Vessel Collision


Dead loggerhead sea turtle from vessel collision. Photo © 2007 MEDASSET.

In areas where recreational boating and ship traffic is intense, propeller and collision injuries are common for marine wildlife
All sea turtles, with the exception of the leatherback turtle, have hard carapaces; but these shells are unable to withstand the strike of a boat or the cut of a powerful propeller. Sea turtles staying close to the sea surface to bask, mate or breathe are vulnerable to boats collisions or being struck by propellers.

Vessel collision contributes to the mortality and maiming of sea turtles. Greater vessel speed increases the probability that turtles would fail to flee from the approaching vessel; while the majority of sea turtles hit by boats do not survive,

Young turtles are very alert so less likely to be hit by vessels. The trauma must be extensive in order to kill them as they have remarkable ability to survive severe damage. Seriously injured or dead turtles may be struck multiple times by vessels before they drift ashore. It is very difficult to distinguish trauma from sharks bites, boat collisions and propeller cuts.
Survivors of vessel collisions

Buoyancy is very important for aquatic animals as the ocean environment changes substantially with depth. To remain at a preferred depth with minimal energy expenditure, sea turtles use pulmonary gas exchange to selectively move lung gas to the front, back, right or left of the lungs to compensate for changes in body weight. Many sea turtles that experience severe trauma, such as boat collision, have buoyancy control issues from their injuries. This means that lead weights and similar devices are required for sea turtle survivors that can no longer control their buoyancy and just ‘bob like a cork’ on the top of the water.

Ways to reduce the threat of boats to sea turtles

1. Vessel strike avoidance for sea turtles
In order to avoid causing injury or death to sea turtles, ship captains and crew should maintain vigilant watch during navigation and slow down and/or stop their vessel to avoid striking. When sea turtles are sighted, they should attempt to maintain a distance of 45 metres or greater whenever possible.

2. Injured or Dead sea turtle Reporting
Vessel crew should report sightings of any injured or dead sea turtle (or protected species in general), regardless of whether the injury or death is caused by the vessel.
Report includes date/location of the strike, name of the vessel involved and species identification.

3. Zoning and speed limits for significant sea turtle nesting/foraging areas
Tiered application of zoning and speed limits for coastal waters is essential in protecting sea turtles in key stages of their reproduction cycle.
For example the National Marine Park of Zakynthos in Greece has:
Zone A: No boating activity or fishing of any kind
Zone B: Boats are allowed with speed limits of 6 miles/hour. Anchoring prohibited.
Zone C: Boats are allowed with speed limit of 6 miles/hour. Anchoring permitted.