Allocentrotus fragilis (Jackson) was obtained from six stations at
depths of 100 to 1,260 m on the continental shelf and upper slope off Newport,
Oregon.
Ages and growth rates of A. fragilis were determined by two methods: (1) from
size-frequency distributions of trawl collections from 200 m, and (2) from growth
zones on skeletal test plates. Collections from other depths were not adequate for
size-frequency analyses. Gonad indices of A. fragilis from 200 m were used to
determine spawning periodicity and frequency. A semiannual frequency was suggested,
with spawning occurring in early spring and early autumn. No individuals
collected below 400 m were reproductively mature. A procedure was developed to
make growth zones of the skeletal test plates visible. Dark growth zones are
thought to correspond to semiannual periods of growth, one-half the number of
dark growth zones indicating the urchin's age.
The growth curve of A. fragilis from 200 m, which was plotted from the mean
test diameter of age groups defined by test plate growth zones, shows a good least-squares
fit to von Bertalanffy's growth equation. Growth rates determined from plate
growth zones appeared to be similar for A.fragilis from 100 to 600 m, but decreased
for specimens from 800 to 1,260 m. The asymptotic size decreased with increasing
depth below 200 m
