Climate change is a global phenomenon that is causing changes in ocean currents, temperature, and chemistry. This can affect marine species in a variety of ways, including through changes in their distribution and health, as well as changes to the structure of marine food webs. Climate change may impact the location, timing (phenology), and abundance of lower trophic level organisms (e.g., planktonic algae, zooplankton) on which fishes, birds, marine mammals, and other species eat. This may particularly affect large whales that require substantial quantities of food for survival and reproduction. To date, most known impacts to marine mammals from changing environmental conditions are due to changes in the relationships between predators and prey. Climate change may also have secondary consequences for marine mammals including impacts to their migratory patterns, energetic reserves, and stress levels. If these impacts are severe, population level consequences could occur. For more detailed information and scientific citations, please see the full FAQ document linked below.

There is evidence that whale distributions are changing in the Northwest Atlantic marine ecosystem. Many species are shifting their feeding areas in response to oceanographic changes, including changes in temperature, currents, and stratification (see How is climate change affecting large whales?), though the degree and direction of change is species- and season-specific. Humpback, minke, and sei whale distributions are generally shifting north, and North Atlantic right whales are spending more time in the Gulf of Saint Lawrence, further offshore, and near canyon areas. There have also been shifts in the phenology (i.e., timing) of habitat use across species. Whales primarily eat schooling fishes (sometimes called “forage fishes”) and zooplankton (such as copepods and shrimp-like crustaceans, called krill). Oceanography-driven prey movement is one of the mechanisms driving range shifts in whales. Copepods and many forage fish species have shown northeasterly distribution shifts and movement into deeper waters. The range of krill has retracted, with animals no longer occurring in the former southerly portions of their range. Shifting prey resources due to increasing oceanographic variability can lead whales to increase travel distances and/or change their diet, and can cause potential mismatches in the presence of whales and their prey. This has the potential to influence population dynamics (e.g., survival, reproduction).

Vessel strikes are a major source of mortality and injury for large whales around the world. The chance of a vessel strike occurring depends on the co-occurrence or overlap of whales and vessels in space and time, with risk increasing as the densities of both ships and whales increase. Both the likelihood and severity of a vessel strike vary based on vessel characteristics (e.g., size, speed) and the species and behavior of the whale involved. Vessel strike avoidance depends on the ability for a whale to be detected, and the time for a vessel to enact a maneuver to avoid a whale. Thus, current efforts to reduce vessel strike risk in the U.S. depend on both relocating shipping lanes away from key whale habitat (i.e. reducing co-occurrence of whales and vessels) and implementing voluntary or mandatory speed restrictions in key areas. Reduced vessel speeds are known to reduce severity of collisions and also likely reduce the probability of collisions by increasing reaction times and chances for whale detection by boaters. For more detailed information and scientific citations, please see the full FAQ document linked below.

Increased levels of “background” sound which can elevate the overall soundscape can mask sounds produced by animals to communicate with each other and locate food, which can lead to changes in behavior and increased stress. The frequency (“pitch”), intensity (“volume”), and duration of sound influence whether an animal may be affected. Marine mammals have a range of hearing capabilities and thus may be affected by anthropogenic (human-caused) sound in different ways. Characteristics of individual animals (such as their age, life history status, behavioral state at time of exposure) can also influence their behavioral response to sound exposure. Discrete, loud sounds and longer-duration sounds can also potentially damage the hearing capabilities of marine mammals, either temporarily or permanently or cause non-auditory injury or even death. For more detailed information and scientific citations, please see the full FAQ document linked below.

Sources of anthropogenic sound include vessels, offshore wind energy development, oil and gas exploration, military exercises, and other activities, all of which have the potential to affect marine mammals to varying degrees. Some anthropogenic sounds are high-intensity and acute (i.e., occur for short durations), while other types of sound are lower-level and chronic (i.e., occur consistently). Sound varies in intensity, frequency, and duration; all of these characteristics influence the potential for sound to affect marine mammals. Sounds produced in relation to offshore wind energy development vary by phase (e.g., site assessment, construction, operations, decommissioning). Some chronic sounds are lower intensity (“volume”) and are nearly continuous (e.g., operational turbine sound). Other offshore wind-related sounds are high-intensity and acute (e.g., pile driving of turbine foundations into the seabed). Offshore wind energy construction, marine oil and gas exploration, military sonar, and vessel activities all produce substantial amounts of underwater sound, but they differ in their intensity and frequency and therefore in their potential effects on marine mammals. For more detailed information and scientific citations, please see the full FAQ document linked below.