Theses and Dissertations


Title: Life-History of Lepisosteidae: Implications for the Conservation and Management of Alligator Gar

Name: Ferrara, Allyse Marie

Degree: PhD

Chair: Elise R. Irwin

Resides:

University: Auburn University

Location: Auburn, Alabama

Date: 2001

Pages: 141

Keywords: gar,habitat modification,fisheries management,conservation

Abstract:

Life-history strategies of three species of gar, alligator gar Atractosteus spatula, longnose gar Lepisosteus osseus, and spotted gar Lepisosteus oculatus, were characterized and compared using demographic variables and elasticity analysis. Deterministic age-structured matrix models were used to determine population growth rates and for elasticity analysis of vital rates to determine which life history stages had the greatest influence on population growth rates. Most demographic variables formed a continuum from spotted gar to longnose gar to alligator gar. Survival of adults had the greatest influence on population growth rate (i.e., highest elasticity value) in alligator gar but not in longnose gar or spotted gar. Although differences in demographic variables and elasticity patterns were found among the species, the overall life-history pattern for all three species was similar to long-lived mammals and birds. Matrix models were also used to simulate various rates of exploitation to determine the response of population growth rates to exploitation. When all life stages were exploited the three species declined at a similar rate. When only adults were exploited, the spotted gar population growth rate declined more slowly than did population growth rates of the larger species. Alligator gar populations have declined throughout much of the species' historical range. Exploitation and habitat alteration have been postulated to be factors contributing to the decline. Three populations of alligator gar with different levels of exploitation were compared to determine the effects of exploitation on conservation and management of alligator gar. Demographic variables and elasticity analysis were also used to compare alligator gar from three populations, one in Alabama and two in Louisiana. Exploitation was highest in Lake Pontchartrain, Louisiana and lowest in Alabama. Although elasticity patterns were similar among the three populations, age structure of the Sabine National Wildlife Refuge, Louisiana and Lake Pontchartrain populations were truncated at twenty-eight years versus the fifty-year age structure of the Alabama population. This truncated age structure of the Louisiana populations resulted in lower generation time, lifetime reproductive output, and population growth rates than the Alabama population. The effect of decreased survival of alligator gar juveniles and stocked individuals on population growth rates was also assessed using matrix models. Management and conservation recommendations were made to prevent increased exploitation, assess juvenile survival rates and habitat usage, and to examine genetic implications of stock enhancement for alligator gar.

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