Incorporating estimates of capture probability and river network covariance in novel habitat – abundance models

Assessing the effects of conservation stocking on catchment-scale production of juvenile Atlantic salmon (Salmo salar) from a long-term electrofishing dataset

Ross S. Glover*, Robert J. Fryer, Chris Soulsby, Philip J. Bacon, Iain A. Malcolm

*Corresponding author for this work

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

There are increasing calls for “conservation stocking” to counter declines in Atlantic salmon (Salmo salar) populations, the assumption being that stocking can bypass population bottlenecks and increase recruitment over natural processes. However, there are too few quantitative studies with sufficient data to assess the efficacy of conservation stocking. The Girnock Burn is a unique long-term monitoring site where adult and juvenile salmon numbers have been monitored for over 50 years, including 11 years with conservation stocking. Adults were monitored at a fixed trap and juveniles were monitored by electrofishing. In stocked years, ova were incubated in surface water to reduce density-independent over-winter mortality. In eight years, eyed ova were stocked at uniform densities to reduce local density-dependence. In three years, stocking replicated natural spatial variability in ova deposition removing any potential benefits of reduced local density-dependence. Juvenile production was estimated by summing the product of reach-scale density estimates and river area obtained from a novel spatial statistical river network model that incorporated the effects of capture probability, habitat and stock level. Capture probability varied with life-stage (age 0+ fry or ≥1+ parr), electrofishing pass and day of the year, but importantly also exhibited a positive temporal trend across years. Survival from ova to fry was density-independent and higher under uniform stocking than natural spawning or simulated natural spawning. Under uniform stocking, fry densities varied smoothly with altitude, while under natural spawning and simulated natural spawning, fry exhibited a more patchy distribution. Increased fry production did not translate to increased parr production, which was strongly density-dependent. This likely reflected the inability of fry to move between stocked locations and suitable overwintering habitat, decreasing survival between fry and parr life-stages. Consequently, there was no overall benefit of stocking. The modelling framework used in this study provides a valuable approach for interpreting long-term datasets where site locations, equipment and staffing vary over time. The long-term Girnock dataset was valuable in separating management action from natural population regulation and permitting understanding of ecological processes. The study indicates that conservation stocking can be ineffective, even where implemented to best scientific standards. It is therefore recommended that a detailed understanding of local population dynamics is obtained, and a realistic appraisal of the expected benefits of stocking is undertaken, before management actions are considered.

Original languageEnglish
Pages (from-to)302-315
Number of pages14
JournalEcological Indicators
Volume93
Early online date21 May 2018
DOIs
Publication statusPublished - 31 Oct 2018

Fingerprint

electrofishing
Salmo salar
fish fry
catchment
rivers
habitat
habitats
ova
river
parr
spawning
density dependence
effect
stocking
Conservation
Habitat
Salmon
population regulation
population bottleneck
stocking density

Keywords

  • Capture probability
  • Electrofishing
  • Habitat
  • Population modelling
  • Spatial statistical river network model
  • Stock-recruitment

ASJC Scopus subject areas

  • Decision Sciences(all)
  • Ecology, Evolution, Behavior and Systematics
  • Ecology

