HQ LIBRARY Head of Administration South West Water Peninsula House Rydon Len© Exeter EX2 7HR CONTENTS
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River Dart fisheries survey 1969 Item Type monograph Authors Nott, F.J. Publisher Devon River Authority Download date 01/10/2021 13:24:58 Link to Item http://hdl.handle.net/1834/27149 DEVON RIVER AUTHORITY RIVER DART FISHERIES SURVEY 1969 HQ LIBRARY Head of Administration South West Water Peninsula House Rydon Len© Exeter EX2 7HR CONTENTS A - INTRODUCTION B - METHODS C - RESULTS D - DISCUSSION E - ACKNOWLEDGEMENTS F - BIBLIOGRAPHY A. INTRODUCTION This the second fisheries survey of the River Dart was made between April and July 1969. In addition to the tributaries examined in the 1965 survey, further sections were studied on the River Hems and the Holy Brook (Map I). Reference should be made to the River Dart Survey Report 1965 for introductory information on Pollution, Anglings Netting, Spawning and Water Abstraction,, Current data on anglers' and netsmen’s returns are included in the Appendix. Bo METHODS Forty seven sections were examined which were accessible and fishable by electro-fishing methods. The sections were grouped as follows:- West Dart and tributaries - 14 (11 in 1965) East Dart and tributaries - 10 (10 in 1965) River Dart and tributaries below Dartmeet - 23 (10 in 1965). Each section was named by reference to a nearby bridge or local land mark. Section Grid Area Date Sur No . Name Ref. sq ,m. 1969 1 A.384 Road Bridge 588750 426 25/6 2 Cairns Bridge 595742 585 25/6 3 Beardown Farm 613753 502 17/6 4 * Upstream Powder Mill 628775 209 16/6 5 Downstream Powder Mill 633770 418 13/6 6 * Cherry Brook Bridge 632748 418 16/6 7 Crockern Tor 609758 368 5/8 8 Two Bridges 609750 1 s 184 2/7 9 Prince Hall 627739 946 2/7 10 * Upstream Swincombe Foot 648738 1,062 9/7 11 Huccaby 659729 689 7/7 12 * Upstream Water Intake 627715 481 11/6 13 Swincombe Farm 642725 669 12/6 14 Sherberton Farm 647730 502 12/6 Section Grid Area Date Surveyed No. Name R e f . sq.m. 1969 15 Hartland Tor 640798 281 21/7 16 Postbridge 650788 803 3/7 17 Believer 658774 455 3/7 18 Laughter Hole 662758 555 15/7 19 Brimpts Farm 672739 828 16/7 20 Stats Bridge 667805 84 10/4 Cor Merripits Bridge) 21 Pizwell 669785 293 14/4 22 * Runnage Bridge 670777 251 9/4 23 Riddon Farm 677764 167 8/8 24 Sherril 672.750 314 8/7 25 * Dartmeet 672731 1,129 22/7 26 New Bridge 712709 428 17/7 27 * Holne Bridge 731706 1,311 17/7 28 * Queen of the Dart 733692 1,484 25/7 29 * Austins Bridge 751659 615 24/7 30 * Staverton 788638 1,171 25/7 31 Grendon Bridge 688785 334 4/6 32 Cator Court Bridge 690765 385 4/ 6 33 Shallowford Bridge 692756 477 5/6 34 Pondsworthy 701738 396 5/6 35 * Bag Park Bridge 722787 251 6/6 36 Widecombe Bridge 721768 205 6/6 37 Cockingford Bridge 718751 397 13/6 38 Lower Lodge Bridge 719720 468 10/6 39 * Hawson Court 720683 180 23/6 40 * Rew 758707 2.50 24/6 41 Pridhamsleigh Bridge 748677 209 24/ 6 -2- Section Grid Area Date Surveyed N o . Name Ref. sq .m. 1969 42 * Bilberry Hill 728666 464 23/6 43 * Bow Bridge 801650 241 26/6 44 * Littlehempston 815630 410 26/6 45 * Yeo Bridge 758595 418 1/7 46 * Roister 772563 460 1/7 47 Growdy Mill 792561 502 27/6 * indicates new or changed sections. Sampling Techniques In this survey "parr of the year" - those fish hatched in the spring of 1969 - were not assessed since their small size made both capture and identification difficult. The following descriptions are used in the text to denote the different year classes of parr and fry; 0+ - fish hatched in 1969 1+ - fish hatched in 1968 2+ - fish hatched in 1967 In the previous survey each section was fished a number of times until the survey crew judged that very few fish remained. In order to reduce the time spent at each section and to expedite the completion of the survey, each section was fished three times. 1. The number of fish caught in each successive 'fish through' was plotted against the sum ) of previous catches. 