The influence of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)on the breeding of the

white-throated dipper (Cinclus cinclus)

Natural History MuseumCentre for Ecological and Evolutionary SynthesisNorwegian Water Resource and Energy DirectorateNorwegian Institute for Nature ResearchNorwegian University of Life Sciences

Anna L. K. NilssonJan Henning L’Abée-Lund

Asbjørn VøllestadKurt Jerstad

Ole Wiggo RøstadSvein Jakob Saltveit

Thomas SkaugenNils C. StensethBjørn Walseng

Hypothesis:• Sharing the same food items, juvenile salmonids may influence on the

breeding and reproductive success of white-throated dipper

Background:• Interactions between birds and fish are often overlooked in aquatic

ecosystems

Suitability:• Before and after recovery of an extinct salmonid population

• The recovery of salmon populations introduced a potential for renewed interactions with the dipper.

Data on dipper breeding success:

• Continuously monitoring data on population size, breeding attempts and breeding success of all dipper pairs in the river system

Two types of fish data to test the associations between dipper success and abundance of fish:

• The total egg production and thus the recruitment of juvenile salmonids was estimated from the catch statistics

• Long-term monitoring data on the density of juvenile salmonids

Study site

River Lygna

Waterfall

Acid rain leading to extinction of the salmon population

Nilsson ALK, Knudsen E, Jerstad K, Røstad OW, Walseng B, Slagsvold T, Stenseth NC. (2011). Climate effects on population fluctuations of the white-throated dipper Cinclus cinclus. Journal of Animal Ecology, 80, 235-243.

• Climate has so far been the most important factor explaining fluctuations in population size

Population fluctuations of the white‐throated dipper Cinclus cinclus

Data on dipper breeding success:

• Continuously monitoring data on population size, breeding attempts and breeding success of all dipper pairs in the river system

Annual salmon fecundity: • Salmon <3 kg 40% females• Salmon 3-7 kg 70% females• Salmon >7 kg 55% females

• 1500 eggs per kg female salmon

Annual trout fecundity:• Ratio of males to females 1:1

• Mean fecundity estimated following the regression ln F=1·009 ln W+0·695,(Jonsson & Jonsson 1999).

• Assumptions: resident female trout only produced a marginal number of eggs

Two types of fish data:

1.Total egg production and recruitment estimated from the catch statistics

0

500

1000

1500

2000

2500

1993 1996 1999 2002 2005 2008 2011 2014

Wei

ght i

n kg

< 3kg 3-7 kg >7 kg Trout kg

0

500

1000

1500

2000

2500

3000

1993 1996 1999 2002 2005 2008 2011 2014

Tota

l fec

undi

ty

Salmon Trout

Two periods: 1978-1992 and 1993-2014

Before After salmon recolonization

0

25

50

75

100

1978 1982 1986 1990 1994 1998 2002 2006 2010

No.

pr.1

00m

2

Atlantic salmon 0+ parrOlder parr

0

25

50

75

100

1978 1982 1986 1990 1994 1998 2002 2006 2010

No.

pr.1

00m

2

Brown trout 0+ parrOlder parr

0

25

50

75

100

1978 1982 1986 1990 1994 1998 2002 2006 2010

No.

pr.1

00m

2

Brown trout 0+ parrOlder parr

Before After salmon recolonization

Fish density non anadromous reachFish density anadromous reach

Testing:

1. Temporal trends in the salmonid and dipper data; least-squares regression analysis

2. Correlations between the estimated fecundity of salmon and trout and:• the dipper population size • the reproductive output

3. Correlations between the estimated average density of the fry and parr and:• the dipper population size• the reproductive output the next spring

4. Relationship between fecundity and winter temperature

Size of the dipper breeding population during 1978-2014

• No significant temporal trend in the total size of the two dipper populations

• Strong correlation between the size of the two dipper populations; r=0.83, P<0.0001)

• Significant increase in both population size during 1978-1992 (p<0.001)

