Otter Survey Report
This is a brief report of the findings from the Spring 2017 otter survey. A full scientific report (25,000 words) is available from myself, but due to the file size cannot be shared via email, so I have summarised all the main aims, findings, conclusions and future plans here in this document instead.
Aims of the Study
1). Find the distribution and level of otter activity in Birmingham and surrounding canals.
Through spraint surveys the aim was to find out which parts of the canal system otters are utilising. A unique element of this survey was that the survey was repeated once a week for up to six weeks (never before done!), meaning the number of otter visits during this time could be determined, giving a measure of not only the distribution of otter activity but also a level of magnitude. It was hypothesised that otters would use the more rural canals around the edge of Birmingham but not utilise the canals in the heavily urbanisedcentre of Birmingham.
2). Determine which canal characteristics influence the distribution and level of otter activity in Birmingham and surrounding canals.
By measuring a number of physical, anthropogenic and biological characteristics of the canals, the study also sought to determine which of these factors correlated with areas of high otter activity and which correlated with levels of low or no otter activity. From this it could be determined the type of canal environment otters found most favourable and what barriers to the dispersal of otters in canal systems there may be. It was hypothesised that similarly to studies done on rivers otters would favour canals with good bankside quality and cover, but may be more influenced by the physical barriers such as locks along a canal and the higher level of disturbance from humans.
3). Give future conservation management suggestions for otters in Birmingham and surrounding canals.
In order for the results of this study to have a positive and beneficial effect for future wildlife in the Birmingham canals, findings need to be used in future conservation management plans for these areas. For the first part this will be continued monitoring of otter populations to see if they remain stable, increase or decrease. A number of suggestions of how to improve canals as corridors for otters and other wildlife will then be made.
Notes on the Study Method
The study was conducted in the canals of Birmingham and the surrounding Black Country areas, in the UK. The study covered 194km of canals, stretching between three counties, Staffordshire, Warwickshire and Worcestershire. In total, 10 different canals were looked at, with the 2 longest canals being split into ‘North’ and ‘South’ sections, namely the Staffordshire and Worcestershire, and the Birmingham and Fazeley canals. This gave a total of 12 different sections of canal to be studied (Table 1), all between 10km and 25km. A preliminary survey assessed how to divide canals into sub-sections by making sure each sub-section had;
a). Access onto the canal and parking at one end of the stretch.
b). A number of monitoring sites that could be checked for otter spraints.
These small sub-sections of canal were between 2-3km, so as to be a reasonable length for volunteers to survey in one go. Each section of canal in Table 1, was made up of between 4 and 8 sub-sections, joined end-to-end. For all canals, the entire length of the canal from the start to the end point, was surveyed, with the exception of the Birmingham Canal Navigations, for which there were areas along the canal chosen not to be surveyed, due to this canal stretch being too long, and of similar characteristics throughout. Each canal section also had a minimum of 20 monitoring sites.
In total over 55 volunteers were recruited through advertisement of the survey by emails, leaflets and a call-out on the local news. Volunteers mostly consisted of; members of wildlife or conservation groups, university students, and canal users.
Canal Section / Total Length Surveyed (km) / Number of Monitoring SitesStaffordshire and Worcestershire (South) / 20 / 37
Staffordshire and Worcestershire (North) / 17 / 20
Birmingham Canal Navigations (Including Old and New Lines) / 13 / 44
Dudley Canal Complex / 24 / 27
Walsall Canal / 13 / 63
Wyreley and Essington Daw End Branch + Rushall / 12 / 24
Tame Valley / 14 / 49
Birmingham and Fazeley (South) / 12 / 55
Birmingham and Fazeley (North) / 13 / 27
Grand Union / 24 / 44
Worcester and Birmingham / 18 / 40
Stratford Upon Avon / 14 / 38
Location of Spraints found
Spraint was recorded at a total of 84/468 (18%) monitoring sites throughout the time period of the survey. Out of the four types of monitoring site looked at 77/84 (92%) spraints recorded were at bridges, 3 (3%) at locks, 4 (5%) at overflow channels or other structures and 0 at canal intersections. The canal section with the highest number of spraints recorded was Staffordshire and Worcestershire (South) with a total of 10/37 monitoring sites recorded as having spraint, 27% of the total monitoring sites looked at for that section. Other sites where a high number of spraints were recorded included the Staffordshire and Worcestershire (North) canal, Stratford Upon Avon canal, Birmingham and Fazeley (North) canal and the Grand Union canal. There were 4 sections of canal for which no spraint was recorded for the whole six weeks of the survey, these were the Birmingham Canal Navigations, Tame Valley Canal, Birmingham and Fazeley (South) and the Walsall Canal.
