Mountain Headwater Streams Research Articles

Sex-biased dispersal in a salmonid fish.

We tested the hypothesis that dispersal is sex biased in an unexploited population of brook trout, Salvelinus fontinalis, on Cape Race, Newfoundland, Canada. Based on the assumptions that trout are promiscuous and that reproductive success is limited primarily by either number of mates (males) or fecundity (females), we predicted that males would disperse greater distances than females. We also tested the hypothesis that trout populations comprise stationary and mobile individuals, predicting that males have greater mobility than females. Based on a mark-recapture study of 943 individually tagged fishes, 191 of which were recaptured over 5 years, we find strong support for our hypothesis of male-biased dispersal in brook trout. Averaged among all 11 resampling periods, males dispersed 2.5 times as far as females; during the spawning period only, male dispersal exceeded that by females almost fourfold. Both sexes were heterogeneous with respect to movement, with a lower incidence of mobility among females (29.6%) than males (41.1%); mobile males dispersed six times further than mobile females. We conclude that this sex bias reduces mate competition among male kin and decreases the probability that males will reproduce with related females.

Trophic relationships and food webs of the benthic invertebrate fauna of two aseasonal tropical streams on Bougainville Island, Papua New Guinea

ABSTRACTThe trophic ecology of Konaino Creek, a small mountain headwater stream draining rainforest in the aseasonal tropics on Bougainville Island, Papua New Guinea, was examined and a food web was constructed. The major source of energy in Konaiano Creek was allochthonous detritus, most of which had been terrestrially degraded to fine particulate organic matter rather than entering the stream as leaf litter. This fine detritus was collected by the filter-feeders (mostly Simuliidae and also Hydropsychidae) which formed the dominant functional feeding group (64.4% of the fauna). Thus filterers processed most of the allochthonous detritus and made the energy available to other trophic levels, rather than shredders (1.7% of the fauna) which perform this role in temperate headwater streams. Collector-gatherers made up 22.7% of the fauna, carnivorses, mostly Odonata, Decapoda (crabs) and Hydrobiosidae, comprised 2.8% of the fauna and grazer-scrapers made up 7.4%. The latter were inhibited by low instream production owing to heavy shading and the instability and abrasion of the substrate due to frequent spates. In comparison, the trophic ecology of the nearby, coastal, Bovo River (with a catchment mainly in rainforest but mostly cleared with introduced species at the study site) was quite different and it was dominated by collector-gatherers (74%) and grazer-scrapers (15%).

Decomposition of Rainbow Trout (Oncorhynchus mykiss) Carcasses in a Forest Stream Ecosystem Inhabited only by Nonanadromous Fish Populations

The overall dynamics of rainbow trout (Oncorhynchus mykiss) carcass decomposition in a woodland stream ecosystem was examined in two experiments conducted in the West Fork of Mink Creek, Idaho: one during winter–spring (mean water temperature 4.2 °C) and one during summer (mean water temperature 8.6 °C). Relative weight loss (%AFDW) from fish during both periods was essentially constant. In spring, mean daily loss per day was 1.5%. Although this rate is comparable with the decay of high-quality ("fast") leaves, it took much longer than expected (> 120 d) for the even higher quality fish protein. In summer, decay was more rapid (4.9%/d) and was completed in less than half the time (~50 d). Most decay appeared to progress from inside the carcasses outward to the skin. The skin remained intact throughout most of both experiments. Nutrients leached from the fish appeared to be utilized rapidly by microbes associated with the carcass, since no stimulation of algal growth occurred immediately downstream of the carcasses. This suggests extremely tight nutrient spirals and high nutrient retention in Mink Creek and other comparable Rocky Mountain headwater streams.

Production and Habitat of Threatened Greenback and Colorado River Cutthroat Trouts in Rocky Mountain Headwater Streams

Abstract Field studies conducted in 1979 and 1980 to assess the production and habitat of cutthroat trouts Salmo clarki in three headwater tributaries in north-central Colorado yielded the following estimates of production (g/m2): Greenback cutthroat trout S.c. stomias in Roaring Creek, 3.3 in 1979 and 2.3 in 1980; greenback cutthroat trout in the Right Hand Fork of Roaring Creek, 3.6 in 1979 and 1.5 in 1980; Colorado River cutthroat trout S.c. pleuriticus in Little Green Creek, 2.2 in 1979 and 3.6 in 1980. Biomass and production in Roaring Creek and Right Hand Fork of Roaring Creek were dominated by old (≥3 years) slow-growing fish. Little Green Creek was the warmest and slowest moving of the creeks studied and had a low diversity of substrates dominated by fine and coarse gravel–it also had the highest biomass and production of young of the year. Right Hand Fork Roaring Creek had faster flows and more extensive undercut banks–it also had the most large fish (≥152 mm long). Biomass and production of cutt...