Evidence for the Presence of a Metamorphic Check in Capelin (Mallotus villosus) Otoliths and Implications for Age Determination

Abstract

The otolith method of aging capelin (Mallotus villosus) from the estuary and western Gulf of St. Lawrence was validated. Hyaline zones are deposited annually in the late fall and winter and thus can be used in age determination. Back-calculated mean length at the first hyaline zone corresponded well with the average length of capelin larvae collected in November and this zone is interpreted as the first annulus. The mean size at the second hyaline zone corresponded exactly with the length at which capelin undergo a profound metamorphosis. This second hyaline zone, which is laid down in the summer of the 2nd yr, was thus interpreted to be a metamorphic check. The third hyaline zone, deposited at a mean length of 95 mm, which corresponded with the peak in the length frequency distribution (when allowance was made for growth), was interpreted as the second annulus. Analysis of two otolith aging techniques currently used suggests that the "Newfoundland" method misinterprets the metamorphic check as the first annulus, rejecting the true first annulus as a "larval check,” a feature having no biological basis in fact. This results in correct ages, but estimates of lengths at the first annulus are exaggerated. The "Greenland" or "Danish" method may misinterpret the metamorphic check as the second annulus thereby resulting in erroneous ages. Key words: capelin, Mallotus villosus, otoliths, age verification, Gulf of St. Lawrence