Variation in body condition of Alligator mississippiensis in Florida

Abstract

We examined body condition (using Fulton’s K with snout-vent length and weight) for 482 American alligators (Alligator mississippiensis) collected from 14 aquatic sites in Florida in 2011 and 2012. An information-theoretic approach using Akaike information criterion (AIC) was used to select the best models for alligator body condition from a suite of seven candidate models created using combinations of trophic state (oligotrophic, eutrophic, hypereutrophic), sex, and alligators/km. Our top model included trophic state and alligators/km indicating that alligator body condition from sites classified as hypereutrophic and eutrophic (2.43 ± 0.07 and 2.45 ± 0.05, respectively) were greater than alligator body condition at oligotrophic sites (2.14 ± 0.01). Alligator body condition was lower at sites with a higher density of alligators ≥ 1.25 m. Across all sites, average alligator body condition ranged from 1.94 ± 0.054 (SE) to 2.78 ± 0.121(SE). This was a 43% difference in alligator body condition between the site with the highest alligator body condition (Lochloosa Lake, a hypereutrophic lake in north-central Florida) compared to the site with lowest body condition (Water Conservation Area 3B, an oligotrophic marsh in the Everglades). Across all sites, average alligator body condition was 12% greater at eutrophic and hypereutrophic sites compared to oligotrophic sites which was consistent with patterns observed in other studies for fish standing stock (highest in eutrophic lakes and lowest in oligotrophic marshes in the Everglades). The same patterns occur in alligator stomach content volume (higher in lakes in north-central Florida, Louisiana fresh, intermediate, and brackish marshes compared to the Everglades). Our results illustrate that variation in alligator body condition is consistent with patterns of aquatic site productivity and is a useful parameter for describing differences in aquatic site ecological condition.