Food and feeding of small fish in the Rakaia River, New Zealand

Abstract

Benthic macroinvertebrates and fish species were collected at monthly intervals during a 12-month period, from 3 areas of the lower Rakaia River. The composition and abundance of the benthos and stomach contents of the fish were analysed for seasonal trends, food niche breadth and overlap between pairs of fish species, and overlap between the benthos and the diet of each fish species. The diets of bluegilled bully (Gobiomorphus hubbsi), upland bully (G. breviceps), juvenile longfinned eel (Anguilla dieffenbachii), Galaxias brevipinnis, G. paucispondylus, and juvenile brown trout (Salmo trutta) were similar to the proportions of prey species in the benthos. Deleatidium and chironomid larvae dominated the benthos in all seasons and formed the majority of food items in the diet of these species. Food niche overlap between these species was high, indicating potential competition, but preferred habitat and feeding habit differences plus low fish population density and abundance of main prey items probably eliminate the occurrence of any serious competition. The diet of the other fish species differed from this pattern. The common bully (Gobiomorphus cotidianus) ate proportionally more chironomid larvae and fish eggs than occurred in the benthos; torrentfish (Cheimarrichthys fosteri) ate proportionally more chironomid larvae than occurred in the benthos; and quinnat salmon (Oncorhynchus tshawytscha) depended largely upon prey species of terrestial origin, such as adult Deleatidium and dipterans.

Effects of hydraulic conditions and larval size on the microdistribution of Hydrobiosidae (Trichoptera) in two New Zealand rivers

“…Representatives of the caddisfly family Hydrobiosidae are widely distributed in rivers throughout New Zealand (Quinn & Hickey 1990) where they can be relatively abundant (e.g., Winterbourn 1978) and comprise important components in the diet of some fish (e.g., Sagar & Eldon 1983;Stephens 1989;Glova & Sagar 1991). The relatively high mobility of the larvae may enable them to adjust to rapidly changing hydraulic conditions in a river, and they might therefore be expected to exhibit strong relationships with hydraulic variables.…”

Prey selection by torrentfish,Cheimarrichthys fosteriHaast, in the Ashley River, North Canterbury, New Zealand

“…This is suggested by my finding that proportionally greater numbers of slow moving prey items, including Hydora, Pycnocentrodes, and chironomid larvae were consumed. Sagar and Eldon (1983) showed that torrentfish in the Rakaia River consumed chironomid larvae in far greater proportions than the larvae occurred in the benthos and indeed chironomid larvae dominated the diet numerically. In contrast, C. fosteri consumed proportionally fewer Deleatidium and Aoteapsyche larvae than were present in the benthos.…”

“…Although large C. fosteri did not consume a wide variety of prey items compared to small fish, they did ingest greater numbers of prey and to some extent larger prey items. Sagar and Eldon (1983) considered that most of the fish species inhabiting the Rakaia River were predatory, opportunistic feeders consuming prey items in similar proportions to their occurrence in the benthos. The results of my study in the Ashley River confirm their contention that the torrentfish is an exception.…”

“…Sagar and Eldon (1983) studied food and feeding of several fish species, including torrentfish, in the Rakaia River and concluded that C. fosteri was a selective feeder. They considered this to be a consequence of the fish's morphology.…”

Effect of the herbicide triclopyr on the abundance and species composition of benthic aquatic macroinvertebrates in the Ahuriri River, New Zealand

“…Aquatic invertebrates are the major food source of native river breeding birds (such as wrybills, terns, and stilts : Lalas 1977;Pierce 1982;Hay 1984) and are also important foods for native and introduced fish species (Sagar & Eldon 1983;McDowall 1990). Therefore, any large decline in invertebrate abundance may have flow-on effects for higher-order biota within the Ahuriri River system.…”