This report provides preliminary information on the biology and ecology of rainbow trout, Oncorhynchus mykiss, in highland streams of Papua New Guinea. The extent of success of its introduction and its implication on any future introductions of other coldwater fish species are discussed.
The relevance of trout to the Sepik River Fish Stock Enhancement Project (SRFSEP) is based on the fact that salmonid trouts were the first exotic fishes to be introduced to Papua New Guinea for the purpose of enhancing fish stocks (West & Glucksman 1976). Furthermore, a follow-on project based on recommendations given by SRFSEP and dealing with stocking higher altitude rivers in order to improve fisheries in highland areas commenced in March 1993 (FISHAID; see Coates 1992). The presence of rainbow trout (presumably the only salmonid species established) may have considerable implications for future stocking of other coldwater fish species recommended by SRFSEP and undertaken during the FISHAID project.
The objectives of the research of the project on which this report is based were:
to get information on previous trout stockings in Papua New Guinea.
to undertake a survey of the established trout population in the highland streams of Papua New Guinea (e.g. production, breeding habits, feeding, effect on other fish species).
From August 1991 to August 1992 a survey of the highland streams of the southern flowing Purari River was undertaken. A report on the general results on fish production/diversity from that work and background information on the Purari River has been produced (Povlsen 1993b). The part of the results concerning rainbow trout is the basis of this report. The exact sampling sites are listed in a separate report (Povlsen 1993a).
The sampling for rainbow trout concentrated on lower order streams of the upper Purari River catchment. This is the area where most of the stockings have taken place. Van Zwieten (1990) sampled lower order streams of Sepik/Ramu catchment and didn't catch any trouts.