Snook

Coastal wetlands across the Indian River Lagoon (IRL) on the east coast of Florida have been impounded for mosquito control purposes, which have been known to have adverse effects on overall fish populations. The objective of this project was to assess the use of culverts by species of larval fish at three impounded mangrove sites in the IRL. Light traps were used to collect samples of larval fish (both inside the basins and in the surrounding lagoon) which were humanely euthanized, preserved, and examined under a digital microscope. A total of 3,926 fish were collected from 24 taxa in 576 samples over the year-long study. Larval seasonality generally followed known reproductive seasonality of the species captured. Inside the impoundments were dominated by species known to spawn in and around mangroves such as the Gambusia holbrooki and Poecilia latipinna. Species that spawn in the IRL or in coastal waters that subsequently use the IRL as a nursery (such as Anchoa mitchilli and Gobiosoma robustum) had relatively low catches in the impoundments. Larvae of the main sportfishery species that have juveniles known to utilize the studied impoundments (Megalops atlanticus, the Atlantic tarpon, and Centropomus undecimalis, the common snook), were rarely caught inside the impoundments or in the surrounding IRL. The low numbers of IRL and offshore spawning larvae that enter the impoundments may be hindered by restricted water flow through culverts connecting the habitats, or by their inability to survive the low DO conditions often found inside the impoundments, especially during the summer. The lack of larval tarpon and snook in the light collections suggest that these species metamorphose from the larval to juvenile stage outside of the impoundments, before they enter the mangrove-dominated nursery habitats. The results of the study can be used to further modify impoundment restoration and management strategies to enhance their role as fish nursery habitats.

Estuarine ecosystems are dynamic habitats, where the convergence of marine and freshwater results in constant fluxes in environmental abiotic parameters. Organisms must balance these variations within their optimal range to minimize physiological costs, often by movement from unsuitable to more suitable areas. Additional disruptions to ecosystem balances, such as anthropogenic hydrologic discharges, further alter environmental conditions and may cause population-wide movement responses of mobile organisms. Responses to anthropogenic and natural fluctuations can differ based on time of year, life history stage, or individual characteristics. These ecologically-balanced dynamics are difficult to model. In this study, I examined variability in estuarine environmental data and common snook (Centropomus undecimalis) movement responses to anthropogenic and natural fluctuations in the environment in a managed waterway. ARIMA time series models were tested as a method of modeling variability in environmental parameters. Monthly variance was well described throughout most of the estuary, especially when the interannual and intra-annual patterns were stable, indicating that these models are a good method for these types of data and could be appropriate for forecasting. Euryhaline sportfish movement responses to high discharge events in a managed waterway were observed with passive acoustic telemetry and did not show large-scale, population-wide consistency. Responses were variable between and within individuals, but individual characteristics appear to have influenced behavior in response to disturbances. Thus, these sportfish populations may be more resilient to this type of disturbance than previously hypothesized. Generalized additive mixed effects models showed that the distribution and movement of individual fishes varied in response to multiple natural and anthropogenic factors, and there was no primary driver. The understanding of the relationships among the distribution and movement of fishes and abiotic and anthropogenic factors can guide management of waterways and provide insight into how changes will affect abiotic factors and communities.

Otolith increment morphology of the protandric hermaphrodite Centropomus undecimalis (snook) was analyzed in relation to age and length for sex specific growth differences to retroactively determine the time of sex change. Growth spurts in the otoliths of female snook, the terminal sex, were identified between ages 4 and 8, corroborating the current understanding of when sex change occurs (between 3 and 8). No such growth increases were identified on the otoliths of male snook, the primary sex. Otolith growth, however, was found to decouple from length, so these growth spurts are not reflected in the length of the fish. This study marks the first time that a distinct growth pattern differentiating the primary and terminal sexes, similar to that seen in the protogynous transitional growth spurt hypothesis, has been identified on the otoliths of a protandric species.

Disturbance events occur outside the normal disturbance regime of a system and
can cause changes in behavior of some organisms. The 2010 cold event is an example of
a disturbance event that influenced the behavior of Common Snook (Centropomus
undecimalis). Common snook are euryhaline sportfish native to Florida, Texas, and the
Caribbean. Florida is the northern most part of their distribution, based on the 15o C
winter isotherm. They move between offshore areas during spawning season and
freshwater coastal rivers during non-spawning season. With the use of previously
collected acoustic telemetry and biological data this project identifies the impact on
population dynamics and movement near the time of the event. The goal is to understand
fine scale movements and physiological conditions under normal and abnormal
conditions to further inform management of the species.