MARINE MAMMAL COMMISSION - Annual Report for 1998 



the Miami Beach Coast Guard Station received a 

 special manatee enforcement award from the Service 

 in March 1998. 



In 1999 the Service plans to maintain a comparable 

 level of enforcement effort, but in the future, the 

 Service hopes to obtain funding to support four full- 

 time manatee enforcement officers. Such support is 

 urgently needed. 



Warm- Water Manatee Refuges 



Over the past two decades, there has been a 

 significant increase in the number of manatees winter- 

 ing at both natural and artificial warm-water refuges. 

 Natural refuges are formed by warm-water springs; 

 artificial refuges are created by thermal outfalls from 

 power plants, paper mills, and other industrial facili- 

 ties. The most important warm- water refuges are 

 located in the lower two-thirds of the state. 



Among the natural warm-water refuges used most 

 extensively by manatees are Blue Spring on the upper 

 St. Johns River, Kings Bay at the head of the Crystal 

 River on Florida's west coast, and Homosassa Springs 

 located at the head of the Homosassa River a few 

 miles south of Kings Bay. Maximum winter counts at 

 these locations have increased severalfold: counts at 

 Blue Spring have increased from about 25 early in the 

 1980s to more than 100 animals in 1998; counts in 

 Kings Bay have increased from about 80 late in the 

 1970s to nearly 300 animals currently; and counts 

 around Homosassa Springs have increased from about 

 40 in the early 1980s to more than 100 in 1998. 



Winter counts also have increased at most major 

 artificial warm- water refuges, the largest of which are 

 power plant outfalls (Figure 12). Manatee counts 

 made at five of the most important power plant 

 outfalls during winter cold fronts over the past 20 

 years have produced maximum aggregate counts that 

 have increased from a range of 270 to 614 manatees 

 between 1978 to 1985 to a range of 587 to 1,068 

 between 1985 to 1997. At four of these plants 

 maximum counts have exceeded 200 manatees, and at 

 two adjacent power plants only a few miles apart in 

 Brevard County, 585 were counted at one time in 

 December 1997. As noted above, a small number of 

 manatees also has been wintering at smaller industrial 



outfalls in northeastern Florida and southern Georgia. 

 Photoidentification and telemetry data show that some 

 animals move between various winter refuges both 

 within and between winters. 



From these counts, it is apparent that the number 

 of manatees, and probably the proportion of the 

 manatee population, using localized warm-water 

 refuges has increased significantly. Because of 

 uncertainty about past and current population sizes and 

 the number of animals wintering in southern Florida 

 where water temperatures usually do not fall below 

 species' tolerance limits, it is not known to what 

 extent the increasing use of refuges in central Florida 

 is due to population growth and/or redistribution of 

 the manatees formerly wintering in southern Florida. 



In either case, it is clear that water temperatures 

 surrounding winter refuges in the middle third of the 

 Florida peninsula can drop annually to potentially 

 lethal levels. In addition, the concentration of animals 

 within confined refuges increases the risk of large- 

 scale die-offs due to the spread of disease, local red 

 tides, pollution events, or exposure to cold. Perhaps 

 the greatest risk in this regard is the possible loss of 

 warm-water industrial outfalls due to (1) transient 

 operational problems or economic conditions that 

 force a temporary plant shutdown, and (2) permanent 

 closures as plants reach the end of their operational 

 life. If a shutdown were to occur at a site used by 

 large numbers of manatees in winter and animals were 

 unable to move to an alternative warm-water refuge, 

 a substantial number of cold-related manatee deaths 

 could ensue. The likelihood of deaths associated with 

 a plant shutdown would probably increase the farther 

 north the plant is located and the farther away it is 

 from alternative warm-water sources. 



To date, artificial refuges have proven to be very 

 reliable. Under provisions of effluent discharge 

 permits issued by the Environmental Protection 

 Agency under the Clean Water Act, operators of 

 facilities that attract manatees in winter have worked 

 with the Fish and Wildlife Service and the state to 

 develop contingency plans and procedures to prevent 

 interruptions in warm-water discharges during the 

 winter. As indicated above, the Florida manatee 

 population now appears to be larger than it was 20 

 years ago and this increase occurred as more animals 



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