Humpback whales feed in large gulps, and often engulf an entire school of krill or teleost (bony) fish in one swallow, then filter out the water through their baleen by raising their tongues (Stevens and Hume, 1995). This is a beneficial way of feeding for the whale, but it means that they cannot control every single type of fish that enters the body. The humpback whale’s main food are krill and small schooling fish. Their diet has been found to be composed of small percentages of other sea creatures, such as larger fish or crustaceans, but this is due to their huge, imprecise mouthfuls (Filatova and Witteveen, 2013). Humpback whales use bubble-lunge feeding, where they produce a curtain of bubbles to distract and disorient the prey, then lunge through it. (Clapham and Mead, 1999). Some humpbacks also use lobtail feeding, where they slap the surface of the water multiple times, and then employ the bubble-lunge feeding method (Allen et al., 2013).
Though humpbacks are seen foraging in shallow waters for schooling fish, they catch most of their prey (krill) in deeper waters (Filatova and Witteveen, 2013).
Nutritional Breakdown of Krill on a wet weight basis:
Protein- 47-51%
Fat-19-25%
Ash (Minerals)- 13.2-14.8%
Carbohydrate- 2%
Moisture- 74.6%
Mean energy content- 6 kJ/g (1.43 kcals/g) (Wang and Jeffs, 2014)
(Nicol et al., 2000; Omori, 1969; Farber-Lorda et al., 2009)
Krill are small creatures, that range from a few millimetres to a few centimetres long (Everson, 2008) and for humpback whales to meet their caloric needs for the day, they must consume a lot of them. This is usually not an issue, since there is evidence that suggests that krill have the highest biomass of any other multicellular animal (Wang and Jeffs, 2014). So there is plenty of krill to go around. Krill are nutritionally beneficial because of their high protein and fat. This allows humpbacks to get a lot of what they need out of one mouthful of krill, since fat and protein are important for their nutrition, and to pack on fat during the feeding season to prepare for their long, fasting migration to their tropical breeding grounds in the winter. The fat content of krill does vary slightly between seasons, however, with a lower fat content in the spring, when whales are returning to feeding grounds (Falk-Petersen et al., 2000).
Nutritional Breakdown of Bassanago albescens (Hairy Conger: a teleost with similar nutritive qualities of a small schooling fish such as herring or lance) on a wet weight basis
Protein- 14.14%
Fat- 4.76%
Ash (Minerals)- 2.58%
Moisture- 75.78%
Mean energy content- 5.25 kJ/g (1.25 kcals/g)
*Carbohydrate content was not measured or found in literature since fish contain very little carbohydrates, which barely contribute to total energy
(Eder and Lewis, 2005)
Teleost fish have much lower protein and fat content than krill, which adds up to a lower caloric value per gram of fish. This makes it a less nutritional food for humpback whales, which helps explain why they prefer krill as their main food. Krill provides the most nutrition by far. However, krill are very tiny, so it is necessary to eat many at a time.
One issue that has come to light from Nash et al. (2013) is the effects of toxins on humpback whales during migration. Since the whales are food deprived during their journey, their fat stores fluctuate and decrease overall, which greatly increases the consequences of lipophilic organochlorides, which are a human- caused toxin. This may be an increasing problem with marine mammals that go through a fasting period. Humpback whales can lose around 10% of their body weight during their 3-4 month fasting migration journey, and organochlorides and other toxins released into the oceans by humans are much more detrimental to these whales then fat, well-fed whales. (Nash et al., 2013).
Sperm whales forage in deep waters as well, but for much larger creatures (McClain et al., 2014). Since sperm whales do not have baleen, they are unable to eat large quantities of nutritious krill in a short period of time. Therefore, they have to eat much larger prey to reach their daily caloric requirement. Sperm whales mainly eat cephalopods, their favourite being squid, and a significant amount of elasmobranchs (sharks and rays). (Whitehead, 2003).
Nutritional Breakdown of Illex argentinus (Greater Hooked Squid) on a wet weight basis:
Protein- 13.88%
Fat- 7.9%
Ash (Minerals)- 1.34%
Moisture- 77.24%
Mean energy content- 5.64 kJ/g (1.34 kcals/g)
*Carbohydrate content was not measured or found in literature since squid contain very little carbohydrates, which barely contribute to total energy
(Eder and Lewis, 2005; Zlatanos et al., 2006)
Nutritional breakdown of Squalus acanthias (Spiny dogfish- An elasmobranch) on a wet weight basis:
Protein- 12.79% wet mass
Fat- 8.55% wet mass
Ash (Minerals)- 2.31%
Moisture- 72.79%
Mean energy content- 6.42 kJ/g (1.53 kcals/g)
*Carbohydrate content was not measured or found in literature since elasmobranchs contain very little carbohydrates, which barely contribute to total energy
(Eder and Lewis, 2005)
Squid, other cephalopods, and elasmobranchs live in deep water where sperm whales hunt. Squid species range in size from 100g to 400kg (Whitehead, 2003). Sperm whales prefer the 400kg Humboldt squid, but will eat a range of species (Whitehead, 2003). Since squid and elasmobranchs do not have a significantly high protein or fat content, they must eat large animals to get all the nutrients they need.
Unfortunately, ocean pollution often causes sperm whales to have garbage and plastic as part of their diet. This affects many marine mammals, and there have been sperm whales found that died from the amount of debris in their stomach (Stephanis et al., 2013).
**All nutritional breakdowns were presented on a wet weight basis to show the nutrient percentages as the whales eat their prey. Presenting it on a wet weight basis allows estimates of how many individuals of each prey species needs to be eaten per day to meet energy requirements, since moisture will be included in the prey as the whales eat in the wild.
whale nutrition 