2. The intercept on the x axis giving a calculated value of the population in the section. (Le Cren & Seber, 1967). CATCH “3- The number of fish caught was 137 but the calculated total was 148. Complete fishing out of the section would have undoubtedly produced more than the number actually caught. In some sections the first 'fish through* yielded fewer fish than the secondj, in which case the first catch figure was not used in the calculation. Second and subsequent 'fish through* catches were used. The catch from the first 'fish through' was added to the calculated total. The first 'fish through' is often less effective than second and third as the initial stunning causes fish to seek cover from which they are drawn by second and subsequent sweeps. It was not possible in field conditions to distinguish between the young stages of migratory and brown trout. Salmonid fish were recorded as either 'salmon' or 'trout' except in the case of smolts or adult migratory trout. C. RESULTS Salmon - Salmo salar (a) Adults Five adult salmon were caught during the survey at the Brimpts Farm section on the East Dart River. This is not significant since the deep water sections favoured by adults were not surveyed for juvenile salmonids. (b) Parr The numbers of parr found in each section are given in Tables 1, 2 and 3. The size distribution of the salmon parr from each section is given in Tables 4, 5 and 6. Also shown are the sample totals, calculated totals and the ratio of sample to calculated total as a percentage. For comparison the population totals for the 1965 survey are included. The population densities of salmon and trout from all sections are given in Tables 10, 11 and 12. The 1+ parr found in this survey would migrate as two-year smolts in the spring of 1970 or as three- year smolts in 1971. The 2+ p.arr" caught in this survey would migrate as three-year smolts in spring 1970. River Dart Scale Readltfg reports 1962-196-7 show that over 90% of parr become smolts and migrate after two river winters. The following table shows the proportions of 1, 2 and 3-year smolts in each scale sample: Year 7o 1-year 7o 2-year % 3-year Smolts Smolts Smolts 1962 3.2 86.9 9.9 1963 2.1 91.0 6.9 1964 2.2 92.9 4.9 1965 1.9 92.0 6.1 1966 1.6 95.2 3.2 1967 0.5 97.7 1.7 Average 1.97 92.36 5.67 The results show that the percentage of 1 and 3-year smolts has tended to decline between 1962 and 1967 and that the percentage of 2-year smolts has tended to increase during the same period. Examination of Tables I, 2 and 3 show that salmon parr were found in the majority of sections surveyed. The Blackbrook river was studied at two sites and the average salmon parr index was found to be 10.5 per 100 sq.m. (8.8 per 100 sq.yds) in comparison with 19.1 trout per 100 sq.m. (15.9 per 100 sq.yds). In 1965 the salmon parr index was 22.1 parr per 100 sq.yds and 20 trout per 100 sq.yds, thereby showing a marked decline in the salmon parr index in 1969. One section on the River Cowsic gave average indices of 0.6 salmon per 100 sq.m. (0.5 per 100 sq.yds). Trout were present as 18.5 per 100 sq.m. (15.5 per 100 sq.yds) in comparison with 17.5 trout per 100 sq.yds found in 1965. In the Cherry Brook the parr density at two sites was found to be 12.6 salmon per 100 sq.m. (10.6 per 100 sq.yds) and 20.7 trout per 100 sq.m. (17.3 per 100 sq.yds). These can be compared with 6.1 salmon and 8.5 trout per 100 sq.yds in 1965. The West Dart gave, on average, a salmon parr index of 6.4 per 100 sq.m. (5.4 per 100 sq.yds) and 7.5 trout per 100 sq.m. (6.3 per 100 sq.yds). 1965 indices were 6.6 salmon per 100 sq.yds and 5.5 trout per 100 sq.yds. The River Swincombe salmon parr index was 6.9 per 100 sq.m. (5.8 per 100 sq.yds) and that for trout 9.5 per 100 sq.m. (7,9 per 100 sq.yds, in comparison with 9.3 salmon per 100 sq.yds and 7.5 trout per 100 sq.yds in 1965. Five sections on the East Dart River gave average indices of 19.6 per 100 sq.m. (16.4 per 100 sq.yds) for salmon and 7.5 per 100 sq.m. (6.3 per 100 sq.yds) for trout. The salmon parr index shows a marked increase over the 1965 figure of 6.5 salmon per 100 sq.yds„ The previous index for trout was 3.6 per 100 sq.yds. The Walla Brook gave salmon parr indices of 12 per 100 sq.m. (10 per 100 sq.yds) and 37.9 trout per 100 sq.m.