Grayling Introduction into the Afon Ceiriog, Report to Countryside Council for Wales concerning the Afon Ceiriog Grayling Introduction, 2009

Transcription

1 Grayling Introduction into the Afon Ceiriog, Report to Countryside Council for Wales concerning the Afon Ceiriog Grayling Introduction, 2009 NOS/FTS/DSAP/10/1 NOS

2 We are the Environment Agency. It's our job to look after your environment and make it a better place - for you, and for future generations. Your environment is the air you breathe, the water you drink and the ground you walk on. Working with business, Government and society as a whole, we are making your environment cleaner and healthier. The Environment Agency. Out there, making your environment a better place. Published by: Environment Agency Chester Road Buckley Flintshire, CH7 3AJ Tel: richard.cove@environment-agency.gov.uk Author: Richard J. Cove Technical Officer Keywords: Grayling, stocking, migration, survival, habitat, Ceiriog Environment Agency All rights reserved. This document may be reproduced with prior permission of the Environment Agency. Environment Agency Grayling Introduction into the Afon Ceiriog 1

3 Contents Contents 1 1 Introduction 3 2 Aims 3 3 Method Fish rearing Fish stocking Monitoring 6 4 Results Electric fishing surveys Impact on SAC species Salmon Bullhead Lamprey Survival and growth of stocked grayling Grayling movements and flow Tag retention rates 10 5 Discussion Effects on SAC species Grayling survival, sampling methodology, movement and acclimation VI tag retention Predation Physical habitat and flows Future monitoring Water Quality 13 6 Conclusions and recommendations 14 7 Acknowledgements 14 Glossary of terms 15 List of abbreviations 15 References 16 1 Environment Agency Grayling Introduction into the Afon Ceiriog

4 Environment Agency Grayling Introduction into the Afon Ceiriog 2

5 1 Introduction For more than ten years the Ceiriog Fly Fishers (CFF) have made requests to the Environment Agency Wales (EAW) and its predecessors to consent the introduction of grayling (Thymallus thymallus, L.) into the lower Afon Ceiriog upstream of Brynkinallt weir (SJ ). In 2007, this issue was discussed at a Local Fisheries Advisory Group (LFAG) meeting where EAW had little objection to the proposal. In July 2009, following lengthy consultation with the Countryside Council for Wales (CCW), CCW consented the Environment Agency Wales to introduce approximately 900 one-year-old grayling into the Afon Ceiriog between Afonfale weir (SJ ) and Brynkinallt weir within the River Dee (Afon Dyfrdwy) SSSI. Consideration was therefore given to: 1. The direct effects of introducing grayling and possible effects on SAC (Special Area of Conservation) features namely: bullhead (Cottus gobio, L.), lamprey (Lampetra fluviatilis, L. & Lampetra planeri) and Atlantic salmon (Salmo salar, L). 2. The effects of changes in angling pressure (due to the presence of grayling) on SAC features. 3. Stocking methods and minimising disturbance to SAC species. 4. Monitoring of grayling post-release to assess prospective survival rates. 2 Aims The key objective of this project was to develop a small sustainable grayling fishery for the Ceiriog Fly Fishers, adding to the existing brown trout (Salmo trutta, L.) fishery and effectively extending their angling season from the 17 th October to the 31 st December. Meeting this objective provided an opportunity to rear juvenile grayling for the first time in Wales and included a programme to monitor their movement and survival post-stocking. Although grayling have been present in the lower Ceiriog for several years and have developed a small yet sustainable population, they have not spread upstream of the gauging weir at Brynkinallt. This weir does not present a significant barrier to the movement of salmon and sea trout (the migratory form of the brown trout), but complex flow patterns around the weir probably deter the upstream passage of grayling. For example, there are few records of adult grayling being encountered upstream of Brynkinallt - except for the occasional fish found dead on the upstream screens at both the Chirk and Upper Mills (Glyn Ceiriog) trout farms and one live fish at Chirk farm. These screens are in place to prevent ingress of salmon and sea trout smolts to the farms. The presence of grayling in the river below the gauging weir and these upstream records ensured that EA Wales was compliant with its Trout & Grayling Fisheries Strategy (T&GFS) policy 21 regarding grayling introductions. This policy states that We will only permit stocking into rivers in catchments where the grayling is already present. 3 Environment Agency Grayling Introduction into the Afon Ceiriog

