DO OTTERS TARGET THE SAME FISH AND SIZES AS ANGLERS? A CASE STUDY FROM A LOWLAND TROUT STREAM IN THE CZECH REPUBLIC ROMAN LYACH* and MARTIN ČECH** *Institute for evaluations and social analyses, email: [email protected], ** Institute for Environmental Studies, Charles University

INTRODUCTION MATERIALS AND METHODS RESULTS CONCLUSIONS

⊲ Lutra lutra is a an ⊲ Otter spraints (n = 281) were collected in ⊲ Otter diet was dominated by gudgeon ⊲ Anglers and otters targeted and caught important piscivorous predator on winter on the Chotýšanka stream in gobio (90 % by number) different fish species and sizes smaller streams in central Europe central Bohemia (Czechia, central – a dominant fish species in the ⊲ The competition for fish between (Czechia, Slovakia, Poland) Europe) ecosystem with no angling value because recreational anglers and otters is likely ⊲ Otter dietary analysis was done using fish of its small body size small ⊲ Intensive restocking with brown trout bones and remains (Figure 1) ⊲ Anglers caught mostly rainbow trout ⊲ Otters are likely not a threat to local Salmo trutta and rainbow trout ⊲ Length-weight equations were used to – a non-native restocked fish species of fisheries sector Oncorhynchus mykiss is common estimate sizes of fish eaten (source: high angling value and no ecosystem fisheries practice on smaller streams in FishBase) importance central Bohemia ⊲ Mandatory angling logbooks of anglers ⊲ Otters caught small fish (median 10 g) were used to analyze fish killed by while anglers caught large fish (median ⊲ Restocked salmonids are often more anglers (source: Czech Fishing Union) 300 g) vulnerable to predation than wild fish ⊲ Restocked trouts were hatched in local ⊲ Fish dominated in otter diet, but otters ACKNOWLEDGEMENTS (Fritts et al. 2007) fish hatcheries also caught frogs Rana sp. and crayfish Astacus fluviatilis This poster was created as a part of a ⊲ Anglers and fisheries managers complain ⊲ Restocked brown and rainbow trout project “Setting the conditions and the that otters compete for „their“ restocked made 11 % of otter diet by biomass environment for international and cross- fish sector cooperation”, registration number 16 CZ.02.2.69/0.0/0.0/18_054/0014660) 14 financed from the Operation Programme 12 Research, Development and Education, 10 European Structural and Investment Funds 8 6 and the Ministry of Educations, Youth and

RESEARCH QUESTION 4 Sports of the Czech Republic. Frequency (%) Frequency ⊲ Do otters and anglers target and catch 2

0 6

similar fish species and similar sizes of 1

16 21 26 31 36 41 fish? 11 Length [cm]

25 Figure 1: Examples of diagnostic bones of selected fish 20 species : pharyngeal bone (os pharyngeum) of (a) Grass 15 REFERENCES RESEARCH HYPOTHESIS Carp (Ctenopharyngodon idella) – reconstructed fish ⊲ We expected to find mostly different fish size 31, 37 and 34 cm LT (from left), (b) European Chub 10 Fritts, A. L., Scott, J. L., & Pearsons, T. N. species and sizes of fish in otter diet in () – 32 and 14 cm LT (from left), (c) Ide (%) Frequency 5 (2007). The effects of domestication on the comparison to angling reports. (Leuciscus idus) - 32 cm LT, (d) Common Carp (Cyprinus

carpio) - 22, 17 and 10 cm LT (from left), (e) Roach 0 relative vulnerability of hatchery and wild

8 0 4

48 16 20 24 28 32 36 40 44 (Rutilus rutilus) - 35, 17 and 11 cm LT (from left), (f) 12 origin spring Chinook salmon Nase (Chondrostoma nasus) – 30 cm LT, lower jaw Weight [g] (Oncorhynchus tshawytscha) to (dentale) of (g) Northern Pike (Esox lucius) - 40 and 38 predation. Canadian Journal of Fisheries cm LT (from up), (h) (Sander lucioperca) – 24 and Figure 2: frequency distribution of fish (n = 1 532) in 26 cm LT (from up) and (i) European Perch (Perca otter diet by length (upper) and biomass (lower) and Aquatic Sciences, 64(5), 813-818. fluviatilis) - 17 and 21 cm LT (from up). Photo: M. Čech