Research Spotlight

User Opinions of Hydrilla and Hydrilla Management at Lake Harris

By Daniel Nelson

Hydrilla (Hydrilla verticillata) was introduced to Florida in the 1950’s and impacted over 140,000 acres of waterways by the early 1990’s (University of Florida Institute of Food and Agricultural Sciences). The rapid spread of this aquatic plant can be attributed to the plant’s ability to establish new infestations based on small fragments, grow an inch or more a day, and grow in deeper water due to lower light requirements. These factors, among others, allow the plant to quickly out-compete other native aquatic plants, quickly developing a monoculture of submerged plants.

The rapid growth of hydrilla creates dense mats of vegetation at or near the water’s surface among many of Florida’s shallow waterbodies. This creates problems for water level control, and recreational uses including access and navigation of Florida’s lakes. Although there is a significant list of negative results of these infestations, there are definite positives as well. Hydrilla provides habitat for many sport fishes in Florida, especially the highly sought-after largemouth bass. Hydrilla also provides an ample food source for many migratory waterfowl species as well as a natural filtering component for nutrient rich waterbodies.

As these infestations have drastically altered areas of Florida, the issues have become extremely polarizing. In recent years, hydrilla has expanded in Lake Harris. In 2017 and 2018, it was estimated that 30% of the lake was covered in submersed plants, of which roughly 70% was hydrilla. Most stakeholder input received by FWC on hydrilla management was through stakeholder meetings or on various social media outlets. To make more informed decisions on hydrilla management, FWC needed a tool to better assess the varying levels of use on waterbodies, as well as the full spectrum of opinions of hydrilla management at these waterbodies. Biologists from FWRI, Division of Freshwater Fisheries Management and Invasive Plant Management worked together to develop this tool at Lake Harris.

Biologists were able to quantify the proportions of different users at Lake Harris by implementing a moving boat count into the annual creel survey. During the surveys, all moving boats were counted, therefore it could be inferred the proportion of boat included and not included in the creel. Boat type activities were then informed by a secondary survey at access points. These access point surveys then revealed the different activity proportions by different boat types and could be applied to all the moving boats seen on the lake. Finally, a 22-question survey was developed to identify the opinions of the various user groups at Lake Harris.

Since November 2018, 2,908 moving boats were identified using Lake Harris. The proportion of activity by each boat type was categorized by interviewing 1,095 boats. Bass boats and pontoons made up 61% of all boats using Lake Harris. The use at Lake Harris was split between angling (45%) and boating (55%). Boaters had a more negative opinion overall of hydrilla than largemouth bass anglers. Black Crappie and Sunfish anglers tended to be more similar to boaters, as their fishing techniques were negatively impacted by dense hydrilla. A high majority (94%) of all users wanted to see native vegetation expand in the absence of hydrilla. When asked about the use of herbicide as a control method, 35% of users voiced some concern. If FWC was to discontinue their treatment, 86% of users thought that hydrilla would expand greatly or cover the entire lake. Overall, users at Lake Harris had somewhat positive opinions (3.48) when asked if they were satisfied with FWC’s management of hydrilla (Likert scale 1-5; Extremely Negative to Extremely Positive).

This survey provided a framework for future research to quantify different user groups at different waterbodies to inform FWC when making aquatic management decisions. The survey also provided a representative, proactive approach to better understanding the user dynamics at Lake Harris and how they relate to the management of hydrilla. FWC can use the results of this study to target specific groups based on the current contact list when deciding on future management actions. This study at Lake Harris concluded that although biologists may hear from a vocal group of users that are displeased with management, overall users are more satisfied than originally thought.