Not Just a Bunch of Hot Air -- The Ecological Impacts of Airboats
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Airboats are commonly used for a variety of activities in the marshes of Southern Florida, such as the Everglades and the Big Cypress Swamp. Ranging in length from 20 to 38 feet, the typical airboat is a flat-bottom boat with a shallowdraft, wide-beam hull driven by an aircraft propeller and powered by a marine or aircraft engine. The largest airboats can carry up to 49 people, and are confined to wider, deeper mangrove lined waterways. Smaller boats can access smaller waterways and are capable of skimming over shallow water in wet marsh and prairie habitats. During the last twenty years, there has be in increase in the number of airboats in South Florida (Johnson 1984).
Commercial airboat tours run hourly from places like Everglades City, taking tourists on 30 min. to 1-hour expeditions. Other activities include hunting, fishing, sightseeing, wildlife viewing, and frogging -- the process of landing an airboat on a patch of grass and harvesting pig frogs that jump on the grass tips to escape the boat's airflow. Patterns of airboat use have changed dramatically over the years, resulting in adverse impacts to the physical and biological resources of South Florida. Subsequently, airboats have been regulated in some areas.
Ecological Impacts
Hydrology
Airboats increase turbidity by causing soil and organic particles to become suspended in the water column. Turbidity increases with airboat traffic and during periods of low water levels (Weeks 1989). It affects the amount of light available to underwater plants, and may affect fish and aquatic wildlife. In addition to increasing turbidity, excessive use of airboats may redirect natural water currents. In marshes, channels created by airboats effectively alter the surface hydrology: sheet flow becomes channel flow; the severity of the channelization is related to the number of passes (Duever et al 1986).
Soils
Airboats create rutting in low water situations and could cause significant soil oxidation (Yamataki 1994). In an Ochopee Prairie Airboat Impacts paper written by Tony Pernas in 1994, he states: "The effects of airboats to soils are potentially the greatest impact to the ecosystem because of the relational changes in hydrology, vegetation and visual aesthetics which can result from from disturbance to intact soil strata." Pernas quotes Yamataki on his visit to Ochopee Prairie later on in the paper: "[N]umerous airboat trails have virtually eliminated vegetation in certain areas, {and} exposed soils during the dry season can result in the oxidation of the soils and could amount to an inch of soil loss per year."
Vegetation
Mangroves have natural channels that allow water flow throughout the ecosystem -- airboaters use these channels in addition to blazing new routes. Repeated passes with an airboat destroy vegetation and displace soil, creating a channel or trail. Wave energy from airboats also causes sediment erosion in mangroves, which are very sensitive to changes in sediment (McKee 1993) and grow best in protected areas with low wave energy (Tomlinson 1986).
Mangrove dieback from propwash can be distinguished from natural dieback (Doyle 1998). Propwash strips leaves from the mangroves exposing epiphytic plants, additional limbs, and other trees: excessive defoliation can stunt the growth of or kill the tree (Smith 1998). In an April 16, 1998 letter from Thomas Doyle, USGS Ecologist, to Wally Hibbard, Superintendent of the Big Cypress (BICY) National Preserve, Doyle states: "Regarding the impacts of commercial boat tours on habitat, there is mangrove dieback evident on nearly every bend of narrow tidal creeks and passages along the designated tour route."
Illegal cutting of mangroves (without the required permits) has posed recent threats as well. Paths as wide as 15 feet have been cut and reinforced by PVC pipe, such as the path blazed in 1997 near Marco Island (Staats 1997).
In a letter from Burkett S. Neely, Loxahatchee NWR, to the Region 4 Director of the Fish and Wildlife Service, Neely states: "An airboat impact study begun on the refuge in 1983 identified that operation of airboats in sawgrass causes a reduction in stem densities and could result in permanent trails in the marsh. It is our opinion also that operation of airboats in wet prairies where short emergent vegetation is common results in a reduction of stem densities of these species: particularly beak rushes and spike rushes." Minor changes in elevation (soil displacement) can result in major changes in the vegetative community in BICY (Duever et al. 1986). In the case of new trails, increased cattail growth has been observed and in no case has broken grass sod returned to its original plant cover (Craighead 1971).
