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Variation in age compositions and growth rates of Acanthopagrus butcheri (Sparidae) among estuaries: some possible contributing factors
Sarre, G.A.; Potter, I.C. (2000). Variation in age compositions and growth rates of Acanthopagrus butcheri (Sparidae) among estuaries: some possible contributing factors. Fish. Bull. 98(4): 785-799
In: Fishery Bulletin. US Government Printing Office: Washington, D.C.. ISSN 0090-0656; e-ISSN 1937-4518
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| Abstract |
Age compositions and growth rates have been determined for populations of Acanthopagrus butcheri in four estuaries and a saline, coastal lake, all of which differ markedly in their morphological, physicochemical, and biotic characteristics. Because the opaque zones in otoliths were shown to form annually, the number of these zones could be used to age individual fish. However, the otoliths of fish that were more than six years old had to be sectioned in order to consistently reveal all opaque zones. The number of annuli on scales did not provide reliable estimates of age. Acanthopagrus butcheri, which typically completes its life cycle in estuaries, was represented in each of the five water bodies by fish >15 years old and lengths and weights >365 mm and >860 g, respectively. The maximum length and weight of A. butcheri recorded in any of the five water bodies were 485 mm and 2196 g, respectively. The values for L in von Bertalanffy growth equations differed significantly between females and males in three of the four estuarine populations (P<0.001 or <0.01), whereas those for both k and to differed significantly between the sexes in only one population and then only at P < 0.05. The values for k and L in the von Bertalanffy growth equations differed significantly among both females and males in the four estuaries at either P < 0.001 or P < 0.05. These parameters also differed significantly between the males in Lake Clifton and the males in each estuary, except the Swan River Estuary. Growth rates in two of the more northern water bodies were greater than those in the two southern and cooler estuaries. The pattern of growth in the Moore River Estuary, as reflected by changes in length with time, differed from that in the other four water bodies in that it was initially slower and subsequently did not show such a marked tendency to form an asymptote. The slow initial rate of increase in length in the Moore River Estuary may be related to particularly high densities of juvenile A. butcheri in nearshore, shallow water, as well as to a relatively lower abundance of appropriate food or very low salinities, or to both of the latter. The percentage contribution made by fish >5 years was the lowest by far in the Swan River Estuary, which was subjected to the greatest fishing pressure. |
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