Evaluation of passive integrated transponder (PIT) tags in studies of sea urchins: caution advised

We evaluated the effect of passive integrated transponder (PIT) tags on feeding, growth, movement and survival of the sea urchin Strongylocentrotus droebachiensis in field and laboratory experiments. In cages supplied with kelp, 80% of urchins (n = 74) retained their tag during an 80 d field experiment. At the end of the experiment, tagged individuals had a lower growth rate (by 42%), lower gonad index (by 23%), lower survival rate (by 30%), and took longer to right themselves (by 30%) than untagged control urchins. In a 24 h feeding experiment in the field, the consumption rate of kelp was lower for tagged urchins (by 67%) than for untagged controls. In release and recapture experiments in the field, tagged urchins moved shorter distances over 2.5 h (by 30%) than controls. Although PIT tagging had a detrimental effect on all measures of sea urchin performance, activity and survival in the field, there was no detectable effect of PIT tagging on urchin feeding rate or survival in a 10 wk laboratory experiment. Our results suggest that natural stressors, such as wave action, may limit the utility of PIT tags in field studies of urchins