Fowey 2013 Semi-‐Quantitative Electro-‐ Fishing Survey
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River Fowey Electrofishing report WRT/FRA Fowey 2013 Semi-Quantitative electro- fishing survey Report prepared for the Fowey Rivers Association by the Westcountry Rivers Trust; Giles Rickard, Bruce Stockley, Matt Healey and Sarah Wigley. Report date: 20.12.13 Westcountry Rivers Trust Kyl Cober Parc Stoke Climsland Callington Cornwall PL17 8PH Copyright © 2012 by the Westcountry Rivers Trust 1 River Fowey Electrofishing report WRT/FRA 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 sites was quicker than in previous years, due to the use of existing contacts, although this process still takes up a considerable portion of time. Sites that were not fished by the Trust fell into Three main categories a) the site had been fished by the Environment Agency in 2013 and was therefore refused/unnecessary. b) contact/permission was not identified/attained in time, c) permission was refused by the landowner. d) one site could not be surveyed because it was recently identified as hosting Phytophora ramorum (sudden oak death) and there where bio-security concerns. 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. Copyright © 2012 by the Westcountry Rivers Trust 2 River Fowey Electrofishing report WRT/FRA 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 Quantitative equivalent (n5min -1) (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 Seven species of freshwater fish were recorded in the Fowey catchment during sampling including; bullhead, brook/river Lamprey, eel, salmon, sea trout, brown trout and roach. 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 This semi-quantitative methodology was designed by Crozier and Kennedy for both salmon and trout. However, the results for trout need adjustments to take into account the difference in the regression line for trout and salmon as described in Crozier and Kennedy 1994. Whilst the difference this will cause to the results is slight, we are currently in discussion with Eden Rivers Trust to fine tune the results for trout using this methodology. Copyright © 2012 by the Westcountry Rivers Trust 3 River Fowey Electrofishing report WRT/FRA Copyright © 2012 by the Westcountry Rivers Trust 4 River Fowey Electrofishing report WRT/FRA Results 2013 Salmon 2013 is the second semi-quantitative electrofishing surveying year since the closure of the Fowey hatchery and salmon fry release program. In contrast to 2012 flow conditions were generally low to very low, generally making electrofishing conditions easier. There were Two ‘A’ classification sites found (none in 2012) in the catchment along with five ‘B’ classification sites (six in 2012). The Cardinham Water once again performed extremely well accounting for one ‘A’ classification and one ‘B’ classification site. There were no salmon fry found in the St Neot River indicating low and isolated recruitment. The middle and upper reaches of the river performed well compared to previous years which maybe partially linked to the high flows in 2012. There were several ‘B’ and ‘C’ classifications attained with a ‘B’ classification found as high as Drayne Woods (above Golitha falls) and salmon fry found as high up as Dozmary Downs (site 3). The lowest two sites Brownqueen Wood Weir and Restormel Farm were well below previous years both achieving ‘D’ classification. Warleggan Unfortunately a limited number of sights were surveyed on the Warleggan in 2013, predominantly due to not receiving permission from a significant landowner. There were concerns that the results maybe published beyond the Trust and it was felt, more productive to maintain good relations with the owner longer term than push for permission in 2013. Three sites were surveyed predominantly in the lower half of the Warleggan reaching as high as Carne Woods (EA site in 2013). Salmon were found at the three sites, with sites classified as ‘C’ or ‘D’ for salmon. The lowest site on the Warleggan, fished for the first time by Westcountry Rivers trust scored ‘D’ which was lower than expected though the site may not be ideal for Salmon. This result is markedly different to the lower sites on the Cardinham, which performed very well. There is again potential that some of these areas were affected by the high flow in the previous autumn, which may have disturbed reds. The survey site at Crabshill wood was ‘C’ which is similar to previous years. Copyright © 2012 by the Westcountry Rivers Trust 5 River Fowey Electrofishing report WRT/FRA Upper Fowey The results for the upper Fowey (Above Draynes Bridge) were relatively similar to the previous year, though generally improved again as two sites achieved C classification and salmon were once again found as high up as site 3, Dozmary downs (‘D’ classification). This would be seen as the best result so far attained during the four years of survey, which may reflect the high 2012 flows and possible improvement works to the Draynes valley. The Drayne Woods site also achieved a ‘B’ classification, which has not been achieved since 2010. Trenant Stream Two sites were surveyed on the Trenant steam (one E.A, one WRT) in 2013. A low density of salmon fry (D) where found by the Environment Agency survey in 2013 at the lowest site Chapel, indicating again that salmon do spawn here, time to time, but in very low numbers. Cardinham Water The Cardinham Water once again produced extremely robust results, further showcasing its significance for salmon spawning with one ‘A’ class site and four ‘B-C’ class sites found within the catchment. Interestingly the lowest site on the Cardinham produced 32 fry in five minutes of surveying which is the highest in the entire catchment. In 2013 salmon fry were found higher up the catchment than in 2012, with salmon found at Cardinham Bridge (‘C’ class) and Milltown (‘D’ class), suggesting that some salmon were able to pass the ladyvale culvert, given the higher flows observed in 2012 over a prolonged period. Plate: Lady vale bridge culverts below sites 42 and 43 Copyright © 2012 by the Westcountry Rivers Trust 6 River Fowey Electrofishing report WRT/FRA Lower Fowey The result for the middle and lower Fowey appeared better in 2013, with several of the middle sites improving from ‘D’ to ‘B’ or ‘C’. All sites in the middle of the river were ‘B’ or ‘C’ with Respryn site also producing an ‘A’ class result. The lowest two sites however were at odds with the others, scoring only ‘D’, compared to the previous years average of ‘B’. The cause of this is unclear and may warrant investigation, although the most obvious cause maybe the very high flood conditions in 2012 destroying reds. Copyright © 2012 by the Westcountry Rivers Trust 7 River Fowey Electrofishing report WRT/FRA Copyright © 2012 by the Westcountry Rivers Trust 8 River Fowey Electrofishing report WRT/FRA Copyright © 2012 by the Westcountry Rivers Trust 9 River Fowey Electrofishing report WRT/FRA Trout The distribution of trout fry generally followed a similar pattern to previous years, with trout fry density highest in the upper reaches of the main river and larger tributaries along with the smaller side tributaries throughout the catchment.