Abstract
Submerged aquatic vegetation (SAV) has long been recognized as a critical habitat for macrofauna and megafauna in freshwater and estuarine ecosystems. Historical and current anthropogenic activities such as canal construction, land development, and water management have had destructive impacts on SAV in the Caloosahatchee River and estuary. Large scale alterations to flow rates, salinity fluctuations, nutrient loading, an expansion of the watershed, and dredging activities have led to a substantial decrease of Vallisneria americana in the Caloosahatchee River. This study focused on three oligohaline locations of the river that underwent restoration of Vallisneria americana, amounting to 20 acres of SAV restoration. Understanding fish communities and associated changes in diversity and abundance is critical in assessing the success of the restoration. Pre-restoration assessments of the fish community in 2018 and early 2019 were compared to post-restoration assessments of the fish community in 2019 for each of the sites. Multiple types of passive and active fish traps were deployed throughout the sampling period. Data were interpreted using univariate statistical techniques and multivariate statistical techniques to examine diversity and abundance of the fish. After initial sampling, the effective passive traps were narrowed down to Breder traps, mesh umbrella traps, and crayfish traps. Active trapping methods initially involved seining and cast netting. Cast nets were found to be ineffective and were not continued. After restoration of Vallisneria americana and introduction of herbivore exclusion cages, seining was more difficult due to the placement of cages and was only utilized once after restoration. Alternative active trapping methods were added: hook and line sampling, trawling, and electroshocking. Electroshocking was found to be the most efficient at capturing large numbers of individuals of many different species. Trawling was found to be moderately effective and hook and line sampling was found to be largely ineffective. For the consistently utilized passive trapping techniques, individual locations did show some variability, but the mean species richness appeared to follow the similar trends as the Control Site over time. For the three consistently utilized passive trapping techniques, a drop in average species richness was seen for the mean of all restored sites and the Control Site. The largest lifts in total abundance were seen in the two downstream locations, Site 1 and the Control Site. Multivariate analyses by site for the pooled pre and post-restoration data indicates that all sites were similar in pre-treatment and differences emerged in post-treatment. Post-treatment similarity appeared to be related to geographical position in the river, with downstream sites showing similarity and upstream sites showing similarity. Such trends might also be related to lack of exclosures which may have affected the establishment of Vallisneria americana at Site 1. Disaggregation of data into individual sampling events indicated two significant groups in the cluster analysis at the p<0.1 level, largely grouping by time, regardless of treatment type. Electroshocking of the sites showed that species richness, abundance, and catch per unit effort (CPUE) increased in the restored sites farther upriver, although not all trends were statistically significant. Abundance and biomass of common snook (Centropomus undecimalis) was statistically significant, with more were captured in upstream sites. The larger numbers in the upstream locations is potentially a result of geographical location or as a result of the presence of cages as structure. Seining abundances significantly increased at all sites when comparing the first seining session to the one post restoration sampling. Seining richness also increased across each site, but the results were not statistically significant. The ecological lifts (richness or abundance) occurring at all sites, including the Control Site, indicates that such changes were likely related to external factors. The lack of significant differences in fish species diversity or abundance following the initial restoration plantings does not signify a failure of the project. Geographical differences of the sites and the lack of long-term data might also mean that lifts in the fish community are difficult to observe and quantify in the short-term. The monitoring of changes in fish abundance and diversity can inform future restoration efforts. Additionally, this research highlights effective methods to record fish abundance and diversity. Restoring SAV will allow future generations to enjoy improved aesthetics, enhanced recreation, a sustainable economy, sustainable fisheries, and most importantly to have a healthy environment to live in that fuel’s happiness and wellbeing. Quantifying changes in diversity and abundance is also of interest to fishermen who are looking to catch more species of fish, ecologists looking to restore ecosystems, and local, state, and federal governments seeking justification for allocating resources to restoration.