Long‐term changes and effects of significant fishery closures on marine survival and biological characteristics of wild and hatchery‐reared Atlantic salmon Salmo salar

• Published in: Journal of Fish Biology
• Main Authors: Cotter, Deirdre, Vaughan, Louise, Bond, Nigel, Dillane, Mary, Duncan, Roxanne, Poole, Russell, Rogan, Gerard, Ó. Maoiléidigh, Niall
• Other Authors: Marine Institute
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2022
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1111/jfb.15078; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jfb.15078; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jfb.15078

Abstract Long‐term data, over four decades, were analysed to examine temporal trends in survival indices and phenotypic characteristics of Atlantic salmon Salmo salar returning to the Burrishoole national salmonid monitored river in Ireland. Before 2007, the marine drift net fishery was the major capture method for salmon in Irish home waters, accounting for over 70% of the commercial catch and targeting mixed stocks from multiple rivers. The authors examined size differences in fish captured in marine and freshwater environments and the impact of closure of this fishery on long‐term survival indices and fish size. Return rates to Irish home waters for wild one sea‐winter (1SW) and a ranching strain of hatchery‐reared 1SW Atlantic salmon stocks showed a declining trend up to the time of closure of the fishery (1985–2006). In contrast, closure of the drift net fishery resulted in the anticipated increase in return rate to fresh water in the short term. Nonetheless, the short‐term upward trend was not sustained in the following years: the trend for return rate to fresh water (1985–2017) was found to be neither increasing nor decreasing. Mean return rates to fresh water 10 years pre‐ and post‐closure of the drift net fishery increased from 7.4% to 8.5% for wild 1SW and significantly from 2.4% to 3.7% for ranched 1SW suggesting some benefit had accrued as a consequence of drift net closure. For ranched 1SW salmon, entry into fresh water was found to be occurring earlier, which is likely a phenotypical response to changing climatic conditions. A declining trend in fish length was found in the pre‐closure period, followed by a more stable trend post‐closure. Similar patterns were observed for fish condition and weight parameters. Significantly, a step change in fish size occurred just before the closure of the Irish drift net fishery in both marine and freshwater habitats, when the average length decreased by 3.8 and 4.6 cm, respectively, between 2005 and 2006. This suggests an environmental effect on the population, ...