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Mazzotti, 1989).
American crocodiles forage primarily from shortly before sunset to shortly
after sunrise. Juveniles typically eat fish, crabs, snakes, and other small
invertebrates. Adults eat fish, crabs, snakes, turtles, birds and small
mammals (Ogden 1978b, Ross and Magnusson, 1989).
Field data collected from Florida Bay, Dunson (1982) documented that
although American crocodile hatchlings are intolerant of 35 ppt water, his
laboratory studies indicated that most small American crocodiles maintained
body mass at salinities up to 17 ppt, and some even gained mass at 26 ppt.
Kushlan (1988) suggests that hatchling crocodiles possess a number of
behavioral adaptations for survival in hypertonic conditions, including
consuming water-laden prey items, drinking freshwater from pools and
lenses riding on top of salt water and avoidance of salt uptake. Also
regarding salinity preferences and tolerances, USFWS (1999) states that:
"Water salinity affects habitat use and may be locally important,
especially during periods of low rainfall. Although American
crocodiles have salt glands that excrete excess salt and physiological
mechanisms to reduce water loss...maintenance of an osmotic balance
requires access to low salinity for juveniles. Hatchling crocodiles are
particular susceptible to osmoregulatory stress and may need to have
brackish to fresh water (4 ppt) available at least once per week to
increase growth (Mazzotti et, al. 1986). Crocodiles larger than 200 g
have sufficient mass to withstand osmoregulatory stress and are not
typically believed to be affected by drought (Mazzotti and Dunson
1984). Freshwater needs of the crocodile are usually met with frequent
rainfall, which results in a “lens” of fresh water on the surface for
several days after rainfall (Mazzotti and Dunson 1984). Hatchling
crocodiles are probably stressed and occasionally die during periods of
low rainfall. Anthropogenic changes in the amount and timing of
fresh water flow to South Florida may have resulted in shifts in the
distribution of American crocodiles.”
Estimates of the population of crocodiles in South Florida suggest that from
historical numbers of 1,000 to 2,000, numbers dropped to all-time lows during
the 1960s and 1970s during which it is thought that there were between 100
and 400 non-hatchlings (USFWS 1999.), and that numbers have increased
substantially since that time.
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-14
The most recent surveys for crocodiles in Biscayne Bay which are reflected in
publications were performed by Mazzotti and Cherkiss (1998) pursuant to a
contract with the SFWMD. Surveys were conducted from September 1996
through May 1998. During that period, a total of 132 crocodile observations
were made. Sightings ranged from Chapman Field and the Coral Gables
Waterway at the north to the U.S. 1 corridor and the Crocodile Lakes National
Wildlife Refuge on Key Largo at the south. Figure 11 shows the locations and
comparative numbers of crocodile sightings and captures as reported by
Mazotti and Cherkiss (1998). Surveys did not include the cooling canal
system at Florida Power and Light Company’s Turkey Point Power Plant, an
area long known for its population of crocodiles.
Limited water quality data were recorded at the locations of observations.
Although salinities varied from 0 ppt to nearly 40 ppt, 45% of all nonhatchling crocodile observations were in water with salinity measurements of
0-5 ppt (Figure 12). In discussion of their findings, Mazzotti and Cherkiss
(1998) state that: “Crocodiles benefit from restoration and maintenance of
freshwater flows into the estuarine habitat. Location, timing, and amount of
flow are important. For example, when possible freshwater flows should be
directed through the remaining fringing mangrove swamp rather than simply
discharged through canals. In general flow should peak at the end of the
rainy season and continue discharging into the dry season. Freshwater flow
should be adequate to maintain estuarine conditions (< 20 ppt salinity) into
December in most years.”
USFWS (1999) corroborates that “The timing and frequency of the freshwater
hydroperiod substantially influences the health of the estuarine environment
in South Florida and may be one of the most important large-scale factors
influencing crocodile populations on the mainland”.
Roseate Spoonbill
The Roseate Spoonbill (Ajaia ajaja), a brightly-colored, long-legged wading
bird with a spatulate bill, is the only spoonbill native to the western
hemisphere. It has been designated as a ‘Species of Special Concern’ by the
State of Florida. Although it is protected pursuant to the federal Migratory
Bird Treat Act, this species is not protected pursuant to the federal
Endangered Species Act. No recovery plan has been developed and there is
no designated critical habitat for this species.
Figure 11
Locations of Crocodile Sightings and Captures
Source: Mazotti and Cherkiss, 1998. Status and Distribution of the
American Crocodile (Crocodylus acutus) in Biscayne Bay
Figure 12
Crocodile Sightings in Relation to Salinities
Source: Mazotti and Cherkiss, 1998. Status and Distribution of the
American Crocodile (Crocodylus acutus) in Biscayne Bay
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-17
Accounts of historical populations suggest that the spoonbill population in
the United States numbered in the thousands prior to the 1850s, after which a
rapid decline occurred. This decline, which was attributed to the disturbance
of colonies, plume hunting and collection of nestlings and adults for food and
which occurred between 1850 and 1920, reduced the nationwide population
to approximately 25 pairs (Allen 1942). By 1941, only one nesting colony
(Bottle Key) was known to exist in Florida (Lorenz et. al., 2002). Populations
began to rebound, however after protection mechanisms were enacted,
particularly in coastal Texas and Louisiana, and estimates were that 2,200 to
2,700 nesting individuals existed in the 1970s.
Presently, although there are several widely-spaced individual nesting sites
in other coastal areas in the southern half of peninsular Florida, the primary
nesting areas for this species are in extreme south Florida. Ninety percent of
spoonbill nesting in Florida has been on mangrove islands in Florida Bay in
Everglades National Park, although a colony was recently documented to
occur in coastal areas west of the mangrove shoreline in southern Biscayne
Bay (Lorenz, pers. comm.). Lorenz et al. (2002) report that in recent years
there have been more than 30 islands in Florida Bay with spoonbill nesting