Abstract

There is growing concern that sound introduced into the sea by human activities has detrimental effects on marine mammals. Evidence suggests that high-intensity anthropogenic sound from sonar leads to strandings of beaked whales, although the mechanisms of injury in these events remains unresolved. A more pervasive problem is the effect of increased noise levels from commercial shipping and seismic exploration. Acoustic communication networks are an emerging source of underwater noise at mid-and high-frequencies.

Sound is an extremely efficient way to propagate energy through the ocean, and marine mammals have evolved to exploit its potential. Marine mammals use sound as a primary means for underwater communication and sensing. Toothed whales have developed sophisticated echolocation systems to sense and track the presence of prey and engage in complex exchanges of vocalizations with members of their own species. Baleen whales have developed long-range acoustic communication systems to facilitate mating and social interaction. Some baleen whales produce intricately patterned songs that continue for hours or days. Marine mammals may use sound from natural sources as a guide for navigation, prey detection, and avoidance of predation. The sound environment of the ocean is an important aspect of marine mammal habitat and we can expect marine mammals to choose their locations and modify their behavior based, in part, on the presence of natural and anthropogenic sounds.

High levels of anthropogenic noise may interfere with marine mammals' ability to detect sounds, such as calls of members of their own species, echoes from prey, or natural sounds that aid in navigation or foraging. Noise may affect reproductive or immune functions and cause more generalized stress. If marine mammals tend to avoid the vicinity of an anthropogenic sound source, they may be kept away from an ecologically important area.

Evidence suggests that given the opportunity, marine mammals avoid high-intensity sound. Acoustic pingers have been demonstrated to be an effective way to keep marine mammals from becoming entangled in fishing gear. It has likewise been shown that acoustic harassment devices can exclude marine mammals from areas of their usage.

A major impediment to assessment of the biological effects of noise is the lack of knowledge about marine mammal behavioral responses to sound. Behavioral data from the wild are needed to examine those responses so that effects can be assessed. Significant effects may prove to be confined to a few individuals exposed at high sound pressure levels, or they may be occurring at a population level as a result of widespread exposure. Discerning population-level effects is challenging since the observations must be conducted over great distances and long time periods.

* Presenting author