Quantifying the energy stores of capital breeding humpback whales and income breeding sperm whales using historical whaling records.

Lyn G Irvine,Clive R Mcmahon,Michele Thums,Mark A Hindell,Christine E Hanson

doi:10.1098/rsos.160290

Abstract

Cetacean energy stores are known to vary according to life history, reproductive status and time of year; however, the opportunity to quantify these relationships is rare. Using a unique set of historical whaling records from Western Australia (1952–1963), we investigated energy stores of large cetaceans with differing life histories, and quantified the relationship between total body lipid and length for humpback whales (Megaptera novaeangliae) (n = 905) and sperm whales (Physeter macrocephalus) (n = 1961). We found that total body lipid increased with body length in both humpback and sperm whales, consistent with size-related energy stores. Male humpback whales stored 2.49 kl (15.6 barrels) (31.9–74.9%) more lipid than male sperm whales of equivalent length, to fuel their annual migration. Relative lipid stores of sperm whales (males) were constant throughout the year, while those of humpback whales varied with reproductive class and sampling date. Pregnant female humpback whales had higher relative energy stores than non-pregnant females and males (26.2% and 37.4%, respectively), to fuel the energy demands of gestation and lactation. Those that reached the sampling site later (en route to their breeding grounds) carried higher lipid stores than those that arrived earlier, possibly reflecting individual variation in residency times in the Antarctic feeding grounds. Importantly, longer pregnant females had relatively larger energy stores than the shorter pregnant females, indicating that the smaller individuals may experience higher levels of energetic stress during the migration fast. The relationships we developed between body lipid and length can be used to inform bioenergetics and ecosystem models when such detailed information is not available.

Highlights

To optimize their fitness, organisms must acquire and allocate resources over their lifetime in a way that maximizes individual survival and reproduction [1]
As the energy stores of the BSD humpback whales decline through the breeding season [32], and those of sperm whales are stable throughout the year, the body lipid difference we found between the two species (2.49 kl) is probably an underestimate of the difference that would be expected when the humpbacks depart from their feeding grounds, carrying maximum energy stores
Given that the sperm whale oil yield records from Cheynes Beach Whaling Station included spermaceti oil as well as sperm oil from the body [41], and that an average of 11% of the total oil produced from a sperm whale is spermaceti oil [57], the difference of 2.49 kl (15.6 barrels) of body lipid that we found between humpback and sperm whales is probably an underestimate of the difference in body lipid that is stored for energy utilization

Summary

Introduction

Organisms must acquire and allocate resources over their lifetime in a way that maximizes individual survival and reproduction [1]. The capital breeding strategy generally involves a life cycle that consists of periods of intensive feeding and fasting that are synchronized with the annual seasonal cycle [7,8,9,10]. For reproductive females, this strategy requires short periods of maternal care with high rates of energy flow to the young [11,12,13]. The income breeding strategy of continuous energy acquisition throughout the year enables longer periods of maternal care [12,13], but requires stable or predictable environments

Methods

Results

Discussion

Conclusion