Cost of feeding is high in whales, due to the speed they must reach to get prey. The large body size is a benefit for the whales, because it allows them to hold more oxygen while diving, allowing them to increase their dive time to catch more prey. They can therefore hold more oxygen relative to their metabolic rate. (Kooyman et al., 1980; McClain et al., 2014). This allows humpback whales to forage, and lunge in quick energy bursts, and sperm whales to chase after more speedy fish and cephalopods (Simon et al., 2012). Dives are an average of 10 minutes for both whale species, although humpback whales have been known to dive for up to 30 minutes, and sperm whales for up to 1 hour (Clapham and Mead, 1999; Gosho et al., 1984).
Humpback whales weigh an average of 40 000 kilograms, with females being larger. Females are larger because they need to be able to lactate and raise young while fasting in tropical waters where they give birth. (Clapham and Mead, 1999). Lactation is a huge energy cost, and the fat content in whale milk is extremely high, at 32-38%. This allows the calves to grow quickly to be able to make the journey back to feeding grounds in higher latitudes. (Clapham, 1996).
Sperm whales range in weight between 15 000 kilograms (females) and 45 000 kilograms (males). (Whitehead, 2003).
Females and males require energy for migration. When they travel to tropical waters to breed during the winter, they are fasting, and this migration can last up to 4 months (Clapham and Mead, 1999). They must be able to live off of the fat stored in their blubber during this time. Whitehead, 2003, estimates that whales the size of sperm and humpback whales can live off of their blubber fat stores for around three months, because larger animals have higher ratios of energy storage to metabolic rate.
Whales are not concerned with energy expenditure due to predator escape, since they have virtually no predators in the ocean, other than the occasional shark going after a whale calf. This is ideal, since humpback whales are slow swimmers compared to other baleen species. They only swim around 15km/h, and their top speed has been measured somewhere around 27km/h. (Clapham and Mead, 1999).
Basal metabolic rate is difficult to measure in marine mammals, and there are no recorded measurements for Megaptera novaeangliae or Physeter macrocephalus. In the past, there has been debate over whether the large size of whales causes them to have a higher metabolic rate than a land mammal of a similar size, but a recent study on an orca (Worthy et al., 2013), shows that if the requirements of testing the basal metabolic rate are met, values similar to terrestrial mammals will be found. Lavigne et al. (1986) shares this view, and states that the Kleiber equation (M=70 x Body weight 0.75) is generally accurate for whales and marine mammals (Kleiber, 1975). Issues in the past would have included whales not being in a rested state, being under more stress than usual, or not being in a post-absorptive (fasted) state (Lavigne et al., 1986; Worthy et al., 2013). Due to these discrepancies, many thought that whales had metabolic rates 2-3 times higher than most terrestrial mammals, but this is not the case (Worthy et al., 2013). Since there is no species- specific data for whales, and since humpback whales and sperm whales are similar in size, energy requirements are estimated below based on an average weight of 40 000kg of an adult, male whale of either species.
Humpback and Sperm Whale Energy Requirements
Basal Metabolic Rate (kcal/day): 70x 40 000kg 0.75= 197 990 kcal per day
Daily Energy Expenditure (Maintenance, Activity, and Thermoregulation): BMR x 2.3= 455 376 kcal per day, which is equivalent to 318.4 kilograms per day of krill for humpback whales, or 339.8 kilograms of squid, for sperm whales.
Energy required for male reproduction: similar to daily energy expenditure, perhaps a little higher if they were being particularly aggressive one day
Energy required for female reproduction (Gestation): No species-specific values exist, but one book estimates that female whales must increase their energy intake by 60-70% during pregnancy, which would require about 728 602 kcal per day. (Lockyer, 1981).
Energy required for growth of calves: No species-specific values exist, but one book states that at birth, the ratio of metabolic energy expenditure to energy gain is about 2:1, and that increases into adulthood to 100:1. (Lockyer, 1981).
Energy required for lactation: (4-7 x BMR)= 791 960 or more calories per day. Females are often lactating while fasting as well, which stresses the point of laying down fatty blubber during the summer to feed off of during the hungry winters.
whale nutrition 