The UK Experience with use of Triploids for Restocking

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1 The UK Experience with use of Triploids for Restocking Management of Brown Trout (Salmo trutta) Stocking in England and Wales Dr Brian Shields Senior Fisheries Scientist GENIMPACT 19 th to 21 st April 2007

2 Environment Agency Fisheries Management and Regulation in England and Wales Salmon and Freshwater Fisheries Act (Section 30) Introduction of Fish to Inland waters

3 Diversity of Trout in England and Wales Sea Trout and Brown Trout

4 Scale of Trout Fisheries Sea Trout Catches 2005, rods 40319, nets Brown trout est ~40,000 Sea Trout (& salmon) Licences rods 34062, nets 385 brown trout est ~400,000 Value (2000 prices) River trout fisheries c. 230m (320m Euro)

5 National Trout & Grayling Fisheries Strategy (2003) to conserve and improve wild stocks of trout, sea trout, char and grayling,...enhancing the environment for all types of fisheries for these species in England and Wales....enhance the social and economic benefits derived from these fisheries.

6 National Trout & Grayling Fisheries Strategy (2003) - Classification Native Trout Waters (green)- waters that have significant natural production of trout, or from which there is ready access to other waters with such production. Other (blue) - waters that do not have such production or access.

7 Trout Stocking - Current Policy In general, we will continue to consent stocking (of farmed brown trout) into native trout waters if: consistent with practice over the last 5 years (1998 to 2002); or stock fish are triploid females; or stock fish are derived from local, naturally produced broodstock under a suitable rearing regime. Policy to be reviewed in 2007

8 Trout Stocking - Current situation c. 800 applications to introduce farmed brown trout to rivers annually c. 700,000 brown trout (~400 tonnes) introduced to rivers annually, ~90% fertile, mixed sex diploids 2.6million farmed rainbow trout (~3000 tonnes) released into still waters ~20% fertile diploid

9 Trout Stocking - Current situation

10 Research Review of Genetic Impacts of Trout Stocking on Indigenous Populations Triploid Trout Phase 1 - Triploiding Technique Triploid Trout Phase 2 - Risk Assessment Triploid Trout Phase 3 - Field Trials - Effects on wild trout, diet, behaviour & angling experiences

11 Genetic Impacts of Stocking on Indigenous Trout Populations Extent of introgression is variable and unpredictable & not related to stocking intensity or history. Genetic changes caused by stocking with farmreared brown trout are almost always detrimental to the fitness and survival of individual populations and potentially to the long-term survival of the species. All supplemental stocking with fertile farm-reared and non-native brown trout in England and Wales should be prohibited. The only forms of stocking permitted should be stocking with sterile triploid fish, or supportive breeding.

12 Triploid Trout Phase 1 Triploiding Process and Review of Biology Most reliable triploiding process for brown trout is to fertilise normal diploid eggs with milt from masculinised genetic females, then pressure shocking the eggs at the second meiotic division stage. Considerable potential for increased triploid brown trout production by both current brown and rainbow trout producers in England and Wales, though this may be constrained by a lack of technical knowledge. Reviewed biology of triploids.

13 Triploid Trout Phase 1 Triploiding Process and Review of Biology Sex reversed males have reduced fertility (~80%) Ova survival to hatching 80-85% Triploid fry and fingerlings grow more slowly than diploids Growth advantages of triploidy begin to show at 16 to 18 months and persist from this time Triploids are less aggressive than diploids. Triploids are more prone to stress - especially low dissolved oxygen. Triploids have been preferred in a number of trout farms due to their higher over-winter survival.

14 Triploid Trout Phase 2 Hazard Identification & Risk Assessment Potential hazards associated with stocking triploid rather than diploid trout arise from: the theoretical possibility of interference with spawning activities of wild stocks, increased competition and subsequent loss of growth performance of wild stocks, suppression of recruitment processes in wild populations, alteration of fish community structure.

15 Site Retention (%) Density (/100m 2 ) Triploid Trout Phase 3 Fields Trials - Preliminary Results Wild trout densities (2004 & 2005) Wild trout recaptures (2005) Control Triploid Diploid Control Triploid Sites Diploid Sites 10 0 Upland Lowland

16 Condition (K) Triploid Trout Phase 3 Fields Trials - Preliminary Results Wild trout Condition Factor (2004 & 2005) Control Triploid Diploid Wild trout growth (2005) G UPLAND LOWLAND Control Sites Diploid Sites Triploid Sites

17 Site Retention (%) Triploid Trout Phase 3 Fields Trials - Preliminary Results Growth of stocked trout Recaptures of stocked trout (survey) G UPLAND LOWLAND Diploids Triploids All sites pooled Upland sites Lowland sites Diploid Triploid

18 Triploid Trout Phase 3 Fields Trials - Preliminary Results Diet No significant differences in wild trout stomach contents (by numbers or volume) between stocked and unstocked sites. Triploids contained significantly less fish in their diet than wild trout

19 Triploid Trout Phase 3 Fields Trials - Preliminary Results Fishery Performance 16.7 % of stocked trips and 11.3 % of stocked dips were recaptured by anglers. No perceived difference in fighting ability and visual condition of triploids compared to diploids. Spawning Behaviour All female triploids do not interfere with spawning wild fish. (from literature, male triploids may try to spawn with wild fish)

20 Other Information A farmer s guide to all-female triploid brown trout production", British Trout Association and The Environment Agency, Available free to BTA members, commercially available to non-bta members. Audit of triploid production technique (pressure) >95% triploiding success.

21 Further Considerations Cost of pressure shocking equipment 5-7K (Euros 7-10K). 4 to 6 year lead-in time to full triploid production. Consumer perception of triploids.