Cite this

@article{174a92e994b145878d59014315d70d50,
title = "Incorporating estimates of capture probability and river network covariance in novel habitat – abundance models: Assessing the effects of conservation stocking on catchment-scale production of juvenile Atlantic salmon (Salmo salar) from a long-term electrofishing dataset",
abstract = "There are increasing calls for “conservation stocking” to counter declines in Atlantic salmon (Salmo salar) populations, the assumption being that stocking can bypass population bottlenecks and increase recruitment over natural processes. However, there are too few quantitative studies with sufficient data to assess the efficacy of conservation stocking. The Girnock Burn is a unique long-term monitoring site where adult and juvenile salmon numbers have been monitored for over 50 years, including 11 years with conservation stocking. Adults were monitored at a fixed trap and juveniles were monitored by electrofishing. In stocked years, ova were incubated in surface water to reduce density-independent over-winter mortality. In eight years, eyed ova were stocked at uniform densities to reduce local density-dependence. In three years, stocking replicated natural spatial variability in ova deposition removing any potential benefits of reduced local density-dependence. Juvenile production was estimated by summing the product of reach-scale density estimates and river area obtained from a novel spatial statistical river network model that incorporated the effects of capture probability, habitat and stock level. Capture probability varied with life-stage (age 0+ fry or ≥1+ parr), electrofishing pass and day of the year, but importantly also exhibited a positive temporal trend across years. Survival from ova to fry was density-independent and higher under uniform stocking than natural spawning or simulated natural spawning. Under uniform stocking, fry densities varied smoothly with altitude, while under natural spawning and simulated natural spawning, fry exhibited a more patchy distribution. Increased fry production did not translate to increased parr production, which was strongly density-dependent. This likely reflected the inability of fry to move between stocked locations and suitable overwintering habitat, decreasing survival between fry and parr life-stages. Consequently, there was no overall benefit of stocking. The modelling framework used in this study provides a valuable approach for interpreting long-term datasets where site locations, equipment and staffing vary over time. The long-term Girnock dataset was valuable in separating management action from natural population regulation and permitting understanding of ecological processes. The study indicates that conservation stocking can be ineffective, even where implemented to best scientific standards. It is therefore recommended that a detailed understanding of local population dynamics is obtained, and a realistic appraisal of the expected benefits of stocking is undertaken, before management actions are considered.",
keywords = "Capture probability, Electrofishing, Habitat, Population modelling, Spatial statistical river network model, Stock-recruitment",
author = "Glover, {Ross S.} and Fryer, {Robert J.} and Chris Soulsby and Bacon, {Philip J.} and Malcolm, {Iain A.}",
note = "We thank staff from the Marine Scotland Freshwater Laboratory for collecting the datasets analysed in this study. Particular thanks are extended to Alan Youngson, Aya Thorne and Iain McLaren for their work during the experimental ova stocking programme. Data collection at the Girnock is funded by the Scottish Government, through Marine Scotland Science Freshwater Fisheries Laboratory under Service Level Agreement FW01t.",
year = "2018",
month = "10",
day = "31",
doi = "10.1016/j.ecolind.2018.05.013",
language = "English",
volume = "93",
pages = "302--315",
journal = "Ecological Indicators",
issn = "1470-160X",
publisher = "Elsevier",

}

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T1 - Incorporating estimates of capture probability and river network covariance in novel habitat – abundance models

T2 - Assessing the effects of conservation stocking on catchment-scale production of juvenile Atlantic salmon (Salmo salar) from a long-term electrofishing dataset

AU - Glover, Ross S.

AU - Fryer, Robert J.

AU - Soulsby, Chris

AU - Bacon, Philip J.

AU - Malcolm, Iain A.

N1 - We thank staff from the Marine Scotland Freshwater Laboratory for collecting the datasets analysed in this study. Particular thanks are extended to Alan Youngson, Aya Thorne and Iain McLaren for their work during the experimental ova stocking programme. Data collection at the Girnock is funded by the Scottish Government, through Marine Scotland Science Freshwater Fisheries Laboratory under Service Level Agreement FW01t.

