Size assortment in mixed-species groups of juvenile-phase striped parrotfish (Scarus iserti) in The Bahamas

Striped parrotfish (Scarus iserti) often form heterospecific groups with other reef fishes. In this study, we examined the species and body size composition of these groups on reefs in The Bahamas. Groups averaged approximately 4 S. iserti and 2 associated species, with surgeonfish (Acanthurus chirurgus and A. bahianus), slippery dick (Halichoeres bivittatus), and bluehead wrasse (Thalassoma bifasciatum) as the most common associates. Fewer groups than expected had only 1 associate; groups with 3 or more associates were more common than expected. Both the S. iserti and associated species tended to be closely sizematched within a group, perhaps due to benefits of size assortment in lowering predation risk. Likewise, the high frequency of groups with greater than a single associate species suggests that associates may benefit from not being the only phenotypically different individual in a group.