Otolith-based assessment of recruitment variation in a North Pacific seamount population of armorhead Pseudopentaceros wheeleri

Abstract

An investigation into armorhead Pseudopentaceros wheeleri recruitment variation at Southeast Hancock Seamount (in the central North Pacific) focused on the examination of recruit characteristics, primarily those derived from otolith-increment analysis. Otoliths from recruits were sampled from years representing relatively strong (509 metric tons (t) in 1980), moderate (58 t in 1986), and weak (1 t in 1989) recruitment biomass. Recruit body length was also examined among these 3 years and from 10 additional years, providing even higher recruitment contrast. Transverse sections of sagittal otoliths were prepared, and yielded information on the mean and variability in pre-recruit pelagic duration and increment-width profiles. Mean length of female recruits, and to a lesser extent of mean pelagic duration, decreased with increasing recruitment strength. Although generally similar in shape, the mean increment-width sequence spanning the first 1.8 yr of the 2+ yr pelagic phase differed among recruit years. Transitions in sequential increment-width (inflection points) were exhibited among all recruit years and occurred primarily within the first pelagic year interval. The weak 1989 recruit year was most distinct among recruit years in exhibiting lower incre- ment widths at each of these inflection points.