Noise
Most airboats are excessively loud, and their noise combined with the physical intrusions can have adverse effects on wildlife (Lodge 1994). Because airboats often travel 40 to 60 miles per hour (even higher speeds are achieved) the possibility of significant adverse wildlife reaction seems inevitable (Lodge 1994). On noise, Pernas states that "the use of airboats are incompatible with other recreation activities, especially those which emphasize wilderness values such as canoeing and hiking" (Pernas 1994).
Birds
A 1990 Noncompatibility documentation for the Loxahachee NWR prepared by Burkett S. Neely, Refuge Manager, states: "Private airboats disturb endangered species, wintering waterfowl and nesting wading birds." A May 1994 BICY Ochopee Prairie Airboat Impact briefing paper cited detrimental effects of airboat usage on bald eagle nests and wading bird nesting colonies, and dramatic effects on birds with floating nests such as pied-billed grebes. It also stated that the cape sable seaside sparrow "was extirpated due to the ongoing water flow alterations (due to heave airboat activity)." Identified human impacts to bird populations are egg and nesting mortality, nest evacuation, reduced nestling body mass and slower growth, premature fledging, and modified adult behaviors (Rodgers and Smith 1995). Increased frogging expeditions may affect food sources for wetland birds. Snail Kite populations have been adversely affected by reduced apple snail populations due to heave airboat use in their egg cluster sites BICY Ochopee Prairie Airboat Impact Briefing Paper, May 1994).
Reptiles and Amphibians
The unregulated harvest of pig frogs in Ochepee prairie and other areas has impacted their normal population structures (Janson 1994). Negative effects include vegetation upheaval, pig frog egg displacement and/or destruction of eggs. An increased demand for frog's legs makes frogging profitable and likely will increase frogging pressures (Janson 1994).
The impacts of airboat usage on American alligator populations are relatively unknown. However, there are documented cases of tourists feeding alligators and tour boats baiting the alligators for better shows (Janson 1994).
Expanding Impacts
The impacts of airboating have been felt in Florida since the early 1980's, but these impacts are not limited to south Florida. Coastal states like Alaska are facing expanding airboating pressures: the 20 Mile River Valley and the Copper River Delta in the Chugach National Forest, and the Minto Flats of interior Alaska, with problems like noise pollution and wildlife disturbance. The Alaska Board of Game recognized this and recently imposed regulations on airboat usage in Minto Flats: airboating is apparently detrimental to the subsistence economy there. The impacts of airboating have yet to be definitively studied in Alaska, but the potential for adverse impacts is clear, as exemplified in south Florida.
Conclusion
Human disturbance can have a significant impact on wildlife (Rodgers 1991) and an ecosystem as a whole. And while more research is needed to document their impacts, it is clear that airboats have the potential to introduce significant disturbance to sensitive wetland and coastal ecosystems. That is precisely what is happening in southern Florida, where increasing airboat use has disrupted the physical and biological balance.
--- Amy Wright is an intern for the Colorado office of Wildlands CPR. Her favorite project is working on "Skid Marks" twice a month.
Bibliography
Craighead, Frank. 1971. The Trees of South Florida Volume 1. University of Miami Press, Coral Gables, Florida.
Doyle, T.W. 1998.ÏQualitative assessment of mangrove/marsh damage from commercial airboat tours of Big Cypress National Preserve.ÏMemorandum from U.S. Geological Survey to National Park Service.
Duever, Riopelle and McCollom.Ï1986. Long term recovery from experimental and off trail off-road vehicle impact the Big Cypress National Preserve. US Department of the Interior, National Park Service.ÏContact No. 5280-5-2106
Eames, Cliff.Ï 2000.ÏPhone conversation on December 11, 2000 per airboating in Alaska.
Janson, Deborah. 1994.ÏImpacts of Cul Airboat Activities and Frogging on the Wildlife Resources of Ochopee Prairie.
Johnston, Joseph E. 1984. Impacts of Airboats on Loxahatchee National Wildlife Refuge Part 2 - long-term impacts of airboat use under the hunt restrictions.Ï Interim report to the Fish and Wildlife service of Vero Beach, Florida.
Lodge, Thomas. 1994. The Everglades Handbook.Ï St. Lucie Press.
McKee, K.L. 1993. Journal of Ecology, 81: 477-487.
National Park Service. May, 1994. Big Cypress National Preserve, Ochopee Prairie Airboat Impact Briefing Paper.
Neely, Burkett.ÏAugust 29, 1990.ÏMemorandum to Regional Director of the Fish and Wildlife Service on the Elimination of public airboat use on the Refuge due to incompatibility and noncompatibility documentation.
Pernas, TonyÏ 1994.ÏOchopee Prairie Airboat Impacts: Soil/Vegetation/Recreation. Unpublished National Park Service report.
Rodgers, James. 1991.ÏMinimum Buffer Zone Requirements to Protect Nesting Bird Colonies from Human Disturbance.Ï Final Report - 1989-91.Ï Bureau of Wildlife research, Florida Game and Fresh Water Fish Commission.ÏTallahassee.
Rodgers and Smith. 1995. Set Back Distances to Protect Nesting Bird Colonies from Human Disturbance in Florida.ÏConservation Biology, Vol. 9 No. 1 Pages 89-99.
Slack, James J.Ï 1999. South Florida Fish and Wildlife Service Memorandum to Wallace Hibbard, Superintendent Big Cypress National Preserve. Internal document.
Smith, T.J. 1998.ÏCommercial airboat operations in the Big Cypress. Memorandum from U.S. Geological Survey to national Park Service.
Staats, Eric. January 30, 1997. State Probes Mangrove Cutting. Naples Daily News.Ï
Tomlinson, P.B. 1986. The Botany of Mangroves. Cambridge Press.
Weeks.Ï 1989.Ï Turbidity Investigation on Halfway Creek - Big Cypress National Preserve.Ï National Park Service.
Yamataki, H. 1994.Ï"Agency Position Statement: Condition of Soils in ORV Use Areas at Big Cypress National Preserve." Letter to P. Kenney, Big Cypress National Preserve. Fort Myers, FL: USDA Soil Conservation Service, 2 pages.
Zaneski, Ciril.Ï May 10, 1999.ÏAirboat Damage Assessed.ÏMiami Herald.
Commercial airboat tours run hourly from places like Everglades City, taking tourists on 30 min. to 1-hour expeditions. Other activities include hunting, fishing, sightseeing, wildlife viewing, and frogging -- the process of landing an airboat on a patch of grass and harvesting pig frogs that jump on the grass tips to escape the boat's airflow. Patterns of airboat use have changed dramatically over the years, resulting in adverse impacts to the physical and biological resources of South Florida. Subsequently, airboats have been regulated in some areas.
Ecological Impacts
Hydrology
Airboats increase turbidity by causing soil and organic particles to become suspended in the water column. Turbidity increases with airboat traffic and during periods of low water levels (Weeks 1989). It affects the amount of light available to underwater plants, and may affect fish and aquatic wildlife. In addition to increasing turbidity, excessive use of airboats may redirect natural water currents. In marshes, channels created by airboats effectively alter the surface hydrology: sheet flow becomes channel flow; the severity of the channelization is related to the number of passes (Duever et al 1986).
Soils
Airboats create rutting in low water situations and could cause significant soil oxidation (Yamataki 1994). In an Ochopee Prairie Airboat Impacts paper written by Tony Pernas in 1994, he states: "The effects of airboats to soils are potentially the greatest impact to the ecosystem because of the relational changes in hydrology, vegetation and visual aesthetics which can result from from disturbance to intact soil strata." Pernas quotes Yamataki on his visit to Ochopee Prairie later on in the paper: "[N]umerous airboat trails have virtually eliminated vegetation in certain areas, {and} exposed soils during the dry season can result in the oxidation of the soils and could amount to an inch of soil loss per year."
Vegetation
Mangroves have natural channels that allow water flow throughout the ecosystem -- airboaters use these channels in addition to blazing new routes. Repeated passes with an airboat destroy vegetation and displace soil, creating a channel or trail. Wave energy from airboats also causes sediment erosion in mangroves, which are very sensitive to changes in sediment (McKee 1993) and grow best in protected areas with low wave energy (Tomlinson 1986).
Mangrove dieback from propwash can be distinguished from natural dieback (Doyle 1998). Propwash strips leaves from the mangroves exposing epiphytic plants, additional limbs, and other trees: excessive defoliation can stunt the growth of or kill the tree (Smith 1998). In an April 16, 1998 letter from Thomas Doyle, USGS Ecologist, to Wally Hibbard, Superintendent of the Big Cypress (BICY) National Preserve, Doyle states: "Regarding the impacts of commercial boat tours on habitat, there is mangrove dieback evident on nearly every bend of narrow tidal creeks and passages along the designated tour route."
Illegal cutting of mangroves (without the required permits) has posed recent threats as well. Paths as wide as 15 feet have been cut and reinforced by PVC pipe, such as the path blazed in 1997 near Marco Island (Staats 1997).
In a letter from Burkett S. Neely, Loxahatchee NWR, to the Region 4 Director of the Fish and Wildlife Service, Neely states: "An airboat impact study begun on the refuge in 1983 identified that operation of airboats in sawgrass causes a reduction in stem densities and could result in permanent trails in the marsh. It is our opinion also that operation of airboats in wet prairies where short emergent vegetation is common results in a reduction of stem densities of these species: particularly beak rushes and spike rushes." Minor changes in elevation (soil displacement) can result in major changes in the vegetative community in BICY (Duever et al. 1986). In the case of new trails, increased cattail growth has been observed and in no case has broken grass sod returned to its original plant cover (Craighead 1971).
Noise
Most airboats are excessively loud, and their noise combined with the physical intrusions can have adverse effects on wildlife (Lodge 1994). Because airboats often travel 40 to 60 miles per hour (even higher speeds are achieved) the possibility of significant adverse wildlife reaction seems inevitable (Lodge 1994). On noise, Pernas states that "the use of airboats are incompatible with other recreation activities, especially those which emphasize wilderness values such as canoeing and hiking" (Pernas 1994).
Birds
A 1990 Noncompatibility documentation for the Loxahachee NWR prepared by Burkett S. Neely, Refuge Manager, states: "Private airboats disturb endangered species, wintering waterfowl and nesting wading birds." A May 1994 BICY Ochopee Prairie Airboat Impact briefing paper cited detrimental effects of airboat usage on bald eagle nests and wading bird nesting colonies, and dramatic effects on birds with floating nests such as pied-billed grebes. It also stated that the cape sable seaside sparrow "was extirpated due to the ongoing water flow alterations (due to heave airboat activity)." Identified human impacts to bird populations are egg and nesting mortality, nest evacuation, reduced nestling body mass and slower growth, premature fledging, and modified adult behaviors (Rodgers and Smith 1995). Increased frogging expeditions may affect food sources for wetland birds. Snail Kite populations have been adversely affected by reduced apple snail populations due to heave airboat use in their egg cluster sites BICY Ochopee Prairie Airboat Impact Briefing Paper, May 1994).
Reptiles and Amphibians
The unregulated harvest of pig frogs in Ochepee prairie and other areas has impacted their normal population structures (Janson 1994). Negative effects include vegetation upheaval, pig frog egg displacement and/or destruction of eggs. An increased demand for frog's legs makes frogging profitable and likely will increase frogging pressures (Janson 1994).
The impacts of airboat usage on American alligator populations are relatively unknown. However, there are documented cases of tourists feeding alligators and tour boats baiting the alligators for better shows (Janson 1994).
Expanding Impacts
The impacts of airboating have been felt in Florida since the early 1980's, but these impacts are not limited to south Florida. Coastal states like Alaska are facing expanding airboating pressures: the 20 Mile River Valley and the Copper River Delta in the Chugach National Forest, and the Minto Flats of interior Alaska, with problems like noise pollution and wildlife disturbance. The Alaska Board of Game recognized this and recently imposed regulations on airboat usage in Minto Flats: airboating is apparently detrimental to the subsistence economy there. The impacts of airboating have yet to be definitively studied in Alaska, but the potential for adverse impacts is clear, as exemplified in south Florida.
Conclusion
Human disturbance can have a significant impact on wildlife (Rodgers 1991) and an ecosystem as a whole. And while more research is needed to document their impacts, it is clear that airboats have the potential to introduce significant disturbance to sensitive wetland and coastal ecosystems. That is precisely what is happening in southern Florida, where increasing airboat use has disrupted the physical and biological balance.
--- Amy Wright is an intern for the Colorado office of Wildlands CPR. Her favorite project is working on "Skid Marks" twice a month.
Bibliography
Craighead, Frank. 1971. The Trees of South Florida Volume 1. University of Miami Press, Coral Gables, Florida.
Doyle, T.W. 1998.ÏQualitative assessment of mangrove/marsh damage from commercial airboat tours of Big Cypress National Preserve.ÏMemorandum from U.S. Geological Survey to National Park Service.
Duever, Riopelle and McCollom.Ï1986. Long term recovery from experimental and off trail off-road vehicle impact the Big Cypress National Preserve. US Department of the Interior, National Park Service.ÏContact No. 5280-5-2106
Eames, Cliff.Ï 2000.ÏPhone conversation on December 11, 2000 per airboating in Alaska.
Janson, Deborah. 1994.ÏImpacts of Cul Airboat Activities and Frogging on the Wildlife Resources of Ochopee Prairie.
Johnston, Joseph E. 1984. Impacts of Airboats on Loxahatchee National Wildlife Refuge Part 2 - long-term impacts of airboat use under the hunt restrictions.Ï Interim report to the Fish and Wildlife service of Vero Beach, Florida.
Lodge, Thomas. 1994. The Everglades Handbook.Ï St. Lucie Press.
McKee, K.L. 1993. Journal of Ecology, 81: 477-487.
National Park Service. May, 1994. Big Cypress National Preserve, Ochopee Prairie Airboat Impact Briefing Paper.
Neely, Burkett.ÏAugust 29, 1990.ÏMemorandum to Regional Director of the Fish and Wildlife Service on the Elimination of public airboat use on the Refuge due to incompatibility and noncompatibility documentation.
Pernas, TonyÏ 1994.ÏOchopee Prairie Airboat Impacts: Soil/Vegetation/Recreation. Unpublished National Park Service report.
Rodgers, James. 1991.ÏMinimum Buffer Zone Requirements to Protect Nesting Bird Colonies from Human Disturbance.Ï Final Report - 1989-91.Ï Bureau of Wildlife research, Florida Game and Fresh Water Fish Commission.ÏTallahassee.
Rodgers and Smith. 1995. Set Back Distances to Protect Nesting Bird Colonies from Human Disturbance in Florida.ÏConservation Biology, Vol. 9 No. 1 Pages 89-99.
Slack, James J.Ï 1999. South Florida Fish and Wildlife Service Memorandum to Wallace Hibbard, Superintendent Big Cypress National Preserve. Internal document.
Smith, T.J. 1998.ÏCommercial airboat operations in the Big Cypress. Memorandum from U.S. Geological Survey to national Park Service.
Staats, Eric. January 30, 1997. State Probes Mangrove Cutting. Naples Daily News.Ï
Tomlinson, P.B. 1986. The Botany of Mangroves. Cambridge Press.
Weeks.Ï 1989.Ï Turbidity Investigation on Halfway Creek - Big Cypress National Preserve.Ï National Park Service.
Yamataki, H. 1994.Ï"Agency Position Statement: Condition of Soils in ORV Use Areas at Big Cypress National Preserve." Letter to P. Kenney, Big Cypress National Preserve. Fort Myers, FL: USDA Soil Conservation Service, 2 pages.
Zaneski, Ciril.Ï May 10, 1999.ÏAirboat Damage Assessed.ÏMiami Herald.