Migrations and Growth of the Thornback Ray (Raia clavata L.)

Abstract

Although workers in several European countries (England, Germany, Russia, Scotland) are stated (5) to be carrying out marking experiments on rays or skates, the writer is not aware of any recently published account of the results of any of these researches. Fulton (4, p. 191), however, records that in the years round about 1890 he marked 71 thornback rays (R. clavata) and 23 specimens of grey skate (R. batis) in Scottish waters. Two of the thornbacks and one skate were subsequently recovered. Of the former, one—about 36·5 cm. in width on marking—remained at liberty for about three months before being recaptured and had travelled about 13 miles from the place where it had been set free. The other—35 cm. in width—remained at liberty for 278 days and travelled about six miles. The single skate, recaptured after only 10 days, had in that time changed its position by 10 miles. No records of size increments are given.