MEPS 136:25-35 (1996)  -  doi:10.3354/meps136025

Response of herbivorous fishes to crown-of-thorns starfish Acanthaster planci outbreaks. III. Age, growth, mortality and maturity indices of Acanthurus nigrofuscus

Hart AM, Russ GR

Age, growth, mortality and maturity indices of Acanthurus nigrofuscus were examined as part of a larger study investigating a long-term response of herbivorous reef fish to crown-of-thorns starfish (COTS) outbreaks. The principal objective was to compare otolith growth, mean age and size, growth, mortality, size-at-age, size-at-maturity, and age-at-maturity of A. nigrofuscus between 2 COTS affected (Yankee, Dip) and 2 non-affected reefs (Bowl, Coil). All reefs were exposed, outer shelf reefs in the central section of the Great Barrier Reef. Additionally, these demographic parameters were also established at 2 mid-shelf reefs (Grub, Centipede). This species is relatively long-lived with the oldest specimen aged at 25 yr. Mean age at each reef ranged from 5.4 to 9.5 yr, while average size ranged from 16 to 12 cm. Mean size and size-at-age was significantly larger on COTS impacted reefs, evidence which supports the hypothesis of a response to increased food resources. There were also significant differences in size-at-age between reefs within a COTS status. No differences in mortality between reefs was detected, while age-at-maturity was 2 yr at all reefs. Size-at-maturity was 13 to 14 cm on mid-shelf reefs Grub and Yankee, in contrast to 10 or 11 cm on outer shelf reefs Yankee, Bowl, Dip and Coil. Importantly, age validation provided 5 response variables (otolith growth, mean age, somatic growth rates, size-at-age, age-at-maturity) which were used to examine the effects of ecological disturbance on the population biology of reef fish. This further illustrates the usefulness of age validation studies for coral reef fish.

Acanthaster planci . Acanthurus nigrofuscus . Age . Growth . Mortality . Response variables

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