The influence of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)on the breeding of the white-throated dipper (Cinclus cinclus)

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1 The influence of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)on the breeding of the white-throated dipper (Cinclus cinclus) Anna L. K. Nilsson Jan Henning L Abée-Lund Asbjørn Vøllestad Kurt Jerstad Ole Wiggo Røstad Svein Jakob Saltveit Thomas Skaugen Nils C. Stenseth Bjørn Walseng Natural History Museum Centre for Ecological and Evolutionary Synthesis Norwegian Water Resource and Energy Directorate Norwegian Institute for Nature Research Norwegian University of Life Sciences

2 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.

3 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

4 Study site Acid rain leading to extinction of the salmon population River Lygna Waterfall

5 Data on dipper breeding success: Continuously monitoring data on population size, breeding attempts and breeding success of all dipper pairs in the river system Population fluctuations of the white throated dipper Cinclus cinclus Climate has so far been the most important factor explaining fluctuations in population size 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,

6 Two types of fish data: 2500 < 3kg 3-7 kg >7 kg Trout kg 1.Total egg production and recruitment estimated from the catch statistics 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 Total fecundity Weight in kg Salmon Trout

7 Two periods: and Fish density anadromous reach Fish density non anadromous reach 100 Atlantic salmon 0+ parr Older parr 100 Brown trout 0+ parr Older parr No. pr.100m2 50 No. pr.100m Brown trout 0+ parr Older parr Before After salmon recolonization No. pr.100m Before After salmon recolonization

8 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

9 Temporal trends in the dipper population: Size of the dipper breeding population during Upstream Downstream Number of breeding pairs R 2 = 0,7588 Salmonid recolonization 0 R 2 = 0, 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 (p<0.001) No temporal trend after salmonid recolonization

10 Temporal trends in salmonids: Annual catch of salmon and trout from 1993 to Trout No Salmon No Catch in number R² = R² = The annual catch of salmon increased; p< The annual catch of trout decreased; p<

11 Temporal trends in salmonids: Annual fecundity of salmon and trout from 1993 to Salmon Trout Total Fecucudity (annual number of eggs in thousands) R= R= R= Increased annual total salmon fecundity; p= Decreased annual total trout fecundity; p=0.02 Increased annual total salmonid fecundity; p= 0.02

12 Temporal trends in salmonids: Annual density of salmon and trout fry from 1991 to Salmon fry Trout fry 60 No. fish per 100 m R² = R² = Increase in juvenile salmon fry density; p< Decrease in juvenile trout fry density; p=0.03 No density change in upstream juvenile trout fry density; p= 0.8 (not on fig.)

13 Impacts on dipper population size 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< Upstream: Dipper population was positively affected by the mean winter temperature; b=0.17, z=8.8, P< Dipper population positively affected by trout fry density; b=0.008, z=4.7, P<0.0001

14 Downstream: Impacts on dipper reproductive output- breeding attempts 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 dipper population Successful versus failed breeding attempts rates Upstream: Difference in successful attempts between before and after (resp and 0.64; P=0.02) Significant decline in success rates during ;p=0.03) Significant increase after 1993;p=0.003).

15 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

16 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

17 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

18 Thanks to: The field crew Financial support: Norwegian Research Council (no ) The Norwegian Water Resources and Energy Directorate Norwegian Environment Agency Thankyou for listening

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