Size characteristics and diet of emergent chinook salmon in a small, stable, New Zealand stream

Abstract

The emergence timing, quality and diet of chinook salmon, Oncorhynchus ishawyrschn, fry were studied as they emerged from ten natural redds. The impact of selected environmental factors on emergence was studied also. Samples of fry were obtained daily using redd traps.The mean period of total emergence for redds with more than 450 fry emerging was 44.8 days (range 25-57 days), but for 80% of the fry in each redd to emerge the mean time elapsed was 10.8 days (range 6 21 days). No fry sampled had a visible yolk sac. The effect oftemperature and light on emergence timing was weak, but stream flow had a strong influence. Fry length was constant for each redd throughout emergence, but fry weight tended to decline; consequently condition factor declined also. There was evidence that fry fed before emergence, but they did not grow. The major prey item. Deleatidium spp. (47.4% of the contents of all stomachs sampled), was the most abundant invertebrate in stream benthos and drift. Empty stomachs were prevalent at the start of emergence, with full stomachs becoming more common as emergence progressed.The time distribution of numbers of fry emerging was usually unimodal, but occasionally bimodal. Over one third of fry emerged during the best 2 days of sampling.

Microhabitats and diel downstream migration of young grayling (Thymallus thymallm L.)

“…In accordance with previous studies, we have considered the influence of discharge (MacCart, 1967;CampbeU & Scott, 1984;Irvine, 1986;Heggenes, 1988a) and of moonlight, although moon influence has only been revealed with a seasonal rhythm (Mason, 1975;Unwin, 1986;Field- Dodgsoti, 1988). Discharge varied during a trapping session only on 19 April, and flow increased only at 06:()0, i.e.…”

Feeding pattern and diet of first feeding brown trout fry under natural conditions

“…These studies demonstrate that the alevins are able to feed before emergence if food is available. Indications of feeding before emergence have also been reported from some field‐studies, as food was found in the stomachs and intestines of newly emerged fry of both Atlantic salmon (Gustafson‐Marjanen & Dowse, 1983) and chinook salmon Oncorhynchus tshawytscha (Walbaum)(Field‐Dodgson, 1988). While the authors of both these studies argued that the fry probably had fed before emergence, Williams (1981) found little evidence for this in his studies of Atlantic salmon and brook trout Salvelinus fontinalis (Mitchill) in Matamek River in Quebec, since newly emerged fry were observed to have little material in their lower intestines compared to older juveniles.…”

“…In this way the alevins may save yolk reserves for periods when external food sources are temporarily limited. It has also been suggested that precocious feeding can have a positive effect by giving the fry practice in taking food particles, thereby giving the fry experience to feed more efficiently when external food becomes nutritionally necessary, or for building up intestinal enzyme activity (Heming et al ., 1982; Field‐Dodgson, 1988). No such effect was found by Heming et al .…”

“…Emerging chinook salmon fry in a small stream in New Zealand were found to feed mostly on ephemeropteran larvae ( Deleatidium spp.) but chironomid and other dipteran pupae were also represented (Field‐Dodgson, 1988). Williams (1981) noted that brook trout fry would attack any moving particle that came along, but rejected items that were inedible.…”

Emergence chronology of brook charr,Salvenus fontinalis, alevins in an acidic stream

“…Peak emergence of brook charr alevins as the spring freshet receded was suggested by White (1930). Indirect evidence that alevin emergence was related to stream discharge was also presented for chinook salmon by Field-Dodgson (1988).…”