Empirical analyses of the length, weight, and condition of adult Atlantic salmon on return to the Scottish coast between 1963 and 2006

Bacon, P. J.; Palmer, Stephen C. F.; MacLean, Julian C.; Smith, Gordon W.; Whyte, B. D. M.; Gurney, William; Youngson, A. F.

doi:10.1093/icesjms/fsp096

Cited by 47 publications

(67 citation statements)

References 27 publications

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“…Two-sea-winter fish are in their turn normally smaller than those who have spent three winters at sea (Bacon et al 2009). These size differences are reflected in differing commercial values to the human consumption fishery which dominated historic catches (Bacon et al 2010) but are considerably amplified in the currently dominant sport fishery where early-run multi-sea-winter (and thus large) fish are most actively sought-after.…”

Section: Biological Backgroundmentioning

confidence: 94%

Sea-Age Variation in Maiden Atlantic Salmon Spawners: Phenotypic Plasticity or Genetic Polymorphism?

et al. 2011

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Atlantic salmon exhibit a partially heritable polymorphism in which the morphs are distinguished by the duration and location of the sea-phase of their life-cycle. These morphs co-occur, albeit in characteristically different proportions, in most Scottish rivers and in both the spring and autumn spawner runs; early running fish being generally associated with upland spawning locations while late running fish are associated with lowland spawning. Thus, differences in riverine and marine environment appear to be linked to differences in the relative abundance of the morphs, rather than to the specific morph which is optimally adapted. In this paper, we report a model-based synthetic study aimed at understanding the key dynamic elements which determine the long-term stability of this polymorphism, and thus determine the relative abundance of the various sea-age morphs. Given the recent accumulation of evidence for a genetic basis for the polymorphism, we argue that the key dynamic mechanism which equalises the realized fitness of the sea-age morphs must be one or more morph-specific density dependencies in the riverine phase of the life-history. We explore a number of specific mechanisms, firmly based in known salmon biology, by which such morph-specific density dependence could occur and investigate the robustness of the co-existence which they imply. We conclude that the co-occurrence of multiple sea-age morphs of Atlantic salmon in Scottish rivers is a stable genetic polymorphism, maintained by some combination of physical separation and asymmetric competition between spawners of different morphs or the riverine stages of their offspring or both.

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Section: Biological Backgroundmentioning

confidence: 94%

Sea-Age Variation in Maiden Atlantic Salmon Spawners: Phenotypic Plasticity or Genetic Polymorphism?

et al. 2011

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“…Friedland et al 2009, Beaugrand & Reid 2012. Similarly, large-scale changes in life history traits, particularly sea age and run time, have been reported in a number of long-term studies (Summers 1995, Boylan 2004, Bacon et al 2009). These are considered to be responses to broaderscale ecosystem dynamics such as the Atlantic Multidecadal Oscillation (Edwards et al 2013, Klöwer et al 2014, Trenkel et al 2014.…”

Section: Discussionmentioning

confidence: 74%

Temporal variation in sea trout Salmo trutta life history traits in the Erriff River, western Ireland

Gargan¹,

Kelly²,

Shephard³

et al. 2016

Aquacult. Environ. Interact.

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The demographic and life history characteristics of sea trout Salmo trutta L. populations can be changed by a range of pressures in both freshwater and marine environments. Few long-term monitoring programmes are in place to assess temporal change in population dynamics. We analysed a 20 yr time series (1985−2004) using 15 sea trout population response variables in the Erriff River, western Ireland. Over this period, when time was considered as a categorical variable comprising 4 sequential periods of 5 yr, important life history changes were observed. The most dramatic of these changes corresponded with the period immediately after the commencement of salmon farming in the local estuary, with significant decreases in the number and length of sea trout kelts, the estimated number of eggs deposited, the sea trout rod catch, the proportion of older (1+ and 2+ sea age) fish and the frequency of repeat spawners. We found a significant positive relationship between the number of salmon lice Lepeophtheirus salmonis in the local salmon farm and the number of lice found on sea trout collected contemporaneously in local rivers. Results of this long-term monitoring programme demonstrate that significant changes in sea trout population structure with respect to quantitative life history traits can occur over a relatively short time period and suggest that the introduction of salmon farming into the local estuary most likely contributed to the observed changes in sea trout population dynamics.

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“…We note that the Girnock Burn data show a pronounced 7-to 8-year periodicity which, given a mean development delay around five and a half years, could be produced by such a mechanism. We further note that an exhaustive search for environmental correlates exhibiting any matching periodicity has failed to elicit any plausible candidates for exogenous causality in either the freshwater or the marine environment Bacon et al, 2009).…”

Section: Discussionmentioning

confidence: 92%

“…This paper is motivated by the problem of managing commercially important UK populations of Atlantic salmon, which is an obligate anadromous species spawning in river gravels (Youngson and Hay, 1996). The ova hatch the following spring and typically grow for 2 to 3 years in fresh water after which they emigrate to sea, where they spend a further 1 to 3 years before returning to the river of their birth to spawn (almost certainly for the only time in their lives, Bacon et al, 2009). The accuracy with which spawners return to their natal river and the constrained geography of the fresh-water environment means that stock observations can (in principle) be considerable more accurate than is practicable for wholly marine species.…”

Section: Introductionmentioning

confidence: 99%

Maturity Dispersion, Stock Auto-Correlation, and Management Strategy in Exploited Populations

2010

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Fishery management policies need to be based on historical summaries of stock status which are well correlated with the size of the group of individuals who will be affected by any harvest. This paper is motivated by the problem of managing stocks of Atlantic salmon, which can be accurately monitored during the riverine stages of their life-history, but which spend a lengthy period at sea before returning to spawn. We begin by formulating a minimal stochastic model of stock-recruitment driven population dynamics, which linearises to a standard ARMA form. We investigate the relation between maturity dispersion and the auto-covariance of stock fluctuations driven by process noise in the recruitment process and/or random variability in survival from recruitment to spawning. We demonstrate that significant reductions in fluctuation intensity and/or increases in long-run average yield can be achieved by controlling harvesting in response to the value of a historical summary focussed on lags at which the uncontrolled population dynamics produce strong correlations. We apply our minimal model to two well-characterised Atlantic salmon populations, and find poor agreement between predicted and observed stock fluctuation ACF. Re-examination of the ancilliary data available for one of our two exemplary systems leads us to propose an extended model which also linearises to ARMA form, and which predicts a fluctuation ACF more closely in agreement with that observed, and could thus form a satisfactory vehicle for policy discussion.

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Empirical analyses of the length, weight, and condition of adult Atlantic salmon on return to the Scottish coast between 1963 and 2006

Cited by 47 publications

References 27 publications

Sea-Age Variation in Maiden Atlantic Salmon Spawners: Phenotypic Plasticity or Genetic Polymorphism?

Sea-Age Variation in Maiden Atlantic Salmon Spawners: Phenotypic Plasticity or Genetic Polymorphism?

Temporal variation in sea trout Salmo trutta life history traits in the Erriff River, western Ireland

Maturity Dispersion, Stock Auto-Correlation, and Management Strategy in Exploited Populations

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