Growth of baleen along the baleen rack is constant in balaenopterid whales

Werth et al. (Werth et al. Polar Biol 43:707–723, 2020) propose that in all mysticete whales the growth rate of baleen varies with the position they occupy in the mouth. If this were true, comparison between individuals and studies of results of chemical tracers in baleen would be compromised. Here we compile results from previous research conducted in balaenopterids using stable isotope ratios as tracers as well as images of baleen racks showing growth ridges and conclude that, at least in the Balaenopteridae family, the growth rate of baleen is constant along the whole baleen rack irrespectively of the position in the mouth, thus ensuring reliability of comparisons.