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River Fowey Electrofishing report WRT/FRA

Copyright © 2011 by the Westcountry Rivers Trust 1

Fowey 2011 Semi-‐Quantitative electro-‐fishing survey

Report prepared for the Fowey Rivers Association by the Westcountry Rivers Trust;

Giles Rickard, Adrian Dowding, Bruce Stockley and Nick Paling. Report date: 23.12.11

Westcountry Rivers Trust

Kyl Cober Parc Stoke Climsland

Callington Cornwall PL17 8PH

Fowey site 2



Context Survival to the end of the first summer is known to be poor for salmonid fry. Up to 90% of the alevins that emerge from the redds will not survive. Even in good quality habitat with a rich food supply, high densities of fish will undergo strong competition for resources with each fish trying to gain a profitable feeding station. The fry index surveys are used as a coarse measure of fry numbers/abundance at each particular site. For each single year it also gives a broad indicator of salmonid spawning success across a catchment. Site Selection and Permissions Sites were selected at regular intervals throughout the catchment as agreed in 2010 (Figure 1). Electrofishing permission was obtained from the Environment Agency. Access to sites was arranged by telephone or cold-‐calling on landowners. A shallow riffle section was chosen at, or as near as possible to, each selected site. The sites marked in Figure 1 represent the actual sites fished, rather than the sites initially identified for sampling. The completion of the walkover survey of the Fowey will prove particularly valuable in the future and will help identify fry habitat in the catchment, which may lead to the revision of some sites. Permission to access previously non-‐electrofished sites was time consuming although the response was positive with permission gained for all new sites where contact was achieved. Sites that were not fished by the Trust fell into Three main categories a) contact/permission was not identified in time, b) permission was refused and alternative sites may need to be considered for next year, c) the site had been fished by the Environment Agency in 2011. Field sampling Each site was electro-‐fished by a two person team using an E-‐fish 500W single anode backpack. The unit was predominantly fished at the same settings of (50Hz at 250v), although the voltage was increased to 300v where the conductivity was found to be particularly low, as identified in the headwaters of the main river Fowey. The operatives fished continuously in a downstream direction for a standard five minutes over suitable fry habitat without the use of stop nets. The fishing area was variable because only the length of fishing time was fixed. Fish were collected in a net and placed into a holding bucket.



All Salmonids were length measured with habitat features such as land use, substrate type and shading recorded at each site. A photograph of each site was also taken. Sites were classified on the basis of fry numbers recorded at each site. This classification scheme is taken from the original fry index produced by Crozier & Kennedy, 1994 (Table 1). Table 1. Semi-‐quantitative abundance categories and their relationship to quantitative electro-‐fishing densities (Crozier & Kennedy, 1994). Density Classification Semi-‐quantitative

(n5min -‐1)

Quantitative equivalent

(n100m-‐2)

A (excellent) >23 >114.7

B (good) 11-‐23 69.1-‐114.6

C (fair) 5-‐10 41.1-‐69.0

D (poor) 1-‐4 0.1-‐41.0

E (absent) 0 0

Six species of freshwater fish were recorded in the Fowey catchment during sampling including; bullhead, eel, lamprey, salmon, sea trout and brown trout. The results of the electro-‐fishing survey are classified according to the methodology of Crozier and Kennedy, as seen in table 1 below, with each site being given an equivalent density classification compared to quantitative monitoring. The results with the classification for each site can be seen in Table 2 in the appendix. The fry that escaped during electro-‐fishing were assigned to either trout or salmon groups depending on the percentage of each species already recorded at the site