PY - 2018/10/31

Y1 - 2018/10/31

N2 - There are increasing calls for “conservation stocking” to counter declines in Atlantic salmon (Salmo salar) populations, the assumption being that stocking can bypass population bottlenecks and increase recruitment over natural processes. However, there are too few quantitative studies with sufficient data to assess the efficacy of conservation stocking. The Girnock Burn is a unique long-term monitoring site where adult and juvenile salmon numbers have been monitored for over 50 years, including 11 years with conservation stocking. Adults were monitored at a fixed trap and juveniles were monitored by electrofishing. In stocked years, ova were incubated in surface water to reduce density-independent over-winter mortality. In eight years, eyed ova were stocked at uniform densities to reduce local density-dependence. In three years, stocking replicated natural spatial variability in ova deposition removing any potential benefits of reduced local density-dependence. Juvenile production was estimated by summing the product of reach-scale density estimates and river area obtained from a novel spatial statistical river network model that incorporated the effects of capture probability, habitat and stock level. Capture probability varied with life-stage (age 0+ fry or ≥1+ parr), electrofishing pass and day of the year, but importantly also exhibited a positive temporal trend across years. Survival from ova to fry was density-independent and higher under uniform stocking than natural spawning or simulated natural spawning. Under uniform stocking, fry densities varied smoothly with altitude, while under natural spawning and simulated natural spawning, fry exhibited a more patchy distribution. Increased fry production did not translate to increased parr production, which was strongly density-dependent. This likely reflected the inability of fry to move between stocked locations and suitable overwintering habitat, decreasing survival between fry and parr life-stages. Consequently, there was no overall benefit of stocking. The modelling framework used in this study provides a valuable approach for interpreting long-term datasets where site locations, equipment and staffing vary over time. The long-term Girnock dataset was valuable in separating management action from natural population regulation and permitting understanding of ecological processes. The study indicates that conservation stocking can be ineffective, even where implemented to best scientific standards. It is therefore recommended that a detailed understanding of local population dynamics is obtained, and a realistic appraisal of the expected benefits of stocking is undertaken, before management actions are considered.

AB - There are increasing calls for “conservation stocking” to counter declines in Atlantic salmon (Salmo salar) populations, the assumption being that stocking can bypass population bottlenecks and increase recruitment over natural processes. However, there are too few quantitative studies with sufficient data to assess the efficacy of conservation stocking. The Girnock Burn is a unique long-term monitoring site where adult and juvenile salmon numbers have been monitored for over 50 years, including 11 years with conservation stocking. Adults were monitored at a fixed trap and juveniles were monitored by electrofishing. In stocked years, ova were incubated in surface water to reduce density-independent over-winter mortality. In eight years, eyed ova were stocked at uniform densities to reduce local density-dependence. In three years, stocking replicated natural spatial variability in ova deposition removing any potential benefits of reduced local density-dependence. Juvenile production was estimated by summing the product of reach-scale density estimates and river area obtained from a novel spatial statistical river network model that incorporated the effects of capture probability, habitat and stock level. Capture probability varied with life-stage (age 0+ fry or ≥1+ parr), electrofishing pass and day of the year, but importantly also exhibited a positive temporal trend across years. Survival from ova to fry was density-independent and higher under uniform stocking than natural spawning or simulated natural spawning. Under uniform stocking, fry densities varied smoothly with altitude, while under natural spawning and simulated natural spawning, fry exhibited a more patchy distribution. Increased fry production did not translate to increased parr production, which was strongly density-dependent. This likely reflected the inability of fry to move between stocked locations and suitable overwintering habitat, decreasing survival between fry and parr life-stages. Consequently, there was no overall benefit of stocking. The modelling framework used in this study provides a valuable approach for interpreting long-term datasets where site locations, equipment and staffing vary over time. The long-term Girnock dataset was valuable in separating management action from natural population regulation and permitting understanding of ecological processes. The study indicates that conservation stocking can be ineffective, even where implemented to best scientific standards. It is therefore recommended that a detailed understanding of local population dynamics is obtained, and a realistic appraisal of the expected benefits of stocking is undertaken, before management actions are considered.

KW - Capture probability

KW - Electrofishing

KW - Habitat

KW - Population modelling

KW - Spatial statistical river network model

KW - Stock-recruitment

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U2 - 10.1016/j.ecolind.2018.05.013

DO - 10.1016/j.ecolind.2018.05.013

M3 - Article

VL - 93

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EP - 315

JO - Ecological Indicators

JF - Ecological Indicators

SN - 1470-160X

ER -