Suffolk Coast Otter Project

Report June 2014 to March 2016 on work in progress

This project has been part funded by the Amenity and Accessibility Fund of the Suffolk Coast and Heaths AONB.

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Table of Contents

Suffolk Coast Otter Project ...... 4 1. Introduction ...... 4 2. The Study Areas...... 4 3. Diet ...... 5 a. Introduction ...... 5 b. Methodology ...... 5 c. Results from the Minsmere Study Site ...... 5 d. Results Alde/Ore Study Site ...... 9 4. Spraint Deposition...... 10 a. Introduction ...... 10 b. Minsmere...... 10 c. Alde/Ore...... 10 5. Activity Patterns...... 11 a. Previously Published Studies...... 11 b. Trail Cameras...... 12 c. Results...... 12 6. Productivity and Population Estimates ...... 14 a. Minsmere - Island Mere ...... 14 b. Minsmere North Marsh...... 16 e. The Alde/Ore...... 17 7. Footprint Study...... 17 8. Behavioural Observations ...... 18 9. Recommendations for Future Action ...... 20 10. Acknowledgements ...... 20 11. References ...... 20

2 Summary

This Report covers work undertaken by the Suffolk Coast Otter Project at the RSPB Minsmere Reserve and on the Alde/Ore Estuary between June 2014 and March 2016.

Spraint analysis results of over 550 spraints are given for the two sites. Analysis covers species present with no relative quantities in individual spraint. No attempt is made to assess the importance in the overall diet of the species present.

 There is no evidence that the Minsmere otters are using the sea for food.  On the Alde/Ore a significant proportion of the prey is obtained from the estuary.  At Minsmere the fish species appearing in the spraint are the same species as identified from the electro-fishing.  Significant amounts of very small fish appear in the spraint with 50% of spraints from Minsmere containing stickleback and on the Alde/Ore over 70% contain stickleback and over 50% containing goby.  At Minsmere proportions of bird, water beetle, shrimp and eel increase in the spraint in the summer.

Otters are frequently seen during the day at Minsmere and the camera results show they are active at any time of the day or night. On the Alde/Ore there are very few daytime sightings and the cameras show a far more nocturnal habit.

At Minsmere during the study period there seem to have been a minimum of three females producing seven sets of cubs. There is some evidence of cub loss soon after they appear with one family of three cubs being reduced to one cub within a fortnight of first appearing.

On the Alde/Ore we get far less camera contact with both otter families and individuals.

A study of footprints in an attempt to identify individual otters is underway in conjunction with an American organization – WildTrack.

A number of behavioural observations have been observed and described.

Recommendations are made for future action.

3 Suffolk Coast Otter Project

1. Introduction Otter monitoring over recent years has concentrated on recording the presence or absence of otters by checking for spraint. This successfully recorded the return of the otter after the near extinction caused in the 1960s and 70s by pollution from agricultural pesticides. However, this provided no information on numbers, breeding success, diet or how they used the habitats they occupied. The Suffolk Coast Otter Project was established to investigate techniques that might shed light on some or all of these areas.

Initially the Project had two main areas of work: -  Spraint analysis – the collection and analysis of spraint to gather information on diet and habitat utilisation.  Trail cameras – Using carefully positioned trail cameras to monitor passing otters. A third area of work was to disseminate any knowledge gained from this project both in Suffolk and further afield. This paper looks at what has been achieved so far and provides a basis for making decisions about future work. Any thoughts or comments gratefully received.

2. The Study Areas. Minsmere is an RSPB nature reserve of some 1000 hectares on the Suffolk coast. The reserve includes over 200 hectares of reed bed, water bodies and interconnecting ditches which are home to such reedbed specialities as bittern; bearded tit and marsh harrier. Considerable effort has been put into boosting the habitat for bitterns with the manipulation of water levels and the creation of ideal conditions for populations of fish. Bittern numbers have grown from a single booming male in 1991 to well into double figures in the summer of 2015. Conditions at Minsmere seem ideal for otters, with daytime sightings proving extremely popular with the 1000s of visitors that flock to the reserve.

