Aquacutture and Fisheries Management 1993, 24, 791-796 SHORT COMMUNICATION Survival of salmon, Salmo salar L., eggs planted in upland streams M. KELLY-QUINN, D. TIERNEY & J. J. BRACKEN Zoology Department, University College Dublin. Republic of Ireland A major national study on the possible impacts of coniferous afforestation on salmonid streams was initiated in Ireland in 1990. The work in Co. Wickiow, on the east coast (Fig. 1), involved an extensive biological and hydrochemical study of 33 poorly buffered headwater streams. Part of the work also involved monitoring the survival of artificially planted salmon eggs. Brown & Sadler (1989) in a literature review of field and laboratory studies concluded that salmonid eggs and juveniles are the life stages which are most sensitive to low pH values in riverine habitats. Experiments commenced in December 1991. Six study sites were selected (Fig. 1). Table 1 lists the characteristics of each site. All streams were upland, fast flowing, typical salmonid nursery waters. Vibert boxes were constructed to a design described by B.R.S. Morrison (personal communication). Each box was slightly modified to include a secure screw-cap which also facilitated faster handling during loading and later examination of the eggs. The Vibert boxes were placed in groups offiveat a depth of approximately 10cm below the gravel surface. Freshly fertilized salmon eggs (green eggs) were obtained in mid-December and were planted in sites 1,2,3 and 4. Twenty boxes were used at each site to allow for four 'lifts' during incubation. Towards the end of January 1992 eyed ova were also obtained and planted at the above sites as well as at two other locations, sites 5 and 6. Only one batch offiveboxes was used at sites 1,3 and 4. At sites 2,5 and 6, three batches offiveboxes were used. The eggs were obtained from ranched salmon, offspring of wildfishfrom the Burrishoolefisheryin the west of Ireland. The green eggs were taken from five hens. The eyed eggs were a random mix of 'shocked' eggs from a larger number of fish. Thirty eggs were placed in each Vibert box together with a small amount gravel. Many of the upland streams in this area experience a depression in pH value when water levels are high. From early January to the end of March checks on survival of ova were carried out to coincide with these 'acid events'. By late March the hatch of alevins was complete. Recovery from low pH often occurs within a few hours with the result that minimum pH values can easily go undetected. To overcome this possibility automatic Sigma 800SL water samplers, programmed to collect hourly samples, were installed at sites 1 and 2. At the remaining sites water samples were collected at the peak of the flood. Results are presented in Table 2. The highest survival value (75%) was obtained at site 3. Reasonably good survival was also recorded at sites 4 and 5. Survival at the remaining sites Correspondence: Dr J.J. Bracken, Department of Zoology, University College Dublin, Belfield, Dublin 4, Republic of Ireland. 791