• No temporal trend after salmonid recolonization

0

20

40

60

80

100

1980 1985 1990 1995 2000 2005 2010 2015

Num

ber o

f bre

edin

g pa

irs

Upstream

DownstreamR2 = 0,7588

R2 = 0,5815

Temporal trends in the dipper population:

Salmonid recolonization

Annual catch of salmon and trout from 1993 to 2014

R² = 0.3575

R² = 0.5892

0

200

400

600

800

1000

1200

1400

1993 1996 1999 2002 2005 2008 2011 2014

Cat

ch in

num

ber

Trout NoSalmon No

• The annual catch of salmon increased; p< 0.0001• The annual catch of trout decreased; p< 0.0042

Temporal trends in salmonids:

Annual fecundity of salmon and trout from 1993 to 2014

• Increased annual total salmon fecundity; p= 0.0001 • Decreased annual total trout fecundity; p=0.02• Increased annual total salmonid fecundity; p= 0.02

Temporal trends in salmonids:

0

500

1000

1500

2000

2500

3000

1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013

Fecu

cudi

ty (a

nnua

l num

ber o

f egg

s in

th

ousa

nds)

Salmon Trout Total

R= 0.2454

R= 0.2778

R= 0.5415

Annual density of salmon and trout fry from 1991 to 2010

• Increase in juvenile salmon fry density; p< 0.0001 • Decrease in juvenile trout fry density; p=0.03• No density change in upstream juvenile trout fry density; p= 0.8 (not on fig.)

R² = 0.5256

R² = 0.2232

0

10

20

30

40

50

60

70

1991 1994 1997 2000 2003 2006 2009

No.

fish

per

100

m2

Salmon fry Trout fry

Temporal trends in salmonids:

Downstream:• Salmon fecundity, trout fecundity, total salmonid fecundity or the juvenile fish density did not explain

any of the variation in the dipper population size

• Mean winter temperature did account for the variation in the dipper population size; z=4.2, P<0.0001

Upstream:• Dipper population was positively affected by the mean winter temperature; b=0.17, z=8.8, P<0.0001

• Dipper population positively affected by trout fry density; b=0.008, z=4.7, P<0.0001

Impacts on dipper population size

Impacts on dipper reproductive output- breeding attempts

Successful versus failed breeding attempts rates

Upstream dipper populationDownstream:

• No difference in success rate between before (0.85) and after (0.80) salmon recolonizing

• No temporal trend in rates• A higher overall success rate p=0.0002).

Upstream:• Difference in successful attempts between before

and after (resp. 0.70 and 0.64; P=0.02)

• Significant decline in success rates during 1978-1992 ;p=0.03)

• Significant increase after 1993;p=0.003).

Impacts on dipper reproductive output- number of chicks

Downstream:

• No temporal trend• No difference in output before (3.9) and after (4.0) salmon recolonizing; p=0.5• No association with the fecundity of salmon or trout or total fecundity• No association with the juvenile salmonid density; salmon, trout or total

Upstream:

• No temporal trend• No difference in output before (3.9) and after (3.9) trout recolonizing; p=0.4• No association with the juvenile trout density; fry or parr

Facts:• The downstream territories were not less attractive for the dipper after the

recolonization by salmon

• The upstream dipper breeding success declined before the recolonization and increased after, linked to the improved water quality, increasing invertebrate prey abundances and biodiversity

Conclusions:

• The breeding dipper population size and reproductive output was not influenced by salmon, trout or total salmonid fecundity

• The upstream dipper population size was positively affected by the density of juvenile trout

• Upstream juvenile trout had a weak positive effect on the dipper population, indicating that dippers may prey on small trout

• Winter temperatures and acid rain with subsequent liming seem to play a more important role in the life history of the dipper

• The improved water quality increased biodiversity and important prey groups for both the dipper and the fish

Thanks to: The field crew

Thankyou for listening

Financial support: Norwegian Research Council (no. 221393) The Norwegian Water Resources and Energy DirectorateNorwegian Environment Agency