Collisions between ships and cetaceans are relatively common, even though the former are quite noisy and the latter have good hearing. While cetaceans are quite capable of reacting rapidly to danger, in certain situations, such as when they are resting at the surface, eating, nursing or mating, they are less alert. If a ship surprises a whale, particularly a slower moving species of whale, it does not always dispose of sufficient time to react or move. Ship strikes are a known cause of cetacean mortality worldwide, yet very little information dealing with the subject exists. Therefore, it is quite difficult to evaluate the scope and repercussions of collisions on cetacean populations. Clearly, for certain severely diminished populations such as the North Atlantic right whale, the threat is real. Still, coming up with appropriate mitigation measures is not an easy task.

Scars that tell a story

A collision between a ship and a cetacean can either injure or kill an animal, depending on the angle and force of impact. Ship propellers can nick and cut a whale’s skin or blubber and slice off pieces of its tail, while other types of injuries require closer inspection before concluding that they are the result of a ship strike. Collision impact can cause fracturing and bruising that is not always noticeable. Given the force required to break large cetacean bones, it is unlikely that cranial, mandibular or vertebral fractures could be the result of anything other than a ship strike. Ribs and pectoral-fin bones, on the other hand, are more fragile than the larger bones and can break when an animal rolls on the shore. These breaks are therefore not necessarily caused by the impact of a ship. Certain cetacean species—generally those with an elongated shape such as the rorqual whales—are sometimes caught on a ship’s bow stem. They may then be transported for a good distance before the ship’s crew becomes aware of the situation or the ship slows down, as upon entering a port. This was the case in 1995 when a fin whale was struck by a cruise ship off Cape Cod, Massachusetts and was transported on the ship’s stem all the way to Bermuda, over 1000 km away.

An incomplete, but troubling portrait

These incidents are not well documented due to the fact that ship’s crews are not always aware of a collision or fail to report it to the proper authorities. Furthermore, carcasses can sink, never to surface again, especially if the impact severs the whale. Navigators are invited to report these incidents so that a search may be carried out for the injured whale to either come to its assistance or locate its drifting carcass, which represents a navigational hazard. Over the long term, reported incidents could be used to determine areas where ship strikes are more common; appropriate measures might then be taken to diminish the threat.

According to a study carried out on collisions between motorized vessels and great whales (baleen whales and sperm whales) in various areas of the world, fatal collisions with cetaceans date back to the 1800s when ships began reaching speeds of 13 to 15 nautical miles per hour (24 to 28 km/h). Ship strikes were fairly rare at the time, but became quite common between the 1950s and the 1970s with an increase in the number of boats and their speed. The authors of the study listed collisions with 11 whale species. While collisions with fin whales are the most frequent, collisions with southern right whales, North Atlantic right whales, grey whales, humpback whales and sperm whales are also common in some regions. Apparently, most fatal or serious injuries are caused by ships that are at least 80 m in length and by ships travelling at least 14 nautical miles per hour (approximately 25 km/h). Even so, all types and sizes of ships can strike whales and inflict more or less serious injuries.

Data dealing with collisions between cetaceans and ships in the St. Lawrence is sparse. Of the 18 cases of collisions reported in the Saguenay—St. Lawrence Marine Park region between 1992 and 2005, at least one was a fatality. Of the 175 beluga whale carcasses recovered along the shores of the St. Lawrence since 1982, 11 deaths were caused by a collision. The MICS analysis of the St. Lawrence blue whale photo-identification catalogue has revealed that approximately 10 percent of these whales bear scars from collisions with ships.

Ship strikes can be quite worrying for smaller cetacean populations. These incidents currently threaten the survival of the North Atlantic right whale. A full 38 percent of the North Atlantic right whale deaths that occurred between 1986 and 2005 were caused by ship strikes. The fact that this population is limited to a mere 300 animals means that ship strikes are a major obstacle to its recovery. Ship strikes likely have a negligible effect on abundant cetacean species such as the humpback whale and the fin whale, however they can be a cause for concern for certain populations where the frequency of collisions is high. In the Mediterranean, where shipping traffic is intense, 26 percent of fin whale deaths between 1986 and 1998 were caused by ship strikes. Because this is a small population that does not breed with other Atlantic populations, the rate of these collisions is alarming.

Possible solutions

What can be done to reduce these fatalities? Apparently most cetaceans that were struck by boats were not noticed before the collision or were spotted only at the last minute. Consequently, avoidance strategies become inefficient for large ships that are not very manoeuvrable. In areas that are used intensively by cetaceans, limiting shipping or reducing speeds to less than 14 knots could prove to be the easiest solutions.

A good example of this was the repositioning, in 2003, of a shipping lane that cut across critical right whale habitat in the Bay of Fundy, Canada. By moving the shipping lane six kilometres to the east, researchers estimate that the risk of collisions was reduced by 95 percent. Only 1.5 percent of the right whale population was spotted in the new shipping lane in 2004 compared to 30 percent in the old one.

The United States is also considering modifying certain East Coast shipping lanes. Meanwhile, a system of aerial surveys used to spot right whales and communicate their positions to navigators has been put in place. Nevertheless, this technology is limited; only one right whale in four is perceived. Furthermore, weather imposes obvious limitations and there are risks for observers. A listening system, developed by Christopher Clark of Cornell University could prove to be more efficient. This system of hydrophones could detect up to 75 percent of right whales, in any weather, 24 hours per day. An integral part of this solution involves negotiations with the shipping and fishing industries to ensure that boats use the information transmitted to them to either slow down or change course.

Shipping traffic is not about to abate, on the contrary. Will this development take place at the expense of the whales? Measures presently being tested to respond to the decline of the North Atlantic right whale may serve as models to limit the consequences on other species of large marine mammals.

For example, the number of incidents reported to the Quebec Marine Mammal Emergency Response Network has shown that ship strikes in the St. Lawrence, which is considered to be one of the main ports of entry to North American continent, may be much more common than previously assumed. With this in mind, could it be possible to determine where rorqual whales congregate in the Gulf and Estuary in the hopes of eventually organizing alternative bypass shipping lanes? While this represents an enormous undertaking, it may eventually become a necessity.