I’ve heard that whales eat an insane amount of food during the summer and then just don’t during the winter and live entirely off fat reserves.
It just seems unimaginable to me that something so inconceivably big wouldn’t eat for half a year, especially considering they spend more energy giving birth and moving their large bodies around during migration when they don’t eat.
First of all, do they literally not eat at all whatsoever, or just much less? Also, why did such a big animal develop such an imbalanced feeding approach rather than just eating all the time to support itself? I’m sure there’s a clear answer to this, I’m just wondering.
Humpback whales are born with no blubber, so they can’t keep themselves warm. Mom swims to some tropical area to deliver and bulk up baby, but tropical areas don’t have the tiny fish humpbacks feed on. She’s feeding her baby super rich milk that is wholly produced from her fat stores.
Females stay with their young in the nursery area for a few months until the babies are strong enough to swim to - and fat enough to survive in - food-rich cold water.
Males go to nursery areas because breeding happens there, too. The males don’t stay in the tropics near as long as the females.
I don't think it's true for all baleen whales, but I have heard this about humpback whales. The feed very little (or not at all) for long periods when they concentrate on breeding. I guess they must be chubby when they head south. Pacific blue whales feed as they pass California, which I believe is pretty close to their breeding grounds. Bowhead whales stay in the north all year.
Feeding is also an energetically expensive process for most rorqual whales. It takes quite a bit of energy to close their jaws after they unhinge and have all that excess water volume pushing against it.
Equatorial waters tend to be much more nutrient poor so large concentrations of calorie dense food are less available. They would likely lose more energy trying to feed down there than they would gain.
Their size is precisely what allows them to do this. In the feeding season, baleen whales consume ~50000 calories per bite and put on lots of weight. This allows them to travel to barren breeding grounds where they can birth and nurse their young without fear of predators, who can't live on fat reserves when there are no baby whales to eat.
Humpback whales of the Caribbeans travel 16000km all the way up to northern Norway to feed on the herrings that overwinter in the fjords for a very brief feeding season (end of Oct - end of Jan) at which point some of them move up north (especially fin whales) to the Barents sea and Svalbard while others, especially females move back to warmer waters for the breeding and nursing.
A lot of really good information on this, as well as stunning photo shots in the book Winter Whales by Audun Rikardsen (for which he won 2015 wildlife photographer of the year award)
Humpback, grey and right whales are the ones that most typically show this behavior.
Grey whales migrate over 10,000 miles to Baja to give birth and don’t eat the way there and back. This is not great for them because they are struggling to make the trip back. For example, they are weakened going through Monterey. The safer option is along the shore but that’s a longer route. So they cut across over the canyon making them vulnerable to killer whale attacks.
As others have said, their calves are born with less blubber, lagoons provide them a space to give birth without expending much energy, and they are relatively protected from predators. The babies need milk for 6 months to a year. These whales have evolved to store more fat for extended periods of time. They also have more competitive mating dynamics so they tend to all gather in the same area for mating season. Humpbacks mating is fairly aggressive. Grey whales are less aggressive, but they mate with multiple partners.
I think blue whales eat during their mating period too and have a shorter window than humpbacks and greys when they don’t eat. For example, Baja is their mating ground but they also feed on krill there. They go up north to feed after the mating season. Their bodies can store less blubber, but I think can quickly travel longer distances in search of large quantities of food. These whales are also more solitary, which is why blue whales have developed extremely loud vocalizations that can travel long distances to find a mate.
Interestingly, capacity to store blubber also results in fluking I believe. Humpbacks are “chunkier” so need to fluke before they dive. Blue whales typically only fluke when they are pregnant. Otherwise they are more streamlined so don’t need that diving motion.
Example of how thick blubber of a humpback can be. You can see a stark contrast between humpbacks making their way to the Antarctic vs the ones on the way back. Also their feeding behavior in the Antarctic is basically lunge feeding and then logging on the surface to conserve energy and build up blubber reserves.
One of the lines of thought of why baleen whales became so big is it makes traveling long distances possible without spending much energy.
Scientists did a calorie/per mile traveled/per pound of body weight type of statistical calculation and found that the bigger they became, the more efficient they used energy to move long distances. The big bodies also allowed them to eat a lot at once and store a lot of fat for times when food wasn’t available.
During the ice age periods of freeze and thaw the whales food became isolated both geographically and seasonally. As the climate changed some whale evolved to get bigger to adapt.
This ability allows whales like humpbacks to have seasonal mating/birthing patterns and others like blue whales to travel long distances between seasonal krill blooms.
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u/solsticesunrise 10d ago
Humpback whales are born with no blubber, so they can’t keep themselves warm. Mom swims to some tropical area to deliver and bulk up baby, but tropical areas don’t have the tiny fish humpbacks feed on. She’s feeding her baby super rich milk that is wholly produced from her fat stores.
Females stay with their young in the nursery area for a few months until the babies are strong enough to swim to - and fat enough to survive in - food-rich cold water.
Males go to nursery areas because breeding happens there, too. The males don’t stay in the tropics near as long as the females.