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Atlantic salmon return rate increases with smolt length.

Gregory, S.D., Ibbotson, A.T., Riley, W.D., Nevoux, M., Lauridsen, R.B., Russell, I.C., Britton, J.R., Gillingham, P.K., Simmons, O.M. and Rivot, E., 2019. Atlantic salmon return rate increases with smolt length. ICES journal of marine science : Journal du conseil, 76 (6), 1702-1712.

Full text available as:

SmoltSizeSurvival-v6-3_r1_1 (1).pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial.


DOI: 10.1093/icesjms/fsz066


Recent declines in Atlantic salmon Salmo salar populations are generally attributed to factors in their marine life-phase. However, it is postulated that factors affecting their freshwater life-phase might impact their marine survival, such as the influence of body size. While larger smolts are widely hypothesized to have higher marine survival rates, empirical support remains scant, in part due to inadequate data and ambiguous statistical analyses. Here, we test the influence of smolt body size on marine return rates, a proxy for marine survival, using a 12-year dataset of 3688 smolts tagged with passive integrated transponders in the River Frome, Southern England. State-space models describe the probability of smolts surviving their marine phase to return as 1 sea-winter (1SW) or multi-sea-winter adults as a function of their length, while accounting for imperfect detection and missing data. Models predicted that larger smolts had higher return rates; the most parsimonious model included the effect of length on 1SW return rate. This prediction is concerning, as freshwater juvenile salmon are decreasing in size on the River Frome, and elsewhere. Thus, to maximize adult returns, restoration efforts should focus on freshwater life-stages, and maximize both the number and the size of emigrating smolts.

Item Type:Article
Additional Information:Direct link to the article on the publisher's webpage -
Uncontrolled Keywords:Bayesian inference; juvenile; marine survival; passive integrated transponder (PIT); probability to return as adult; salmonid; size effect; state space model;
Group:Faculty of Science & Technology
ID Code:32542
Deposited By: Symplectic RT2
Deposited On:18 Jul 2019 15:12
Last Modified:14 Mar 2022 14:17


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