.64 | 431 | 0.336 |
| Transmitter 4 | 3 | 113 | 111 | 26.22 | 431 | 0.262 |
| Transmitter 2 | 1 | 83 | 83 | 19.26 | 431 | 0.193 |
| Transmitter 3 | 3 | 78 | 76 | 18.10 | 431 | 0.181 |
| Transmitter 7 | 5 | 72 | 68 | 16.71 | 431 | 0.167 |
| Transmitter 8 | 2 | 65 | 64 | 15.08 | 431 | 0.151 |
| Transmitter 10 | 8 | 32 | 25 | 7.42 | 431 | 0.074 |
| Transmitter 5 | 2 | 23 | 22 | 5.34 | 431 | 0.053 |
| Transmitter 1 | 6 | 21 | 16 | 4.87 | 431 | 0.049 |
| Transmitter 16 | 2 | 20 | 19 | 4.64 | 431 | 0.046 |
| Transmitter 17 | 3 | 13 | 11 | 3.02 | 431 | 0.030 |
| Transmitter 12 | 2 | 12 | 11 | 2.78 | 431 | 0.028 |
| Transmitter 15 | 5 | 6 | 2 | 1.39 | 431 | 0.014 |
| Transmitter 13 | 1 | 4 | 4 | 0.93 | 431 | 0.009 |
| Transmitter 18 | 1 | 2 | 2 | 0.46 | 431 | 0.005 |
| Transmitter 14 | 1 | 2 | 2 | 0.46 | 431 | 0.005 |
| Transmitter 9 | 1 | 2 | 2 | 0.46 | 431 | 0.005 |
| Transmitter 6 | 1 | 2 | 2 | 0.46 | 431 | 0.005 |
Figure 3: Abacus plot displaying the distribution of spotted seatrout detections over time and across different receivers. Each horizontal line represents a detection event, with color-coded lines indicating the specific receiver that recorded the detection. Red asterisks (*) denote spotted seatrout classified as deceased. Refer to Figure 1 for receiver locations.
Discussion
Spotted seatrout showed strong site fidelity and high residency within the Sabine Lake estuary, consistent with previous research in other Texas estuaries (Hendon et al., 2002; O’Donnell et al., 2014; Moulton et al., 2017). While most individuals remained in the system, a few exhibited lower residency (0.46–0.93%), possibly due to sex-based movement differences, as males are known to disperse more frequently (Callihan et al., 2013). Keith Lake emerged as a key habitat, with most detections and tagging events occurring at Receiver 1 in that area, suggesting it offers favorable conditions such as prey availability or shelter. Though Sabine Lake has seen less telemetry research than other bays, our study reinforces its ecological importance for this species. This site-specific residency mirrors findings from other studies where certain habitats within estuaries, like tidal creeks, seagrass beds, or areas with stable salinity regimes, were preferentially used by spotted seatrout (O’Donnell et al., 2014; Moulton et al., 2017). While our study did not directly assess habitat variables, the repeated presence of tagged fish in Keith Lakeindicates its importance and suggests it warrants further investigation as a potentially high-value conservation area. While many spotted seatrout demonstrated high site fidelity to Keith Lake, with a large portion of the detections originating from this area, the study also revealed that some individuals temporarily moved to other parts of the estuary. As such, comprehensive management strategies should focus on the entire Sabine Lake estuary, considering its role as a multifunctional habitat for the species. Protecting areas like Keith Lake while also ensuring other vital habitats are preserved will be essential for the sustainability of spotted seatrout populations. Further investigation into habitat use could help explain these patterns, as certain habitats within the estuary may offer more favorable conditions, leading to differences in residency. Habitat preference, such as proximity to seagrass beds or deeper channels, might influence movement behavior, with some areas potentially serving as critical habitats. Fishing pressure and predation poses a significant challenge to spotted seatrout populations. Moving forward, future analysis could further investigate habitat use and how environmental variables impact the movement patterns to determine if certain habitats within the estuary offer more favorable conditions, leading to differences in residency. Habitat preference, such as proximity to seagrass beds or deeper channels, might influence movement behavior, with some areas potentially serving as critical habitats. Additional studies could also look at environmental variables such as water temperature, salinity, and dissolved oxygen and if those variables have any impact on the timing and extent of seatrout movement. Incorporating environmental variables could identify drivers of bay-scale movements and predict the probability of movement for spotted seatrout in changing environmental conditions (i.e. large scale temperature changes or salinity shifts). Since all but two of our fish had their last detection on a receiver in the middle of Sabine Lake, future studies could examine predation on spotted seatrout. Predation on tagged fish is a known challenge in telemetry studies, especially in systems with high predator density, and it can result in an abrupt lack of detections (Heupel & Simpfendorfer, 2002). Innovasea has developed a predation tag that makes a unique ping once the tag has been exposed to stomach acid which would indicate a predation event. Incorporating predation tags into future studies could help distinguish between fish mortality due to predation versus other causes, such as emigration or natural mortality. Their implementation could significantly improve our understanding of predator-prey interactions and mortality sources in Sabine Lake’s spotted seatrout population.
References
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