In this study,we used data-logging tags to examine the depth, swim
speed (relative to water), tail-beat frequency (which reflects the contraction
speed of locomotorymuscles), and ambientwater temperature
of free-ranging Greenland sharks in Svalbard, Norway. The behavioural
data allowed us to examine whether their swimming performance is (1) limited by cold water and (2) sufficient to catch swimming seals.
The first question was addressed by comparing the data on Greenland
sharks to those in the literature on other wild fishes at various
ambient water temperatures. Given the wide range in body size
(0.2–3900 kg) for fish species in the collected literature, the possible
effect of body size needed to be considered in inter-specific comparisons.
We therefore used a scaling approach, in which the locomotory
parameters were regressed against body mass, and the residuals
around the regression line were compared. The effect of phylogeny,
the tendency of closely related species to resemble each other because
of common ancestry (Felsenstein, 1985), was also accounted
for in the regression. The second question was addressed by comparing
data on Greenland sharks to those on seals in the literature