Study: A Speed Limit on 3% of the Ocean Would Protect Whales

An international group of researchers has published a new study that maps areas of whale activity with areas of high shipping activity in order to find the places with the highest risk of whale strikes, a leading cause of whale mortality (alongside fishing). The upshot, according to the research team, is that it should be possible to reduce the number of strikes by regulating marine traffic on just 2.6 percent of the ocean's surface - though that 2.6 percent happens to be in areas that are very important to shipping. 

“This is the first study to look at this problem at a global scale, enabling global patterns of collision risk to be identified using an extremely large contemporary dataset of four recovering whale species," said coauthor Dr. Jennifer Jackson of the British Antarctic Survey. 

Shipping is a global phenomenon, and the merchant fleet is larger and more active now than at any point in history. The study found that marine traffic overlaps 92 percent of the habitat for blue, humpback, fin and sperm whales, the globe-spanning species covered by the study. Hotspots of ship strike risk were identified in every ocean region, except for the Southern Ocean, where there is little commercial interest for shipping. As might be expected, the risk tends to be concentrated on the coastal margins, where whales gather to seek feeding or breeding grounds and ships congregate to call at ports. 

Clear high risk zones include the southwest coast of India; the southern tip of Africa; the southern coast of Brazil; the Strait of Gibraltar; and the coast of California, a well-studied whale strike corridor. Some of the areas analyzed have not been previously identified as risk zones for whale strikes, particularly areas off the coasts of developing nations in the global south. 

The study found that "virtually no ship-strike risk hotspots were protected by mandatory measures" for speed reduction or routing. Adding mandatory measures for another 2.6 percent of the global ocean surface would cover all the hotspots; alternatively, protecting just 0.6 percent of the ocean's surface would cover multi-species hotspots (affecting two or more of the four whale species studied). The team noted that previous research on voluntary speed reduction programs have found evidence of only partial compliance, as some shipowners are willing to continue operation at full speed, despite encouragement to slow down. 

"Changes in ocean ecosystems caused by the loss of historic whale populations have been hard to reverse. Ship-strike risk is a ubiquitous yet solvable conservation challenge for large whales, and our results can provide a foundation for expanded management measures to protect these ocean giants," the authors concluded. 

The identified hot-spot areas may be comparatively small, but they include some of the busiest waterways in shipping, like the Strait of Gibraltar and the Cape of Good Hope route, where traffic has soared because of security issues in the Red Sea. The mandatory measures discussed could include a 10-knot speed limit, which could have a significant impact on transit times for container ship and car carrier operators on these routes.