Comment on the ecophysiology of the Greenland shark, Somniosus microcephalus

Abstract

The recent finding that the Greenland shark, Somniosus microcephalus, reaches a life-span of almost 4 centuries and attains sexual maturity around 1.5 centuries, made us wonder what metabolic differences were responsible for these seemingly extreme values, compared to the related and better known spurdog Squalus acanthias. We studied this in the context of the dynamic energy budget (DEB) theory for metabolic organisation, which was applied to some 700 animal species from all large phyla and all chordate orders. The referenced data, estimated parameters and implied properties for all these species are published in the online Add-my-Pet collection, which provides a frame of reference for metabolic and life history properties. Given the few known data on S. microcephalus, we were able to estimate ageing parameters and gestation time, by application of the standard DEB model. We inferred that a recently estimated life-span of 392 years is probably too short for life at 2 °C, rather than too long. The ageing acceleration is only slightly smaller than that of the spurdog, and the gestation time is very likely between 8 and 18 years with the implication of around 200–700 pups per life-time. The low body temperature and high maximum reserve density of S. microcephalus could be identified as the causes of its long life-span. We see the latter cause as an adaptation to a life in the deep sea sporadically preying on big carcasses, where it is necessary to survive long spells of starvation. This application of the standard DEB model shows that it can be applied in situations where few data are available and how implied properties (gestation) can be used to constrain parameter values. The methods used here could be further developed by fisheries biologists working with deep sea species for which very little is known.