Inter-oceanic analysis of demographic variation in a widely distributed Indo-Pacific coral reef fish

Abstract

The surgeonfish Ctenochaetus striatus is abundant and widely distributed on reefs throughout the Indian and Pacific Oceans. Population samples at 15 sites that spanned 158° of longitude and 40° of latitude across both hemispheres of the Indian and Pacific oceans allowed us to examine geographic variation in longevity, growth rate and adult size of this species. Samples from 5 sites in the Indian Ocean, 6 in the western Pacific and 4 in the central Pacific provided otolith-based estimates of size-at-age for 1537 individuals. All populations displayed rapid growth to a distinct asymptotic size, a pattern characteristic of many acanthuroid fishes. In both oceans, fish lived longer at higher latitudes; in addition, Indian Ocean populations tended to be shorter-lived than those in the Pacific Ocean. In contrast, growth rate and adult size did not differ between the 2 oceans, and were not related to temperature (as a proxy for latitude) in either the Pacific or the Indian Ocean. Further, we found no relationship between fishing pressure and longevity, growth or adult size across our set of sampling sites, among which fishing pressure on this species varied from intense to zero. We hypothesize that (1) growth and adult size are most responsive to local environmental features unre- lated to latitudinal (temperature) effects; and (2) variation in longevity reflects a combination of responses to latitudinal (temperature) gradients and as yet unidentified environmental differences between the Indian and Pacific oceans.