Browsing Irish Fisheries Bulletin by Author "Nixon, J. J."
Salmonid carrying capacity of streams in the Connemara region, a resource appraisalFahy, E.; Nixon, J. J.; Murphy, M.; Dempster, S. (Department of Fisheries and Forestry, 1984)Standing crops of salmonids in the Connemara region are described from 80 site fishings made between March 1982 and May of the following year. Trout were more widely distributed than salmon, being able to exploit isolated water bodies as resident populations. High salmonid densities were associated with salmon which during the dry summer months were caught in large numbers on riffles. The smallest streams in the region supported only trout presumably because there was insufficient depth of water to permit the entry of salmon. Trout biomass and density within the region were distributed within the lower range reported from a number of countries in which brown trout are endemic and naturalised. Low saimonid densities at 16% of sites were in some cases associated with the rooting of angiosperms, and possibly oligotrophic conditions resulting from geological structure. Length at age of salmon and trout was similar to measurements recorded in Britain. The streams were important only for the first year of the trout life cycle. Because trout move downstream as they grow, occupying lakes during the later parr phase, and the entire streambed area in Connemara is one fortieth of the lake area, space is unlikely to be a critical constraint on the later parr phase. The condition of the stream substratum may be a factor in the production of sea trout; where loose gravels do not occur in shallow nursery streams, the catchments tend towards producing "brown" or "resident" rather than sea trout.
Spawning Trout in Eastern ConnemaraFahy, E.; Nixon, J. J. (Department of Fisheries and Forestry, 1982)Concentrations totalling 299 trout from nine spawning sites in eastern Connemara in 1981 were examined to elucidate the spawning biology of these stocks. Sea trout made up the majority. Brown liveried fish predominated among migratory males (75%) but were few among females (2.5%). Males were of younger sea and river age than females and the ratio of females to males was lowest among the younger age categories. Scars and marks were evenly distributed between the sexes and 51% of females showed signs of being spent. Spawning Connemara sea trout were similar to spawning Cummeragh, Co. Kerry, sea trout in a number of, respects as for example their length at age but the spawning behaviour of fish in the two places differed considerably: the density of spawning fish was greater in the Cummeragh than in Connemara where immature trout occurred in the vicinity of the redds. The ratio of females to males was lower in Connemara than in the Cummeragh and males appeared to be more heavily marked in Connemara. The relevance of these observations to some known genetic characteristics of the stocks is briefly discussed.