MAY 14, 2020
Every summer (November-April), the Magellan Strait in the southwestern part of Chile becomes a popular feeding area for migrating humpback whales (Megaptera novaeangliae). The narrow strait is also a heavily used shipping route. A new study by scientists at the Smithsonian Tropical Research Institute (STRI) and collaborating institutions tracked and modelled the movement of individual whales in order to evaluate the potential of vessel collisions and provide policy recommendations for the protection of whale species.
Humpback whales have the longest migratory journeys of any mammal on Earth. The Southern Hemisphere population spends its summer months feeding in the Antarctic and Chile and their winters in the warmer tropical Pacific waters of northern South America and Central America, as far as Nicaragua. Their movements often overlap with boat traffic and may put them at risk of collision, leading to injury or death. Years ago, STRI researcher Héctor M. Guzmán led a study that resulted in international regulations to separate vessel traffic from whale routes near the Panama Canal and in southern Costa Rica, which drastically reduced collision rates in the breeding areas.
"Designing and implementing traffic-separation schemes for Panama and Costa Rica was difficult, because any measures had to be adopted by the International Maritime Organization," said Guzmán, also lead author of the new study in Chile. "It was achieved by having the scientific information explain the whale movements and thanks to the unconditional support of both governments."
The new study, published in Marine Policy, took place in southern Chile, where about 100 humpback whales feed each summer: a population small enough for occasional ship strikes to have important consequences. By tagging and tracking 25 individuals over different years and comparing their movements with available records of vessels traversing the Strait, the team found that, on average, each whale was near a ship about seven times per season. Due to the detailed tracking records of multiple whales, the researchers were able to show that individual animals differed enormously in how often they encountered ships: from less than one to as many as 18 encounters per season.
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