Reproductive biology and population dynamics of a bowfin (Amia calva) population in southeastern Louisiana

A Master of Science Thesis Proposal

Johnathan Davis

Department of Biological Sciences

Nicholls State University

15 December 2005

Summary

Bowfin Amia calva are a top-level predator in the swamps and bayous of Louisiana. Because of the popularity of their meat and roe as food and their local recreational appeal, bowfin are a valuable commodity within south Louisiana. An understanding of their reproductive biology, most notably egg size, number, and time of development, is not only important commercially for individuals who sell the roe, but also for the refinement of population models for the management of the species. In this study, age and growth data as well as the reproductive data will be quantified for a population of bowfin from southeastern Louisiana. Fishes will be collected with gill nets from the Bayou Chevreuil-Grand Bayou system near Chackbay, Louisiana, using gill nets and from various locations across southeast Louisiana with the assistance of commercial fisherman. Total length, weight, egg size and number, sex, and gonad weight will be collected for each fish. This information will be used to improve existing population models and to develop an individual-based harvest model for bowfin using data from populations within southeast Louisiana. Estimating reproductive potential and describing the population characteristics of bowfin can potentially insure protection of the stocks of bowfin and aid in providing a sustainable and prosperous bowfin fishery for the users in Louisiana.

Introduction

Bowfin belong to one of the oldest groups of fishes and are the last extant species of Amiidae. The lineage has been traced back to the Mesozoic era (Patterson and Longbottom 1989). Bowfin are important to Louisiana as a commercial species for both their meat and their roe. The population dynamics of bowfin in southeastern Louisiana is poorly understood, and information on current stocks is limited also. Found in the swamps and backwaters throughout the region, bowfin may become stressed from changes in their habitat. These swamps and backwaters are no longer subjected to yearly flood pulses that contribute to the productivity of the system. Although the bowfin adapts well to these hypoxic habitats, reductions in primary and secondary production can affect populations of top-level predators such as bowfin. Nutrients that are available on the floodplain are no greatly reduced in the system in the absence of a flood pulse, reducing the amount of energy available to species. This energy is not transported up the food chain to bowfin, and therefore, less energy is available for growth and reproduction.

Regarded as a non-game species in some areas of their range, bowfin are not actively sought after by anglers nor are they a primary species of concern for fisheries managers. Bowfin can be an excellent recreational species (Reighard 1903; McClane 1957). Bowfin have often been viewed as harmful and nuisance species to game fishes and recreational anglers (Scarnecchia 1992). Therefore, most management has focused on eliminating this fish, and, as a result, research on this fish species is limited. Furthermore, the ecological role that this species plays is not yet fully understood and could be a vital element in the structure and function of swamp ecosystems. Although bowfin may consume some gamefish species, they also consume many non-game species (Lagler and Hubbs 1940; Berry 1955; Cook 1959, Dugas et al. 1976). Other species once considered as “trash” species such as alligator gar Atractosteus spatula may play important an ecological role by maintaining balanced populations of various fish species (Scarnecchia 1992; Scott 1968; Haase 1969; Becker 1983). Bowfin may play such a role.

Without proper management based on population models and knowledge of reproduction, this species can become prone to over harvest. Bowfin are commercially fished throughout this region, and in 2003, the commercial fisheries landings of bowfin in Louisiana totaled more than 128, 157 dollars from 203,607 pounds harvested (Louisiana Department of Wildlife and Fisheries 2005). The meat must be harvested from the fish immediately or very soon after death due to the release of an enzyme that causes the tissue to break down.

Assessment of bowfin populations is needed for the effective management of bowfin in areas from which the species is harvested. Currently, research on other long-lived commercially fished species in Louisiana is being conducted. These studies on focused on the hatching and rearing of alligator gar and the genetic differences among gar populations from different regions in order to support scientifically-based restocking of alligator gar in native areas (Campbell, U.S. Fish and Wildlife Service, pers. communication; Graves, pers. communication). Little information on the bowfin is available (Davidson 1991). The study of bowfin is important for providing accurate information so that future management strategies will be effective in allowing this species to be protected, yet productive.

