Life History Parameters and Population Dynamics of Freshwater Fishes of South Florida Canal Systems

LEO G. NICO & JEFFREY J. HEROD
UNITED STATES GEOLOGICAL SURVEY, Florida Integrated Science Center,
7920 NW 71^st Street, Gainesville, FL 32563   (e-mail: Leo_Nico@usgs.gov)

WILLIAM F. LOFTUS
UNITED STATES GEOLOGICAL SURVEY, Florida Integrated Science Centers,
Everglades National Park Field Station, 40001 State Road 9336, Homestead, FL 33034

Presented at the American Society of Ichthyologists and Herpetologists 81st annual meeting,
Pennsylvania State University, State College, Pennsylvania (5-10 July 2001).

Introduction

Fishes are essential to the successful functioning of wetland food webs in southern Florida through their roles as prey and predators. Any changes that reduce the population sizes, community composition, or availability of aquatic animals will affect all facets of the ecology of these wetlands. For these reasons, fishes have been recognized as key indicators by which to measure success of Florida Everglades restoration plans. However, gaps in baseline knowledge remain.  Basic demographic information, termed life-history parameters (i.e., growth rate, age at maturation, fecundity and life expectancy), is needed to make predictions about their resilience under alternative management scenarios.  To date, most basic life-history parameters remain to be characterized, even for abundant fishes.  Adding to the challenge, life-history characteristics of important Everglades species are known to be plastic in response to environmental conditions and survivorship and recruitment schedules are certain to be influenced by variation in hydroperiod. This project looks at the effect of hydroperiod on recruitment, size/age structure, growth, and fecundity, which, in turn, determine fish population dynamics. Final results will provide a characterization for populations and communities in canal habitats across space and time, as well as, among various hydrological conditions and different levels of anthropogenic activity.

Study Design

To document the life history parameters of Everglades fishes, we divided target fishes into small- and large-bodied species. Small-bodied fishes are typically short-lived and are most common in shallow marsh habitats.  Large-bodied fishes are generally long-lived and are common in canal habitats and other deepwater areas. The present study takes advantage of existing or newly funded fish studies in south Florida. These include the throw-trap program for small-fish monitoring, and an electrofishing study of native and introduced species in canals.

The present work involves counts of daily rings on otoliths from small fishes and of annual rings on otoliths from large fishes, as well as size-frequency analyses of all target fishes.  Ultimately, the results will allow us to create an age-at-size table for each species, and to estimate growth in two different seasons.  Furthermore, we will be able to construct life-tables for the species under different conditions in the Everglades.  In addition to our own field fish collections, we will analyze past data from extensive spatial and temporal marsh and canal study collections for reproductive analyses of fecundity, size at maturity, seasonality of reproduction, and sex ratios.

Large Fishes

As part of a series of studies on Florida fishes, we are researching age and growth patterns and population dynamics of selected common large-bodied fishes inhabiting south Florida canals. Target species include introduced Spotted Tilapia (Tilapia mariae), and four native fishes, Florida Gar (Lepisosteus platyrhincus), Yellow Bullhead (Ameiurus natalis), Warmouth (Chaenobryttus gulosus), and Spotted Sunfish (Lepomis punctatus). All five species are common to abundant in many south Florida freshwater habitats and most are predators that prey on other fishes and various crustaceans (i.e., crayfish and shrimp).

Preliminary sampling of canal fishes began in 1999 with intensive quarterly sampling beginning in January 2000. Focus has been on sites in three major south Florida waterways: Tamiami Canal (C-4) (see map above), Canal L-31W, and Snake Creek Canal (C-9).  Reaches sampled in the first two canals have direct surface water connections to adjacent marsh habitats.  The C-9 reach is located in a heavily disturbed urban area and is not associated with a natural marsh. Each of the three study sites sampled encompasses four linear kilometers. Quarterly visits in January, April, July, and October 2000, and January 2001 involved quantitative sampling with a shocker boat of different 1-km reaches at each canal. Supplemental samples between quarters were made in canals L-31W and C-9. More than 5,000 target fishes have been collected. Phase II and Phase III of the project involves dietary analysis, food-web dynamics, fecundity, and seasonality of reproduction within and among study sites.

Small Fishes

In conjunction with our investigations on large fishes, Dr. Joel Trexler and others from Florida International University are collaborating with W. Loftus in studies on the life history of small marsh fishes.  For small-bodied species, age-to-size relationships are being established for three marsh fishes not yet studied: Sailfin Molly (Poecilia latipinna); Flagfish (Jordanella floridae); and Spotted Sunfish (Lepomis punctatus). These relationships will be estimated at one representative short (at Shark Valley) and one representative long hydroperiod location (at Shark River Slough).  For small fishes, experiments include the rearing of each species to a known age in field cages in anticipation of otolith removal and interpretation.  In past efforts, this approach has demonstrated a very high fidelity of daily ring deposition in sailfin mollies up to the age of 21 days. This result needs to be repeated and expanded to other species.  The study includes documenting reproductive phenology and output in six marsh fish species: least killifish (Heterandria formosa); bluefin killifish (Lucania goodei); golden topminnow (Fundulus chrysotus); eastern mosquitofish (Gambusia holbrooki); sailfin molly; and flagfish.

Applications

Accurate life-history data are important in building credible models like the Across Trophic Level System Simulation (ATLSS) ecological model.  Without empirical life-history data from a range of environments, such models will be simplistic and inadequate.  By applying the fish models to restoration alternatives and predicting fish-community responses, we can choose the alternatives that result in biotic characteristics that approximate historical conditions. The iterative process of evaluating and testing the fish-community simulation model in ATLSS also helps identify important data gaps to guide future research.  One of the most obvious gaps is the absence of good life-history data, critical to model performance, for most of the fishes.  The benefits to restoration include having more confidence in improved tools, like the ATLSS models and performance measures from conceptual models, that are used to evaluate alternatives for ecological effects of the Central and Southern Florida Project Restudy, C-111 Project, and Modified Water Deliveries Plan to Shark Slough. In addition to the application of the life-history data to modeling and to interpretation of the data time-series, these data represent new information about the adaptations of many of these species in wetland habitats that form the southern extent of their geographic ranges. These also represent the first life-history data for some of the most abundant introduced species in Florida, and may identify vulnerable life stages for controlling these species.

Acknowledgments

For their valuable assistance in the field and laboratory during the year 2000, we acknowledge the following researchers, technicians, students, and volunteers:  Lynn Albert, Frank Aramzamendi, Amy Benson, Holly Blalock-Herod, Mary Brown, Tim Collins, John Curnutt, Chris Diel, Dan Doroshef, Kathryn Fitzpatrick, Nick Flavin, T. Lynn Fullbright, Pam Fuller, Phil George, Gary Hill, Garbriela Hogue, Stan Howarter, Howard Jelks, Jeff Kline, Eddie Leonard, Robert Lewis, Andrew Martin, Linda Nico, Michael Perry, Morgan Raley, Eric Rolla, Patrica Serralles,Wayne Starnes, Rita Taylor, Jim Williams, and others. Debra Murie and her University of Florida staff are assisting us in aging fishes.  They also provided the otolith microphotographs.

Please do not cite text or use images without permission of the authors
 and the Florida Integrated Science Center, U.S. Geological Survey, Gainesville, Florida.
352-378-8181

Revised 2 July 2001