Figure 1 shows the distribution of the spraints recorded. Most spraints recorded were on the periphery of the study area. Apart from the Wolverhampton area, for which a lot of spraint was recorded, there were only 6 other locations where spraint was recorded within the central Birmingham boundaries, all on different canals. There were a total of 35 monitoring sites for which fresh spraint was recorded there on more than one week, indicated by the darker points on Figure 5. There were 2 monitoring sites on the Birmingham and Fazeley (North) for which fresh spraint was recorded for all six weeks of the survey. The upper stretch of the Staffordshire and Worcestershire Canal, particularly North of Wolverhampton had the densest set of monitoring sites for which otter spraints were recorded at. Almost every monitoring site in this stretch was positive for otter spraint on at least one week of the survey, with many having fresh spraints for up to five weeks.
DNA Verified Spraints and Sex identified
In total 45 samples were collected in the week commencing 13th February 2017 and sent off for DNA analysis. Out of these samples, 34 (76%) were confirmed by DNA as being otter. There were 11 samples for which the species could not be identified which could have been due to a). The sample was not otter, b). The size of the sample was too small for DNA analysis, c). The DNA had degraded within the sample. Although not confirmed by DNA, experts carrying out the analysis noted that at least two of the samples probably belonged to mink, and at least one other to fox. The 34 samples confirmed as otter were located on 5 different canals; Staffordshire and Worcestershire (North and South sections), Birmingham and Fazeley (North), Grand Union, Stratford Upon Avon and the Worcester and Birmingham (Figure 6). Only one spraint confirmed as otter was within the central Birmingham borders, on the Worcester and Birmingham Canal, and was located in Edgbaston, close to the University of Birmingham.
Out of the 34 samples confirmed as otter there were 16 for which sex could be determined. Out of these 16, 12 (75%) were male and 4 (25%) were female. The spraints identified as female were located in the South section of the Staffordshire and Worcestershire (3/4), and the Grand Union (1/4). Spraints identified as male were located in the North section of the Staffordshire and Worcestershire Canal (2/12), Birmingham and Fazeley Canal (5/12), Stratford Upon Avon Canal (2/12), Grand Union Canal (2/12) and the Worcester and Birmingham Canal (1/12).
Measures of Otter Activity
For the four stretches of canal for which no otter spraint was found, all measures of otter activity were 0. All measures of otter activity for the remaining eight canal stretches can be seen in Figure 7. Correlations between all three measures of otter activity were significant at p<0.01. Although all three otter activity values in general increased with each other, there were some exceptions, for example the Birmingham and Fazeley (North) had the highest value for minimum number of otter visits (6) but had a value of only 18% for average % positive. The canal stretch with the lowest scores for all three otter activity measurements was the Dudley Canal Complex. The highest score for both average % positive and average spraints/km was the Staffordshire and Worcestershire (South), but that stretch only had a minimum number of otter visits of 4. The Birmingham and Fazeley (North), Staffordshire and Worcestershire (North) and Stratford Upon Avon all had minimum number of otter visits of 6, the highest recorded. Looking at the average ranking between all three otter activity measurements canal stretches were grouped according to Table 5.
No Otter Activity / Low Otter Activity / High Otter ActivityBirmingham Canal Navigations / Grand Union Canal / Staffordshire and Worcestershire (South)
Walsall Canal / Wyreley and Essington Daw End Branch + Rushall Canal / Staffordshire and Worcestershire (North)
Tame Valley Canal / Worcester and Birmingham / Stratford Upon Avon
Birmingham and Fazeley (South) / Dudley Canal Complex / Birmingham and Fazeley (North)
Otter Activity Correlated with Canal Characteristics
After the otter activity measurements seen in figure 3 were calculated these were then looked at against the canal characteristic measures for each stretch. It was seen that canals with high otter activity tended to have a high number of anglers, good offside vegetation and a good connectivity with rivers. Canals with low otter activity tended to have good connectivity with other watercourses. Canals with no otter activity tended to have high levels of emergent vegetation and high numbers of locks. Interestingly good towpath vegetation and a high number of boats/walkers did not appear to correlate with otter activity.
Discussion
In just the six weeks of this survey more signs of otters (in the form of spraints) were recorded than the total number of signs and sightings reported to the Canals and Rivers Trust and EcoRecord in the past 17 years. Although the odd sightings reported to CRT and EcoRecord cannot be directly compared with this organised survey it does, if nothing else, highlight the real need for proper surveys of otter surveys in this area, in order to monitor the populations that obviously are present in the area.