The Alde/Ore Estuary. The estuary stretches 28km. from Snape Bridge to the sea at Shingle Street. There are extensive areas of embanked freshwater grazing marsh and in the upper reaches there are extensive mud flats. On this estuary we have several regular sites for the collection of spraint samples and sites where we have trail cameras. Together these sites include saline conditions in the estuary itself, extensive mudflat and saltmarsh and on the other side of the river wall freshwater grazing marsh with intersecting ditches. The sites are: Stanny House Farm, Iken, (private owner); Orford Ness, (National Trust); Boyton and Hollesley Marshes, (RSPB); and Snape Marshes (RSPB).

A group has recently been established and has started work on the River Blyth and a group for the River Deben is planned for this Autumn.

4 3. Diet

a. Introduction Finding out what otters eat by analysing their droppings (spraint) has been used by various researchers in different parts of the otter’s geographical range. It is not a perfect tool in that large prey, eaten by biting off chunks of flesh, may leave few remains in the spraint whereas small prey such as sticklebacks, which are eaten whole, may be exaggerated. It does not therefore allow for the relative importance of species to the overall diet to be calculated but the frequency of occurrence of different species can give an important insight into how the otter is using its range.

b. Methodology Spraint collection is carried out on a regular basis usually fortnightly. Spraints are collected separately in small plastic pots, soaked in a solution of biological washing powder for at least 24 hours, gently washed through a sieve, then laid out on paper and either air dried or dried in an electric herb drier. They are examined under a microscope and any species identified are recorded on an Excel spreadsheet. For each spraint we record all species identified, but not quantity. For example, a spraint that was predominantly stickleback bones, with 3 perch scales and 2 bird feathers, would be recorded as containing stickleback, perch and bird, with no indication of the relative quantities. Most birds have not been identified yet because although feathers pass through the otter intact they seem to be mostly breast feathers which have proved difficult to identify by sight. Some mammals have been identified to species when teeth are present but our attempts to look at cross sections of hair have not been successful. With some groups, identification to species is not always possible. For example, with the Cyprinid group of fish, identification to species is possible if pharyngeal teeth which have the same function as teeth but are situated in the arch of the throat are present in the spraint. However, they are not always present so for the analysis, the Cyprinids are grouped together. When a positive ID has been made the species is noted in the comments column. Photographs are taken of any material in doubt. Each spraint is analysed separately by two members of the group. All spraints have been retained. Dates and locations within the site are recorded to enable separate analysis if required. When analysing the figures after the initial division into the main prey groups those spraints containing fish are then analysed for the proportion of the fish species they contain. Again no attempt is made to count the relative numbers of each species contained within each spraint.

c. Results from the Minsmere Study Site To date over 300 spraints have been collected at the Minsmere study site and they are included in this analysis. Fish appear in 95% of the spraint samples with bird and water beetle remains occurring in about 25%. As noted above most birds have not been identified although the distinctive feathers of bearded tit and kingfisher have both been found each in one spraint. We do not of course know whether these were caught alive or were eaten as carrion. Coot, great crested grebe, cormorant,

Charts 1 and 2 Showing a complete year’s results (n=number of spraints analysed)

