Collisions between ships and cetaceans are rather frequent despite the former being relatively loud and the latter having an excellent sense of hearing. Cetaceans are nevertheless capable of reacting to danger quickly, but in certain situations are less alert, for example when they are sleeping or resting at the surface, feeding, nursing their young or reproducing. If taken by surprise by a ship, they don’t always have the time to react or move out of the way, particularly in the case of the slower species. Although collisions are a recognized cause of cetacean mortality in the world, data on the subject remain scarce. It is therefore difficult to evaluate the importance and the repercussions of ship strikes on cetacean populations. Clearly, for certain populations such as that of the North Atlantic right whale, the threat is real. It is not easy to develop appropriate mitigation measures, however.
Injuries that speak for themselves
A collision between a ship and a cetacean can injure or kill the animal, depending on the angle and the force of the impact. A ship’s propellers can gash and cut into the animal’s flesh and blubber and sever off pieces of its tail. Other types of injuries require closer examination to identify a collision with a ship. The impact can result in fractures and ecchymosis (bruises) that are not always apparent. Given the force necessary to break the large bones of cetaceans, it is unlikely that fractures to the skull, jaw and vertebrae could be caused by anything but a strike by a vessel. The ribs and the bones of the pectoral fins, more fragile than the larger bones, may be broken by stranded animals writhing on shore and are not necessarily attributable to the impact of a boat. Some cetaceans, generally the more streamlined species like rorquals, occasionally get caught by the stem of a ship. They are then transported a certain distance until the crew takes notice of the situation or the ship slows down, generally upon arrival to port. For example, a fin whale struck by a cruise ship off the coast of Cape Cod, Massachusetts in 1995 was transported on the bow of the ship all the way to Bermuda, over 1,000 km away.
An incomplete but worrying picture
These incidents are poorly documented, as crews are not always aware of the collision or fail to report them to the responsible authorities. Further, the carcasses may sink or never resurface, especially if the impact severed the animal. Navigators are encouraged to report such collisions. Doing so enables authorities to search for and come to the aid of a wounded cetacean or to locate a floating carcass representing a navigation hazard. In the longer term, it will help pinpoint the places where these strikes are most frequent and to take measures accordingly.
According to a study conducted on collisions between motorized vessels and great cetaceans (baleen whales and sperm whales) in various regions of the world, fatal cetacean collisions date back to the end of the 1800s, when ships first began to attain speeds in the range of 13 to 15 knots (24 to 28 km/h). Collisions were uncommon back then, but became more frequent between 1950 and 1970 as boats increased both in number and in speed. The authors of the study cited collisions with 11 different whale species. Although impacts with fin whales are the most common, those with southern right whales, North Atlantic right whales, gray whales, humpback whales and sperm whales are rather frequent in certain regions. It seems that most fatal or serious injuries are caused by ships exceeding 80 m in length and travelling at speeds of at least 14 knots (approximately 25 km/h). But vessels of all sizes and types can strike whales and inflict more or less serious injuries.
In the St. Lawrence, data on collisions between cetaceans and ships are scarce. Of 18 collision incidents reported in the region of the Saguenay-St. Lawrence Marine Park between 1992 and 2005, there was at least one mortality, and between 1983 and 2004, 6% of beluga mortalities were attributable to ship strikes. However, since the Marine Activities in the Saguenay-St. Lawrence Marine Park Regulations took effect in 2002, a maximum of three collisions per year have been reported. A MICS analysis of the St. Lawrence blue whale photo-ID bank has revealed that at least 5% of individuals bear marks of collision with a ship.
Collisions between ships and cetaceans can be of particular concern for small populations. They currently threaten the survival of the North Atlantic right whale. Notably, 38% of mortalities in this species are attributable to boat collisions. Since this population numbers less than 500 individuals, collisions are the main obstacle to its recovery. Ship strikes probably have a negligible effect on cetacean species that are abundant such as the humpback whale and the fin whale, but may be a source of concern for certain populations for which collision frequency is high. For example, in the Mediterranean, where shipping traffic is intense, 26% of fin whale mortalities between 1986 and 1998 were attributable to a ship strike. Since this population is small and does not reproduce with other populations of the Atlantic, this statistic is a matter of concern.
Du côté des États-Unis, certaines voies navigables ont été reconfigurées sur la côte Est. Parallèlement, un système de survols aériens permettant de repérer les baleines noires et de communiquer leurs positions aux navigateurs a été mis en place. Mais cette technologie ne permettrait de repérer qu’une baleine noire sur quatre; qui plus est, elle est limitée par la météo et est risquée pour les observateurs. Un système d’écoute a donc été développé par Christopher Clark de Cornell University et financé par les compagnies gazières ; il signale la présence des cétacés aux navires gaziers qui doivent ralentir et les éviter.
In the United States, some shipping lanes on the East Coast have been reconfigured. In parallel, aerial flyovers are performed to spot North Atlantic right whales and communicate their positions. But this technology is believed to detect only one right whale in four; further, it is limited by meteorological conditions and can be hazardous for observers. A listening system was thus developed by Christopher Clark of Cornell University and financed by gas companies; the system signals the presence of cetaceans to gas tankers who can then slow down to avoid them.
Maritime traffic is not about to plateau or taper off, quite the contrary. Will this development take place to the detriment of whales? The measures tested today to urgently address the decline of the North Atlantic right whale might serve as a model to limit the consequences on other populations of large marine mammals.