people's trust for endangered species (ptes) - action for ......evidence of an overall...

A Report for the People’s Trust for Endangered Species

Action for Riparian Mammal Conservation in the Erewash Valley

by

Esther F. Kettel

October 2014


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Abstract

Riparian mammals have suffered declines in recent decades in the UK due to water pollution, loss of

habitat, persecution and the introduction of non-native species. This project aims to determine the

distribution of otters, water voles, American mink and water shrews in the Erewash Valley with the

aim of updating information which is now very out-dated or non-existent. 58 sites were surveyed,

which included river, canal (working and disused), brooks and any other water bodies in the Valley;

60 percent showed signs of water voles and findings suggest that signs are more likely to be found in

areas with a high water quality score, and in the river and disused canal. Only two signs of otter were

found and five signs of mink, four of which also showed signs of water voles. Of the 42 sites which

had bait tubes, 33 contained water shrew scat and the likelihood of finding water shrew scat in a

bait tube was not affected by the habitat quality or other habitat characteristics.

Acknowledgments

First of all I would like to thank the People’s Trust for Endangered Species for kindly funding this

project. I would also like to thank Nottinghamshire Wildlife Trust, in particular to Michael Walker

and Janice Bradley for providing me with the opportunity to carry out the work, and to Ruth Testa

and Claire Sambridge for help with fieldwork. Finally, to Matthew Edwards, Philip Bych and Katie

Freeman for all their hard work and help with surveys.


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Contents

Introduction ................................................................................................................................ 3

Otters (Lutra lutra) .............................................................................................................................. 3

Water Voles (Arvicola amphibious) .................................................................................................... 5

Water Shrews (Neomys fodiens) ......................................................................................................... 7

Project Aims ........................................................................................................................................ 9

Study Area and Methodology ....................................................................................................... 9

Study Area ........................................................................................................................................... 9

Survey Methodology ........................................................................................................................... 9

Statistical Analysis ............................................................................................................................. 10

Results ....................................................................................................................................... 11

Habitat Quality Score ........................................................................................................................ 11

General .............................................................................................................................................. 11

Discussion .................................................................................................................................. 16

References ................................................................................................................................. 18

Appendix ................................................................................................................................... 19


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Introduction

Rivers in the UK support a variety of life including aquatic plants and invertebrates, fish, birds, bats

and other mammals, including three which are particularly iconic: otters (Lutra lutra), water voles

(Arvicola amphibious) and water shrews (Neomys fodiens). However, past engineering works,

pollution, and invasive species have all had a harmful impact on the habitat and the life which it

supports. Some taxonomic groups of invertebrates (Boon, 1988), including white-clawed crayfish

(Austropotamobius pallipes) (Holdich and Reeve, 1991) and bats (Vaughan, Jones and Harris, 1996),

for example, have all been adversely affected.

More recently, however, effort has been put in to the restoration and improvement of Britain’s

rivers and their tributaries by non-governmental organisations and through the Water Framework

Directive. Despite our efforts, the success in restoring communities has shown varying results;

white-clawed crayfish are still declining and are in danger of extinction (Buglife, 2013), whilst macro-

invertebrate communities have shown to recover after restoration (Frieberg et al., 1998). For others,

their recovery and distribution is less clear in some parts of the UK, emphasising the need for

surveys in order to improve our understanding and thus our conservation efforts.

Otters (Lutra lutra)

One of Britain’s largest carnivores, the Eurasian otter is a semi-aquatic mammal with dark brown fur,

a pale throat and underparts with short legs, a long, sinuous body and webbed feet, adept for an

aquatic lifestyle (Woodroffe, 2007). With the exception of coastal populations in Scotland the otter

is largely nocturnal, feeding primarily on fish (Woodroffe, 2007); as opportunistic hunters, they will

also feed on a small number of frogs, birds, mammals and invertebrates (Copp and Roche, 2003).

The species has a rather large distribution worldwide and can be found throughout Europe, parts of

Asia and Africa (Corbet and Southern, 1977). In the UK, it suffered substantial declines during the

1950s onwards due to the use of pesticides and habitat loss (Ward, Holmes and José, 1994); the

most recent national otter survey, however, has indicated that it is recovering throughout much of

the country as a result of legal protection, an improvement in water quality and the ban on certain

pesticides (Crawford, 2010). Since 2000, the majority of otter reports in Nottinghamshire have been

to the south of the county, including in and around Attenborough Nature Reserve and around the

River Trent (Figure 1.1).


