Movement Behavior of Manatees and Dugongs: I. Environmental Challenges Drive Diversity in Migratory Patterns and Other Large-Scale Movements

Abstract

The seemingly unhurried nature of manateesManatee and dugongsDugong (Dugong dugon) belies their great capacity for undertaking long-distance journeys, often repeatedly in the form of round-trip seasonal migrations, but sometimes as movementsSeason/ seasonal movements independent of seasonal influence. Unique attributes of sirenian biology that interact with features of their environment to mold patternsPatterns, of movement and habitatHabitats, use include herbivory, limited thermoregulatory physiology for coping with cold, and, for manateesManatee, an apparent need to ingest fresh water. ManateesManatee and dugongsDugong (Dugong dugon) are remarkably adaptable in their large-scale movement behaviorMovement behavior, as manifested by the considerable variation in the occurrence and extent of migrations across populations within species, and among individuals within populations. Some populations and individuals are relatively sedentary year-round, whereas others migrate hundreds of kilometers between seasonal ranges. The environmental selective pressures that drive seasonal movementsSeason/ seasonal movements vary across species, climatesClimate, and ecosystems,Ecosystem but are most commonly generated by predictable fluctuations in water temperatureWater temperature (Florida manateeFlorida manatee (Trichechus Manatus Latirostris) , some dugongDugong (Dugong dugon) populations), rainfall (coastal populations of Antillean and African manateesAfrican manatee (Trichechus senegalensis)), or water levelWater level (inland populations of all three manateeManatee species living in floodFlood-pulse river systems) over the annual cycleSeason/ seasonal cycles/variation. In each case, there is a season (winter, dry, or low-water) of heightened environmental stressStress where the animals' range is restricted to areas around a key limiting resource (warm water, fresh water, or deep water, respectively) and, therefore, forageForage is less available or of lower nutritional quality. Because dugongsDugong (Dugong dugon) are strictly marine and do not require fresh water, they experience fewer seasonally imposed constraints and are less likely to migrate than manateesManatee. Consequently, the large-scale movements of dugongsDugong (Dugong dugon) seem more stochastic; assessing the status of forageForage over a wide area through occasional long-distance exploratory forays may represent a behavioral adaptation to periodic extensive declines in seagrass caused by extreme weather eventsExtreme weather events . The available evidence for manateesManatee indicates strong fidelity to seasonal or year-round rangesSeagrass range across years. A common finding from tracking studies is the existence of considerable variation in large-scale movement behaviorMovement behavior among and within individuals, which should confer adaptability to environmental change in the short term and provide the raw material for evolutionary change over the long term.

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