Orcas, also known as killer whales, are highly intelligent and socially complex apex predators of the marine environment, with no natural predators. Despite their dominant position, orcas can experience stress and discomfort from various environmental factors. Understanding these elements provides insight into the challenges these remarkable marine mammals face.
Environmental Aversions
Orcas avoid certain natural conditions. They avoid shallow waters to prevent stranding.
Their hunting strategies can lead them to avoid areas with scarce prey. Some orca populations specialize in specific prey like Chinook salmon; a reduction in these prey impacts their foraging success.
Orcas interact with other large marine animals. Female sperm whales, for example, form protective circles around their calves to repel orca attacks, using their strong flukes. This demonstrates avoidance by prey species that orcas must navigate.
Some orca groups that rely on ice for hunting seals face challenges with diminishing sea ice due to climate change, limiting their access to food.
Acoustic Sensitivities
Orcas rely heavily on sound for communication, navigation, and hunting. They use echolocation, emitting high-frequency clicks that bounce off objects, allowing them to interpret their environment and locate prey. This acute reliance on sound makes them vulnerable to underwater noise pollution.
Anthropogenic, or human-made, sounds significantly affect orcas. Sources like naval sonar, seismic surveys for oil and gas, and commercial shipping traffic introduce disruptive noise.
Naval sonar, particularly mid-frequency active sonar, can cause orcas to change their diving behavior and avoid areas, even at relatively low sound levels.
Seismic surveys, which use loud pulses of sound, can force whales to avoid their preferred feeding grounds and normal ranges.
Shipping noise creates persistent background noise that can mask orcas’ calls and interfere with their ability to communicate and echolocate. Studies indicate that vessel noise can reduce orcas’ communication range and foraging efficiency.
Human-Caused Disturbances
Beyond acoustic impacts, other human activities directly disturb orcas and affect their well-being.
The physical presence of vessels, including recreational boats and whale-watching tours, can disrupt orcas’ normal behaviors. When boats are too close, orcas may make fewer foraging dives, swim away, or make shallower dives, leading to reduced food intake. This disturbance can be particularly impactful for females, who might forgo foraging opportunities in noisy waters, potentially affecting their health and that of their calves.
Entanglement in fishing gear and marine debris is a threat. Orcas can become entangled in fishing lines, pots, and trawl gear, which can lead to injury or death.
Additionally, habitat degradation from pollution, such as persistent organic pollutants (POPs) like PCBs, poses a long-term risk. These toxins accumulate in the food chain, reaching high concentrations in orcas, and can impair their immune and reproductive systems.
Climate change also impacts orcas by altering prey availability and distribution, as warmer waters can affect salmon populations and shift migration patterns, pushing some orcas to new, potentially less suitable, habitats.