Salinity Relations of Crocodiles in Florida Bay

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Abstract
The importance of high salinity as a limiting factor to the Florida Bay population of Crocodylus acutus was investigated, since hatchlings in captivity are unable to survive in seawater. Na, K, Cl and osmotic pressure were measured in samples of plasma and cloacal fluid. The ion and uric acid content of solid cloacal excretions was also determined. Na influx and efflux of small crocodiles submerged in seawater and of isolated skin keratin were measured. The relationships beween snout-vent length, body mass and surface area were estimated. It was found that the head-neck, tail, legs and body regions each account for about one-fourth of the total area. Studies were conducted on hatchling crocodiles of evaporative water loss, behavioral osmoregulation and on the water and ion content of possible food items. Wild hatchlings have a plasma osmotic pressure near 330 mOsm [milli-osmolar], a level typical of vertebrates. Body Na influx and efflux are quite low; there is a net uptake in sea water of about 9 .mu.moles/100 g body mass hr. The skin is probably very low in Na permeability. There is a substantial loss of water from fasting hatchling crocodiles submerged in seawater (35.permill.) or held in moist air. Feeding is an important means of balancing these water losses. When fed fish ad lib. and kept in an aquarium divided into land and water portions, most small (100-480 g) crocodiles maintained body mass at salinities up to 17.5.permill. (50% sea water). Some even gained mass at 26.permill.. Field data from Florida Bay tend to confirm that C. acutus hatchlings are intolerant of 35.permill. (100%) sea water.