Scottish Marine and Freshwater Science Vol 6 No 5: Ranching to the rod: an evaluation of adult returns from hatchery-reared Atlantic salmon smolts released in Scottish rivers

Results

Rod-caught recaptures from hatchery-reared smolts

The release of 90,073 tagged smolts into four river catchments over a twelve year period resulted in 48 tagged adult fish reported caught by anglers in the river of release (Table 1). Most recaptures (42) were caught as 1 SW fish with the remainder (6) caught as two-sea-winter (2 SW) fish (Table 1).

There was considerable variation between rivers and years with the best returns recorded from releases on the Dionard (1992) and Tay (1997), when each rod-caught salmon was generated by the release of c. 450 smolts. In contrast, zero returns were recorded on five occasions on three different rivers (Table 1). Overall, combining both sites and years, each rod-caught fish that was reported required the release of c. 1800 hatchery-reared smolts.

Table 1. Rod-caught recaptures from tagged hatchery-reared smolts released in four Scottish rivers between 1987 and 2000. Recaptures from the Tay are represented by two periods: before (1991-94) and after (1996-98) commercial netting in the river ceased.

Return rates from comparative releases

The percentage return rates of both wild and ranched salmon smolts differed between years and release sites and therefore are considered as within-year, within-site comparisons (Table 2). In all paired tests wild-reared smolts gave higher return rates than hatchery-reared smolts. In cases where there was at least one returning hatchery-reared fish, the average elevation in survival of wild compared with reared salmon was ten-fold (range 6 to 13-fold).

Table 2. Adult returns from comparative releases of wild and hatchery-reared smolts. Returns on the River Conon were derived from automatic data loggers. Returns on the River Tay were from captures reported from net and rod fisheries. P values were determined using Fishers Exact test.