Blue whales, the largest animals on Earth, are an integral part of marine ecosystems. Despite their immense size, their populations have drastically declined, pushing them to endangered status. This overview explores the primary factors contributing to their decline, from historical exploitation to ongoing environmental challenges.
The Era of Commercial Whaling
Commercial whaling is the foremost historical cause of the blue whale’s population collapse. Beginning around the 11th century, the industry initially targeted slower species. Technological advancements in the late 19th and early 20th centuries, like steam-powered ships and explosive harpoons, revolutionized the practice, enabling pursuit of faster whales and increasing hunting efficiency.
Blue whales were sought after due to their immense size, yielding large quantities of oil and other products. The profitability led to a competitive international market. Whaling operations expanded globally, especially in the Antarctic where large feeding aggregations were found.
Approximately 350,000 blue whales were killed between 1904 and 1967. By the 1960s, populations fell from an estimated 340,000 to as few as 5,000, a reduction of about 98.5%. The International Whaling Commission (IWC) was established in 1946, and a moratorium on blue whale hunting was implemented in 1966, with a full commercial whaling ban in 1986.
Direct Collisions and Entanglements
Beyond historical whaling, contemporary human activities threaten blue whales through vessel strikes and entanglement in fishing gear. As global shipping traffic increases, so does the risk of collisions. Blue whales can be difficult to spot, leading to accidental strikes by ships. These collisions cause severe injuries or death, especially in high-traffic coastal areas.
Entanglement in fishing gear is another serious threat. Blue whales can become caught in active or abandoned lines, nets, and traps. Once entangled, whales may carry the gear for extended periods, leading to exhaustion, starvation, trauma, infections, or drowning. Many blue whales show scars from previous entanglements.
Oceanic Noise and Chemical Pollution
The underwater environment is increasingly dominated by human-generated noise from shipping, seismic surveys, and naval sonar. Blue whales rely on sound for communication, navigation, feeding, and breeding. Increased noise can mask their calls, forcing them to vocalize more loudly or cease communication, disrupting their social structure and ability to find food or mates.
Seismic surveys use powerful air guns, producing intense noise that can displace whales from important grounds and increase stress levels. Chemical pollution poses a pervasive threat. Pollutants like PCBs and DDT, along with heavy metals, accumulate in whales’ tissues through their food chain. These chemicals can weaken immune systems, impair reproduction, and compromise overall health.
The Impact of a Changing Climate
Climate change presents a substantial threat to blue whales by impacting their food source, krill. Blue whales feed almost exclusively on krill. Krill populations are sensitive to changes in ocean temperature, sea ice coverage, and ocean chemistry. Warming waters and reduced sea ice can lead to a decline in krill abundance and alter their distribution.
Ocean acidification, caused by increased carbon dioxide absorption, further stresses krill. Higher acidity can affect krill growth and reproduction. Reductions in krill availability force blue whales to travel greater distances for food, shorten foraging seasons, and affect their ability to gain energy for survival and reproduction.