FIELD ESTIMATES OF GROWTH AND MORTALITY OF THE GREEN SEA-URCHIN, STRONGYLOCENTROTUS-DROEBACHIENSIS

Growth and annual mortality rates of the green sea urchin, Strongyloce ntrotus droebachiensis, were estimated by marking individuals with flu orescent tags, releasing them in the field, and collecting them 1 year later. In 1994, 533 animals were tagged in 7 tidepools and in 1995, 4 58 were collected of which 262 were tagged. Tanaka function growth par ameters were estimated for the demi-pyramids, or ''jaws,'' one of the ossicles of Aristotle's lantern. Estimates of annual test diameter gro wth were attained by calculating the allometric relationship between j aw and test diameter. By assuming size at settlement (0.5 mm test diam eter) is age zero, and using the size specific growth rates, the relat ionship between test diameter and age was established. Our results ind icate that these animals are long lived and slow growing. The largest sea urchins in our samples may be more than 50 years. The difference i n size between tagged and untagged sea urchins in the 1995 collections strongly suggests that smaller individuals may tend to migrate more t han larger ones.