5 shoveler and greylag goose have all been seen being taken by otter from Island Mere in the last year. The water beetles are mostly the Great Diving Beetle (Dytiscus marginalis) although the Great Silver Water Beetle (Hydrophilus piceous) has also been identified. Crustaceans appeared in 6% of the spraint but most of this was collected at the eastern end of the Reserve and for a limited period mostly in May. They were predominantly shrimp although only one positive identification was made of the Atlantic ditch shrimp (Palaemonetes varians) which is commonly found in brackish ditches. Three spraints were found with the remains of a crab (Carcinus sp.) which could have come from the sluice and about six goby (Pomatoschistus sp.) vertebrae were found. An otter has been reported on one occasion coming from the beach direction heading for the reserve but there is no definite evidence that otters are using the sea for feeding. Frog remains were found in 3% of spraint mostly during the spring and newt vertebrae were identified from just two spraints. Mammal remains were found in 3% of spraint. Water voles (Arvicola terrestris) were positively identified from teeth in two spraints but the other species await identification from microscopic examination of cross sections of the hair. As in many other studies, fish remains were in the majority of spraint. What surprised us was the amount of stickleback that were consumed. These are described by Hans Kruuk as ‘a fish which is rather miserably small and bony prey for an otter’. They do not just crop up in the spraint as one or two individuals; sometimes the whole spraint is made up of stickleback and little else. Both 3- spined (Gasterosteus aculeatus) and 9-spined (Pungitius pungitius) were identified but as distinguishing between the two is not always possible they have been grouped together in the analysis. Chanin quotes the figure of otters needing 1.5kg of food per day which would require an awful lot of stickleback - one wonders how hungry they must be to make it worth the effort or how easy they are to catch in bulk. Many of the other fish remains were of small fish. Observations of otters feeding at Island Mere show either a remarkable number of unsuccessful dives or the prey is so small it is swallowed without being seen. The water is very shallow and the dives very short. It is not unusual to see the tail waving above the surface when an otter is foraging. During the summer the water is very warm, so less energy is being expended by the otter through heat loss. Diving through two metres of Atlantic Ocean around Shetland is very different from fishing at Island Mere. Perhaps feeding on sticklebacks at Island Mere is not as inefficient as it might be in Shetland. Remains in spraint from the carp family (Cyprinids), such as rudd (Scardinius erythrophthalmus), roach (Rutilus rutilus) and tench (Tinca tinca), are difficult to separate without a good set of pharyngeal teeth, so in our analysis are grouped together. Eels (Anguilla Anguilla), thought to be the most Pharyngeal teeth of Tench nutritious prey for an otter, are not present in spraint in any great quantity at 18% overall and this may reflect the decline in this species nationally .

i. Comparing spraint results with electro fishing results. ‘Otters living in freshwater generally take whatever fish are most readily available whether they be sticklebacks, trout, roach, perch or eels. However, where there is a choice there seems to be a tendency for them to take disproportionate numbers of certain type of fish, particularly those that are easier to catch’. (Paul Chanin (2013) Otters) Minsmere Electro-fishing Results 2013 We have the results from 2013 for the (Number per ha.) electro fishing carried out annually by RSPB 300 which rather reassuringly shows the same 250 species as we have identified in the spraint. 200 One of the cyprinids, roach, makes up over 150 half of the number of fish caught and when 100 50 added to the other cyprinids, rudd and 0 tench, they dwarf the numbers of all sticklebacks cyprinids perch eel pike other fish species caught. The mean Chart 3. Showing the results from the electro-fishing.

6 weight of the fish caught is given – with sticklebacks weighing in at a miniscule one gram while the mean weight of roach was seven grams, perch (Perca fluviatilis) and rudd were nearly 20 grams and tench 31 grams. We have not attempted to assess the size of prey in the spraint we have analysed. The species in the spraint correlate with the electro-fishing results but the proportions caught are different.

ii. Seasonal Changes. Within the main prey groups fish have appeared in around 95% of spraint throughout the study period but the proportion of birds found in the spraint increased from appearing in 13% of spraints in the winter to 40% of spraint samples in the summer. Amphibians appeared more often at the end of March/beginning of April presumably when they are gathered for breeding purposes. Shrimp were restricted to a short period in the spring and water beetles were appearing in more spraint during the summer. The proportion of stickleback peaked in March/April with over 90% of spraints containing stickleback. Cyprinids seemed to be taken more often in the winter appearing in 90% of spraint and

Charts 4 and 5 Showing the results from the summer months (n=number of spraints analysed)

Charts 6 and 7 Showing the results from the winter months (n=number of spraints analysed) down to 60% in the summer whereas stickleback and eel were both in a higher proportion of spraint during the summer. One significant variant for the otter is the major contrast in water temperature. Averages of 0°C in winter to 20°C in summer making a huge difference to its energetic needs.

iii. Locational Differences For the purposes of this analysis spraint has been grouped as follows:

 ‘Eastbridge’ is anywhere between the village and Island Mere.  Spraint collected from around the Scrape is termed ‘East End’  ‘The Causeway’ is on the North Marsh and there is an easy connection from this area to the area of the Scrape across the North Wall.

7 There appears to be differences in the species mix based on the different locations at which we collect spraint. For example, there appeared to be less stickleback and eel from the Eastbridge end but more perch and cyprinid. Whereas Crustacea are mostly found in spraint from the eastern end of the Reserve.

