Studies in Stream Life in Tributaries of the Welsh Dee

This study attempts to investigate the fauna of some streams of the Dee river system in Wales, with reference to seasonal variation, food cycles and the available food for the fish population. The field work, apart from preliminary summer samples, extended from September I946 to July I947, and involved quantitative studies of the lithophilic fauna in two streams, the Ceirw and the Merddwr, amplified by general collections from various habitats. The gut contents of many forms were investigated and considered in relation to mode of feeding and the'constitution of the microscopic planktonic and benthic fauna and flora. Many of the earlier investigations on the benthic fauna of running waters, both continental and American, are cited by Carpenter (1928) and by Welch (I935). In Britain, the main general surveys of unpolluted waters are those of Carpenter (I 927), Percival & Whitehead (I 929, I930), Butcher, Longwell & Pentelow (I937) and Jones (94I, I943, I948). Edmonds (I939, unpublished) made an extensive study of the plankton of the Dee, and some observations on the benthos. The chief seasonal quantitative surveys deal with the fauna of a chalk stream (Whitehead, I935), and of submerged mosses (Frost, 1942). Neill (1938) discusses the fauna of the Scottish Don quantitatively in relation to the food of brown trout. The food of salmon parr has been considered in relation to available fauna of the Eden and Thuirso (Allen, 194I) and the Welsh Dee (Carpenter, I940). 2. METHODS