Chatham Strait, Southeast Alaska
Our story begins last winter in the waters around Hawaii, where humpback whales are found during this season. Pregnant females are there to give birth and nurse their single calf in the warm tropical water, converting their bodies’ blubber layer into fat-rich milk. Females who gave birth the previous season have recently parted company from that calf. They enter estrous and are soon the object of attention of groups of persistent males competing none-too-gently to father her next calf. What the whales are not doing is feeding, for the tropical waters provide little in the way of food.
By late winter the whales’ energy stores are depleted; it is time to head north. Swimming at a steady but leisurely pace, it may take them two months to reach the cold but productive waters of Southeast Alaska. There they begin feeding to rebuild their blubber layer. Some feed on krill, others on herring, depending on the areas that they have chosen.
This afternoon we encountered humpbacks feeding on herring in Chatham Strait, between Baranof and Chichagof Islands to the west and Admiralty Island to the east. Remarkably, three different modes of feeding were in use. A group of four whales, later joined by a fifth, were engaged in the amazing behavior of cooperative bubble-net feeding. The whales would dive in close succession, each lifting its massive flukes as it slid beneath the surface. In the water below the whales seek out a school of herring. If they find a school they circle the fish, spiraling upward, with one whale releasing a curtain of air from its blowhole. This concentrates the fish into a tight ball. At a vocal signal given by one whale, all come up through the bubble net and burst, together, onto the surface with their huge mouths agape, engulfing tons of water and the herring that it contains (photo below). The food is then strained from the water as the massive tongue pushes it through the whales’ baleen plates. Other whales (including the one seen above with open mouth, showing its baleen) were feeding solitarily by lunging up through schools of herring without the benefit of a bubble-net. Finally, one whale that was conspicuously white on the underside of its tail, easily identified as the same individual that we watched last night, was again engaged in “flick-feeding”, using its tail to concentrate the fish. How do the whales “decide” which feeding behavior they will use at any time? Are individuals consistent in their feeding mode over time? Is entry into a cooperative feeding group somehow limited? We have much to learn about these remarkable animals. This wonderful day of whale-watching ended with an encounter with a female and her young calf, swimming languidly side by side, almost in contact. It was a beautiful sight.
Did I mention the beautiful clear and calm weather that we so richly deserved? After dinner we gathered on the bow to enjoy the colors of the setting sun over Icy Strait, with the mountains of the Fairweather Range in clear view to the north. On the other side of the mountains lies Glacier Bay National Park, our destination for tomorrow.
Our story begins last winter in the waters around Hawaii, where humpback whales are found during this season. Pregnant females are there to give birth and nurse their single calf in the warm tropical water, converting their bodies’ blubber layer into fat-rich milk. Females who gave birth the previous season have recently parted company from that calf. They enter estrous and are soon the object of attention of groups of persistent males competing none-too-gently to father her next calf. What the whales are not doing is feeding, for the tropical waters provide little in the way of food.
By late winter the whales’ energy stores are depleted; it is time to head north. Swimming at a steady but leisurely pace, it may take them two months to reach the cold but productive waters of Southeast Alaska. There they begin feeding to rebuild their blubber layer. Some feed on krill, others on herring, depending on the areas that they have chosen.
This afternoon we encountered humpbacks feeding on herring in Chatham Strait, between Baranof and Chichagof Islands to the west and Admiralty Island to the east. Remarkably, three different modes of feeding were in use. A group of four whales, later joined by a fifth, were engaged in the amazing behavior of cooperative bubble-net feeding. The whales would dive in close succession, each lifting its massive flukes as it slid beneath the surface. In the water below the whales seek out a school of herring. If they find a school they circle the fish, spiraling upward, with one whale releasing a curtain of air from its blowhole. This concentrates the fish into a tight ball. At a vocal signal given by one whale, all come up through the bubble net and burst, together, onto the surface with their huge mouths agape, engulfing tons of water and the herring that it contains (photo below). The food is then strained from the water as the massive tongue pushes it through the whales’ baleen plates. Other whales (including the one seen above with open mouth, showing its baleen) were feeding solitarily by lunging up through schools of herring without the benefit of a bubble-net. Finally, one whale that was conspicuously white on the underside of its tail, easily identified as the same individual that we watched last night, was again engaged in “flick-feeding”, using its tail to concentrate the fish. How do the whales “decide” which feeding behavior they will use at any time? Are individuals consistent in their feeding mode over time? Is entry into a cooperative feeding group somehow limited? We have much to learn about these remarkable animals. This wonderful day of whale-watching ended with an encounter with a female and her young calf, swimming languidly side by side, almost in contact. It was a beautiful sight.
Did I mention the beautiful clear and calm weather that we so richly deserved? After dinner we gathered on the bow to enjoy the colors of the setting sun over Icy Strait, with the mountains of the Fairweather Range in clear view to the north. On the other side of the mountains lies Glacier Bay National Park, our destination for tomorrow.
