Development of the darkening of Todarodes sagittatus beaks and its relation to growth and reproduction

Abstract

Beaks of 133 specimens of Todarodes sagittatus caught in the central East Atlantic were studied. Relationships between several measurements of the upper and lower beaks and dorsal mantle length (DML) and total mass were calculated. The darkening process or pigmentation of both beaks was investigated and a qualitative scale of eight degrees of pigmentation developed. Except for the hood of the lower beak, the growth of both beaks was allometrically negative in relation to DML in males, whereas the growth of several parts of both beaks of females was allometrically positive. The hood grew faster than all other parts of the male beak and faster than all parts of the lower beak of females. Regression coefficients calculated for the growth of the beaks revealed differences between the growth patterns of females and males (p < 0.05). The results relating to darkening and the maturing process suggest that they are related and that they take place over a very short period in the life of the squid.