published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

Abstract not available

During the last three decades of coral reefs studies, the large areal coverage of data derived from satellite images has increasingly been used to complement the more detailed but spatially limited data produced by conventional fieldwork. Continuous improvement in sensor capabilities, along with the development of increasingly refined methods for image processing, has lead to ever more accurate maps of physical and biological variables of importance to reef ecology. During the same period, an abundance of field studies have documented statistical relationships between aspects of the reef habitat and its fish community. Despite numerous stochastic influences, such as spatially concentrated and temporally variable fish recruitment pulses or the selective and patchy mortality caused by fishing, several aspects of habitat have been shown to significantly influence the fish community. Fortunately the most important of these, water depth, the structural complexity of the reef, and the cover of live coral, are possible to estimate from currently available satellite imagery. The research presented in the following pages has combined the statistical relationships between the fish community and its habitat with the capability of satellite imagery to map that habitat, thereby answering the research question: How can remote sensing be used to map coral reef fish communities? In the process, a set of new techniques for predictive modeling of complex relationships have been compared, the influence of a range of habitat variables on the fish community quantified, the spatial scales at which the fish-habitat relationships are strongest have been explored, and new methods for deriving estimates of some aspects of the coral reef habitat from satellite imagery have been developed. The results presented in this thesis thus contribute to the further understanding of fish-habitat relationships, while providing a template for producing spatially explicit predictive models of fish community variables. This is not only of scientific interest, but also of substantial value to the conservation community that tries to protect the world’s remaining healthy coral reef ecosystems, and their fish communities, from an array of man-made influences.

During the last three decades of coral reefs studies, the large areal coverage of data derived from satellite images has increasingly been used to complement the more detailed but spatially limited data produced by conventional fieldwork. Continuous improvement in sensor capabilities, along with the development of increasingly refined methods for image processing, has lead to ever more accurate maps of physical and biological variables of importance to reef ecology. During the same period, an abundance of field studies have documented statistical relationships between aspects of the reef habitat and its fish community. Despite numerous stochastic influences, such as spatially concentrated and temporally variable fish recruitment pulses or the selective and patchy mortality caused by fishing, several aspects of habitat have been shown to significantly influence the fish community. Fortunately the most important of these, water depth, the structural complexity of the reef, and the cover of live coral, are possible to estimate from currently available satellite imagery. The research presented in the following pages has combined the statistical relationships between the fish community and its habitat with the capability of satellite imagery to map that habitat, thereby answering the research question: How can remote sensing be used to map coral reef fish communities? In the process, a set of new techniques for predictive modeling of complex relationships have been compared, the influence of a range of habitat variables on the fish community quantified, the spatial scales at which the fish-habitat relationships are strongest have been explored, and new methods for deriving estimates of some aspects of the coral reef habitat from satellite imagery have been developed. The results presented in this thesis thus contribute to the further understanding of fish-habitat relationships, while providing a template for producing spatially explicit predictive models of fish community variables. This is not only of scientific interest, but also of substantial value to the conservation community that tries to protect the world’s remaining healthy coral reef ecosystems, and their fish communities, from an array of man-made influences.

Juvenile reef fishes often have a color pattern different from that of adults. It has been theorized that this reduces the aggression received by juveniles from adult conspecifics. This was tested using two species of Labroides cleaning wrasses in which certain-sized individuals can quickly shift back and forth between the adult and juvenile color patterns. Adult Labroides phthirophagus has the same single-male grouping social structure as previously described for L. dimidiatus. Small L. phthirophagus and L. dimidiatus in juvenile coloration shifted to adult coloration when isolated and then quickly shifted back to juvenile coloration when chased by an adult conspecific female. In L. phthirophagus the adult females attacked small cleaners more frequently when they displayed the adult color pattern, indicating that juvenile coloration gives some protection from conspecific aggression. Two other species oflabrids, Thalassoma duperrey and Coris gaimard, showed the ability to shift back to juvenile coloration when aggression was received from con specific adults, although the shift was not nearly as rapid as seen in Labroides species. Dascyllus albisella and Zebrasomajlavescens, common reef fishes, preferred to solicit cleaning (by posing) from the adult-colored L. phthirophagus, indicating that some hosts prefer the adult color pattern. Small L. phthirophagus shifted to adult coloration more quickly when starved than when provided with host fish on which to feed, indicating that the coloration shift is motivated by hunger. Even though juvenile coloration in some fishes may reduce the aggression received from adults, in cleaner wrasses it also reduces food availability, making it advantageous for them to shift to adult-coloration as soon as possible. Cleaner wrasses have developed a quick, reversible coloration shift that allows changing to adult coloration at a small size but allows reversing coloration if too much aggression is received. / x, 59 leaves, bound : ill., maps ; 29 cm.