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Otter

= pre 2000 record= recorded since 2000

Key

Figure 1.1 Records of otters in Nottinghamshire pre and post 2000.


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Water Voles (Arvicola amphibious)

Water voles are rat-sized semi-aquatic rodents with a rounded muzzle, small, non-protruding ears

and chestnut brown (or occasionally black) fur (Corbet and Southern, 1977). Active day and night,

water voles create runways and burrows close to the water’s edge and are predominantly

vegetarian, consuming roots and rhizomes and coarse vegetation such as grasses, rushes, reeds and

sedges (Strachan and Jefferies, 1990).

Found throughout the slow-flowing rivers, ditches, ponds and streams of Europe, except for parts of

France, Italy and Greece, extending in to Asia, the water vole is rather widely distributed (Corbet and

Southern, 1977). They are widespread throughout the lowland regions of the UK, but are absent

from Ireland, north-west Scotland and many islands (Ward, Holmes and José, 1994). However, water

voles have recently suffered substantial declines across much of their range due to pollution and loss

of habitat and predation from the non-native American mink (Neovison vison) (Strachan and

Jefferies, 1990). In Nottinghamshire, water voles are rather widespread and signs of them have been

recorded across the county, including along the River Erewash, Nottingham Canal and around

Attenborough Nature Reserve (Figure 1.2).


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Figure 1.2 Records of water voles in Nottinghamshire pre and post 2000.

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Water Vole


Key


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Water Shrews (Neomys fodiens)

One of the least known British mammals, the water shrew is the only aquatic species of the

country’s shrews, occupying similar habitat to the water vole. They have high metabolic demands

and need to feed at regular intervals, thus are active day and night but activity is mostly at dawn and

dusk (Carter and Churchfield, 2006a). Water shrews feed on terrestrial invertebrates, but unlike

other species of shrew in the UK, also consume aquatic invertebrates, making up 50 percent of their

diet (Carter and Churchfield, 2006a). They can be distinguished from other shrew species by their

black upper fur and larger size (Corbet and Southern, 1977).

Not unlike water voles, water shrews can be found in most of Europe except for the Mediterranean

region, stretching to some western parts of Asia; in the UK, they are widely spread but absent from

Ireland and some northern parts of Scotland (Corbet and Southern, 1977). There has been no

evidence of an overall population decline (due to the paucity of data), but local declines have been

noted, with pollution and habitat loss the likely cause (Carter and Churchfield, 2006b). Signs for

water shrew are less obvious than for otters and water voles, thus reports of water shrew in

Nottinghamshire are severely lacking; nevertheless, there has been a small number of sporadic

reports across the county (Figure 1.3).


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Figure 1.3 Records of water shrews in Nottinghamshire pre and post 2000.

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Water Shrew


Key


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Project Aims

The aim of this project is to comprehensively survey the River Erewash, its associated canals and its

main tributaries for any signs of otters and water voles (as well as mink) and to place bait tubes in

suitable areas to establish the presence of water shrews. Records of these species in the Erewash

Valley are now very outdated or non-existent so the current status of these three iconic species is

unknown. By searching the area for field signs a deeper understanding of their distribution will be

known and a Conservation Action Plan can be drawn up so that these species are better protected

from the threats that they face.

Study Area and Methodology

Study Area

The study was conducted along the River Erewash, which runs from Kirkby-in-Ashfield, flowing

through both Derbyshire and Nottinghamshire, where it eventually meets Attenborough Nature

Reserve and the River Trent. The associated working canal, the Erewash Canal, runs 12 miles through

Derbyshire adjacent to the River and was also surveyed. Finally, disused parts of the Nottingham

Canal, near Cossall, and the Nutbrook Canal, near Kirk Hallam, were also surveyed as well as any

contributory streams or other water bodies which were suitable for survey. All surveyed areas are

part of the Living Landscapes Area and is part of a scheme by the Wildlife Trusts to restore, buffer

and link habitats to create connections between habitats.

