Age, growth and feeding ecology of five co-occurring fishes in southern New Zealand
Information on the biology and ecology of fishes is essential for resource management. However, knowledge of the biology and ecology of some shallow reef fish around New Zealand is incomplete. For the need of better understanding of their biology and ecology, and improved fisheries management, this thesis presents the results of studies into the age, growth and the feeding ecology of five co-occurring species of fish at Karitane and Cape Saunders, southern New Zealand: blue cod (Parapercis colia), banded wrasse (Latris lineata), spotty (Notolabrus celidotus), moki (Latridopsis ciliaris) and trumpeter (Latris lineata). For each species, age and growth were estimated with respect to sex and geographical area. A significant difference in the growth of male blue cod was found between Karitane and Cape Saunders. Male blue cod were also found to reach a significantly larger size than females. A significant difference in growth of spotty was observed between sexes, whilst no significant difference between sexes was detected for banded wrasse, trumpeter and moki. areas. Whereas sex-specific growth may be related to reproduction, geographic variation in growth appeared to be a result of food availability. Seasonal differences in feeding intensity were observed, with higher feeding intensity coinciding with higher growth rate of fish in warm months. Dietary composition varied with season and site, reflecting food availability. In addition, fish also displayed ontogenetic variation in diet composition. Multivariate analysis showed that diet was more similar within species than between species. One-way ANOSIM permutation test showed that diet differed significantly between species. In each season, the mean dietary overlap between species was below 30%, indicating that fishes living together tended to partition rather than compete for their food resources. The mean dietary overlap was significantly higher within species (30- 60%), but still in the range of insignificant overlap. This thesis also examines the diet and growth of blue cod living on undisturbed biogenic reefs and on seabed modified by oyster dredging in Foveaux Strait. Whilst no significant site or habitat effects on feeding intensity were detected, habitat types significantly influenced dietary composition. Blue cod living on dredged habitats fed more on crustaceans than those on undisturbed habitats. Blue cod from biogenic reefs also displayed a more diverse diet than those taken from dredged habitats. In addition, prey diversity (Shannon-Wiener index) increased with increase of fish size. Apart from effects of dredging on the diet of blue cod, the long-term oyster fishery also appears to affect the early growth of blue cod. A causal relationship between the difference in diet and that in the early period of growth is thus possible. The present findings suggest that management measures need to take into consideration geographic differences in fish growth. In addition, fisheries management should take account of trophic interaction, as co-occurring fishes interact through predation, and partition resources along trophic, temporal and spatial gradients. The detection of the impact of oyster dredging on the diet and growth of blue cod suggests that biogenic reefs are important habitats for reef species, particularly for young fish. Hence, such habitats may need to be protected from damage by bottom fishing gear, such as oyster dredging.
Advisor: Probert, Keith; Wing, Steve
Degree Name: Doctor of Philosophy
Degree Discipline: Marine Science
Publisher: University of Otago
Research Type: Thesis
x, 340 leaves :ill. (some col.) ; 30 cm. Includes bibliographical references. University of Otago department: Marine Science