"Hampshire Avon Egg Box Project".
Egg-box Update
(Left)View downstream covering about half the release site for 2,198 swim-up salmon fry (March-April 2007). (Right)September - same release reach (closer view) later in the year
(Left)Monthly mapping of river habitats (displayed as % areas present), used to assess changes in suitability for developing salmon parr.
(Middle) The release site was divided into reaches (identified by numbering the fence posts).In each of 8 reaches (not all are shown) the % cover of in-river habitats were assessed by eye and recorded each month. For clarity - the main habitats and their locations are shown on the slide. Water Crowfoot (dark green) increased slightly in area between April and May, but is less prolific than would be expected in this type of stream. As stream discharge fell the marginal vegetation wss expected to spread into the stream, tending to maintain water depth and speed whilst increasing cover, helping young fish to avoid predation.
(Right)Numbered fence posts indicated (c. 3.5m apart on the right) Downstream section (of 8 sections mapped)
(Left) Bournemouth University staff: Rob Britton (left) and Rodolphe Gozlan recording HABSCORE data (habitat suitability score for salmonids).
The release site was assessed at 12 points along the 200m length of stream.
(Right)Bold text - the only frequent habitat types available - Note HABSCORE set up for salmonids >10cm - not parr, habitat suitability assessment will take account of this
ASG discussion points.
The high survival rate of emerging swim-up fry demonstrated the eggs were fertile, egg-box management and water quality were appropriate at the selected site.
Moving forward - a modest increase of the project to use three egg boxes was proposed and agreed. Details - discussed between Jon Bass, Andy Martin, Graham Lightfoot (in early August). The subsequent monitoring of released parr is a costly but most critical requirement of the project.
The purpose of the project was again emphasised: its purpose is to see whether suitable river reaches are capable of yielding a higher density of salmon parr than is generally found (i.e., compared with the average - c.3 per 100 square metres - recorded at the EA long-term monitoring sites).
Previous studies have predicted that salmon egg survival in Avon redds is relatively low (15-35%) and constrained by fine sediment infill to natural redds. What is not clear is whether this alone is responsible for the low densities of salmon parr recorded. Robust evidence is required before more effective interception/prevention of fine sediment run-off is managed/imposed.
Following the ASG meetings (05.05.06 and 28.07.06) on the applicability of using egg boxes on the Avon in relation to salmon it was agreed that a revised proposal would be drawn up by Jon Bass (WSRT) in consultation with Andy Martin (EA Blandford - Fisheries Technical Specialist).
The Initial Proposal
Aims
This proposal is designed to:
- develop the necessary skills and assess the practicalities of using egg boxes as a management tool on the Hampshire Avon.
- investigate population densities of parr produced from known numbers of swim-up salmon fry released into selected reaches of the Avon that currently have very few or no salmon parr.
- establish the extent to which the numbers per unit area and growth rates of Avon parr from egg boxes are influenced by contrasting in-stream habitats.
- relate findings to management approaches to instream habitats in the Avon.
Background
Following the major decline in Avon salmon in the 1980s, attempts to restore the native salmon stocks have not as yet delivered a clear or sustained recovery. A series of research needs for chalk stream salmon stocks were identified in 2002 (Environment Agency Technical Report: W2-010/TR), recommendations included the monitoring of parr densities in areas stocked with fry from incubators. Progress on this approach has, of necessity, awaited the outcomes from egg-box studies on the Test and Itchen. Those studies are currently expected to suggest that survival rate to smolt stage can be higher from egg-boxes than from natural spawning.
The small scale of this current proposal will not in itself significantly increase the numbers of returning adult fish. The trial is designed to establish the survival and growth rates of Avon salmon parr achieved by swim-up fry stocked at two pre-determined and realistic densities (‘low’ and ‘high’), mimicking as far as possible the range of egg deposition within natural redds on the Avon.
