Dietary and spatial overlap between stream populations of a native and two introduced fish species in New Zealand

Abstract

Benthic and drifting invertebrates as well as fish were sampled in a lake-inlet stream over a 24-h period in summer in order to investigate interactions for food and space between a native fish species (Galaxias brevipinnis, Galaxiidae) and juveniles of two exotic fish species (Salmo trutta and Oncorhynchus mykiss, Salmonidae) in New Zealand. Galaxias brevipinnis fed almost exclusively at night on the benthos, whereas both trout species fed mostly during the day on drifting and benthic prey. Larvae of Deleatidium (Ephemeroptera), Hydrobiosis and Oxyethira (Trichoptera), and Austro-simulium and Chironomidae (Diptera) were the major prey in the diets of all three fish species. Small prey made up a greater proportion of the diet of G. brevipinnis than for either trout species. All three species of fish were found primarily in riffles and runs in water depths of 0.1-0.3 rn, with G. brevipinnis frequently being in faster-flowing areas (water velocity 0.8-1.1 m s-1) than was either trout species (water velocity 0.4-0.7 rn s-1). These differences in pattern of die1 feeding and micro- habitat use no doubt lessen the interaction between the galaxiid and salrnonid fish species.

Prey availability and diet of juvenile brown trout (Salmo trutta) in relation to riparian willows (Salix‐spp.) in three New Zealand streams

“…Size selection of prey has also been demonstrated in wild fish (Glova & Sagar 1991, 1993Glova et al 1992), and in the laboratory (Ringler 1979), so prey size may well be the most important factor affecting prey vulnerability to drift-feeding brown trout.…”

“…The total abundance and biomass of benthic invertebrates were also greater in most willowed than non-willowed sections of these streams, as were the abundance and biomass of several invertebrate taxa. In New Zealand, juvenile brown trout have been shown to feed selectively on particular macroinvertebrate taxa and sizes of prey (Glova & Sagar 1991, 1993Glova et al 1992). Therefore, the objectives of the present study were to determine quantitatively differences in abundance and biomass of potential prey associated with the density of riparian willows, compare the foods consumed by juvenile brown trout in willowed and non-willowed sections of streams, and assess whether juvenile brown trout show consistent preferences for particular macroinvertebrate taxa.…”

The influence of juvenile brown trout (Salmo trutta)on habitat use of inanga(Galaxias maculatus)in a stream simulator

“…There have been various reports of trout diet overlapping with that of galaxiids in New Zealand, and suggestions that competition for food may partly explain the incompatibility of some galaxiids and trout (Cadwallader 1975;Glova & Sagar 1991;Kusabs & Swales 1991). However, McDowall (2003) suggested that there might be complex interactions between stream dwelling galaxiids and trout, and that the intensity of trout predation on fish and invertebrates may result in galaxiid populations being food limited.…”

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.…”