Home : Features : Manatee Projects : Caloosahatchee River Study

A Special Study of the Caloosahatchee River and Mullock Creek

This article provides an executive summary of the study. A digital file of the complete study is also available.

---

View the Complete Report

---

A Special Study of the Caloosahatchee River Eastward
to the Edison Bridge and of Mullock Creek

Executive Summary

Researchers from the FWC examined manatee use of the Caloosahatchee River in Lee County eastward to the Edison Bridge and manatee use of Mullock Creek in partial fulfillment of the Consent Decree incorporating the Settlement Agreement between various environmental groups and the FWC in Save the Manatee Club, Inc., et al. v. Egbert, Case No. 4: 00CV17/RV United States District Court, Northern District of Florida. Among other relevant data and information, this study evaluated aerial survey, telemetry, mortality, manatee habitat, and boating-activity data.

Caloosahatchee River
The section of the Caloosahatchee River between the Edison Bridge and the mouth of the River near Shell Point constitutes an important manatee travel corridor between essential habitats such as warm-water refugia, feeding grounds, and resting areas. The distribution of submerged aquatic vegetation (marine and freshwater) in this travel corridor is variable and patchy, so manatees are frequently moving from one area to the next. Although manatees presumably feed opportunistically on submerged and floating aquatic vegetation while traveling through this study area, they primarily use the area as a passageway between the more stable feeding areas found upstream (fresh water) and downstream (estuarine). Selected areas in the Cape Coral and Ft. Myers canals provide manatees with sheltered habitats for resting, fresh water (from storm-water runoff and drainage), and nursery areas. In winter, manatees use a few of these canals as temporary warm-water sites. Accordingly, this special study evaluated manatee use of areas adjacent to the focal study area, including areas east of the Edison Bridge (East region) and areas west of Shell Point (West region).

While traveling up or downriver in the Caloosahatchee, manatees appear to use shallow areas near seawalls in highly urbanized locations for feeding, drinking, or thermoregulation. Best available data indicate that manatees travel relatively close to the shoreline. While en route, manatees sometimes stop at secondary aggregation areas.

Aerial surveys documented more manatee sightings east of the Edison Bridge (East region) and west of Shell Point (West region) than in the study area proper. These sightings were seasonally dependent with higher manatee use in the East region during winter (December–February) than the other two regions. The distribution of manatee carcass recovery locations between 1976 and 2001 was similar to that of live manatee sightings based on aerial surveys, with more carcasses and sightings in the East region in January and in the West region in October. The relative density of manatees is much higher in the East region than the West region during winter not only because the warm water is extremely important to manatees, but also because the East region is so much smaller than the West region. In fact, the East region has a higher relative density of animals year-round as well. Analysis of telemetry data indicated that manatees often cross the River in the relatively narrow areas near Shell Point and Redfish Point.

Almost 80% of the aerial survey sightings in the West region of the Caloosahatchee River were recorded in the warm season (March–November). Manatees use Matlacha Pass and San Carlos Bay (located in the West region) for feeding and as a travel corridor. Increased sightings in October in the West region may reflect an overlapping of winter- and warm-season resident manatees as they travel from and to the Caloosahatchee River. Matlacha Pass and San Carlos Bay appear to be frequently-used, stop-over feeding areas for individuals that are traveling north or south along Florida’s west coast, in addition to the manatees entering and leaving the River.

From 1976 to 2001 there has been an increasing trend of manatee deaths in all three regions of the Caloosahatchee River. Frequent exposure to red tide appears to have decreased adult survival rates and may have decreased the average age of the regional manatee population in Southwest Florida. This decreased average age is reflected by the higher proportion of subadult carcasses retrieved from the study area. The Ft. Myers power plant, and to a lesser extent canals at Matlacha Isles, have protected some manatees from exposure to severe cold. If these warm-water sources become unavailable as thermal refugia, manatees in this region would be severely threatened. Over the past 13 years, watercraft-related manatee mortality has increased at a faster rate in the Caloosahatchee River than in either southwest Florida or the State as a whole, based upon carcass recovery locations. Available data indicated that the mouth of the river (from Sword Point to Shell Point), San Carlos Bay, Redfish Point, and Matlacha Pass are areas where manatees are at a relatively higher risk of harmful collisions with motorboats than in other waters of Lee County.

There are more than 40,000 boats registered in Lee County. Many of the boats traveling in the lower Caloosahatchee River originate in the Cape Coral Canal system, and travel toward the Gulf of Mexico. Highest traffic densities occur at Shell Point, where the Caloosahatchee River and San Carlos Bay converge. Vessel compliance rates with manatee speed zones may not be as important as the absolute number of blatant violators and the relatively narrow configuration of the waterway in terms of the threat of harmful collisions. The Caloosahatchee River adjacent to Shell Point represents such a location.

Mullock Creek
Mullock Creek which also has characteristics of a suitable manatee travel corridor, connects the feeding areas in Estero Bay with the freshwater, resting, and warm-water habitats in Ten-Mile Canal. As was found in the East region of the Caloosahatchee River, aerial survey data gathered in Mullock Creek and Ten-Mile Canal showed increased manatee use in fall and winter, from November to February. From 1976 to 2001 there has been an increasing trend of manatee deaths in the Mullock Creek/Ten-Mile Canal area. Of all manatee carcasses recovered in this area from 1976 to 2001, 95% of them were recovered between 1989 and 2001. Over this 13-year period, manatee deaths (all categories) have increased at a faster rate in Mullock Creek and Ten-Mile Canal than in either southwest Florida or the state as a whole. The combination of the high percentage of boaters committing blatant violations in manatee speed zones in Mullock Creek, and the shallow, narrow configuration of the creek places manatees at a relatively high risk of collisions with motorboats.

---

Complete Report

The complete report for the Caloosahatchee River study is below. The files are in PDF format and require Adobe Acrobat Reader to view.

A Special Study of the Caloosahatchee River Eastward to the Edison Bridge and of Mullock Creek (4.39 MB)

Report Figures

Due to the size of the report figures, they have been separated for easier viewing. A list of the figures is also available.

List of Figures
Figures 1-3 (2.19 MB)	Figures 4-6 (1.18 MB)	Figures 7-9 (1.80 MB)
Figures 10-12 (2.13 MB)	Figures 13-15 (3.52 MB)	Figures 16-18 (3.03 MB)
Figures 19-21 (1.77 MB)	Figures 22-24 (179 KB)	Figures 25-27 (103 KB)
Figures 28-30 (1.00 MB)	Figures 31-33 (0.98 MB)	Figures 34-36 (2.48 MB)
Figures 37-39 (1.73 MB)	Figures 40-42 (1.70 MB)	Figures 43-45 (951 KB)
All Figures Warning: This file is 23.22 MB!

---

To download Adobe Reader, please visit the Adobe Web site at http://www.adobe.com/products/acrobat/readstep.html