A comparison of trends in population size and life history features of Atlantic salmon (Salmo salar) and anadromous and non-anadromous Brown trout (Salmo trutta) in a single catchment over 116\xa0years

Colin E Adams,Jennifer A Dodd,Hannele M Honkanen,Malcolm Maccormick,Ellen Bryson,Isabel E Moore

doi:10.1007/s10750-021-04751-2

Colin E Adams, Jennifer A Dodd + Show 4 more

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https://doi.org/10.1007/s10750-021-04751-2

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Abstract

We use a long time series of catch abundance from a recreational fishery over 116 years to look for population trends in Atlantic salmon, and anadromous (sea trout) and non-anadromous (brown) trout for a single catchment, Loch Lomond, west central Scotland. Year strongly predicted variation in catches but catch effort did not meaningfully increase explained variation. Salmon showed periods of increasing and decreasing trends, for sea trout and brown trout there was an overall declining trend. Since 1952, Lomond salmon population trends differed from both wider Scotland and southern Europe, indicating that the Lomond population is partially buffered from drivers of change in salmon populations more widely. In contrast Lomond sea trout showed a similar declining trend to that of populations from the wider west of Scotland over this period. The Lomond populations showed some evidence of shorter-term cycling patterns; the drivers for which are unknown. Body size in salmon and sea trout declined but increased in brown trout; salmon returned to freshwater later, and the relative proportion of all caught trout that were anadromous increased across the time series. This study shows a long and protracted period of fundamental change to populations of these two species over 116 years.

Highlights

There is compelling evidence that populations of Atlantic salmon (Salmo salar Linnaeus, 1758) have been declining over time (Condron et al, 2005)
The best model describing the change in salmon catches included a first and second order polynomial of year and accounted for 91.8% of the variation (R2 = 0.918) (Online resource Table S2 Model 1). b Pre-fishery abundance (PFA) estimates across ICES Working Group on North Atlantic salmon (WGNAS) reporting countries for southern Europe (Scotland, Northern Ireland, England & Wales, Ireland, France and south and west Iceland) between 1972 and 2016; PFA declined significantly (LRstat(45,43) = 93.99, P \ 0.001) over the study period
The model best describing the change in brown trout catches included a first and second order polynomial and a harmonic function with a wavelength of 32 years (LRstat(56.53) = 80.44, P \ 0.001) and explained 52.1% of the variation in catch (Online Resources Table S2 Model 8)

Summary

Introduction

There is compelling evidence that populations of Atlantic salmon (Salmo salar Linnaeus, 1758) have been declining over time (Condron et al, 2005). A The change in national reported catches (in tonnes) across all ICES WGNAS reporting countries (Canada, USA, Norway, Russia, Iceland, Sweden, Denmark, Finland, Ireland, England, Wales, Scotland, Northern Ireland, France and Spain) between 1960 and 2016; Salmon catches declined significantly (LRstat(56,54) = 168.6, P \ 0.001); over the period. B Pre-fishery abundance (PFA) estimates (fish number) across ICES WGNAS reporting countries for southern Europe (Scotland, Northern Ireland, England & Wales (combined), Ireland, France and south and west Iceland) between 1972 and 2016; PFA declined significantly (LRstat(45,43) = 93.99, P \ 0.001) over the study period. The best model describing the change in pre-fishery abundance was a first order polynomial including a harmonic function with a wavelength of 13 years This model year accounted for 86.1% of the variation in PFA (R2 = 0.861) (Online resource Table S2 Model 2a).

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