Thesis (Ph.D.) - James Cook University, 2004. / Typescript (photocopy). Bibliography: leaves 195-202.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2006. / Advisor: Joseph Travis, Florida State University, College of Arts and Sciences, Dept. of Biological Science. Title and description from dissertation home page (viewed June 13, 2006). Document formatted into pages; contains xvi, 160 pages. Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Carpenter, Argyrozona argyrozona (Valenciennes, 1830), is an endemic South African sparid fish. They form an important component of the commercial linefishery on the South African east coast, where they are the third most important species landed. Recent investigations revealed that the catch per unit effort (cpue) of this species has declined markedly since the early 1900’s. Despite these declines and the importance of this resource, remarkably little biological information on this species exists for providing management advice. This thesis investigates the life history of carpenter, particularly those aspects that are used for management. This includes an investigation into the stock distribution and identification of nursery areas, and an assessment of age, growth, reproduction and movement patterns. Age and growth was assessed using methods based on both otoliths and mark-recapture. Transverse sagittal sections from the Tsitsikamma National Park showed clear opaque and translucent growth increments. Marginal growth zone analysis and mark-recapture of chemically tagged fish (Oxytetracycline) revealed that these were deposited on an annual basis: opaque in summer and translucent in winter. A. argyrozona were found to be long lived (up to 27 years) and slow growing. Within reader (between counts) and between readers average percent error (APE) was 5.3 and 1.8, respectively, showing that readability of carpenter otoliths is high. Comparison between whole and sectioned otoliths showed that the former significantly under-estimated the age of fish older than 10 years (p<0.01). A large proportion (68%) of the individual growth rates derived from mark-recapture data were below those predicted by the otolith based von Bertalanffy growth model (p<0.01). This was attributed to the negative influence of external tags, as hydroids, frequently occurring on the tags of recaptured fish, were observed to cause severe lesions and in some cases, extensive fin damage. This brings into question the use of mark-recapture studies to calculate growth of some species. The effects of sampling design and sample size on age and growth estimation were assessed. The minimum sample size required to accurately estimate growth and mortality, and the effects of using either random or stratified sampling procedures were tested. Decimal and integer ageing both produced similar estimates of von Bertalanffy growth parameters, growth curves, spawner biomass-per-recruit (SB/R) and fishing mortality (F) estimates. Sampling monthly throughout the year and collecting data in a single large sample provided similar growth curves, von Bertalanffy, F and SB/R estimates. The data showed that estimates based on less than 300 random samples were unreliable. However, accurate growth parameter estimates were achievable with less than 200 samples if the sample was stratified with 10 or more samples per 2 cm size class. An investigation into the reproductive biology of A. argyrozona within the Tsitsikamma National Park revealed that they were serial spawning late gonochorists. The size at 50% maturity (L₅₀) was estimated at 292 and 297 mm FL for females and males, respectively. Both monthly gonadosomatic indices and macroscopically determined ovarian stages strongly suggest that A. argyrozona within the Tsitsikamma National Park spawn in the austral summer between November and April. The presence of post-ovulatory follicles (POF's) confirmed the six month spawning season, while monthly proportions of early (0-6 hour old) POF's showed that spawning frequency was highest (once every 1-2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature (r = -0.161), the daily proportion of spawning fish was strongly correlated (r = 0.93) to ambient temperature over the range 9-22⁰C. Both spawning frequency and season increased with fish length. As a result of the allometric relationship between annual fecundity and fish mass a 3 kg fish was calculated to produce 5 fold more eggs per kilogram of body weight than a fish of 1 kg. In addition to producing more eggs per unit weight each year, larger fish also produce significantly larger eggs. Adult emigration and larval dispersal of A. argyrozona from the Tsitsikamma National Park (TNP), South Africa, were investigated using mark-recapture data and Acoustic Doppler Current Profiler measurements of currents. Tagging data showed that adult carpenter were mainly resident, with a small proportion (7%) leaving the TNP in both easterly and westerly directions. No relationship was found between fish movement patterns and fish size or time-at-liberty. Current patterns suggest that eggs and larvae spawned within the TNP are mainly transported eastwards towards established nursery grounds; the median estimated distance moved was 299 km (range 42-561 km) in 30 days (time to flexion). Given this pattern of ichthyoplankton dispersal together with the fact that adult carpenter within the TNP display a high degree of residency and that they are much more abundant than in adjacent fishing grounds (cpue = 23 times greater), it appears that the TNP protects a viable carpenter spawner population capable of seeding adjacent fishing grounds. Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of A. argyrozona distributed along the South African continental shelf. Two distinct areas of abundance were determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Two distinct nursery areas were identified. These data suggest that in each area juvenile A. argyrozona settle and move inshore, and then move offshore as they grow. Otolith readability and growth rates varied between regions, with fish from the Eastern Cape having the lowest average percentage error and the slowest growth rates, readability decreased westward. L₅₀ varied between the central and eastern Agulhas Bank as did mass at length. Based on the distribution of carpenter, variability in otolith readability, mass at length, variation in growth and size at maturity, it is concluded that carpenter exist as two separate stocks, one on the central Agulhas Bank and the other on the eastern Agulhas Bank. SB/R, fecundity-per-recruit (Egg/R) and yield-per-recruit (Y/R) models were used to model both South African carpenter stocks. Owing to the allometric relationship between annual fecundity and individual size, Egg/R ratios were between 40 and 74% of SB/R at equivalent F. Egg/R ratios account for allometric increases in fecundity with size/age, and are therefore regarded as more accurate estimates of reproductive potential, and biological reference points for per-recruit analysis should wherever possible be based on this quantum. It is shown that the current length at first capture (lc) (250 mm TL) and F (at M = 0.1) will reduce Egg/R to 6.41% of the pristine value in the Eastern Cape and between 6.06 and 14.15% on the central Agulhas Bank, indicating that both stocks are heavily over exploited. An increase in lc from 250 to 350 mm TL and a 70% reduction in commercial fishing effort is recommended to attain a target reference point of 40% Egg/RF=0. Bag frequency analysis indicates that a reduction in daily bag limit from 10 to 4 fish.person¹.day⁻¹ would effect an equivalent reduction in recreational F. The trawl bycatch of carpenter is only 3% of the reported line catch, consequently restrictions to this fishery are not recommended.