Purpose

The purpose of this project is to analyze fecundity, age, and growth of bowfin to assess the population in southeast Louisiana in order to develop and to adjust population models.

Goal

The goal of this study is to learn more about the age and growth and the reproductive biology of bowfin for population management and modeling purposes through the study of life history traits such as fecundity, egg size, age of maturation, length of spawning season, and gonad development. This project will also define the spawning period of bowfin and the age of maturation for a southeast Louisiana population, as well as describe population structure using age, growth, length and weight data. This information will be used to improve population models for bowfin using data from populations within southeast Louisiana.

Objectives of Research

Specific objectives of the research are to:

1.)  Estimate total fecundity of female bowfin in a southeast Louisiana population.

2.)  Determine the age of maturation for bowfin from a southeast Louisiana population.

3.)  Define the spawning period of bowfin from a southeast Louisiana population.

4.)  Characterize the population structure of a southeast Louisiana population of bowfin using age, growth, and fecundity data.

5.)  Compare results to historical data.

Preliminary Data

A total of 51 individuals have been collected. With the addition of fish collected in March 2005 for other research, 45 sets of otoliths and 68 gular plates have been collected for determining age and growth. Data on weight, length, girth, sex, and gonad weight are available for 51 individuals (Appendix). No data on egg number or egg diameter is has been calculated to date. The Louisiana Department of Wildlife and Fisheries published a report in which the spawning period for bowfin was late January to early March (Davidson 1991). 29 ripe ovaries were sampled, and average fecundity per ovary was 36, 179.

Methods

Bowfin will be collected on a monthly basis from September 2005 through September 2006 from the swamps and bayous of the Grand Bayou-Bayou Chrevelle complex. Twice a month researchers will collect fish using gill nets and also trot lines when possible. Bowfin will also be collected from commercial fisherman in the local swamps and bayous when possible. Bowfin will be weighed to the nearest tenth of a kilogram and measured for total length and pre-pelvic girth to the nearest millimeter. The heads and gonads will be collected and put on ice for processing in the lab. Otoliths will be removed, washed and dried, and placed in labeled vials for aging. Whole otoliths will be viewed under a dissecting microscope for age determination Multiple readers will age otoliths and gular plates, and any discrepancies in age will be discussed until an age is agreed upon (Nash and Irwin 2000). Photographs of each otolith and gular plate will be taken for documentation and reference. The feasibility of using otoliths for age determination will be assessed. Observation of otolith annuli formation from different age classes throughout the year of sampling will provide a time of annulus formation (Maceina and Betsill 1987). Gular plates will also be removed. They will be boiled on a hot plate in order to remove skin and tissue and then washed, dried, and stored for aging.

Sex determinations will be made based on externally visible characteristics such as the presence (male) or absence (female) of a tail spot and fin coloration. Sexual identification will be confirmed by observation of the gonads. After sex determination is made, gonads will be weighed to the nearest gram and gonad developmental state will be determined (Burr and Ladonski, in press). Gonad descriptions will be made based on color, texture, appearance, and any other noticeable trait. Following the procedures of Ladonski and Burr (in press), a subsample of eggs will be taken, and individual egg diameters will be measured to the nearest millimeter. Additionally, an estimate of the total number of eggs will be made. Egg diameter will be determined using digital calipers and imaging software (Ferrara 2001). Another subsample of eggs weighing 10% of the total ovary weight will be removed from the ovary, and the total number of eggs in the subsample will be counted (Ladonski and Burr, in press). The accuracy of this method will be tested by making a count of all eggs from the ovaries of a few individuals and comparing the actual egg count to the estimated egg count. Ovaries will be labeled and stored in a 10% formulin solution for reference. Gonadosomatic index (GSI) will also be determined for males and females to assist in determination of spawning period (Wilson and Nieland 1994; Ferrara 2001). GSI will be calculated following the method of Johnson and Noltie (1997) according to the following equation:

GSI= (gonad weight)/(total body weight) x 100

Significance of Research

A majority of bowfin research has focused on stomach contents (Ashley and Rachels 1999, Dugas et al. 1976, Todd 1970) and air-breathing capabilities (Daxboeck et al. 1981, Hendrick 1994), with some work studying biology and populations (Davidson 1991). However, recent work has begun assessing nitrite uptake of bowfin (Boudreaux 2005). Unfortunately, the reproductive biology of bowfin is poorly understood. A single population of bowfin will be collected over a single year. Furthermore, determining the times of the year in which egg diameter is greatest within females could provide commercial anglers a guideline for the most profitable time to harvest bowfin eggs. This could limit harvest of under developed individuals during early times of the year.