River Fowey electrofishing 2011

Figure 1



Results Salmon Three ‘A’ classifications were found this year which maybe considered an improvement to 2010 where no ‘A’ class sites were found. There was also a tangible increase in fry present on the Cardinham Water and the St Neot where full 2010 and 2011 surveys could be compared like for like. Salmon fry presence in the upper Fowey (Trenant confluence and above) was relatively similar if not slightly down in 2011. These results may potentially be related to autumn flows and successful negation of Golitha Falls. A comparison of 2010 and 2011 data for the middle and lower fowey is more difficult as there is not a full overlap of data between years. Crude assessment however would suggest a similar or improved density of fry in 2011. Warleggan The assessment of the Warleggan in 2011 was of particular interest as only two sites were electro fished the previous year. Although the very bottom site near the confluence was not fished, the distribution was very linear with salmon numbers steadily increasing from the headwaters near Temple new Bridge down river. The results here suggest that the Warleggan is a significant tributary for salmon fry and spawning with two ‘B’ classification sites found along with two ‘C’ classifications. The Warleggan was stocked at two sites in 2011 so some of the results from the lower sites may need to be assessed with caution and compared to a baseline year where no stocking has taken place. Upper Fowey By contrast the upper fowey catchment (Above Draynes Bridge) was for the second year relatively poor given the size of the river and assumed good habitat with no fish found above Westerlake Farm with the Trust survey, although a very low density of fry were found with the 2011 Environment Agency survey at Harrowbridge. Six sites were assessed above the bridge with low numbers found in two (‘D’ class sites) and no salmon found in four sites (‘E’ class). It would be particularly interesting to fully understand why the classification here is not higher given the extent of habitat work improvement already undertaken here. This maybe related to the identified difficulty in salmon navigating Golitha falls, particularly when there are low flows in the Autumn or siltation of spawning sites from sand further up the river. An assessment of historical Environment Agency electrofishing data, suggests that few fry or par have been recorded above Palmers Bridge since the mid 1970’s (Pilcher, 2000).



It would be useful to conclude whether the low fry density in this area is due to a lack of adult fish reaching high up the catchment or whether it is down to poor spawning and egg survival, due to the aforementioned sand deposition causing the siltation of spawning habitat. Trenant Stream All sites on the Trenant Stream were fished in 2011 with the Park pit site being fished by the Environment Agency in 2011. Three other sites on the Trenant Stream were also fished by the Environment Agency in 2011 that provides very useful additional data. Of the six sites surveyed only the two lowest sites (1 WRT, 1 EA) both below Periock Wood recorded salmon fry and both at low densities ‘Class D’. Both WRT electro fished sites fish in 2011 produced identical classifications to 2010. A higher salmon density may have been predicted as it is a relatively significant tributary to the Fowey and is not known to have major water quality issues as when compared to the St Neot. The Trenant is notably smaller however and this may deter salmon from traveling further up it or indeed it may make it flow dependent. Also there were no salmon classifications above ‘C’ found above the Trenant confluence, which may indicate that salmon densities are starting to reduce this far up the catchment. Cardinham Water The distribution of salmon in the Cardinham Water was generally linear with increasing numbers found moving down the catchment, other than the lowest site. However the lowest site (Upstream of Dreasonmoor Wood confluence) does not contain ideal fry habitat and maybe a candidate for site change after the walkover has been completed here. The site above at Fletchers bridge was found to have a class ‘A’ density and represents an improvement on 2010 and indicates highly successful spawning above here. There were another three ‘C’ class sites above here including a very small minor tributary (Deviock Wood) which can be considered a notable nursery area for fry. When compared to the 2010 survey all bar one site in the 2011 survey was equal to or higher than the previous years survey, suggesting a clear improvement in salmon spawning/ fry survival.



Plate 1: Site 46 Below Fletchers Bridge Lower Fowey The 2011 results for the lower Fowey were mixed with five sites below the Trenant confluence achieving good results (A and B class) and four relatively poor results (D class). The majority of sites fished in both 2010 and 2011 were relatively similar although the Ashford Bridge site changed significantly from class D (2010) to class A in 2011. However it is understood that fry have been stocked out near Treverbyn Bridge, which may explain the significant increase in abundance, which therefore makes the result somewhat unreliable. There maybe a case too review the location of some of the electrofishing sites on the main river as they do not contain optimum fry habitat given the larger flows. The results of the walkover survey would be useful in assessing this and locating fry habitat. The Environment Agency fish counter at Restormal Weir, which is a particularly useful resource, indicates that more salmon entered the Fowey in 2010 (1220) compared to 2009 (717). It would be interesting to compare this data to the following years fry index survey data over a number of years to observe any correlation.



Although its is difficult to accurately compare fry numbers from 2010 to 2011 without a full 2010 dataset, the impression is of a overall rise from 2010 to 2011 which would correlate with the greater number of fish entering the river.

Figure 2



Figure 3



Trout Trout could generally be found throughout the catchment with the best sites (A and B class) predominantly found in the headwaters and in the smaller side tributaries, which may enter the river at any point along the catchment. There were only four sites where no trout were present that included two sites on the lower Fowey, which had high salmon abundance and two sites on the St Neot. St Neot The survey data from the St Neot was again significant with no salmonids (class E) detected in the East Colliford site below the dam, with only one trout (Class D) identified at Trewindle (next site below). These results strongly suggest that there are ongoing water quality/turbidity issues in the upper St Neot, which was formally considered a significant trout and salmon spawning tributary. Below these sites the number of trout was still generally low (class D and E), although the number of salmon fry present did increase. The number of salmon fry present however should be considered with caution and assessed in conjunction with the 2011 stocking of hatchery fish.

Minor tributaries The results from the minor Fowey tributaries indicate that they are significant and important areas for trout fry and spawning potentially. Of the six minor main stem tributaries fished one was class ‘A’ and four were class ‘B’ indicating that these very small tributaries are essential for trout recruitment and are likely to play a considerable role in total trout fry numbers across the catchment. When comparing 2010 to 2011 survey data the results are relatively similar and vary less when compared to salmon fry as may be predicted. A comparison of Cardinham Water indicates a similar fry abundance between 2010 and 2011 with relatively minor changes. A comparison of the upper Fowey down to Bodithiel Wood showed a similar pattern, although trout fry were more abundant in the top two sites in 2010. Although Brown Trout numbers are generally stable from year to year given their life cycle, the migration and passage of sea tout can influence fry numbers and may therefore have a noticeable affect on the classification of sites.



Discussion This survey is the second of its kind on the Fowey and allows us to begin to assess year on year (temporal) variation as well as spatial. Initial observations suggest the spatial distribution is relatively similar to the previous year, although there are a number of new sites surveyed which will need to be compared to next year. The general trend was again for salmon to be found in the middle and lower main river stem and in the lower reaches of major tributaries. The results highlight that the larger tributaries particularly the Cardinham Water and Warleggan are significant spawning and juvenile habitat areas for salmon supporting a number of A and B class sites. The St Neot however given its similar size performed poorly in comparison as maybe predicted and shows that it lags someway behind the other major tributaries. The St Neot is understood to have historically supported notable salmon populations and the river would have significant scope if suitable remediation could be achieved. If stocking is too be undertaken, the St Neot would be considered a suitable system as this can be targeted as direct compensation for the dam as opposed to a fisheries enhancement tool. The walkover survey on the Fowey is currently ongoing and the information from this will prove particularly useful for future electrofishing surveys. Given the specific habitat requirement of fry there maybe a case for adjusting some of the sites particularly on the main stem on the river and larger tributaries where fry habitat is generally less abundant. The information from the walkovers should allow us to identify these areas and adjust electrofishing sites where appropriate or deemed necessary. Further work As suggested in the 2010 report a comparison of the fry data with historic salmon red data if available would be of particular interest. It would also be useful to conduct salmon red surveying over winter 2011/2012 to identify areas of spawning and compare this to fry survey results. This may indicate how far fry drop down from their spawning sites and potential egg and fry survival in the river. Invertebrate sampling across the catchment would also be of interest to assess long term water quality and potential food sources. There is a planned program of invertebrate sampling that should be undertaken by Westcountry Rivers Trust through a different initiative next year that should provide useful additional data.



As discussed in the 2010 report, the genetic analysis of the local stock would be of particular interest and is of relevance when stocking out fry across the catchment to preserve genetic integrity and where associated physiological local adaptions may also be present. An assessment of possible obstructions to migration and fish passage would also be of particular interest and the influence of these maybe detectable with fry surveys over a number of years.

Plate 2: Treverbyn Weir Natural obstructions such as Golitha falls and Carpuan Falls may not be suitable for remediation, however other obstacles such as Treverbyn and Doublebois weirs may benefit from removal or easement along with the gauging stations found along the Warleggan and St Neot. Although these cannot be considered impassible, they may slow fish passage and reduce penetration further up the river. References Pilcher, W. (2000). A report On the Impact of Ditching Works And Sand Intrusion On the Upper River Fowey In Cornwall. Environment Agency Environment Agency (2003). River Fowey Salmon Action Plan



Acknowledgements Thanks to all landowners involved for their kind permission and to the Environment Agency for providing valuable extra data.

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