Fish migration and barriers

1. Fish migration and barriers Anthony Watkins Fish ecologist SEPA (original by: Dr Alistair Duguid Senior fish ecologist, SEPA) Photos: Colin Bull, Stirling University

2. Talk overview • What is the issue? • Key aspects of fish migration • Types of barrier • Tools for assessment

3. Why are barriers important? • UK: High density of river obstacles • Highly managed river systems • A major impact on spatial & temporal distribution of fish • Secondary effects, including increased predation, exploitation, behavioural changes • Mitigation via action at obstacles is possible • Single biggest restoration and management potential for fish Photos: Colin Bull, Stirling University

4. Fish need to migrate • Most fish species migrate • Between marine and freshwater environments: • Eels- from breeding grounds in the Caribbean sea to freshwater rivers across Europe • Salmon- from breeding grounds in freshwaters to seas off Greenland • Sea trout- between streams, rivers, estuaries and the open sea • Sea lamprey and river lamprey- from breeding grounds in rivers to estuaries and open sea • Between different freshwater habitats: • Brown trout - very flexible behaviour • Coarse fish (e.g. pike, perch, roach, grayling) Photos: Colin Bull, Stirling University

5. Key issues: • Which species need to be considered? • Which life stages and sizes? • Which direction? Likely up and down! • Usually consider adults moving upstream to spawn but downstream movement equally important • Adults following spawning • Juveniles (e.g. smolts) • Seasonal - which times of year are important? • River discharge - elevated flows trigger some species (e.g. salmon); low flows needed by others (e.g. elvers) Photos: Colin Bull, Stirling University

6. Key issues (continued): • What are their swimming abilities? • Burst swimming • Sustained swimming • Swimming form and behaviour – trout very different to eels, and lamprey! • Height fish swim in the water column – dictates where entrance to a fish pass should be.

7. Swimming ability • Ability depends on fish size, species, health and reproductive status • Sufficient depth is critical for generating thrust (for salmonids) • Water temperature affects maximum speed (+ve) and endurance (-ve) (Beach, 1984)

8. Swimming ability Source: WFD111 barrier assessment project

9. Behavioural considerations • Fish also react to: • Light- particularly sharp contrast between light and dark; lighting in culverts can help; affects migration timing • Noise - piling/construction impacts • Hydraulic conditions (e.g. abrupt change at weir crests – fast, shallow water) • Cover – instream (e.g. rocks) and overhead (e.g. trees)

10. Structure types• Culverts• Weirs • Fords / bridge footings• Abstraction off-takes• Dams• Sluices• Natural obstacles

11. Culverts: key considerations • Slope, length and water velocity- determine how quickly and for how long a fish has to swim for • Depth- key for successful swimming/ leaping • Outlet design- elevated entrances require a leap • Light (?)- may affect fish behaviour • Debris • Very common- cumulative effect Photos: Colin Bull, Stirling University

12. Fords and bridge footings • Velocities & depths • Length of swim required • Associated outlet drop characteristics Photos: Colin Bull, Stirling University

13. Weirs: key considerations • Hydraulic head difference (usually require a leap) • Velocity and depth on weir face • Gradient and length • Presence of lip or step is particularly challenging Photos: Colin Bull, Stirling University

14. Impact of weirs on downstream migrating salmon smolts Gauld, 2013

15. Assessment tools • WFD111 (2a) Coarse resolution rapid-assessment methodology to assess obstacles to fish migration Photos: Colin Bull, Stirling University

16. More assessment tools • Observation • Direct surveys • Fisheries records • Redd counts • DNA • Tagging and tracking • Fish counters – to monitor passage