Rice’s whales weigh up to 27 tonnes and grow up to 13m long – Bryde’s whales are lighter at up to 25 tonnes but have a maximum length of 15m.
Little is known about their life expectancy, though closely related species reach sexual maturity at 9 and live about 60 years. The main threats are ship-strikes, ocean noise, energy exploration and production, oil spills, fishing-gear entanglement and ocean debris.
**** MEANWHILE, off South America’s Pacific coast, an extensive satellite-tracking survey has revealed a pattern of blue whales constantly zig-zagging to avoid up to 1000 ships that pass through their feeding grounds in Chile’s northern Patagonia region daily.
Blue whales (Balaenoptera musculus), the largest animal on Earth, surface to feed on krill, making them vulnerable to ship-strikes. “In most countries unreported cases, limited monitoring and insufficiently documented incidents have precluded any accurate assessment of the true collision prevalence,” write the researchers from Chile, Argentina and the USA, whose study has just been published in Science Reports.
Chile’s coastal waters are the main summer foraging and nursing ground for the eastern South Pacific blue whale population, which numbers only a few hundred. They also feature one of the world’s largest salmon-farming industries, the source of up to 83% of the traffic.
The team tagged and tracked 15 blue whales in the study, and are now calling for legislation to re-route the intensive shipping traffic seasonally or introduce speed limits, which could reduce the dangers of both ship-strikes and noise exposure to the whales.