Management of many salmon populations is based on maintaining individual stocks above a conservation limit defined as the maximum sustainable yield point from a stock recruitment (SR) relationship. A crucial input parameter of any SR analysis is an accurate measure of fecundity. Atlantic salmon (Salmo salar L) fecundity data from nine rivers in Ireland were collated and analysed, providing the first comprehensive multi-river assessment of egg numbers for Irish stocks. The number of eggs in wild 1 SW fish (1 sea winter, also known as grilse) varied with fish size and also according to the source river. When expressed as eggs per kg of fish, river was a less important explanatory variable. The number of eggs in wild fish averaged 3441 for 1 SW fish and 6059 for MSW (multi-sea winter) fish, respectively. Egg diameter also varied with fish size and source river. A negative binomial model of egg number per fish, with weight as the only explanatory variable, accounted for 60% of the explained deviance in this dataset. When applied to a large national dataset of fish weights from angling records, this model allows river-specific fecundity to be estimated for salmon populations with varying life history characteristics. The model predicts that the fecundity of Irish salmon is at the lower end of the range reported for Atlantic salmon across Europe. (C) 2014 Elsevier B.V. All rights reserved.

The lifetime success and performance characteristics of communally reared offspring of wild native Burrishoole (native), ranched native (ranched) and non‐native (non‐native) Atlantic salmon Salmo salar from the adjacent Owenmore River were compared. Non‐native 0+ year parr showed a substantial downstream migration, which was not shown by native and ranched parr. This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic conditions within the Owenmore River catchment where the main nursery habitat is downstream of the spawning area. There were no differences between native and ranched in smolt output or adult return. Both of these measures, however, were significantly lower for the non‐native group. A greater proportion of the non‐native Atlantic salmon was taken in the coastal drift nets compared to the return to the Burrishoole system, probably as a result of the greater size of the non‐native fish. The overall lifetime success of the non‐native group, from fertilized egg to returning adult, was some 35% of native and ranched. The ranched group showed a significantly greater male parr maturity, a greater proportion of 1+ year smolts, and differences in sex ratio and timing of freshwater entry of returning adults compared to native, which may have fitness implications under specific conditions.

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