6 3 Method 3.1. Fish rearing To conform to Environment Agency T&GFS guidance on the use of local or indigenous grayling broodstock, in April 2008, 17 adult fish (eleven hen fish and six cocks) were captured by angling in the main River Dee at Maelor (Ty Nant Country Park) (SJ ) and Carrog (SJ ). These fish were transported to the Agency s fish hatchery at Maerdy (near Corwen). On arrival at the hatchery each grayling was assessed for maturation before being held in circular (4m diam.) tanks. They were fed on a diet of maggots, red worms (Eisenia fetida) and cased caddis (Rhyacophila sp.) to keep them in good condition in readiness for spawning. Three of the 11 hen fish produced eggs (Photo 1) and all six males produced milt. After spawning, the surviving adults were returned to the main river at Carrog. In all, 2,650 eggs were fertilised between 17 th and 30 th April. These eggs were retained in trays in the incubation unit where they developed rapidly (particularly compared to salmon) to the eyed ova stage. After 170 degree days the eyed ova hatched and a further three days saw alevins actively searching for food. They were fed a diet consisting of two different foods: crushed up hard boiled eggs and salmon fry starter food. This combination was mixed in a muslin bag with a water supply slowly running through it, ensuring a slow constant supply of food leaching into the fry tank. The majority of grayling mortality occurred at the fry life stage. After 3 months, the fry were moved to 1m diameter outdoor tanks and fed on live Artemia (early life stage of the brine shrimp) and ground up salmon fry feed. In the larger tanks survival rates improved markedly and the fry grew rapidly, reaching average weights of 1.5g by week 10 (Photo 2) and 7.2g at 6 months (mean fork length ~100mm). This was the first successful rearing of grayling in a Welsh hatchery. Photos 1 and 2. After 12 months, the juvenile grayling were large enough (mean length 145mm, range mm) to be tagged using standard size Visible Implant (VI) tags ( inserted in the clear adipose eye tissue behind the left eye (Photo 3). Where this tissue was insufficient or the fish considered too small, a Coded Wire Tag (or Microtag) ( was embedded in the snout. All grayling were adipose fin-clipped to distinguish them from Environment Agency Grayling Introduction into the Afon Ceiriog 4

7 potential wild specimens. Overall survival rate from egg to stocking was 39.3%, producing a total of 921 sub-adult grayling to be introduced to the Afon Ceiriog. Photo Fish stocking On the 26 th of June and 1 st & 2 nd of July 2009, 796 grayling were moved by fish transporter from Maerdy hatchery to Chirk Fishery. On arrival all fish were then checked for the presence of VI tags. These fish were then held in the river in keepnets or in a soft mesh cage in the fishery leat for periods of 24 or 48 hours to acclimate them to the different water chemistry in the Afon Ceiriog. Post-acclimation, VI tagged grayling were placed into hand held buckets then evenly distributed within the 1,942m upper stocking zone (SJ to SJ ) according to their tag batch code and colour (orange, red & yellow) (Photo 4). This type of stocking was undertaken to ensure no increase in angling pressure due to the presence of grayling. The stocking process was stopped briefly when the river coloured up (high suspended solid loading) due to mechanical digging at Chirk trout farm. The 125 microtagged (CWT) grayling were transported directly to the downstream 328m long stocking zone (SJ to SJ ) on the 30 th June with only one hour acclimation before release. 5 Environment Agency Grayling Introduction into the Afon Ceiriog

