Demography of parrotfish: age, size and reproductive variables
Barba, Jacquelyn (2010) Demography of parrotfish: age, size and reproductive variables. Masters (Research) thesis, James Cook University.
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Abstract
This thesis examined variation in demography and life history traits of scarine labrids across broad (across 27˚ latitude) and local (10-100's of kilometre) scales, as well as to what extent fishing had an influence. Eight parrotfish species were initially examined at a local level (GBR) to interpret differences in growth using an age-based approach. From this preliminary analysis parrotfish were then classified into two groups according to their growth pattern, indeterminate and asymptotic. This analysis revealed growth to be associated with other essential life history traits such as: growth, longevity and maturity. Next, a more detailed look was taken for five species on the GBR to examine variation at a local scale. For large parrotfish species, Chlorurus microrhinos, no differences in growth and life span were found between populations from mid and outer shelf reefs. However, for all small parrotfish species, populations from outer reefs had significantly reduced growth rates and shorter life spans. These results suggested that there will be short term changes in growth patterns depending on the habitat in which individuals will recruit into. Comparison of reproductive parameters, age and size at maturation and sex change, revealed earlier maturation and sexual transformation occurred in populations from outer shelf reefs. Timing of both maturation and sex change was not only driven by how long an individual lived or how big they are, but by reproductive behavior. Two species, Chlorurus sordidus and Scarus psittacus were then used to address in more detail other drivers on life history variation. First, the demography and life history of both species was compared at a broad (geographic) scale between Guam and the GBR. Broad scale variation is generally explained by the temperature size rule, however in both species growth, life span and reproductive parameters were reduced at Guam locations (higher latitudes) compared to GBR locations (lower latitudes). Second, the potential impacts of fishing on demographic characteristics of both species were examined. Populations of both C. sordidus and S. psittacus from fished areas represented reduced growth, shorter life spans, earlier maturation and earlier sex reversal. However, this variation was minimal when compared variation in similar traits occurring at a local scale.