Are Ships To Blame For Whale Shark Decline?
Large amounts of international trade comes across the ocean. In fact almost 80% of the world’s trade is transported via huge container ships.
The routes taken by these ships are fixed shipping lanes connected to large international ports.
These shipping lanes or marine highways can cut across the migratory routes of marine animals. The larger sea animals, such as whales and sharks are particularly vulnerable to being hit by large vessels as they often spend time near the surface.
Death toll higher than thought?
According to a new study this may be the cause of death for a higher number of whale sharks than previously thought.
Whale sharks are the worlds largest fish. They can reach lengths of up to 20 metres. Their numbers have been in sharp decline over the past century, dropping by nearly 50%. They are one of the most endangered sharks.
Several factors point towards shipping being a major cause of whale shark death. They spend a lot of time near the ocean surface feeding on plankton. If fatally hit by a ship, their body will sink leaving no trace of the fatality.
New data makes compelling case
Therefore recording the collisions is difficult and up until recently there was little evidence to strongly suggest this was an issue. Only a handful of eye witness accounts and non fatal wounds from smaller vessels gave any indication that larger vessels could be causing a population decline.
The latest study, run by the Global Shark Movement Project, satellite tracked nearly 350 whale sharks by fitting them with electronic tags, and mapping their positions.
The sharks movements were compared with the movements of ships within shipping lanes. The project kept an eye on container ships, passenger ships and larger fishing vessels. The team identified that 92% of the areas occupied by whale sharks overlapped with the shipping lanes and 50% of the time the sharks were at the same depth as the vessels.
High risk areas identified
The collision risk was then analysed, and the areas of most concern were identified. The Gulf of Mexico, Arabian Gulf and the Red Sea were seen to be the highest risk areas for whale sharks. These regions host some of the busiest shipping and ports in the world.
Within these high risk areas, the sharks regularly crossed paths with the larger vessels. These ships travel much faster than the sharks giving them little time to react.
Where the team lost contact with the sharks with electronic tags, it was often when a shark was within a shipping lane. Even taking in to account the occasional technical failure, 24% of tags stopped working in busy shipping lanes. The likely cause being that the shark was fatally hit.
Urgent action needed
The new study gives a fairly compelling need to bring in some urgent protection measures. Currently there are no regulations to protect whale sharks from collisions, but action is needed.
Better recording of fatal collisions with wildlife is needed by the shipping industry. Occurrences of fatalities need to be logged so that an understanding of where they are concentrated can be mapped. This could then lead to requirements for ships to slow down and navigate certain high risk areas more carefully.