THE STRAYING OF ICELANDIC RANCHED ATLANTIC SALMON, SALMO-SALAR L - RELEASE AND RECAPTURE TECHNIQUES

The straying rate of ranched Atlantic salmon, Salmo salar L., into riv ers in Iceland was estimated on the basis of coded wire tag recoveries . Out of a total of 15 158 recaptured tagged salmon from the releases between 1987 and 1992, 189 fish (1.3%) strayed into 25 out of the 79 s almon rivers observed. Most of the strayers were found in neighbouring rivers to the ranching stations. There were no significant difference s in straying rate between different age classes of salmon returning f rom the same smelt year class. Generally, there was a delay of 26-27 d ays in running time between strayers in rivers and salmon returning to the ranching station. Higher straying rates were observed for ranchin g stations using riverine traps than for stations using estuary traps. By close inspection of seven key rivers in Iceland and assuming a 50% exploitation rate (fishing effort) in the rivers, on average, 2.1% of the returning salmon in ranching were estimated to stray to native sa lmon rivers over the years. A limitation of using these numbers to est imate geneflow between ranching stocks and wild populations is discuss ed.