Riversearch 2011-13
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2011-13 (Incorporating the Essex Otter Survey) Darren Tansley - March 2014 Protecting Wildlife for the Future and for the People of Essex Essex Riversearch 2011-2013 Introduction RIVERSEARCH was originally set up to train volunteers the skills required to undertake the annual Essex Otter Survey. That survey has been carried out every year since 1996 and was recognised as a significant project by Andrew Crawford, author of the Environment Agency’s Fifth Otter Survey of England. Otters have been part of the fossil record of the British Isles for a staggering half a million years, illustrating just how resilient they have been as a feature of our native fauna. But with a sharp decline in the Essex water vole population, and a lack of knowledge about the distribution of other semi-aquatic mammals such as water shrew, it seemed logical to evolve RIVERSEARCH into a more comprehensive report. ■ 2007 - RIVERSEARCH launched to undertake the annual Essex Otter Survey. Otter survey training days held at Dedham on the River Stour. ■ 2008 - First water vole survey course held at Blue House Farm EWT Reserve. ■ 2009 - RIVERSEARCH surveys used for the Essex section of the Fifth Otter Survey of England, co-ordinated by the Environment Agency. ■ 2010 - Volunteers trained to radio-track water voles for a five year reintroduction project on the River Colne. ■ 2011 - Water voles officially included in the RIVERSEARCH survey. The first water shrew bait tube survey is piloted. The otter NIGHTWATCH is launched to observe nocturnal wildlife on live IR cameras. Positive otter survey sites exceed negative for the first time. ■ 2012 - Unprecedented flooding hampers the survey. Less than half of the regular sites are “The yearly surveys carried out visited. by Essex Wildlife Trust provide ■ 2013 - First harvest mouse course held at Hanningfield Reservoir in conjunction with Jim one of the few opportunities to Jones from Surrey Wildlife Trust’s RIVERSEARCH project. monitor the movement of a leading edge in detail.” Andrew Crawford This report is an amalgamation of all the surveys undertaken from 2011-2013 and I would like to Environment Agency thank all the RIVERSEARCH volunteers for their efforts. Without their dedication and passion for Essex rivers, this work would not be possible. Flooding 2012-2013 Although this report covers 2011-2013, the last two years included some of the most extreme and prolonged river flooding in living memory. This severely hampered the efforts of volunteers and staff to conduct their surveys. Whilst we normally complete 75%-85% of the 255 transects, this figure dropped below 50% for the first time in 2012 (chart 1, p4). Although 2011 produced the most Rivers overtopped their banks in May and July threatening breeding populations of water fowl, positive results since the otter kingfisher and water vole. This was followed by winter flooding early in November which continued survey began, only 45% of the into the spring of 2013. It has therefore been impossible to draw statistically relevant comparisons survey sites were visited during the prolonged and extensive of the 2012 and 2013 datasets with those of previous years. However it was interesting to note that flooding in 2012. where we were able to carry out our surveys there was still an upward trend in the percentage of sites with positive otter signs (chart 2, p4). 2 Darren Tansley - Essex Wildlife Trust Otter Lutra lutra [Survey all year but easiest February-May or October-December] Even when otters are using a river they are rarely seen. Their main prey, eels and other fish, are more Otter spraints vary in size but sluggish and easier to catch at night so this might explain why Essex otters have adopted a nocturnal usually contain fish bones and lifestyle. They can also occupy very large territories with males potentially holding as much as 15km of fish scales. river corridor, overlapping several female ranges. It has therefore been important to develop a method of surveying that does not rely on actual sightings. Otters communicate with each other by depositing droppings, known as spraints, on prominent features such as fallen trees, boulders, grass tussocks, shingle bars and road bridge supports. The males travel greater distances and need to territory mark more regularly so their spraints tend to be smaller than the females or juveniles. With training and practice spraints can be easily located and identified. Dark and sticky when fresh, spraints contain fish bones and scales and have a distinctive scent, variously described as smelling like fresh hay, ‘jasmine tea’ or fishy and musty. Survey transects generally begin at bridges or other prominent features and include a total of 600m of bank in the most easily accessible direction from the starting point. When a sprainting site is found the spraints are counted (but not removed) and the survey is complete. Footprints and other field signs are noted but a survey point is only identified A popular sprainting location as positive if spraints are present or suitable photographic evidence is produced for verification. under a road bridge at a survey point on the River Colne. The easiest time for surveying is from February to the end of May before waterside vegetation becomes too dense. Surveys should not be undertaken during times of flood or high water as field signs will be washed away. Spraints generally begin to reappear a few days after flood waters recede as a result of resident otters re-marking their territories. Footprints may also be more obvious at these times in freshly deposited silt. Water vole Arvicola amphibius [Survey April-October] Water voles face an uncertain future in Essex due to predation by invasive mink and the twin threats of sea-level rise and industrial development in the coastal areas that are their main stronghold. In order to better understand their distribution, RIVERSEARCH volunteers are encouraged to search for water vole signs while undertaking their otter surveys, in particular the distinctive latrines (piles of droppings) and feeding stations. Water vole surveys are best undertaken during the breeding season from April to October when voles are most active. The percentage of sites surveyed for water voles is smaller than for otters (chart 3, p4) as we have fewer trained water vole surveyors, but this does help to supplement the records generated by the Essex Water Vole Recovery Project. This Essex Wildlife Trust led initiative co-ordinates the efforts of several hundred land managers and involves habitat restoration, reintroductions and work to exclude mink from sensitive water vole populations. Where mink control has been in place for five years or more, the distribution of water voles has increased substantially. However, where mink control is patchy, especially to the south west and along many of our major inland rivers, water voles have declined dramatically since the 1990s. LEFT Water vole feeding remains from the Tenpenny Brook show the distinctive 45° angled cut. RIGHT Water vole latrines are piles of ‘tic-tac’ shaped droppings. Female water voles leave their scent mark on the droppings as a territory marker during the breeding season. 3 Essex Riversearch 2011-2013 Results - otter and water vole Chart 1: Status of otter survey sites 2006-2013 After a successful survey in 2011, severe flooding adversely impacted access in 2012 and 2013. 100% 90% 80% 70% 60% Not surveyed 50% Negative 40% Probable 30% Positive 20% 10% Severe Flooding 0% 2006 2007 2008 2009 2010 2011 2012 2013 Chart 2: Results from sites surveyed for otters 2006-2013 Of the sites that were surveyed for otters, the percentage of positive results climbed steadily from 25% in 2006 to 56% in 2011. Whilst the results were even better in 2013 these data must be treated with caution as only 52% of the sites were surveyed that year. 100% 90% 80% 70% 60% Negative 50% Probable 40% Positive 30% 20% 10% Severe Flooding 0% 2006 2007 2008 2009 2010 2011 2012 2013 Chart 3: Comparison of sites surveyed for otters and water voles 2011-2013 Although there are fewer RIVERSEARCH surveyors trained to look for water vole signs than otters, Water vole. Photo - Roger Hance we were able to survey over 40% of the sites despite very challenging flood conditions in 2012-2013. 100% 90% 80% 70% 60% Not surveyed 50% Negative 40% Probable 30% Positive 20% 10% 0% Otter 2011-13 Water vole 2011-13 4 Darren Tansley - Essex Wildlife Trust River Stour (Box, Brett, Chad Brook, Glem) Surveyors:- Liz Brooks, Les Cousins, Bill Johnson, Carole Mander, William Mann, Darren Tansley and Sarah White Otters 2011-2013 otter results Total Positive Possible Negative Unsurveyed Crayfish remains are common where otters have been feeding. Stour 27 24 0 2 1 Box 6 1 0 4 1 Brett 12 9 0 2 1 Chad Brook 5 4 0 1 0 Glem 10 8 0 2 0 Catchment Total 60 46 0 11 3 The River Stour forms the border between Essex and Suffolk for much of its course but the catchment includes a number of substantial tributaries which drain south into the river from the Suffolk side. This was the first ‘Essex’ catchment to be re-colonised by otters during the late 1980s although only two sites were found to be positive during a survey in 1991. By 1996, 66% of the catchment was occupied. That year the Environment Agency reported that otters were breeding at Flatford. An otter swims past on the River Stour. Photo - Steve Brown This river continues to provide good habitat for otters that have exploited the abundance of invasive American signal crayfish as a food resource. Many spraints are comprised almost entirely of crayfish and the remains of claws and carapaces can be found piled up on the river banks.