The Seaplane Pathway

Seaplanes as a Pathway for AIS Spread

The information on this website under the Phase 1 menu tab incorporates information compiled from the first phase of a four-phase project to produce a risk analysis to assess the potential to spread aquatic invasive species via seaplanes. At the conclusion of the project, recommendations will be made to enhance U.S. aquatic invasive species-seaplane prevention efforts. The DRAFT material posted in the Phase I section of the website represents a compilation of material from numerous sources, some of which may ultimately inform the risk analysis. The purpose of compiling this information was to better understand the seaplane pathway and identify key data gaps and information needed to inform the risk analysis. No analysis of this information has been conducted to date as content is refined and additional sources and content are added.

The Convention on Biological Diversity defines pathway as “any direct or indirect human activity, which enables the entry or spread of nonindigenous invasive species” (CBD 2014). Identification and prioritization of pathways help prevent the establishment and spread of invasive species (Roy et al. 2014). This is often referred to as biosecurity planning—managing and lowering the risk associated with invasive species.

Although little has been quantified about the risk of aviation-based AIS transmission (Carey et al. 2016), seaplanes have been identified as a pathway for the spread of aquatic invasive species (US Coast Guard 2000, Aquatic Nuisance Species Digest 2001, National Invasive Species Council 2007, Randall 2009, Warren and Sytsma 2009, Strayer and McNeil 2009, McNeil and Strayer 2010, Lake Superior Binational Program 2014, Ontario Invasive Species Awareness Program 2021, Invasive Species Council of British Columbia 2023) (Figure 15). In Figure 15, seaplanes are listed under T1.1 (air transportation), however, category T1.2 (water/aquatic transportation) is also a relevant category for seaplanes because they are “aquatic vehicles.”

The 18th Subsidiary Body on Scientific, Technical, and Technological Advice to the Convention on Biological Diversity determined there were six principle pathways nonindigenous species are introduced, one of which is Transport-Stowaway, which refers to the moving of live organisms attached to transporting vessels and associated equipment and media (Lipinskaya et al. 2020). Seaplanes are in the transport-stowaway pathway.

Lipinskaya et al. (2020) analyzed pathways of introduction and spread of AIS in Belarus. They identified 24 aquatic nonindigenous species that arrived in Belarus via six pathways involving 10 separate vectors. The most introductions occurred through the “transport stowaway” pathway, and hull fouling played an important role in the spread of these species to and through Belarus (Lipinskaya et al. 2020). Linpinskaya et al. (2020) document the Transport-Stowaway pathway, which includes hull fouling and hitchhikers, both of which pertain to seaplanes.

Although long-distance dispersal of AIS through aircraft has been attributed to the accelerated rate of spread across vast and remote landscapes (Schwoerer et al. 2022), Warren and Sytsma (2009) characterized the risk of seaplanes transporting AIS to Oswego Lake in Oregon as minimal because seaplanes land infrequently on the water body. Seaplanes were determined to be a key pathway for the transport of Elodea spp. in Alaska (Schwoerer et al. 2022); management recommendations to mitigate risk include maintaining floatplane bases free of AIS and immediate cleanup of Elodea spp. to reduce risk of reintroduction (Schwoerer et al. 2022).

There may be factors associated with seaplane construction as well as operations that create opportunities for AIS to be unintentionally transported from one water body to another. Seaplanes naturally must come in contact with water during takeoff and landing. The high dynamic water pressure and the physical stresses of takeoffs and landings can momentarily open tiny gaps between float components, allowing small amounts of water to enter (FAA 2004), especially on older riveted aluminum floats (fiberglass Aerocet floats are essentially waterproof). Sitting idle in the water also results in a small amount of seepage and condensation. Small amounts of water may contain AIS, such as dreissenids, microscopic invasives, or aquatic plant parts. Further, movement of a seaplane through vegetation on the waterbody can result in vegetation becoming entangled with seaplane components.

The Minnesota Department of Natural Resources (n.d.) identified locations on seaplane floats where pilots should check for aquatic invasive species. They include water rudders, the transom, step area, wheel wells, trailing line, and chine (see figure below). The U.S. Army Corps of Engineers (2016) suggested that aquatic invasive species can be transported via foul ing of cables, cross members, rudders, transoms, step areas, wheel wells, and chine of the floats/pontoons, or the water inside the floats. Aquatic invasive species can become attached to seaplanes during taxiing, storage and moorage, landing, and takeoff (USACE 2016).

Because it is difficult for floats to be cleaned between lake landings, seaplanes create an opportunity for AIS to be transported among watersheds when they land on multiple lakes (Bayfield County Lakes Forum 2008). Adult zebra mussels can attach to submersed areas of the plane, such as floats/pontoons and rudders, and species such as spiny waterflea (Bythotrephes longimanus) and microscopic larval dreissenids (Dreissena spp.) can be found inside any space that holds water, including floats and pontoons. Acorn Welding describes one of six unique maintenance problems for seaplanes being water forces that lead to cumulative damage of the float, including distorting skin, dents, or loose rivets or gaps that open between floats; they note that water in more than one-fourth of a compartment indicates a maintenance problem. Water that accumulates in a float creates an opportunity for the transport of aquatic invasive species.

Some AIS, such as invasive freshwater snails in the Great Lakes region, move into shallow water in the summer (Jokinen et al. 1982, 1992), which increases their susceptibility for being picked up by seaplanes.

Once established in a waterbody, AIS can more easily spread to nearby waterbodies (Havel et al. 2015), and once established in a region, the change of persistence is enhanced (Hanski 1999).

Parts of a seaplane that have potential to carry aquatic invasive species

Locations on a seaplane where pilots should inspect for aquatic invasive species include the water rudders, landing gear, and cables. Floats should be inspected and pumped to minimize transport of AIS in water in the floats. Source: Invasive Species Council of British Columbia (2023).

12-15-foot mooring line

Survivability of AIS on Seaplanes

Numerous studies have examined the survival of aquatic plants, bivalves, snails, and other aquatic species and aquatic invasive species to desiccation, however, none of these studies have documented the compounding effects of altitude, lower levels of oxygen, and temperature with air drying and wind speed to estimate survivability of AIS on seaplane structures. Examples of survivability studies include:

Bruckerhoff et al. (2014) found that single aquatic plant stems were viable up to 18 and 12 hours of air exposure, respectively, coiling stems extended the viability up to 48 hours of air exposure, and turions sprouted after 28 days of drying.
Havel et al. (2013) concluded invasive snails readily survive long periods of overland trans port desiccation after two species of snail that invaded the Great Lakes region survived for 42 days, one species survived for 63 days, and viable young were released by one species after 54 days.
Multiple studies have examined the survival of dreissenid mussels to desiccation or air exposure. Adult mussels may survive up to five days or longer based on temperature and humidity conditions (Ricciardi et al. 1995, Ussery and McMahon 1995) whereas veligers can survive up to 24 days in small amounts of water (Craft and Myrick 2011, Snider et al. 2014, Campbell et al. 2016).
Collas et al. (2018) noted three conditions must be met before boats become successful vectors of dreissenids, including attachment to the hull, air exposure survival during overland transport, and the ability to establish a viable population either after detachment or release of spat during launching and sailing. Collas et al. (2018) found alive detachment during rewetting was significantly higher after 24 hours compared to 48 hours of air exposure, and concluded zebra mussels were more likely to attach to common boat materials than quagga mussels. Collas et al. (2018) noted that shaking and vibration of boats may affect the number of mussels that attached, survive air exposure, and subsequently detach during rewetting. This conclusion has implications for sea planes, which undergo considerable shaking and vibration during takeoff and landing.

Helping Seaplane Pilots Address AIS

Acme Tools sells a Turbo Float Pump, which is designed to be used with a cordless drill to pump up to six gallons a minute from seaplane floats (Figure 17). An additional “Invasive Species Water Filter Kit” can be purchased for as an option – it claims to “stop invasive species as small as 20 microns” from exiting the pump. Patent is pending. The invasive species water filter needs to be changed after 2,000 gallons have been pumped.

The Seaplane Pilots Association created a Water Landing Directory Smartphone App in 2013 (Figure 18). The app allows pilots to search for bodies of water, seaplane bases, fuel, flight training, destinations, upcoming events, and share information about ways pilots can get involved or advertise with, or donate to, the Seaplane Pilots Association. If the app is maintained and updated on a regular basis, another potential topic that could be added to the app is a search for bodies of water regionally and at the statewide level, with known high-risk AIS so that they can either avoid those waterbodies, or ensure their seaplanes are decontaminated before visit ing another water body.

Working with industry to identify technology and strategies, such as installing sensors that detect when vegetation or anything else is attached to a seaplane float, would help detect the presence of aquatic invasive species prior to takeoff from an AIS-infested water body. This type of technology would improve pilot safety, helping pilots ensure that their aircraft is free from any type of debris either attached, or clinging to seaplane gear/parts.

A long-handled adjustable length brush with an articulating joint would help pilots reach the bottom of floats and awkward spots near water rudders.

USGS publishes and maintains a database of nonindigenous aquatic species (https://nas.er.usgs.gov/). The website allows the user to search by state and drainage area (at a variety of scales). Al though the USGS database provides a significant amount of information in a variety of formats, the site would likely be difficult for a pilot to use to assess the level of AIS risk associated with landing on a particular waterbody. The following example illustrates both the complexity of what a pilot would have to navigate as well as the potential that exists to display and access the information in ways that seaplane pilots could use to mitigate risk.

A pilot intends to fly from the Sage Lake seaplane base south of Huron National Forest to Higgins Lake, Michigan in Roscommon County (Figure 19). The pilot can check the USGS NAS database and query Higgins Lake by drawing a polygon around the lake and clicking submit. The database provides a list of all aquatic invasive species in the lake. A map of the lake will appear with specific locations that AIS have been detected.

The pilot has the option of clicking on a dot or can click on the Query tab and obtain a list of AIS detected in Higgins Lake. In the case of Higgins Lake, there are numerous AIS, including zebra mussels, water milfoil, and a variety of other AIS that can be trans ported by seaplanes. If the pilot decides to follow through with a trip to Higgins Lake, he/she must be aware of the need to fully decontaminate the aircraft prior to flying into another waterbody. Although it is possible to navigate the USGS website and locate information about AIS populations, it is unlikely pilots would use that resource for trip planning. Opportunities exist to make it more intuitive and efficient for seaplane pilots to determine documented AIS populations at destination lakes through an app, such as Foreflight or Garmin Pilot, or other approach that takes fewer steps and less familiarity with navigating the USGS site.