8 Photo Monitoring Post-stocking monitoring was undertaken using electric fishing (Intelisys backpack, single anode, 280 volts, 50 Hz frequency). The first assessment took place on 19 th October 2009 and involved a two-man team electric fishing a single anode near-continuously through the downstream control zone - a 561m long reach (area of 5,049m 2 ) between Brynkinallt weir and downstream of the lowest stocking location (SJ ). This survey was undertaken purely to assess whether any grayling had dropped downstream of the stocking area. On the 22 nd and 29 th October 2009, three and two men teams respectively, fished eight timed 5-minute fry sites - targeting salmon fry (technique used by Dee Stock Assessment Programme, DSAP) within the grayling stocking zone (area of 457m 2 ) (Fig. 1). These sites consisted of shallow riffle habitat. Further fishing took place solely for grayling in areas between the 5-minute fry sites. This was done over considerably larger areas than the timed sites but less intensively as it was intended to capture and process only stocked grayling. From these surveys it was hoped to detect any grayling movement from their release sites and to estimate a post-stocking survival rate. On the 29 th October, the river again began to colour up as a result of excavation works being undertaken at Chirk fish farm. Environment Agency Grayling Introduction into the Afon Ceiriog 6

9 Figure 1. River Ceiriog grayling stocking zone and 5-minute fry electric fishing sites.!( Site G!( Site E!(!( Site D Site C!( Site A!(!( Site B!( Site 1 Site F Upstream stocking zone Downstream stocking zone Legend Metres 4 Results 4.1. Electric fishing surveys Several fish species were caught during the post-stocking 5-minute fry surveys. These included adult and juvenile salmon, sea trout, brown trout and juveniles, rainbow trout (Oncorhynchus mykiss), grayling, eel (Anguilla anguilla, L) and bullhead. Catches of juvenile salmon & trout and bullhead are recorded for each of the eight timed fry sites in Table 1. At sites 1 and A to G (wetted area 622m 2 ), a total of 348 salmon fry (0+) were caught equating to a density of 56 fish per 100m 2. Sixty salmon parr (>0+) were captured producing a density of 9.6 parr per 100m 2. 7 Environment Agency Grayling Introduction into the Afon Ceiriog

10 Table 1. Electric fishing 5-minute fry sampling results (post grayling stocking). Site 1 (double) Area fished Catch Fish per Length Length Site D Area fished Catch Fish per Length Length SJ m m 2 Mean (mm) Range SJ m m 2 Mean (mm) Range 0+ SL ( ) 0+ SL ( ) >0+SL ( ) >0+SL ( ) 0+TR ( ) 0+TR >0+TR ( ) >0+TR Bullhead unknown - Bullhead ( ) Total Total Site A Area fished Catch Fish per Length Length Site E Area fished Catch Fish per Length Length SJ m m 2 Mean (mm) Range SJ m m 2 Mean (mm) Range 0+ SL ( ) 0+ SL ( ) >0+SL ( ) >0+SL ( ) 0+TR TR >0+TR >0+TR Bullhead Bullhead Total Total Site B Area fished Catch Fish per Length Length Site F Area fished Catch Fish per Length Length SJ m m 2 Mean (mm) Range SJ m m 2 Mean (mm) Range 0+ SL ( ) 0+ SL ( ) >0+SL ( ) >0+SL ( ) 0+TR ( ) 0+TR >0+TR >0+TR ( ) Bullhead ( ) Bullhead ( ) Total Total Site C Area fished Catch Fish per Length Length Site G Area fished Catch Fish per Length Length SJ m m 2 Mean (mm) Range SJ m m 2 Mean (mm) Range 0+ SL ( ) 0+ SL ( ) >0+SL >0+SL ( ) 0+TR ( ) 0+TR >0+TR >0+TR ( ) Bullhead ( ) Bullhead ( ) Total Total SL = Salmon TR = Trout 0+ = fry >0+ = parr 4.2. Impact on SAC species Salmon Mean salmon fry and parr density estimates for 5-minute fry sites fished within the stocking zone (sites A to G) were compared with mean density estimates for the nine (DSAP) Ceiriog sites sampled outside the stocking zone in late summer This was undertaken to assess the impact of grayling stocking on native populations of juvenile salmon. No DSAP sites were within the stocking zone but included sites 2.3km upstream and 0.79km downstream of the stocking zone. In both cases (fry and parr), mean densities within and outside the stocking zone were not significantly different (i.e. P>0.05) (Fig. 2). Mean lengths of 61.6mm (range 44-84mm) and 108.4mm (range mm) for salmon fry and parr respectively were recorded pre-stocking with slightly increased lengths of 63.1mm and 123.7mm in the latter surveys. Environment Agency Grayling Introduction into the Afon Ceiriog 8