This study will collect data from populations within a defined area and will provide additional reproduction data which can be used to create population models as well as to develop a population specific harvest model. Management strategies such as creel and harvest limits are based upon population models. Therefore, by improving models and developing new population specific models, more appropriate and effective management strategies will result.

A better understanding of spawning season duration will help to develop measures of protection for bowfin during critical spawning times if necessary. Additionally, determination of age of maturation from a population within one region will allow managers to better evaluate regulations restricting harvest of immature individuals in areas where protection of the population is necessary. Because of this study’s significance in describing a self-sustaining population, many researchers will cite this publication, and many agencies will look to this study in facilitating protection of bowfin in native areas.

Potential for Additional Funding and Eminence

Results of this study will be presented at the annual meeting of the Louisiana state chapter of the American Fisheries Society, with the potential to be presented at other scientific meetings. This research will also be published as a master’s thesis and submitted for publication to a peer-reviewed journal.

The potential exists for collaboration with agencies interested in the protection and management of bowfin populations. This data can be used to justify management actions taken by these agencies. It will also provide the opportunity to garner agency funding in the future for in-depth studies of other bowfin populations and assessments of other species. Completion of this research will demonstrate that the researchers are capable of conducting investigations of this nature in the future. Finally, it will serve as an opportunity to promote the research capabilities of Nicholls State University.

Bibliography/ Citations

Ashley, K.W. and R.T. Rachels. 1999. Food habits of bowfin in the Black and Lumber Rivers, North Carolina. Proceedings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 53: 50-60.

Becker, G. C. 1983. Fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin.

Berry, F.H. 1955. Food of the mudfish (Amia calva) in Lake Newman, Florida, in relation to its management. Journal of the Florida Academy of Sciences. 18: 69-75.

Boudreaux, P.J. 2005. Acute ammonia toxicity and chloride inhibition of nitrite uptake in non-teleost Actinopterygiian fishes. A Master’s Thesis. Nicholls State University.

Chivers, C. J. 2005. Fishing for dinosaurs. Field and Stream. 1005: 58-61, 91-92.

Cook, F.A. 1959. Freshwater fishes in Mississippi. Mississippi Game and Fish Commission. Jackson, Mississippi.

Davidson, R.B. 1991. Bowfin (Amia calva) population, biology, and gillnet selectivity research report, 1990-1991. Louisiana Department of Wildlife and Fisheries. Baton Rouge, Louisiana.

Daxboeck, C., D.K. Barnard, and D.J. Randall. 1981. Functional morphology of the gills of the bowfin, Amia calva, with special reference to their significance during air exposure. Respiration Physiology. 43: 349-364.

Dugas, C.N., M. Konikoff, and M.F. Trahan. 1976. Stomach contents of bowfin (Amia calva) and spotted gar (Lepisosteus oculatus) taken in Henderson Lake, Louisiana. Louisiana Academy of Sciences. 39: 28-34.

Ferrara, A. M. 2001. Life-history strategy of Lepisosteidae: Implications for the conservation and management of alligator gar. Doctoral dissertation. Auburn University, Alabama.

Ferrara, A. M. and E. Irwin. 2001. Standardized procedure for internal sex identification in Lepisosteidae. North American Journal of Fisheries Management. 21:956-961.

Goodyear, C. P. 1967. Feeding habits of three species of gars, Lepisosteus, along the Mississippi Gulf Coast. Transactions of the American Fisheries Society. 96:438-449.

Gowanloch, J. N. 1940. Control of garfish in Louisiana. Transactions of the North American Wildlife Conference. 5:292-295.

Graves, K. 2005. Personal communication. United States Fish and Wildlife Service. Tishomingo National Fish Hatchery.