Abstract
Free-ranging manatees (Trichechus manatus latirostris) are grazing herbivores that consume a variety of sea grasses, including Thalassia testudinum, Halodule wrightii, and Syringodium filiforme.1-4 The purpose of this study was to compare the nutrient analysis of these sea grasses with that of romaine lettuce fed to captive manatees.
Samples of sea grass (~ 1 kg each) were collected in the spring, summer and fall in Florida from one (Skyway; spring) or two (Skyway, Apollo Beach; summer, fall) sites. Rhizome and leaf portions of the sea grasses were separated. Grass (n=13) and romaine lettuce (n=2) were freeze dried to determine moisture content. Crude protein, crude fat, acid-detergent fiber (ADF), neutral-detergent fiber (NDF), lignin, and ash were determined using standard methods. Results presented on a dry matter basis. Crude protein and fat were lower in grasses (5.1-17.8% and 0.2-1.5%, respectively) compared to romaine lettuce (23.5-24.9% and 2.2-3.3%, respectively). ADF, NDF and lignin were greater in sea grasses (5.8-23.7%, 12.1-33.5% and 0.1-3.9%, respectively) than in romaine lettuce (12.5-23.2%, 15.8-30.5% and 1.1-2.6%, respectively). Fiber was higher and fat and protein lower in sea grasses collected in summer and fall than in spring.
In conclusion, captive manatees fed primarily romaine lettuce consume much less fiber than wild manatees consuming sea grass. Low fiber diets have been associated with abnormal intestinal function in other herbivores. Feeding forages that more closely mimic the manatee's natural diet may improve the health of captive manatees; alternative commercial diets are recommended.
Acknowledgements
The authors would like to thank Dr. Darryl Heard and the University of Florida College of Veterinary Medicine Zoological Medicine Research Fund for financial support, and Gaye Brewer at Dairy One, Cornell University for assistance with data processing. This work was completed under USFWS permit MA067116-0.
References
1. Burn DM, DK Odell. 1987. Volatile fatty acid concentrations in the digestive tract of the West Indian manatee, Trichechus manatus. Comp Biochem Physiol B 1987; 88(1):47-9.
2. Lefebvre LW, JP Reid, WJ Kenworthy, JA Powell. 2000. Characterizing manatee habitat use and seagrass grazing in Florida and Puerto Rico: implications for conservation and management. Pacific Conservation Biology. 5(4): 289-298.
3. Rommel SA, LJ Lowenstine. 2001. Gross and Microscopic Anatomy. In: Dierauf, L. A., and F. M. D. Gulland, eds. Marine Mammal Medicine, 2nd Ed. CRC Press, New York, New York. Pp. 146-147.
4. Reynolds JE, SA Rommel. 1996. Structure and function of the gastrointestinal tract of the Florida manatee, Trichechus manatus latirostris. Anat. Rec. 245(3): 539-58.