Age-length relationships in UK harbour seals during a period of population decline

Ailsa J. Hall (Corresponding Author), Beth Mackey, Joanna L. Kershaw, Paul Thompson

Research output: Contribution to journalArticle

Abstract

1. The abundance of harbour seals (Phoca vitulina) in the UK as a whole has increased over the past 10 years, after a 30% decline during the preceding 10 years and two major viral epidemics. However, population trends vary greatly among regions, with those on the east coast of Scotland and in the northern isles experiencing dramatic declines since the early 2000s and populations on the west coast being either stable or increasing. The reasons for these differences in population dynamics are unknown.

2. Determining whether there has been a change in somatic growth among populations can assist in assessing potential causes for abundance declines, as shifts in juvenile growth rates or maximum length at maturity may indicate changes in environmental conditions. Resource limitations are likely to result in slower growth and later age at sexual maturity, whereas causes of acute mortality could have the opposite effect.

3. Here, analysis of the most comprehensive length-at-age dataset for UK harbour seals found no evidence for major differences, or changes over time, in asymptotic length or growth parameters from fitted von Bertalanffy growth curves, across all regions, with the exception of one pairwise comparison; males from East Scotland were significantly shorter than males from all other areas by an average of almost 9 cm. However, the power to detect small changes was limited by measurement uncertainty and differences in spatial and temporal sampling effort.

4. Asymptotic lengths at maturity across all regions were slightly lower than published lengths for harbour seal populations in Europe, the Arctic and Canada, with females being on average 140.5cm (95% CI, 139.4, 141.6) and males 149.4cm (147.8, 151.1) at adulthood.
Original languageEnglish
JournalAquatic Conservation: Marine and Freshwater Ecosystems
Publication statusAccepted/In press - 24 Feb 2019

Fingerprint

Phoca vitulina
population decline
harbor
coast
Scotland
growth curve
sexual maturity
population growth
population dynamics
coasts
environmental conditions
mortality
adulthood
sampling
resource
Arctic region
uncertainty
Canada
environmental factors

Keywords

  • growth layer groups
  • phoca vitulina
  • population dynamics
  • top predator

Cite this

Age-length relationships in UK harbour seals during a period of population decline. / Hall, Ailsa J. (Corresponding Author); Mackey, Beth; Kershaw, Joanna L.; Thompson, Paul.

In: Aquatic Conservation: Marine and Freshwater Ecosystems, 24.02.2019.

Research output: Contribution to journalArticle

@article{afd51f2ca71f4e989e34a5815aae8cc1,
title = "Age-length relationships in UK harbour seals during a period of population decline",
abstract = "1. The abundance of harbour seals (Phoca vitulina) in the UK as a whole has increased over the past 10 years, after a 30{\%} decline during the preceding 10 years and two major viral epidemics. However, population trends vary greatly among regions, with those on the east coast of Scotland and in the northern isles experiencing dramatic declines since the early 2000s and populations on the west coast being either stable or increasing. The reasons for these differences in population dynamics are unknown.2. Determining whether there has been a change in somatic growth among populations can assist in assessing potential causes for abundance declines, as shifts in juvenile growth rates or maximum length at maturity may indicate changes in environmental conditions. Resource limitations are likely to result in slower growth and later age at sexual maturity, whereas causes of acute mortality could have the opposite effect.3. Here, analysis of the most comprehensive length-at-age dataset for UK harbour seals found no evidence for major differences, or changes over time, in asymptotic length or growth parameters from fitted von Bertalanffy growth curves, across all regions, with the exception of one pairwise comparison; males from East Scotland were significantly shorter than males from all other areas by an average of almost 9 cm. However, the power to detect small changes was limited by measurement uncertainty and differences in spatial and temporal sampling effort.4. Asymptotic lengths at maturity across all regions were slightly lower than published lengths for harbour seal populations in Europe, the Arctic and Canada, with females being on average 140.5cm (95{\%} CI, 139.4, 141.6) and males 149.4cm (147.8, 151.1) at adulthood.",
keywords = "growth layer groups, phoca vitulina, population dynamics, top predator",
author = "Hall, {Ailsa J.} and Beth Mackey and Kershaw, {Joanna L.} and Paul Thompson",
note = "The authors would like to thank Scottish Natural Heritage, Scottish Government and the UK Natural Environment Research Council (grant code SMRU/10001) for funding this study. We would also like to thank Simon Moss and all the SMRU and University of Aberdeen staff and students who have provided invaluable help in the field.",
year = "2019",
month = "2",
day = "24",
language = "English",
journal = "Aquatic Conservation: Marine and Freshwater Ecosystems",
issn = "1052-7613",
publisher = "Wiley-Blackwell",

