Differential Growth Rate in the Tail of the Pacific Big Skate, Raja binoculata

Over a period of years the egg cases of Raja binoculata Girard were collected from waters in the Strait of Georgia, British Columbia, and measurements of the total body lengths and tail lengths were recorded. From these data an hypothesis was formulated suggesting that the relative growth rate of the tail to the growth of embryos is related to the mode of respiration utilized at a given time during development.The method of respiration employed by embryos of elasmobranchs follows a chronological sequence of integumentary, external gill filament, and spiracular–branchial respiration. To determine whether this hypothesis was tenable the data were subjected to a statistical analysis. A linear regression on the logarithms of the data was performed for caudal lengths below and above 8.5 cm. In each instance the probability that the resulting slope was not zero was Jess than 0.0001. Further, an analysis of covariance was performed that indicated that the two slopes were significantly different with a probability of less than 0.005.It would seem reasonable on the basis of the above analysis to assume that the tail length-respiration relation is a tenable hypothesis.