Patterns of Lipid Content and Stratification in the Blubber of Fin Whales (Balaenoptera physalus)

TLDR: The lipid content and layering structure of the blubber of 82 fin whales caught off Spain were studied in relation to individual biological attributes to propose the mean of the values of the three layers as the best index of condition for fin whales.

Abstract: The lipid content and layering structure of the blubber of 82 fin whales ( Balaenoptera physalus ) caught off Spain were studied in relation to individual biological attributes. The lipid content of the external blubber stratum is stable and shows no apparent variation with age, reproductive status, or day of capture in either sex. This indicates that this stratum does not play a significant role in the dynamics of fat storage in fin whales. The internal stratum, in contrast, is variable, clearly reflecting the nutritive reserves of individuals. The mid-stratum is a transition between the external and internal layers. Reproductive categories are discriminated best by the mean of the values of the three layers than by any of them used independently. For this reason, this mean is proposed as the best index of condition for fin whales. Reproductive status is the main factor determining variation in lipid content of blubber in females, but is meaningless in males. Ranking of blubber fatness for the reproductive categories is: pregnant females > males = immature females > resting females > lactating females. These dissimilarities are explained by the energetic, migrational, and physiological characteristics of the different population components. In males, lipid content of blubber decreased significantly with age, whereas in immature females it increased with age. In both sexes, lipid reserves accrued from early May until mid-August, but tended to decrease afterwards, following variations in food availability. The nutritive condition of lactating females improved during late lactation probably because of increasing food consumption and decreasing energetic demands of suckling young.