11 Figure 2. Comparison of salmon abundance in stocked & unstocked zones. Geometric mean denisty 100m Stocked Juvenile salmon mean densities 82.2 Unstocked (DSAP) Stocked Error bars indicate 2 x Standard Error Fry Parr Unstocked (DSAP) Bullhead During monitoring of the eight 5-minute fry post-stocking sites, a total of 30 bullheads were captured, with a mean length of 62mm and an average density of 4.8 fish per 100m 2. There was no comparable data from DSAP as these surveys only record the absence / presence of bullheads, however this species was present at all nine DSAP fished in A semi-quantitative site, 10km upstream of Afondale weir, was fished in 2008 and 2009 by EAW and produced only one bullhead in 2009 equating to densities of 0 and 0.29 fish per 100m 2 in 2008 and 2009 respectively Lamprey No lamprey were caught during the post-stocking electric fishing surveys Survival and growth of stocked grayling Nineteen grayling were caught during the surveys and a further two fish were seen and partially stunned but evaded capture. This total equates to a minimum survival rate from release to monitoring (108 days) of 2.28%. Of these fish, 14 had retained their VI tags and had an average length at the time of stocking of 147.8mm. This was greater than the overall mean length of all stocked fish (144.5mm), although this difference in size was not statistically significant. At recapture, the same fish had an average length of 181.3mm, equivalent to average growth of 43mm (range 30-54mm) over the 108 day period between stocking and monitoring. No grayling were captured in the downstream control zone. 9 Environment Agency Grayling Introduction into the Afon Ceiriog

12 4.4. Grayling movements and flow Of the 14 fish that had retained their tag, only one had moved upstream of its stocking location (a distance of 268m). Four were resident in their original stocked zone (+/- 100m) and nine had moved downstream. The latter ranged in distance from 123 to 1,700m (mean downstream dispersal of 600m, median 450m). A near significant correlation (P=0.087) was apparent between size at stocking and the distance travelled downstream (Fig. 3), with larger fish tending to remain closer to their stocking location. Figure 3. Grayling stocked length and movement. SQRT Distance moved (m) Grayling movement and stocked length y = x R 2 = Fish fork length (mm) The time that fish were held prior to release may also have been a contributory factor in dispersal - those held for 48 hours as opposed to 24 hours (shown in blue), dispersed less but with no statistically significant difference between these two groups. Excluding lost tags, survival appeared greater for the more acclimatised group of fish (3.53% compared to 1.56% but sample size for the former group were very small). Flow remained fairly stable throughout the period of fish acclimation with a mean flow of 1.2 cumecs (m 3 /s). A small spate (~5 cumecs) occurred two weeks after the grayling introduction (Fig. 4) which may have contributed to the widespread distribution of recently stocked grayling Tag retention rates Despite the presence of very little periocular tissue on juvenile grayling, extremely good tag retention rates were obtained within Maerdy hatchery (93%). Thirty-two VI tagged fish lost their tag during the transportation process (probably due to netting in and out of the transport vehicle and vehicle movement) and 27 of these were re-tagged at Chirk Fishery. The post-stocking retention rate was 74%. Environment Agency Grayling Introduction into the Afon Ceiriog 10

13 Figure 4. Date of grayling stocking and sampling with respect to mean daily flow at Brynkinallt Brynkinallt Weir Mean Daily Flow [m3/s] FQ [m3/s] Stocking Sampling /06/ /06/ /06/ /07/ /07/ /08/ /08/ /09/ /09/ /10/ /10/ /11/ Discussion Before the study began, a habitat assessment by the author within the stocked reach suggested that this section of the Ceiriog was suitable for grayling although, due to the predominantly shallow and at times torrential nature of this river, unlikely to support the densities of grayling found in more favourable habitats in the main River Dee Effects on SAC species Results from pre and post-stocking electric fishing surveys provided no evidence that the introduction of grayling had been detrimental to resident juvenile salmon or bullhead. Although mean densities of salmon fry were lower in the stocked than the control (unstocked) reach, this difference was not statistically significant and could be explained by the fact that the control survey was carried out around two months prior to stocking when salmon densities, in general, would be expected to be higher due to natural mortality. Similarly, the control electric fishing surveys were undertaken in late summer when juvenile salmon would tend to be more active and more easily captured than in colder late October temperatures. Given the increase in growth of fry and parr between survey dates, the differential in biomass would have been less pronounced than just examining fish numbers. Certainly with few surviving grayling resident in the stocked zone, far greater impacts upon SAC species would have come from other sources (see section 5.4) Grayling survival, sampling methodology, movement and acclimation It is difficult to judge whether the minimum survival rates estimated for the grayling stocked in this study (2.3%) could be considered reasonable or not due to the lack of equivalent studies against which to make comparisons. What is clear is that, despite periods of high flow, grayling were still present in the stocked zone at the end of October and were growing well. Typically growth of grayling in their second year of life would be in the order of 75mm fork length (Cove, pers. ob.) indicating that the surviving grayling were 11 Environment Agency Grayling Introduction into the Afon Ceiriog

14 growing at a healthy rate (mean increase of 43mm for the three-plus months poststocking). The true measure of stocking success will be whether the introduced fish go on to reproduce in this section in future years. It is likely that there was an under-estimate in grayling survival due to the sampling methodology. Electric fishing with backpacks is more efficient and primarily used in shallow riffles (<50cm deep). These habitats provide suitable areas for salmon fry however grayling (particularly immature fish) tend to occupy territories in deeper, slower water. Although efforts were made to sample most of these areas for grayling, single run upstream fishing with one anode is unlikely to be effective enough to accurately measure the survival rate. Downstream fishing with duel anode and stop nets would have been preferential but was not possible due to manpower constraints. Although the minimal survival rate within the stocking zone was around 2.3%, not all areas were thoroughly fished, particularly the downstream stocking zone (Fig. 1), so a more realistic value of survival was likely to be in the region of 5% (which includes fish that migrated outside the stocked reach). Note: Despite electric fishing 561m of river, no grayling were detected in the downstream control zone. The majority of grayling dispersed downstream (mean 600m, median 450m) and the distances moved were of a similar magnitude to those observed by Carlstein & Eriksson (1996) who reported most grayling move about 800m downstream from the release site within a few days. It is worthy of note that larger stocked grayling appeared to disperse less than smaller fish. Most of the grayling that are now being released from the Environment Agency fish farm at Calverton are 30 to 50mm in length (approximately 4 months old) and this may give rise to much greater dispersal. No grayling were recaptured from the microtagged (CWT) batch that was acclimatised for only one hour. This was possibly due to the shortfall of electric fishing within their stocked section. That said, no fish were encountered within the control zone which would have offered the natural downstream dispersal zone for this section. The fact that the fish acclimatised (or preconditioned) for the longest time (48 hours) tended to have better survival rates and dispersed the least distance, suggests that longer acclimation may be an important part of grayling fish culture (Kaya & Jeanes 1995). Thorfve and Carlstein (1998) also reported that most stocked grayling left their release site within two hours VI tag retention Tag retention rates were better in larger grayling as a result of the greater area and depth of adipose eye tissue available. Tag retention in-river (74%) was much lower than in Maerdy hatchery (93%). This may be due to the former environment being a more hostile one or could reflect a growing physiological tag rejection response by the fish. It was noted, with the majority of grayling that had their adipose fin clipped at the hatchery, that fin regeneration had begun Predation Rainbow trout abundance in the stocking zone was far higher than that of grayling and all of these fish were likely escapees from Chirk and Upper Mills trout farms since rainbows are not consented to be stocked into the Ceiriog. More than 35 were captured within the stocking zone (mostly >30cm in length) - all were removed from the river and placed into the lakes at the Chirk fishery. The presence of non-native rainbow trout in the river (previously fed continuously in the farm) is likely to have a bigger impact upon SAC species than the stocking of grayling (through competition and predation). The Environment Agency Grayling Introduction into the Afon Ceiriog 12

15 Environment Agency Wales fisheries department should ensure that the fish farms are compliant with adequate screening by the Ceiriog fish farms and the angling club encourage their anglers to remove all the rainbow trout that they catch. Grey heron (Ardea cinerea) were also abundant in the stocking zone as a result of the plentiful food source created by the trout farms and fishery. Other piscivorous birds were observed in the stocking zone particularly goosander (Mergus merganser). Again these could have had a detrimental effect on naive and vulnerable stocked grayling, or even native fish. During electric fishing, physical damage by birds (scarring and scale loss) was recorded on both wild trout and stocked grayling Physical habitat and flows Pre-stocking, concerns were expressed to the CFF about the scarcity of suitable refuge sites (in the form of large in-river boulders and slow deep pools) offering grayling protection from predators and spates. This rivers steep gradient can result in much elevated velocities during flood events and coupled with insufficient refuge, increases the likelihood of the fish being forced downstream and potentially out of the system. Such an event occurred two weeks post-stocking (mid-july) following heavy rainfall (Fig. 4). This may have contributed to the low level survival of stocked grayling. During Environment Agency smolt trapping within the stocking zone, a high frequency of downstream dispersal of juvenile trout is evident each year (Cove pers. ob.). Much higher flows were observed after sampling in November (Fig. 4) but is probable that surviving grayling would have grown and naturalized sufficiently to seek out available refuge from fluctuating velocities. The addition of several large boulders in this reach is likely to be beneficial to larger resident trout and grayling but would require the permission of CCW Future monitoring No future monitoring of grayling by electric fishing is planned for the Afon Ceiriog. The Ceiriog Fly Fishers Club annually collates catch returns from their anglers which includes grayling catches downstream of Brynkinallt. It would be advisable for the club to continue to do so but also record grayling catches in the stretch from Brynkinallt to Afondale weir and any tag numbers (and colours) if possible these may become increasingly difficult with time to read as the eye tissue becomes opaque. This could provide baseline data on population status and fish movements Water Quality During both stocking and monitoring elements of the project, excavation work was halted at Chirk fish farm to stop fine sediments entering the river. This is unacceptable and was reported to the EAW Environmental Management team 5. It is highly unlikely that these events only occurred during study days so enhanced monitoring and site visits to Chirk trout farm to ensure no repeat of this practice, was suggested. The deposition of considerable fine sediments could seriously impact upon the survival of salmonid fish eggs laid in the Ceiriog gravels. 13 Environment Agency Grayling Introduction into the Afon Ceiriog

