Motorised Boats & Shallow Water Systems

Motorised Boats & Shallow Water Systems

Institute of Marine and Coastal Services
Rutgers University
New Brunswick. NJ 08901. U.S.A


Propeller-driven motorized watercraft potentially impact shallow water systems by altering water and sediment quality, benthic habitats, and biotic communities. 

Water quality changes and mediated by inputs of chemical contaminants (hydrocarbons and metals) from boat engines and hulls as well as propeller-induced sediment resuspension, which not only can raise turbidity levels but also nutrient and chemical contaminant concentrations in the water column via elemental remobilization from bottom sediments. 

However, there is evidence based on data presented at the workshop that, if motorized boats are operated in compliance with no-wake conditions, impacts on turbidity an the water column may be negligible. Hydrocarbon compounds and trace metals released from two- and four-cycle engines and boat hulls are particle reactive , and therefore they tend to accumulate in bottom sediments.

These contaminants can significantly alter sediment quality, particularly in heavy used urbanized regions.  Propeller wash and propeller cutting directly impact benthic habitats by damaging submerged aquatic vegetation (SAV), scarring the substrate and eroding sediments.  These effects are detrimental to benthic communities, which may be completely eradicated at scarred sites. 

The impacts of scarring are often protracted due to the number of years (3 to 7 years or more) needed for natural recovery by seagrasses.  Deep propeller cutting also creates steep topographic depressions in the substrate that may remain uncolonized and barren for as long as 10-20 years.  Benthic communities are most severely impacted where the water depth is less than 1 mtr and boating activity produces multiple scars on the substrate.  

The most notable impacts of PWCs on shallow water estuarine and coastal marine systems are those related to noise disturbances.  The high speeds and audible sounds of these water-jet-driven vessels have been shown to adversely affect the behavior, reproduction and distribution of colonial nesting birds (eg, common terns) in coastal environments. 

PWCs may also affect nearshore habitats by accelerating sediment  resuspension and eroding shoreline areas.  The relationship between PWC use and scarring impacts, however, has not been established in New Jersey waters or elsewhere.  More baseline data must be collected on PWC impacts an shallow water systems to help formulate effective environmental management strategies.

Noise Impacts

Burger (Effects of Motorboats and Personal Watercraft on Nesting Terns ; Conflict Resolution and the Need for Vigilance) presented information on the behavior of nesting common terns as a function of exposure to PWC and motorboats.  She reported that the noise from fast moving PWCs and outboard-powered vessels disturbs wildlife. 

The behavior of nesting birds is often modified in response to excessive noise, which can lead to reproductive failure and other detrimental effects due to reduction of ‘loafing activities’.  According to Burger, PWCs tend to travel faster than motorboats near bird nesting sites on land.  Hence, the noise of PWCs appears to have a greater impact than the noise of motorboats on bird populations. 

Heavy use of motorized watercraft may also disturb finfish and other aquatic organisms in shallow water areas.

Source: Adapted from Kennish (2002). Reproduced with permission from the Coastal Education and Research Foundation, Inc.

Kennish, M.J. (ed.), 2002. Impacts of Motorized Watercraft on Shallow Estuarine and Coastal Marine EnvironmentsJournal of Coastal Research, Special Issue #37, 202p.

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