Bearing in mind that other studies have shown average travel of nine km. (male) and three to seven km. for females and it is only 2.5 km. from one end of the reserve to the other, we might have expected more uniformity in the spraint results. Our results might suggest the otters are keeping to their own parts of the reserve. Females in Shetland had overlapping ranges but spent most of their time in their own core areas and one study in South Uist with lots of shoreline and small islands had a female territory that was only 500 metres in diameter. The subject of range size at Minsmere deserves further study.

Charts 8 and 9 Results from the Eastbridge end of the Reserve (N=number of spraints analysed)

Charts 10 and 11 Results from the Eastern end of the Reserve (N=number of spraints analysed)

Charts 12 and 13 Results from the Causeway on the northern edge of the Reserve (N=number of spraints analysed)

8 d. Results Alde/Ore Study Site 250 spraints have been analysed from the Alde/Ore. Spraints from the lower estuary at Orford Ness National Trust Land, RSPB Butley and RSPB Hollesley have been grouped together and compared with the spraint from Stanny Farm, Iken some 10km further up river. Both stretches of the river have extensive mud flats, some salt marsh and areas of grazing marsh behind the river walls. Varying amounts of salt water flooding of the fresh water marshes occurred in the surge in December 2013. Fish remains are recorded in 90% of spraint but compared with Minsmere, crabs and other estuarine species form a substantial part of the diet. Stickleback are ever present in the spraint but as they can be present in both habitats (saline and freshwater) we do not know, at present, whether the otters are getting these primarily from the estuary or the freshwater ditches. However as far as we know the goby are definitely from the estuary but seem very small for an otter to bother with. The freshwater species, particularly the cyprinids, are far less common than at Minsmere. The amount of spraint with cyprinid and perch remains from Stanny Farm is much lower than further down the estuary and this might be because Stanny Farm and Hazelwood Marshes on the opposite bank were flooded to a substantial depth with salt water in 2013.

Charts 14 and 15 Results from the Lower Alde/Ore Estuary (N=number of spraints analysed)

Charts 16 and 17 Results from Stanny Farm, Iken (N=number of spraints analysed)

9 4. Spraint Deposition.

a. Introduction Kruuk in Shetland found no increase in spraint at territory boundaries and because spraint deposition was seasonal and ceased when food was plentiful he concluded that sprainting was important for passing messages between related otters about recent feeding activity. At our sites spraint seems more difficult to find in mid-summer but this could be partly to do with dense vegetation growth. In Shetland the sea fish move away into deeper water during the winter and so are unavailable to the otters whereas we assume our fish are available at reasonably constant levels.

b. Minsmere. A number of sprainting places have been identified and spraint has been collected throughout the study period. Access to the majority of the reedbed and associated ditches and water bodies is impractical so these collection points are usually at ‘‘crossing points’’ where otters are either forced to leave a ditch system because of culverts at gateways (East Hide), through flood banks (North Wall and Causeway) or moving between water bodies or ditch systems (along the central path at ‘’N’’ and the Eastbridge end). A survey was carried out along the central path in March 2016. This path runs generally east/west between Bittern Hide and the Eastbridge Road for a distance of approximately 2km. There were large piles of spraint, much larger than was ‘’normal’’ for the rest of the Reserve, at intervals along the path. For the first 600 metres there were 12 piles of spraint, an average of one pile every 50 metres. 10 of the 12 sprainting places were on the ditch side of the path only and were not obviously associated with crossing points. The remainder of them were on average 300 metres apart

and the majority had spraint on both sides and the middle of the path or just in the middle and were associated with crossing points. The mother and 3 cubs were present in the area when the survey was carried out but they were active throughout the survey area so this wouldn’t explain the clustering at the western end.

c. Alde/Ore. When studies started at Stanny Farm, Iken, a survey was undertaken of the grazing marsh and river wall for signs of otter. The majority of signs were found in the vicinity of the borrow dyke that follows the river wall through the site. All the gateways across the borrow dyke have culverts that are full of

