Recruitment dynamics and first year growth of the coral reef surgeonfish Ctenochaetus striatus, with implications for acanthurid growth models

Abstract

Newly recruited Ctenochaetus striatus were monitored over a 16-month period in American Samoa, 2002–2003. During this period, a mass recruitment of age-0 C. striatus occurred in March 2002 with numbers reaching 22.9 recruits m−2. This program provided an invaluable opportunity to (1) analyze the dynamics of a mass recruitment episode and to assess its significance with respect to more typical patterns of recruitment and (2) establish the pattern of recruit growth during their first year of life. Age-based analysis indicated that the mass recruitment generated about 90 % of annual recruitment, but recruit mortality was high; thus, most recruitment was provided by continuous settlement throughout the year. The mass event appeared to be a short-lived pulse with recruits residing on the reef an average of 14.1 d compared with 161.1 d for other recruits. Recruits grew rapidly, achieving 90 % of their adult size during their first year, and they formed their first otolith annulus after 1 yr, thereby providing a firm basis for otolith interpretation of fish ages during the early life history phase of this species. The extensive age-based documentation of their first year growth in this study validates the distinctive “square” growth pattern exhibited by acanthurids as described in the literature (i.e., long life span with rapid initial growth that quickly reaches an asymptotic size), and it demonstrates the impact that the presence of age-0 fish has when generating growth parameters for populations exhibiting square growth. We found that the parameters from the re-parameterized von Bertalanffy growth function have preferred characteristics when modeling square growth in fish and that fixing age-at-length zero to pelagic larval duration is a preferable method to constrain growth models when lacking age-0 fish.