Top-down pressure on a coastal ecosystem by harbor seals

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels and may have regained their prominent position as top predator in marine ecosystems. Also, the harbor seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960s, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbor seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in fecal samples and published estimates on the seal’s daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbor seals hauling-out in the Dutch Wadden Sea fed predominantly on demersal fish, for example, flatfish species (flounder, sole, plaice, dab), but also on sandeel, cod, and whiting. Although harbor seals acquire the majority of prey further offshore in the adjacent North Sea, and only spend 14% of their diving time in the Wadden Sea, seal predation was still estimated to cause an average annual mortality of 43% of the remaining fish in the Wadden Sea and 60% in the nearby shallow coastal waters (<20 m). There were however large sources of uncertainty in the estimated impact of seals on fish, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down pressure by harbor seals on demersal fish. However, predation by seals may also alleviate density-dependent competition between the remaining fish, allowing for increased fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could become an important component in the functioning of shallow coastal ecosystems.
LanguageEnglish
Pagese02538
JournalEcosphere
Volume10
Issue number1
DOIs
Publication statusPublished - 1 Jan 2019

Fingerprint

Phoca vitulina
North Sea
harbor
seals
ecosystems
fish
demersal fish
hunting
marine mammals
predation
marine mammal
coastal water
Pleuronectes
coastal ecosystem
whiting
catchability
Pleuronectiformes
prey selection
pelagic fish
flounder

Keywords

  • demersal fish
  • diet
  • harbor seal
  • impact
  • intertidaL
  • Phoca vitulina
  • predation pressure
  • sealing
  • Subtidal
  • top-down regulation
  • top predator

Cite this

@article{222d199ceeb047e5b771d0fa6744598c,
title = "Top-down pressure on a coastal ecosystem by harbor seals",
abstract = "Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels and may have regained their prominent position as top predator in marine ecosystems. Also, the harbor seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960s, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbor seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in fecal samples and published estimates on the seal’s daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbor seals hauling-out in the Dutch Wadden Sea fed predominantly on demersal fish, for example, flatfish species (flounder, sole, plaice, dab), but also on sandeel, cod, and whiting. Although harbor seals acquire the majority of prey further offshore in the adjacent North Sea, and only spend 14{\%} of their diving time in the Wadden Sea, seal predation was still estimated to cause an average annual mortality of 43{\%} of the remaining fish in the Wadden Sea and 60{\%} in the nearby shallow coastal waters (<20 m). There were however large sources of uncertainty in the estimated impact of seals on fish, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down pressure by harbor seals on demersal fish. However, predation by seals may also alleviate density-dependent competition between the remaining fish, allowing for increased fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could become an important component in the functioning of shallow coastal ecosystems.",
keywords = "demersal fish, diet, harbor seal, impact, intertidaL, Phoca vitulina, predation pressure, sealing, Subtidal, top-down regulation, top predator",
author = "Geert Aarts and Sophie Brasseur and Poos, {Jan Jaap} and Jessica Schop and Roger Kirkwood and {Van Kooten}, Tobias and Evert Mul and Peter Reijnders and Rijnsdorp, {Adriaan D.} and Ingrid Tulp",
year = "2019",
month = "1",
day = "1",
doi = "10.1002/ecs2.2538",
language = "English",
volume = "10",
pages = "e02538",
journal = "Ecosphere",
issn = "2150-8925",
publisher = "Ecological Society of America",
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}

Top-down pressure on a coastal ecosystem by harbor seals. / Aarts, Geert; Brasseur, Sophie; Poos, Jan Jaap; Schop, Jessica; Kirkwood, Roger; Van Kooten, Tobias; Mul, Evert; Reijnders, Peter; Rijnsdorp, Adriaan D.; Tulp, Ingrid.

In: Ecosphere, Vol. 10, No. 1, 01.01.2019, p. e02538.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Top-down pressure on a coastal ecosystem by harbor seals

AU - Aarts, Geert

AU - Brasseur, Sophie

AU - Poos, Jan Jaap

AU - Schop, Jessica

AU - Kirkwood, Roger

AU - Van Kooten, Tobias

AU - Mul, Evert

AU - Reijnders, Peter

AU - Rijnsdorp, Adriaan D.

AU - Tulp, Ingrid

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels and may have regained their prominent position as top predator in marine ecosystems. Also, the harbor seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960s, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbor seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in fecal samples and published estimates on the seal’s daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbor seals hauling-out in the Dutch Wadden Sea fed predominantly on demersal fish, for example, flatfish species (flounder, sole, plaice, dab), but also on sandeel, cod, and whiting. Although harbor seals acquire the majority of prey further offshore in the adjacent North Sea, and only spend 14% of their diving time in the Wadden Sea, seal predation was still estimated to cause an average annual mortality of 43% of the remaining fish in the Wadden Sea and 60% in the nearby shallow coastal waters (<20 m). There were however large sources of uncertainty in the estimated impact of seals on fish, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down pressure by harbor seals on demersal fish. However, predation by seals may also alleviate density-dependent competition between the remaining fish, allowing for increased fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could become an important component in the functioning of shallow coastal ecosystems.

AB - Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels and may have regained their prominent position as top predator in marine ecosystems. Also, the harbor seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960s, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbor seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in fecal samples and published estimates on the seal’s daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbor seals hauling-out in the Dutch Wadden Sea fed predominantly on demersal fish, for example, flatfish species (flounder, sole, plaice, dab), but also on sandeel, cod, and whiting. Although harbor seals acquire the majority of prey further offshore in the adjacent North Sea, and only spend 14% of their diving time in the Wadden Sea, seal predation was still estimated to cause an average annual mortality of 43% of the remaining fish in the Wadden Sea and 60% in the nearby shallow coastal waters (<20 m). There were however large sources of uncertainty in the estimated impact of seals on fish, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down pressure by harbor seals on demersal fish. However, predation by seals may also alleviate density-dependent competition between the remaining fish, allowing for increased fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could become an important component in the functioning of shallow coastal ecosystems.

KW - demersal fish

KW - diet

KW - harbor seal

KW - impact

KW - intertidaL

KW - Phoca vitulina

KW - predation pressure

KW - sealing

KW - Subtidal

KW - top-down regulation

KW - top predator

U2 - 10.1002/ecs2.2538

DO - 10.1002/ecs2.2538

M3 - Article

VL - 10

SP - e02538

JO - Ecosphere

T2 - Ecosphere

JF - Ecosphere

SN - 2150-8925

IS - 1

ER -