16 6 Conclusions & recommendations 6.1. Monitoring post-stocking suggests that the introduction of grayling has not negatively affected the SAC fish species - particularly juvenile salmon. Other competitors and predators already present on the Ceiriog (piscivorous birds and rainbow trout) are likely to pose a greater threat to SAC fish species Stocked grayling were resident within the stocking zone and survival for the 108 day period post-release was 2.28% (minimum). Many factors could have adversely affected survival including predation and a paucity of refuges. The electric fishing technique adopted (single anode backpack fished upstream) probably resulted in an under-estimate of survival Despite periods of high flow, grayling were present in the stocked zone at the end of October and were growing well. The main measure of success will be whether the introduced grayling go on to reproduce in this section in future years Downstream dispersal of grayling within the stocking zone was common but not universal (median distance travelled: 450m, range -268m to 1,700m). Larger stocked grayling tended to disperse less distance than smaller fish. The length of acclimation to the receiving river is likely to influence both survival and the extent of dispersal of stocked grayling No future monitoring of Ceiriog grayling is planned but the Ceiriog Fly Fishers Club should continue to collate records of grayling caught (including any tag numbers and colours) in the stretch from Brynkinallt to Afondale weir. This should provide baseline data on population status and fish movements The EAW Environmental Management team should make impromptu visits to Chirk trout farm to ensure that fine sediments are not entering the river during rearing pond excavation works - these could impact upon survival of salmonid fish eggs laid in the gravels. EAW fisheries should regularly assess the integrity of fish screens on intakes and outlets of both Ceiriog fish farms. 7 Acknowledgements Thanks go to the following: John Roe (Carrog syndicate) and Ken Bathers (Maelor Angling Association) for their kind permission in allowing the collection of grayling broodstock. Shaun Coadey and Rob Davies at Chirk Fishery for permitting the retention of grayling on site. Chirk Fly Fishers (particularly Ben Kelly) for their assistance with fish stocking. Eryl Morris for access permission to monitor the survival of grayling. Maerdy hatchery staff for rearing the grayling (Keith Scriven, Joel Rees-Jones, Cerys Cowley, Bregan Brown & Paddy Mahon) and Gethin Morris for fish transportation. Joel Rees-Jones & Ian Davidson for helping with the electric fishing surveys and Ian for his assistance with reporting. Environment Agency Grayling Introduction into the Afon Ceiriog 14

17 Glossary of terms Coded Wire Tag A coded wire tag 1.1 mm long and 0.25 mm in diameter, inserted into the nasal cartilage (snout) of fish and detectable in live fish. Fry Young salmonids that have hatched out in the current year at the stage of independence on yolk sac as the primary source of nutrition. Parr Juvenile salmonid in the stage following fry until its migration as a smolt. Salmon parr are typically <16 cm long and have parr-marks (dark vertical bars) on the sides of the body. Special Areas of Conservation (SACs) To comply with the EU Habitats Directive (92/43/EEC) on Conservation of Natural Habitat and of Wild Fauna and Flora, which stipulates that member states maintain and restore habitats of species to favourable conservation status. Where salmon is a qualifying species, additional protection measures specifically for salmon are required. Stocking The intentional release of fish into an ecosystem. Survival Rate(s) The number of fish alive after a specified time, divided by the number alive at the beginning of the period. Tagging Marking or attaching a tag to an animal so that it can be identified when recaptured; used to study fish growth, movement, migration, stock structure and size. List of abbreviations CCW Countryside Council for Wales CFF Ceiriog Fly Fishers DSAP Dee Stock Assessment Programme EAW Environment Agency Wales LFAG Local Fisheries Advisory Group SSSI Site of Special Scientific Interest T&GFS Trout and Grayling Fisheries Strategy VI Visible Implant (tag) 15 Environment Agency Grayling Introduction into the Afon Ceiriog

18 References Carlstein M. and Eriksson L.-O. (1996). Post-stocking dispersal of European grayling (Thymallus thymallus, L.) in a semi-natural experimental stream. Fisheries Management and Ecology 1996, 3, Environment Agency Trout and Grayling Fisheries Strategy. HO-08/03-5K-BHMC-SP- WM094. Kaya, C. M. and E. D. Jeanes (1995). Retention of adaptive rheotactic behavior by F 1 fluvial Arctic grayling. Transactions of the American Fisheries Society 124: Thorfve, S. and Carlstein, M. (1998). Post-stocking behaviour of hatchery-reared European grayling, Thymallus thymallus (L.) and brown trout, Salmo trutta L., in a seminatural stream. Fisheries Management and Ecology 1998, 5, Environment Agency Grayling Introduction into the Afon Ceiriog 16

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