}

TY - JOUR

T1 - Age-length relationships in UK harbour seals during a period of population decline

AU - Hall, Ailsa J.

AU - Mackey, Beth

AU - Kershaw, Joanna L.

AU - Thompson, Paul

N1 - The authors would like to thank Scottish Natural Heritage, Scottish Government and the UK Natural Environment Research Council (grant code SMRU/10001) for funding this study. We would also like to thank Simon Moss and all the SMRU and University of Aberdeen staff and students who have provided invaluable help in the field.

PY - 2019/2/24

Y1 - 2019/2/24

N2 - 1. The abundance of harbour seals (Phoca vitulina) in the UK as a whole has increased over the past 10 years, after a 30% decline during the preceding 10 years and two major viral epidemics. However, population trends vary greatly among regions, with those on the east coast of Scotland and in the northern isles experiencing dramatic declines since the early 2000s and populations on the west coast being either stable or increasing. The reasons for these differences in population dynamics are unknown.2. Determining whether there has been a change in somatic growth among populations can assist in assessing potential causes for abundance declines, as shifts in juvenile growth rates or maximum length at maturity may indicate changes in environmental conditions. Resource limitations are likely to result in slower growth and later age at sexual maturity, whereas causes of acute mortality could have the opposite effect.3. Here, analysis of the most comprehensive length-at-age dataset for UK harbour seals found no evidence for major differences, or changes over time, in asymptotic length or growth parameters from fitted von Bertalanffy growth curves, across all regions, with the exception of one pairwise comparison; males from East Scotland were significantly shorter than males from all other areas by an average of almost 9 cm. However, the power to detect small changes was limited by measurement uncertainty and differences in spatial and temporal sampling effort.4. Asymptotic lengths at maturity across all regions were slightly lower than published lengths for harbour seal populations in Europe, the Arctic and Canada, with females being on average 140.5cm (95% CI, 139.4, 141.6) and males 149.4cm (147.8, 151.1) at adulthood.

AB - 1. The abundance of harbour seals (Phoca vitulina) in the UK as a whole has increased over the past 10 years, after a 30% decline during the preceding 10 years and two major viral epidemics. However, population trends vary greatly among regions, with those on the east coast of Scotland and in the northern isles experiencing dramatic declines since the early 2000s and populations on the west coast being either stable or increasing. The reasons for these differences in population dynamics are unknown.2. Determining whether there has been a change in somatic growth among populations can assist in assessing potential causes for abundance declines, as shifts in juvenile growth rates or maximum length at maturity may indicate changes in environmental conditions. Resource limitations are likely to result in slower growth and later age at sexual maturity, whereas causes of acute mortality could have the opposite effect.3. Here, analysis of the most comprehensive length-at-age dataset for UK harbour seals found no evidence for major differences, or changes over time, in asymptotic length or growth parameters from fitted von Bertalanffy growth curves, across all regions, with the exception of one pairwise comparison; males from East Scotland were significantly shorter than males from all other areas by an average of almost 9 cm. However, the power to detect small changes was limited by measurement uncertainty and differences in spatial and temporal sampling effort.4. Asymptotic lengths at maturity across all regions were slightly lower than published lengths for harbour seal populations in Europe, the Arctic and Canada, with females being on average 140.5cm (95% CI, 139.4, 141.6) and males 149.4cm (147.8, 151.1) at adulthood.

KW - growth layer groups

KW - phoca vitulina

KW - population dynamics

KW - top predator

M3 - Article

JO - Aquatic Conservation: Marine and Freshwater Ecosystems

JF - Aquatic Conservation: Marine and Freshwater Ecosystems

SN - 1052-7613

ER -