10 water throughout the year and the otters leave the water rather than go through the culverts. There are regular sprainting places at all the culverts. All obvious trails that went between the estuary and the borrow dyke were mapped. Obvious paths with otter spraint were designated as grade 1 and other

paths without spraint were designated as Grade 2 or 3 depending on usage. Many of the grade 2 and 3 trails turned out to be made by rats. The Grade 1 sites have been used by otter throughout the study period with R3, R7 and R11 yielding spraint most often. No other otter-runs across the wall have been identified during this study. The most used runs are either on the river wall where it juts out into the estuary (R3&7) or at a narrow crossing point of the estuary (R11). The corner of the river wall on the opposite side of the river to R11 also proved to be a sprainting place. The tracks do not seem to provide direct access to the areas of salt marsh on the river side of the wall. The only other sprainting places identified during the study were associated with newly constructed water bodies and no sprainting places were found on the grazing marsh ditches. Other surveys at Boyton and Snape found well-used paths across the river wall but little evidence on the freshwater grazing marsh ditches despite the fact that in both cases the water is at high level and they ‘look good’. Fish surveys on the ditches have not so far been successful. At Stanny electro-fishing was not effective because the water was brackish. This area needs further work. At the start of the work at Stanny Farm, spraint collection was carried out weekly but this later was reduced to fortnightly. There has only been one occasion when no spraint was found on the regular collections but we need to do more analysis to see if there has been any seasonal pattern to spraint deposition.

5. Activity Patterns. Otters in freshwater areas in the British Isles are described as mostly nocturnal whereas in Shetland and the west coast of Scotland where they hunt in salt water they are diurnal. We have looked at daily activity patterns on the Suffolk Coast at Minsmere and in the Alde Estuary at Iken by studying results from trail cameras triggered by passive infra-red beams.

a. Previously Published Studies. Radio tracking by Jim and Rosemary Green on Scottish rivers found that otters left the holt around sunset and were active in the following 3 to 5 hours. This was usually followed by another bout of 11 activity later in the night before they settled down for the day around dawn (Chanin, 2013). In Shetland Hans Kruuk found that his radio-tracked otters were only active during the day. In the short days of winter, the otters showed a clear peak of activity just before midday but in summer their swimming and foraging was spread throughout the entire daylight hours with one main peak early in the morning and a lesser one in late afternoon. So his animals were diurnal. He also quotes Watt 1991 who found a similar situation on Mull. (Wild Otters: Predation and Populations by Hans Kruuk 1995). The Handbook of British Mammals (1977) states that otters are usually nocturnal, especially in disturbed habitats. Various other earlier references make the connection between an otter’s nocturnal habits and disturbance. However, Hans Kruuk demonstrated that the daytime activity of his Shetland otters was more connected to the habits of the fish - with the otters hunting when the fish were easier to catch.

b. Trail Cameras. Trail cameras are self-operating cameras activated by subjects passing through a passive infra-red (PIR) sensor which measures light radiating from objects in its field. The sensors don’t actually detect motion but respond to abrupt changes in temperature. They can operate throughout the 24 hours taking colour pictures in daylight and black and white pictures at night using infra-red light emitting diodes (LEDs). Some of the cameras use red LEDs which are visible to most animals but later models use black LEDs which are not. Although deer and foxes for example are very aware of the red LEDs, otters seem to ignore both types. If the cameras are set low to the ground, they will often become the object of otter’s inquisitiveness and if not fixed securely will be displaced.

Cameras have been placed at regular sprainting places and set to record one minute videos with a one second gap so that if the subject remains in front of the camera, activity will continue to be recorded. We do not know whether every otter active in the area visits these sprainting places but they are obviously important to the otters that do visit. It is unusual for an otter to pass through without leaving a spraint and there are often intensive rolling about and rubbing sessions in view of the camera.

The cameras do not perform equally. One of our top of the range Bushnell models with black LEDs seemed to be particularly effective when set up side by side with a standard model, and the results from this camera have been used in calculating the Minsmere results. The ineffectiveness of some cameras introduces further uncertainty to the interpretation of results. It has been reported elsewhere that the PIR sensor fails to pick up very wet otters, especially if they do not hang around in front of the camera. Problems with picking up otters on the cameras seems to increase in the summer. At Stanny we used the results from just one camera, but to get a reasonable sample we had to take the results from the whole year. So the two charts 22 and 23 are not entirely comparable.