The location of otter spraints around the periphery of the study area (Figure 1), is somewhat expected, and supports the original hypothesis of otters using canals in rural areas but not the canals of the heavily urban centre. It has been hypothesised by others previously that urban areas pose a barrier to otters, and looking solely at the distribution of spraints on the map (Figure 1), this does seem to be the case, with quite definitive boundaries of where the otters appear to ‘stop’ using canals (E.g. at Hasluck’s Green on the Stratford Upon Avon and at Bodymoor Heath on the Birmingham and Fazeley). Level of urbanisation cannot be the sole cause of the distribution seen in figure 1 however, as some individual spraints were recorded in the more suburban areas of Edgbaston on the Worcester and Birmingham, Daisy Bank on the Rushall Canal and Aldridge on the Wyreley and Essington Daw End Branch. As well as this a single spraint was found on the Dudley Canal, an urbanised area.
For the purpose of this study the aim was to find out which sections of canal otters were using as corridors and which they were not, and therefore it is of most interest to look at the areas where there were no intersections with river/streams yet otter spraint was still found. One such area of interest is the North section of the Staffordshire and Worcestershire. The river Stour, which then turns into the Smestowbrook ends just North of Wolverhampton, but otter spraint was found regularly, in abundance further North of this point on the Staffordshire and Worcestershire (Figure 1). It is likely therefore that otters are using this section of canal, as oppose to just ‘travelling through’ from nearby rivers and streams. There were a number of other areas where this was the case as well, including spraint sites on the Grand Union canal, Stratford Upon Avon canal, Dudley canal complex and the Wyreley and Essington Daw End Branch. Two other areas to note were the three spraints found in the South section of the Worcester and Birmingham and the Southern most spraint sites found on the Birmingham and Fazeley canal. As shown by figure 1 at these points there are no intersections with major rivers and streams, however although not included on the map, these sections of canal are in very close proximity reservoirs, lakes or ponds, namely the Bittell reservoirs (close to the Worcester and Birmingham canal) and Kingsbury water park (close to the Birmingham and Fazeley). It is likely then that similarly to otters on the Staffordshire and Worcestershire canal with the river Stour, otters are taking advantage of both the canal and reservoir, lake and pond environments.
The unevenness in the number of males to females (4:10) found in this study can be attributed not to the fact that there are more males than females in a population but because males are more territorial they are likely to spraint more often than female otters. It should be noted that the distribution of DNA verified otter spraint found cannot give a reliable estimation of population size. Otters can travel up to around 20km each day, with some recorded as travelling over 100km and therefore spraints that are found substantial distances apart does not necessarily mean that there are two otters present, it could be the same otter travelling. In order to get a definite population estimate DNA fingerprinting, which is both costly and time consuming would need to be used.
Although DNA fingerprinting was not a possibility in this study the locations of the females and males in the study area can give an indication of the minimum number of otters in an area. All of the fresh otter spraints which yielded information about the sex of the otter were collected within 2 days of each other. Therefore assuming otters travel on average between 4-7km each day it can be assumed that there are two female otters found in this study, one on the Staffordshire and Worcestershire (South) and one on the Grand Union canal. The assumptions can be made to say that there are at least three male otters, one on the Staffordshire and Worcestershire (North), one on the Birmingham and Fazeley (North) and one on the Grand Union/Stratford Upon Avon/Worcester and Birmingham canal. Of course otters can travel greater distances than 7km each day, however considering how many times fresh otter spraint was found in these areas (often once a week) it is unlikely that all of the male spraints found in this study belonged to just one otter.
It can therefore be presumed that there are a minimum of 5 otters utilising the Birmingham canal system regularly. Even this could be an underrepresentation however as a previous study found that out of the 13 spraints for which DNA fingerprinting was carried out only one male was recaptured, with 11/13 samples belonging to different individual otters. Assuming that there were 5 different otters found within this survey which covered around 40km2 this is a reasonably high density when compared to previous studies which found only 3 otters within 75km2 in East Anglia and 4 otters within 57km2 in Perthshire, especially considering this study looked only at canals and not the other rivers and watercourses within the study area.
The values obtained for otter activity seen in figure 3 appear to be relatively low, with the highest value for % positive being just 27 and the highest value for spraint/km being just over 1 (both on the Staffordshire and Worcestershire, South). Previous studies have yielded results of over 90% positive and one study in Italy found 31.7 spraints/km. However the results of those studies can not be accurately compared with this one considering the fact that a). This study was done in central England where otter densities are lower to start with, (the latest national otter survey yielding results of only 35% and 12% positive for the Warwickshire Avon and West Midlands Tame catchments) and b). This study being done on canals for which there are a lot more potential sprainting sites, and values for spraint/km and % positive do not currently exist. In some small sections of canal such as the very North section of the Staffordshire and Worcestershire spraint was found at almost every monitoring site, and as shown by a previous study the presence of a negative site does not necessarily correlate with the absence of otters, particularly if positive sites are found on both sides of negative sites. This, plus the high number of time otter re-visited stretches of canal within the six-week survey period, has to be seen as a positive indicator that otters are using the Birmingham and surrounding canal system.