Change of foraging behavior of cormorants and the effect on river fish

Niels Jepsen*, Henrik Dalby Ravn, Stig Pedersen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

80 Downloads (Pure)

Abstract

Since the European population of great cormorants (Phalacrocorax carbo sinensis) rapidly increased 30 years ago, Denmark has been one of the
core breeding areas for this colonial water bird. Following a 10-year period with stable breeding numbers in Denmark, the population of great cormorants
decreased. At the same time, a combination of cold winters and low availability of coastal prey fish apparently triggered birds to seek new foraging areas.
Thus, cormorants began to appear in rivers and streams coinciding with an observed massive decline of fish, mainly brown trout (Salmo trutta) and grayling
(Thymallus thymallus). In this paper, we present the results from studies using radio-telemetry, PIT-tagging, and traditional fish surveys to estimate the
impact of predation in Danish lowland rivers. Recovery of PIT-tags revealed that an estimated 30% of wild trout and 72% of wild grayling tagged in a small river
were eaten by cormorants. In another medium-sized river, 79% of radio-tagged adult grayling were removed, presumably by cormorants during winter. Thus, predation from cormorants appears to be at a level that explains the observed collapse of grayling and brown trout populations in many Danish streams
Original languageEnglish
JournalHydrobiologia
Volume820
Issue number1
Pages (from-to)189-199
ISSN0018-8158
DOIs
Publication statusPublished - 2018

Cite this

@article{c4dd4a6e4a80493eba926a5db24090c7,
title = "Change of foraging behavior of cormorants and the effect on river fish",
abstract = "Since the European population of great cormorants (Phalacrocorax carbo sinensis) rapidly increased 30 years ago, Denmark has been one of thecore breeding areas for this colonial water bird. Following a 10-year period with stable breeding numbers in Denmark, the population of great cormorantsdecreased. At the same time, a combination of cold winters and low availability of coastal prey fish apparently triggered birds to seek new foraging areas.Thus, cormorants began to appear in rivers and streams coinciding with an observed massive decline of fish, mainly brown trout (Salmo trutta) and grayling(Thymallus thymallus). In this paper, we present the results from studies using radio-telemetry, PIT-tagging, and traditional fish surveys to estimate theimpact of predation in Danish lowland rivers. Recovery of PIT-tags revealed that an estimated 30{\%} of wild trout and 72{\%} of wild grayling tagged in a small riverwere eaten by cormorants. In another medium-sized river, 79{\%} of radio-tagged adult grayling were removed, presumably by cormorants during winter. Thus, predation from cormorants appears to be at a level that explains the observed collapse of grayling and brown trout populations in many Danish streams",
author = "Niels Jepsen and Ravn, {Henrik Dalby} and Stig Pedersen",
year = "2018",
doi = "10.1007/s10750-018-3656-2",
language = "English",
volume = "820",
pages = "189--199",
journal = "Hydrobiologia",
issn = "0018-8158",
publisher = "Springer Netherlands",
number = "1",

}

Change of foraging behavior of cormorants and the effect on river fish. / Jepsen, Niels; Ravn, Henrik Dalby; Pedersen, Stig.

In: Hydrobiologia, Vol. 820, No. 1, 2018, p. 189-199.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Change of foraging behavior of cormorants and the effect on river fish

AU - Jepsen, Niels

AU - Ravn, Henrik Dalby

AU - Pedersen, Stig

PY - 2018

Y1 - 2018

N2 - Since the European population of great cormorants (Phalacrocorax carbo sinensis) rapidly increased 30 years ago, Denmark has been one of thecore breeding areas for this colonial water bird. Following a 10-year period with stable breeding numbers in Denmark, the population of great cormorantsdecreased. At the same time, a combination of cold winters and low availability of coastal prey fish apparently triggered birds to seek new foraging areas.Thus, cormorants began to appear in rivers and streams coinciding with an observed massive decline of fish, mainly brown trout (Salmo trutta) and grayling(Thymallus thymallus). In this paper, we present the results from studies using radio-telemetry, PIT-tagging, and traditional fish surveys to estimate theimpact of predation in Danish lowland rivers. Recovery of PIT-tags revealed that an estimated 30% of wild trout and 72% of wild grayling tagged in a small riverwere eaten by cormorants. In another medium-sized river, 79% of radio-tagged adult grayling were removed, presumably by cormorants during winter. Thus, predation from cormorants appears to be at a level that explains the observed collapse of grayling and brown trout populations in many Danish streams

AB - Since the European population of great cormorants (Phalacrocorax carbo sinensis) rapidly increased 30 years ago, Denmark has been one of thecore breeding areas for this colonial water bird. Following a 10-year period with stable breeding numbers in Denmark, the population of great cormorantsdecreased. At the same time, a combination of cold winters and low availability of coastal prey fish apparently triggered birds to seek new foraging areas.Thus, cormorants began to appear in rivers and streams coinciding with an observed massive decline of fish, mainly brown trout (Salmo trutta) and grayling(Thymallus thymallus). In this paper, we present the results from studies using radio-telemetry, PIT-tagging, and traditional fish surveys to estimate theimpact of predation in Danish lowland rivers. Recovery of PIT-tags revealed that an estimated 30% of wild trout and 72% of wild grayling tagged in a small riverwere eaten by cormorants. In another medium-sized river, 79% of radio-tagged adult grayling were removed, presumably by cormorants during winter. Thus, predation from cormorants appears to be at a level that explains the observed collapse of grayling and brown trout populations in many Danish streams

U2 - 10.1007/s10750-018-3656-2

DO - 10.1007/s10750-018-3656-2

M3 - Journal article

VL - 820

SP - 189

EP - 199

JO - Hydrobiologia

JF - Hydrobiologia

SN - 0018-8158

IS - 1

ER -