The ecology of brown trout Salmo trutta in English chalk streams

Abstract

SUMMARY. .1. Chalkstream trout are fast‐growing, short‐lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro‐habitat distributions between fish species.4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly‐emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearling trout.