American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades

Abstract

The federally threatened American crocodile (Crocodylus acutus) is a flagship species and ecological indicator of hydrologic restoration in the Florida Everglades. We conducted a long-term capture-recapture study on the South Florida population of American crocodiles from 1978 to 2015 to evaluate the effects of restoration efforts to more historic hydrologic conditions. The study produced 10,040 crocodile capture events of 9,865 individuals and more than 90% of captures were of hatchlings. Body condition and growth rates of crocodiles were highly age-structured with younger crocodiles presenting with the poorest body condition and highest growth rates. Mean crocodile body condition in this study was 2.14±0.35 SD across the South Florida population. Crocodiles exposed to hypersaline conditions (> 40 psu) during the dry season maintained lower body condition scores and reduced growth rate by 13% after one year, by 24% after five years, and by 29% after ten years. Estimated hatchling survival for the South Florida population was 25% increasing with ontogeny and reaching near 90% survival at year six. Hatchling survival was 34% in NE Florida Bay relative to a 69% hatchling survival at Crocodile Lake National Wildlife Refuge and 53% in Flamingo area of Everglades National Park. Hypersaline conditions negatively affected survival, growth and body condition and was most pronounced in NE Florida Bay, where the hydrologic conditions have been most disturbed. The American crocodile, a long-lived animal, with relatively slow growth rate provides an excellent model system to measure the effects of altered hydropatterns in the Everglades landscape. These results illustrate the need for continued long-term monitoring to assess system-wide restoration outcomes and inform resource managers.

Natural and Anthropogenic Factors Influencing Nesting Ecology of the American Crocodile in Florida, United States

“…Increases in both numbers of nests and areas where nesting occurs were associated with crocodiles nesting on artificial substrates, especially along levees and berms of canals and ditches, which were dug for drainage, navigation, or cooling purposes (Mazzotti et al, 2007a; Figure 2). For instance, the expansion of crocodile nesting to the Flamingo/Cape Sable area in the mid 1980's concurrent with plugging of Buttonwood and East Cape canals, provided new locations as well as lower salinities in interior wetlands leading to increased growth and survival of hatchling crocodiles (Mazzotti et al, 2007a(Mazzotti et al, , 2009Briggs-Gonzalez et al, 2021). That crocodiles found and nested in these new locations and habitats illustrates the dispersal and wandering instincts of this species (Kushlan and Mazzotti, 1989b;Cherkiss et al, 2014) and crocodylians in general (Read et al, 2007;Campbell et al, 2013;Calverley and Downs, 2015) as well as the willingness to nest in any diggable substrate at suitable elevation.…”

“…The incubation period is around 90 days and is temperature dependent (Mazzotti, 1989;Thorbjarnarson, 1989). Hatching generally occurs in July and August (Mazzotti, 1989) though hatchlings have also been found in September (see Briggs-Gonzalez et al, 2021). More recently, Cherkiss et al (2020), found that hatching is occurring earlier in Florida (late June) over a 37-year nesting period illustrating that increasing temperature could be influencing earlier hatching.…”

Ecological implications of allometric relationships in American alligators (Alligator mississippiensis)

“…Thus, the parameters of the allometric equation can be used to summarize trait–size covariation and compare morphologies among populations. Allometric coefficients have proved to be useful for management and conservation purposes, especially those relating weight and length, and have been implemented to assess the effect of environmental factors on the health of individuals and populations 6 , 7 and to understand how differences in individual’s weight given a length can be influenced by landscape transformation 8 – 10 .…”

Global conservation prioritization areas in three dimensions of crocodilian diversity

“…Crocodilians are the largest inhabitants of freshwater ecosystems and are highly exposed to anthropogenic pressures, mainly due to habitat loss 3 , with half of the living species threatened with extinction 4 . Despite limited empirical knowledge, they have been globally identified as potential bioindicators due to their sensitivity to pollution, and dependence on aquatic habitats 5 – 8 . Crocodilians are semiaquatic predators and may be of crucial importance in aquatic and terrestrial ecosystems 2 , 9 .…”