Abstract:
The food and feeding of red gurnard from the west coast, Golden and Tasman Bays of New Zealand is examined. Samples of fish stomachs were collected from two trawl surveys conducted on board the Fisheries Research vessel Kaharoa. The quantity of food consumed is determined by measuring the stomach fullness, the number of prey items consumed, and the volume of each food item. The composition of the diet is measured using the Index of Relative Importance (IRI) applied to ecological groups of prey species. Differences in food and feeding are rigorously quantified in relation to fish length and sex, sample depth, geographic area, and time of day. Bootstrapping and randomisation tests are used to determine 95% confidence limits and statistical significance levels of differences in IRI values within and between groups of fish. Mathematical modelling using a multiple regression technique is used to determine the relative importance of various factors on the measures of food and feeding. Both the analyses carried out for each factor separately, and the mathematical modelling confirm the main influences on red gurnard food and feeding. The stomach fullness of red gurnard changes significantly throughout the day, and also varies to a lesser extent between fish from different areas, and between fish of different lengths. The volume and number of prey items consumed are influenced primarily by fish length, and also by geographic area. This reflects the relationship of increasing prey item size with increasing fish size, and also the apparent availability of different sized prey items in different habitats. The overall diet of red gurnard is dominated by crabs, and the prey consumed indicate that red gurnard feed almost exclusively on prey species resident on, or buried within the sediment. The prey composition overall and within each of the ecological prey groups reflects changes in prey size preference between different sizes of red gurnard, and different availability of prey items between areas and depths. The trends in prey composition, size and number of prey items consumed, while showing that red gurnard peak in their feeding activity at around midday, also show that red gurnard do not feed during the period of darkness. There are no differences in food and feeding between male and female red gurnard.