Survey Methodology

Following standard survey methodology for water voles (Strachan and Jeffries, 1990) and otters

(Strachan and Jeffries, 1996) a 600 metre stretch of the River bank or canal was walked, looking for

field signs of water voles, otters and mink. For water voles this included any sightings, sounds

entering water, latrines, footprints, tunnel entrances, cropped garden around tunnel entrance,

distinctive chopped vegetation and runways in the vegetation. For otters and mink, signs included

footprints, scat, feeding remains, dens/holts and sightings. Within every one kilometre of the canals

and tributaries, 600 metres of suitable habitat were surveyed. The entire River was surveyed, where

accessible, to allow for a fully comprehensive survey effort; each 600 metre stretch was surveyed

and considered separately. Approximately 45 minutes to an hour was spent surveying each of the

58 sites. All sites surveyed, along with the signs found were mapped using ArcMap Version 10.


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For each site, details on the habitat were noted, and included terrestrial and aquatic vegetation

scores (using the DAFORN scale), water flow (rapid, fast, slow, sluggish, static), bank incline (shallow:

< 45⁰ or steep: > 45⁰), shore type (earth, gravel, stone etc.), adjacent land-use, mean depth and

width of river or canal and height of bank. Terrestrial and aquatic vegetation scores were taken using

the DAFORN scale, and were subsequently reduced to one orthogonal variable which is hereafter

called ‘habitat quality score’ using a Principal Component Analysis (PCA) on SPSS® version 22 (SPSS

Inc., Chicago, IL, USA). This allowed for analysis on the probability of finding signs at sites with

different habitat quality scores.

To survey for water shrews, bait tubes, made from plastic waste pipe cut 20 cm in length and baited

with dried mealworms, were placed 10 metres apart approximately 2 – 3 metres from the water’s

edge on suitable sites (i.e., those not too exposed to human disturbance or those lacking in

vegetation). In each 600 metre site, 10 bait tubes (15 at two sites) were placed in optimal habitat,

covering a total of 100 metres (150 metres at two sites). A total of 42 sites were surveyed, including

a total of 430 bait tubes. Each tube location was marked on a GPS (Garmin GPSmap 62s) so they

could later be found, and were left in place for 14 days. On collection of tubes, the scat contents

were put in to separately labelled containers for later examination. Following advice from Carter and

Churchfield (2006a), identification of water shrew scat was made by visual examination; water

shrew scats are distinct from other shrew species’ due to their larger size and difference in diet.

Statistical Analysis

To test the effect of bank incline, shore, width of the water body, depth of the water and habitat

quality score on the probability of finding water vole signs and water shrew scat in bait tubes a

generalised linear mixed model (GLMM) was fitted, assuming binomial errors, using the statistical

programme R Version 3.0.3 (R Core Team, 2014). No statistical analyses were carried out for otters

or mink as there was too few data.


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Results

Habitat Quality Score

There were strong correlations among the seven habitat characteristics measured. PCA yielded a

single principle component capturing nearly 40 percent of the variance in the raw variables (Table

1.1). This component correlated positively with all seven variables and can be interpreted as a

measure of habitat quality: sites with positive scores have abundant terrestrial and aquatic

vegetation, whilst those with negative scores have little vegetation.

Table 1.1 The Factor loadings and the percentage of variance explained from the PCA of habitat

variables at all sites.

General

Of the 58 sites, 35 had signs of water voles (Figure 1.4); of these 35 positive sites, 21 were definite

(i.e., showed signs of recent activity such as latrines) and 14 were possible signs (i.e., only tunnel

entrances). Only two signs of otter were recorded (one scat and one footprint; Figure 1.5); both

were well in the potential home-range of those found previously at Attenborough Nature Reserve,

and could thus be that individual or individuals. Mink scat was found at five of the sites (Figure 1.6),

four of which also showed signs of water vole (see Appendix A).

1

Bankside trees 2.728

Herbs/forbs 1.842

Shrubs 0.896

Grasses 0.54

Submerged 0.398

Emergent 0.326

Floating 0.27

Percent variation explained 38.97


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Evidence of water voles was statistically more likely to be found in sites which had a higher habitat

quality score (GLMM: X2(1) = 9.771, P = 0.001; Figure 1.7). There was a strong significant difference

among the habitat types in the probability of finding water vole signs (GLMM: X2(4) = 17.192, P =

0.001); the river and disused canals had the highest percentage of signs and working canals the least,

perhaps due to high levels of human disturbance (Figure 1.8).

Figure 1.4 Water vole latrine. Figure 1.5 Otter print.