Release site characteristics
Release reaches for swim-up fry will be selected on the basis that they provide:
- suitable conditions for juvenile salmon
- locations not currently populated with (or with very few) juvenile salmon
- accessibility for monitoring
- reaches representative of a significant part of the Avon system
- scope for small-scale manual habitat manipulation
Practicalities
Recovery of ripe salmon will be undertaken by an experienced fishing team prepared to work during Christmas week as the opportunity to capture and strip suitable fish is during a very short period. The capture/re-capture of unripe fish and unwanted by-catch will be minimised by choosing sites that present the easiest conditions for targeting specific fish, removing them with least stress. If electro-fishing equipment is the most appropriate technique that can be used at the site it will be of the smooth direct current type. Stripped fish will be returned alive to the river on the basis that a small proportion of kelts survive to return and spawn a second time.
Suitable sites for egg-box locations in the Avon catchment will be determined after obtaining advice from Agency staff with recent experience of managing egg-boxes on the Test and Itchen. Egg –boxes of suitable design for salmon (recommended carrying capacity up to 6000 eggs) are available to order. These boxes retain the swim-up fry in a separate holding chamber, allowing them to be removed, the numbers recorded and a sub-sample measured for calculating average fry length.
The swim-up fry are released daily to the reaches being stocked. The number of eggs will not be known prior to stripping, therefore reaches selected for stocking will be of sufficient total area to accommodate swim-up fry from 10,000 eggs.
Resources required
(WSRT have provisionally indicated willingness to part-fund this project, but this is conditional on the final project plan fitting their expectations).
Activities 1 & 2 require a firm commitment for funding.
Activity 3 onwards will only proceed if a minimum of 5,000 fertilised eggs are obtained.
There are three interlinked parts to Activity 4, they will all proceed if sufficient swim-up fry are produced, but the number of release sites used (and related costs) depend on the yield of swim-up fry.
The final assessment (Activity 5) will be undertaken in full if the planned Activities (1-4) are completed.
1. Egg-box installation (autumn 2006)
4 egg-boxes c.£500 each
installation costs £150 each (based on 2 boxes per site)
(1 day at each site - 2 people, with on-site transport).
Costs:
2. Capture and stripping of ripe fish (Dec 06/Jan 07)
6 experienced fishery operatives - with daily reconnaissance visits (by one) for up to one week. Obtain two pairs of salmon that are ready for stripping. Consider the use of sperm from precocious male parr - if these are also captured. Take small fin-clip samples preserved for DNA ‘fingerprinting’ from each fish used. Return stripped fish to the river after monitoring their recovery. Measure the egg volume from each female, take sub-sample egg counts to calculate the total number of eggs from each female. Transfer eggs to egg-boxes, splitting the eggs from each female between two egg-boxes.
Costs: (notional cost - depends on personnel used)
3. Incubation sites (spring 2007)
Daily record of incubation temperature, water throughflow rates and debris clearance required, for each egg-box and site. (30 minutes per day at 2 sites – for 10-12 weeks)
Daily record of swim-up fry numbers in the overflow chamber, total lengths of a sub-sample of fry, with fry released daily in each pre-selected river reach. From each incubator box a small sample of swim-up fry will be preserved for DNA ‘fingerprinting’ analysis.
(Commitment: around 0.5 hours per day for each of four egg boxes for 2 about weeks, includes daily release of swim-up fry at two release sites).
Costs: (negotiable)
4. Release sites (spring-autumn 2007)
4a. Within-river habitat mapping in alternate months, with habitat control option at some release sites.
Suitable for supervised student projects - site mapping visits in April, June, August, October, on reaches at and adjacent to the two release sites.
Supervisor time with travel/subsistence for site visits by two overlapping MSc students (April-July/July-October).
Costs:
4b. Parr monitoring.
After three months (July) and five months (September), analyse numbers and size of parr recovered at the release reaches and reaches immediately upstream and downstream. (Using catch-depletion EA parr survey techniques).
Electro-fishing team of four, 1 day for each release area, series of sampling locations within 1 km upstream and 2 km downstream of release points, on two occasions - 16 mandays, plus 4 mandays data collation/summary report).
Costs:
4c. Relate in-river habitats to parr distribution, size and numbers.
MSc Student project (August-November) - relate salmon parr distribution, growth and numbers to in-river habitat availability. (Reliant on parr monitoring data obtained in July and September). Supervisor time, with travel and subsistence for 1 site visit by student.
Costs:
5. Assess the egg-box trial outcomes (winter 2007)
Independent assessment and report of the outcomes, 5 days at the going rate for an experienced consultant.
Cost: