Experimental analysis of 3 internal marking methods for Red Sea urchins

Red sea urchin, Strongylocentrotus franciscanus, mark loss, mortality, and growth rates were compared among combinations of 3 marking methods: coded-wire tag (CWT), passive integrated transponder (PIT), and tetracycline (8 chemical mark). Red sea urchins ranging in size from 12 to 89 mm test diameter were collected from the subtidal zone near Fort Bragg, California and held in a closed, recirculating seawater system for up to 205 days. Growth measurements were made at 93 and 205 days. Overall CWT loss rate was 17.6%; PIT loss was 10.0%. Mortality was 5.0%, with no significant difference among treatments. Growth, as measured by final test diameters adjusted for initial sizes by regression, was not significantly different among marking methods for the first 93-day period. For the entire 205-day period, adjusted mean test size differed significantly among marking methods. Mean test diameter growth ranged from 6.2 to 6.6 mm after 93 days and 8.0 to 11.5 mm after 205 days; 69% of the mean gonadosomatic index increase occurred by 93 days. Back-calculated growth rate of tetracycline-marked urchins after 205 days was 80% of their directly measured growth rate.