Figure 1.6 Mink scat.


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-2 to -1.1 -1 to 0.01 0 to 0.9 1 to 1.9 >2

Pe

rcen

tage

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site

s w

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vole

sig

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Binned habitat score

Figure 1.7 The relationship between the habitat score and the percentage of sites which had

evidence of water voles. Error bars show 95% confidence intervals calculated from the binomial

distribution.

Figure 1.8 The percentage of sites in which water voles signs were found in the different habitat

types surveyed. Error bars show 95% confidence intervals calculated from the binomial distribution.

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River Canal (disused) Canal (working) Brook

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There was no significant effect of the depth of the water (GLMM: X2(3) = 0.928, P = 0.818), the flow of

water (GLMM: X2(3) = 2.961, P = 0.3977), bank incline (GLMM: X2

(1) = 1.504, P = 0.220), or the

presence of mink (GLMM: X2(1) = 0.164, P = 0.685); however, only a small number of mink signs (n =

5) were found and should be considered when drawing conclusions.

Of the 430 bait tubes, 219 contained mammal faeces including water shrew (n = 97; Figure 1.9),

other shrew species (n = 104), rodents (n = 7) and some which were unidentifiable due to loss of

structure and/or because they were too wet (n = 11). Water shrew scats were found in 33 of the 42

sites surveyed (see Appendix A). There was no significant effect of the depth of the water (GLMM:

X2(3) = 5.412, P = 0.144), the flow of the water (GLMM: X2

(3) = 1.218, P = 0.749), bank incline (GLMM:

X2(1) > 0.001, P = 0.987), the width of the water body (GLMM: X2

(3) = 3.519, P = 0.3183) or habitat

score (GLMM: X2(1) = 2.819, P = 0.093) on the probability of finding water shrew scat in a bait tube.

The type of habitat was also non-significant (GLMM: X2(3) = 7.104, P = 0.0686), but as Figure 1.10

shows, the least amount of scats were found at the working canal, whilst brooks contained the most

(though bait tubes were only placed on four brooks), followed by the river and disused canals.

Figure 1.9 Water shrew scat through a microscope, determined by the size, structure and colour.


15

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River Canal (disused) Canal (working) Brook

Pe

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cat

Habitat type

Figure 1.10 The percentage of sites which contained water shrew scats in bait tubes in the different

habitat types surveyed. Error bars show 95% confidence intervals calculated from the binomial

distribution.


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Discussion

Despite reported significant declines of water voles on a national scale, the surveys carried out here

create a more positive image of the species in the Erewash Valley. Of the 58 sites surveyed, 60

percent of them contained either definite (36%) or possible (24%) signs. The surveys do, however,

imply that some areas are completely absent of water voles, creating isolated populations which

may be prevented from dispersing and should thus be monitored closely. Future conservation

efforts should attempt to connect these populations; it is clear from the results that the working

canals support fewer water voles, perhaps dues to greater levels of human disturbance, including

boat traffic and regular cutting of bankside vegetation. Thus habitat restoration and maintenance in

these areas where water voles are not present may be a first step in connecting populations.

Furthermore, water voles were present at four of the five sites where mink signs were also found,

suggesting that they have either reached an equilibrium or, more bleakly, that those current water

vole populations are in danger of future reduction or extinction due to the presence of the mink.

Either way, the populations should be closely monitored for any changes and, if necessary, mink

control should be used to prevent predation.

A huge proportion of sites surveyed contained water shrew scat, illustrating the extent of their

distribution in the valley, which was previously poorly understood. This study showed no significant

interaction with any of the habitat characteristics or habitat quality which illustrates their tolerance

of a range of habitats and environmental conditions, as is stated by Carter and Churchfield (2006a),

and may explain their success in the Valley. Furthermore, it demonstrates the need for more bait

tube surveys to be carried out in the region so a clearer understanding of their distribution can be

learnt; the method has proved successful in this study and should equally be so in other parts of

Nottinghamshire.

