AST/IBIS – Stocking WorkshopCase Study - River Bush, Northern Ireland.R. Kennedy1, W. Crozier1, D. Ensing1, J. Kane2, P. Prodohl3 & C. Johnston3.1) ABFI, 2) Dept Culture, Arts & Leisure, 3) Queens University Belfast.
Contents • The River Bush as a monitored river. • Pressures on the River Bush salmon stock. • Enhancement on the River Bush, history, rationale & management objectives. • Review of enhancement activities.
Main Salmon Producing Rivers In N. Ireland River Bush
River Bush Salmon Station Bush River Length 67 km Catchment Area 340km2 5 km
River Bush Salmon Station • Facility established in 1973-4. • A series of upstream/downstream traps were set up at the station (Adult/Smolt). • A series of long term databases on salmon survival established. • One of relatively few long term monitoring stations across the Atlantic basin.
SMOLT TRAP ADULT TRAP
PARR The complete Atlantic Salmon Lifecycle is monitored on the River Bush stock. SMOLT ALEVIN OVA POST SMOLT ADULT
Pressures on Freshwater Production – Habitat Issues • Arterial Drainage Scheme. • Excessive weed growth; degradation of spawning habitats. • Intensive agricultural practices. • Degradation of the riparian zone. • Reduction in habitat quality 1980s-1990s.
Pressures on Freshwater Production - Predation • Major issues with avian predation. • Kennedy & Greer (1988) estimated total daily predation by cormorants on the River Bush to range c. 653-1214 smolts in late April/early May. • Potential annual predation rates c. 51-66% of the total smolt run. No. of breeding pairs of cormorants on Sheep Island (Kennedy & Greer, 1988)
1983 0+ Salmon Survey SQ Category
SQ Category 1996 0+ Salmon Survey
Enhancement Plan • Enhancement stock using hatchery produced 0+ age class salmon. • Target barren/underproductive freshwater habitats which historically supported juvenile fish. • Improve freshwater production and compensate for loss/deterioration of spawning areas.
Management Objectives • Increase annual smolt production from the river to a target of 20,000 fish. • Assist the stock to consistently attain CL. • Monitor impact and outcomes of the management action.
R. Bush Stocking Plan Challenge Overstocking/competitive interaction with wild juveniles. Relatively low survival of introduced juvenile life stages Removal of wild spawners ‘broodstock mining’ Effective monitoring of outcomes. Mitigation Reference to extensive annual electric fishing survey, i.d. ‘recruitment gaps’ Implementation of best practice during stocking (low density/acclimation etc.) Utilisation of ranched salmon, derived from wild stock and outcrossed annually Long term monitoring capacity; EF, smolt trap etc.
Stocking History • Between 1997-2007 c. 3.87 million 0+ salmon stocked directly into freshwater habitats in the R. Bush. • Between 1997-2001 unfed fry stocked, 2002 onwards unfed fry plus fed summerling fry stocked.
Estimation of Survival –Wild Cohorts Total smolt production Ova to smolt survival Ova Cohort YEAR X
Estimation of Contribution – Supplemented Wild Cohorts Variability in Survival Stock Recruitment Relationship Model and Predict Smolt Production from Wild Ova Cohorts
Smolt output from annual ova cohorts From: Kennedy, R.J., Crozier, W.W., Allen, M.M (2012). Journal of Fish Biology, 81(5):1730-1746.
Use of genetic tools for the monitoring of the River Bush supplemental stocking programme – Unfed Fry • 40 unique family pairings 40 male + 40 female broodstock (2002). • Fertilized eggs (avg 3,798 per family) maintained in the hatchery. • 90,500 unfed fry were stocked in the upper reaches of the R Bush (Characterized by limited suitable spawning habitat). • During the smolt runs of 2004 and 2005, 1,212 and 1,262 (total N = 2,474) smolts trapped & sampled for genetic analysis. • Broodstock screened for 25 microsatellite markers – following modelling work (FAP and COLONY software), all smolts screened for a selected informative marker panel consisting of 6 markers (100% assignment to family). • .
Summary results - parentage assignment TSR – Total Smolt Run Capt – smolts intercepted and sampled at the River Bush Research Station
River Bush Salmon Station Bush River Fed fry survival experiment 2007 5 km 30,165 Fin clipped summerlings stocked in 2008 Aug/Sep
Survival of Fed 0+ Summerlings • 2008 an experimental group of 30,165 summerlings adipose fin clipped and stocked. • Areas selected after electric fishing surveys to reduce overstocking/competition. • 1+ & 2+ FC smolts picked up in 2009 & 2010. • Total survival fry to smolt = 5.12%
Management Outcomes • Smolt runs • Adult escapement/Attainment of CL.
Freshwater Production – Smolts Monitoring Phase Management Phase
Biological Characteristics – Smolts Younger 1+ stocked origin smolts Smaller Lower CF
Biological Characteristics – Smolts Stocked origin smolts Differential Run Timing Younger
Potential Implications for Marine Survival • Older larger smolts; higher survival. • Risk from enhancing younger smolts?
Potential Implications for Marine Survival Critical local importance of smolt run timing on the R. Bush. From: Russell et al (2012). ICES J. Mar. Sci. 69 (9): 1549-1562 .
Appraisal of Objectives • Increase annual smolt production from the river to a target of 20,000 fish. • Assist the stock to consistently attain CL. • Monitor impact and outcomes of the management action.
Changing Management Priorities? Scientific assessment conducted on the Bush has been useful to local management e.g. Abundance is not all important. Stocking was a relatively ‘quick’ option BUT it cannot address and solve underlying habitat issues. Stocking has RISKS.... Important to maximise the production of wild spawned smolts with optimum fitness. Other ‘longer term’ conservation tools include habitat & fishery management
Fishery Management to Maximise Wild Escapement to NI Rivers. Cessation of mixed stock fisheries Catch & Release Angling
Habitat Improvement and Restoration on the River Bush Weed Clearance Gravel Addition
Future, the next phase.... Emphasis on maximising wild production via habitat management. Collaborative assessment of overall lifetime fitness of stocked fish.