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Scarring of Florida's Seagrass: Assessment and Management Options (1995)Propeller scarring has become one of the fastest growing types of marine habitat degradation caused by motor boats traveling in waters shallower than the draft of the vessel. To document the extent of the problem, a statewide assessment was completed.Download a Complete PDF File of This Technical Report (3.57 MB) To view this PDF file, you will need Adobe Reader. SCARRING OF FLORIDA'S FLORIDA'S SEAGRASS: F.J. Sargent, W.B. Sargent, T.J. Leary, D.W. Crewz, and C.R. Kruer
EXECUTIVE SUMMARY Seagrasses are submerged, grass-like plants that inhabit the shallow coastal waters of Florida. Seagrasses are a vital component of Florida’s coastal ecology and economy. They provide nutrition and shelter to animals important to marine fisheries; they provide critical habitat for animals such as wading birds, manatees and sea turtles; and they improve the water quality. Marine-habitat degradation in Florida is continuing at an
alarming rate as the coastal residential population and the
number of seasonal visitors increase. Habitat degradation has
many sources (e.g., pollution, dredge and fill), but an
increasingly common cause of habitat degradation is the scarring of seagrasses. In this report, scarring can refer to either the activity of scarring or to a group of scars in a seagrass bed. The Florida Department of Environmental Protection recognized the need to reduce scarring of seagrasses by boats, and committed resources to address this issue. As one component of this effort, the Florida Marine Research Institute (FMRI) investigated the distribution of scarred seagrass beds in the shallow marine waters of Florida’s coastal counties. Aerial photography was used to locate seagrass scarring. Aerial surveys were then conducted in 1992 and 1993 to confirm the location of scarred seagrasses. We did not attempt to distinguish among the different specific causes of seagrass scarring. During aerial surveys, observations of scarred seagrasses were recorded on National Oceanic and Atmospheric Administration nautical charts and U.S. Geological Survey quadrangle maps. Scarring intensity was categorized as light, moderate, or severe. Areas with substantial scarring recognizable on 1:24,000-scale aerial photography were delineated on the maps with polygons that were assigned a scarring intensity. Polygons categorized as light contained less than 5 percent scarring, those categorized as moderate contained 5 to 20 percent scarring and those categorized as severe contained more than 20 percent scarring. The information acquired in this survey was incorporated into the FMRI’s Marine Resources Geographic Information System (MRGIS), which produces maps and tabular products so that geographically based data can be effectively disseminated to resource managers, appropriate regional and county governments and other interests (e.g., conservation groups and private citizens).  Scarred seagrasses were observed in all areas of the state, mostly in shallow coastal waters less than six feet deep. More than 173,000 acres of the Florida's 2.7 million acres of seagrasses were scarred, most of it lightly. This is a conservative estimate of scarring because we mapped groups of scars, not isolated, individual propeller scars. The total seagrass acreage in Florida (2.7 million acres) includes areas in the Florida Keys that have sparse seagrass and hardbottom with dense-seagrass patches. Excluding these areas, seagrasses totaled approximately 1.9 million acres. Also, these totals do not include sparse, deep Halophila beds that are offshore in the Big Bend region. The greatest acreage of moderate and severe (M/S) scarring occurred in areas having denser human populations and more registered boats. The Florida Keys (Monroe and Dade counties), Tampa Bay (Hillsborough, Manatee and Pinellas counties), Charlotte Harbor (Lee County) and the north Indian River Lagoon (Brevard and Volusia counties) had the greatest M/S scarring. Monroe County, which includes most of the Florida Keys, had the greatest acreage of M/S-scarred acreage of all the counties in the survey. The Panhandle and Big Bend regions had little M/S-scarred acreage, but in the western Panhandle embayments, M/S scarring was prevalent in the few acres of seagrasses. If an area has little seagrass acreage, then any scarring may have a critical effect on habitat functions. All boating user-groups are responsible for scarring seagrasses. Although we did not attempt to identify each user-group’s role in scarring, we believe general statements about the situations that lead to scarring are valid. The most severe, single instances of scarring are caused by large commercial vessels, but most seagrass disruption results from widespread scarring by smaller boats. Our discussions with boaters, as well as our own personal experiences, suggest that scarring of seagrasses could result when one or more of the following situations occur:
Management programs that address scarring of seagrasses should be based on an approach that involves (1) education, (2) channel marking, (3) increased enforcement, and (4) limited-motoring-zones. Aerial monitoring and photography of the managed area are essential in evaluating the effectiveness of a program. Management programs that use this multifaceted approach have been instituted by a few local governments and at several state parks. Initial results of the programs indicate that in some areas seagrass scarring has been reduced and that in other areas emphasis may need to be increased on one or more of the components of the four-point approach. A statewide management plan is needed to address the most egregious scarring over large areas that may be difficult to regulate at the local-government level.
Seagrass calculations (based on data created in
6/2000) Propscar calculations (revised 11/2000) Light Damage = 38978 hectares (96,315 acres) Moderate Damage = 17122 hectares (42,309 acres) Severe Damage = 5652 hectares (13,966) * Florida Statistical Abstract, 1999. ** Florida Department of Highway and Motor Vehicle Safety, 10/2000 |
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Fish and Wildlife Research Institute 100 Eighth Avenue SE St. Petersburg, Florida 33701-5020 PH: 727-896-8626 |
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Seagrass beds can be scarred by many activities, but scars are most commonly made when a boat propeller tears and cuts up seagrass roots, stems and leaves producing a long narrow furrow devoid of seagrasses. Boats operating in shallow waters are severely scarring, and sometimes completely denuding to seagrass beds throughout the state.