Recently, otters have re-colonised some areas of the UK where they had previously suffered declines

due to pollution, persecution and habitat loss. In this current survey effort, despite the vast area

covered, only two signs of the species were found. Adult females may have a home range of 25 – 40

km and males up to 70 km (Woodroffe, 2007) so although impossible to tell without a more detailed

survey effort, it could be assumed that this otter or otters were those from the Attenborough area,

where there has been a number of records of them in recent years. It is clear from the extensive

survey effort that there does appear to be good habitat for the species to disperse through the

Erewash Valley; The River Erewash in particular appears to have adequate cover and shelter, and


17

healthy fish populations. However, it was also apparent that much of the river was grazed by sheep,

cattle and horses, which may be putting pressure on the regeneration of shrub cover and potential

holt sites (Ward, Holmes and José, 1994). Therefore there needs to be protection and management

of this habitat, including the encouragement of scrub growth, if otters are to re-colonise the area.

When drawing conclusions, the limitations of the survey methodology should be noted; just because

no signs were found, for example, does not mean that the species is not there. Surveys were only

carried out once at each site, and thus signs would have to be there at the same time; otter prints,

for example, can easily be lost by rising water levels. Despite this caveat, this study has shown that

riparian mammals in the Erewash Valley appear to be fairing relatively well, and conservation efforts

should focus on preserving the current populations and enhancing the habitats to allow for

dispersal. The study has provided an up-to-date understanding of riparian mammal distribution in

the Erewash Valley, but populations should be closely monitored to prevent the loss of these iconic

species.


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References

BOON, P.J. (1988) The Impact of River Regulation on Invertebrate Communities in the UK, Regulated

Rivers: Research and Management 2(3): 389 – 409.

BUGLIFE. (2013) White-Clawed Crayfish (Austropotamobius pallipes). Buglife, Peterborough.

CARTER, P. AND CHURCHFIELD, S. (2006a) The Water Shrew Handbook. The Mammal Society,

London.

CARTER, P. AND CHURCHFIELD, S. (2006b) Distribution and Habitat Occurrence of Water Shrews in

Great Britain. A Report by the Environment Agency. The Environment Agency, Bristol.

COPP, G.H. AND ROCHE, K. (2003) Range and Diet of Eurasian Otters Lutra lutra (L.) in the Catchment

of the River Lee (South-East England) Since Re-Introduction, Aquatic Conservation: Marine and

Freshwater Ecosystems 13(1): 65 – 67.

CORBET, G.B. AND SOUTHERN, H.N. (1977) The Handbook of British Mammals. Second edition.

Blackwell Scientific Publications, London.

CRAWFORD, A. (2010) Fifth Otter Survey of England, 2009 – 2010. A Report by the Environment

Agency. The Environment Agency, Bristol.

FRIEBERG, N., KRONUANG, B., HANSEN, H.O. AND SVENDSEN, L.M. (1998) Long Term, Habitat

Specific Response of a Macroinvertebrate Community to River Restoration, Aquatic Conservation 8:

87 – 99.

HOLDICH, D.M. AND REEVE, I.D. A (1991) Distribution of Freshwater Crayfish in the British Isles, with

Particular Reference to Crayfish Plague, Alien Introduction and Water Quality, Aquatic Conservation:

Marine and Freshwater Ecosystems 1(2): 139 – 158.

R CORE TEAM. (2014) R: A Language and Environment for Statistical Computing. R Foundation for

Statistical Computing, Vienna, Austria. Available at URL: http://www.R-project.org/.

STRACHAN, R. AND JEFFERIES, D.J. (1990) The Water Vole Arvicola terrestris in Britain 1989 – 1990:

Its distribution and Changing Status. A Report by the Vincent Wildlife Trust. Vincent Wildlife Trust,

London.

STRACHAN, R. AND JEFFERIES, D.J. (1996) Otter Survey of England 1991 – 1994: A Report on the

Decline and Recovery of the Otter in England and on its Distribution, Status and Conservation in

1991 – 1994. A Report by the Vincent Wildlife Trust. The Vincent Wildlife Trust, London.

VAUGHAN, N., JONES, G. AND HARRIS, S. (1996) Effects of Sewage Effluent on the Activity of Bats

(Chiroptera: Vespertilionidae) Foraging Along Rivers, Biological Conservation 78: 337 – 343.

WARD, D., HOLMES, N. AND JOSÉ, P. (1994) The New Rivers and Wildlife Handbook. RSPB, Sandy.

WOODROFFE, G. (2007) The Otter. Third edition. The Mammal Society, London.

Appendix A Maps showing the location of water vole, otter, American mink and water shrew signs found during the surveys.

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