1. Wild Trout in an English Chalk stream: Modelling Habitat Juxtaposition as an Aid to Watershed Rehabilitation A.Burrows, S.Kett and M.A.House Flood Hazard Research Centre, Middlesex University, Queensway, Enfield London, UK,

2. The River Piddle: A Classic English Chalkstream
Stable flow regime
gravel substrate
high primary and secondary production
complex structure of riparian zone providing great “edge” habitat
cover

3. RIVER PIDDLE Location of study sites

4. Problems of bankside grazing
Poached unfenced banks
Bank collapse
Absence of littoral margin
Wider & shallower channel

5. Research Aims
Analyse response of a wild brown trout population to temporal and spatial habitat variation in an English chalk-stream using Physical Habitat Simulation Model
Examine habitat factors limiting carrying capacity for adult trout
Assess importance of juxtaposition of spawning and nursery habits for 0+ recruitment
Quantify importance of reach scale meso-habitats for different life stages and seasons.
Improve understanding of natural mechanisms regulating brown trout populations to improve effectiveness of habitat rehabilitations

6. Stages in Methodology
Quantitative electrofishing

7. Transect Based Meso-Habitat Survey
Depth
Column velocity
Cover
Substrate

8. Cells defined by surveying channel cross sections

10. Habitat Time Series Generation

11. POPULATION DYNAMICS

12. Length - frequency plot Upstream sector - 199935 30
age 0+ = 115cm
age 1+ = 210
age 2+ = 265
age >2+ = 325 25 20 15 10 5 50
100
150
200
250
300
350
400
450
500

13. Population Structures

14. Length – frequency histograms
Comparison of length-frequencies between river sectors

15. Von Bertalanffy Growth Curve from mark-recapture data showing length gain for tagged trout in the Cobbs Wood reaches
Result - Brody-Bertalanffy
Results
k (growth rate) = 0.329
L infinity = 420.3
To (Time when length is 0) = 0.866
95% Confidence for K +/
95% Confidence for L infinity +/

16. RELATIONSHIPS BETWEEN HABITAT AND POPULATION STRUCTURE
ANALYSIS II
RELATIONSHIPS
BETWEEN HABITAT AND POPULATION STRUCTURE

17. Adult Habitat Overhanging cover Pool Deep undercut bank
Half-log cover board

18. Adult Winter Habitat Durations
500
1000
1500
2000
2500 93 94 95 96 97 98 99
Cover
Near shore
Fig.1. Adult winter habitat durations for marginal and total reach habitats (WUA) in the Upper River

19. Adult Marginal Habitat-Upper River
200
400
600
800
1000
1200
1400 93 94 95 96 97 98 99
2000
Summer
Winter
Seasonal Time Series comparison for Adult Marginal Habitat

21. Winter view

24. Adult density v marginal habitat
Relationships between adult density and mean marginal habitat in winter

25. Fry Habitat
Medium gravel - good spawning habitat

26. Spawning Quality by Habitat Type

28. Riffles - spawning R2 = 0.65; p=0.05 Fry
56.00
57.00
58.00
59.00
Mean Riffle Habitat during hatching period
-1.00
0.00
1.00
2.00
Fry ^
R2 = 0.65; p=0.05

29. Young of Year Growing Season
Relationship between 0+ density and minimum summer habitat
R2= 0.49; p=0.01
Growing Season Habitat Minima
-1.00
0.00
1.00
2.00
3.00
Fry ^
fryd = * ys.min
R-Square = 0.49

30. Meso-habitat Time Series (GS)

31. Spawning and Nursery Habitat Related to Fry Density in Lower River

32. SUMMARY
Adult carrying capacity at reach scale related to winter marginal habitat
Refugia from winter peak flows more important than from summer low flows
Riffles are critical meso-habitats for early life stages (especially during hatching period)
Glides are critical meso-habitats during first growing season at low flows
Glides are more important for juveniles age1+
Sequence of meso-habitat juxtaposition important for early life stages
Lower sector reaching biological carrying capacity ?

33. CODA: Wild Trout 8 context
Similar anthropogenic problems as in US
BUT:
relatively few, small catchments with wild trout populations
populations are isolated and fragmented (‘contracted’)
limited refugia from which potential re-colonisation can occur
In tiny catchments meso-habitat juxtaposition is more important to maximise recruitment and offers an effective management technique with potential catchment wide benefits
No second chance
- chalk catchments are a small and unique ecotype

34. FISHERIES SCIENTIST FOR SALE
27 years fly fishing experience
Salmonid habitat assessment and mapping
Channel survey and habitat enhancement
Electofishing
Habitat modelling
Population dynamics analyses

35. FLY FISH IN ENGLAND