Where otters stay in front of the camera for more than one video this is counted as only one hit. We have decided there has to be a gap of at least 10 minutes for hits to be counted separately. Dawn and dusk for each month is calculated as 2 hours either side of sunrise and sunset for the mid-date in that month. Dawn and dusk are rather vague concepts and the presentation of these results needs refinement.

c. Results. Otters at Minsmere are active throughout the 24 hours. Since December 2014 we have had a log book in the hide at Island Mere for visitors to detail their otter sightings and it is extremely unusual for a day to go by without an otter being seen. Admittedly Island Mere is over 20 acres of otter fishable water and it is watched over by observers for most of the daylight hours. However, the difference between the number of daylight hits on the cameras between Minsmere and Stanny is most marked. At Stanny there are only two daytime videos out of 180 and these were on two consecutive days in April. There is no evidence that the Stanny cameras are failing to record daytime otters since they are recording

12 plenty of other animals during the day. Otters are seen during the day on the estuary but it does not seem to be common. Snape Bridge has very many human visitors and we are told that otters are ‘often’ seen there. We now have a camera at Snape and it will be interesting to see how many daytime shots it records.

The activity rhythms of the Stanny otters seem to be more like the ‘typical’ pattern quoted for lowland freshwater-feeding otters where they are ‘mostly nocturnal’.

The evidence we have suggests that there is a marked difference between the activity rhythms at Minsmere and Stanny. Hans Kruuk puts forward a convincing argument for the differences between saltwater and freshwater areas in Scotland being food-related. We have a marked difference between the food being consumed in the different areas, with the Alde/Ore otters sourcing a significant amount of their food from the estuary. Unfortunately, we have no information on the activity patterns of the main prey. We have not yet even been able to catch a goby, let alone keep them alive in an aquarium to study their habits. We have a video of an otter that seems to be pushing its nose through the surface layer of mud that has a thin layer of water over it, almost in the manner of pushing a shrimp net through it. But it is not obvious whether it is catching anything. This is an area for further study!

Our first attempt to relate otter activity at Stanny to the tidal cycle did not show any relationship but we are looking again at this.

Disturbance does not seem to be a factor. At Minsmere the smell of humans is everywhere and at Island Mere the noise of cameras going off like machine guns causes a momentary reaction if any at all. They are not tame and they are not fed but having got used to certain levels of human disturbance they seem to be acting as they would if there was no disturbance. On the Alde/Ore the level of disturbance is very low in most areas. There are dog walkers in a few hotspots at Aldeburgh, Orford and Iken but otherwise there is very little disturbance on the bank or in the estuary.

It may be that because of the density of the otters at Minsmere they are active at different times of the day to avoid each other. This is discussed further in the next section.

Chart 18. Contacts per hour Nov. 2015 Chart 19. Average Contacts per hour Nov. 2015 (N=number of camera contacts)

13 Chart 20. Contacts per hour Nov. 2015 Chart 21. Average Contacts per hour Nov. 2015 (N=number of camera contacts)

Stanny farm, Iken Camera Hits Minsmere "N" Winter Camera Hits 2015. (n=184) (n= 267) Day 3% Night 18%

Day 36% Dawn/Dusk 41% Night 56%

Dawn/dusk 46%

Chart 22. Stanny Farm, Alde/Ore Chart 23. Minsmere Camera Contacts Whole Year 2015 Camera Contacts Winter2015/2016

6. Productivity and Population Estimates

a. Minsmere - Island Mere The majority of otter sightings at Minsmere come from the Island Mere Hide. We started keeping records in March 2014, and as mentioned earlier we have maintained a visitors’ log book since December 2014. Not every sighting is recorded in the book but it provides a useful minimum record of what is being seen. At the same time as the log book was started we also installed trail cameras near the south side of the Mere and further west towards Eastbridge village.

To try and estimate productivity, the chart below lists the sightings of any group of more than one otter from the log book and from the trail cameras. Male and female otters spend very little time together other than during the mating period, so when more than one otter is seen we assume it is a mother and cub(s). If there is only a single

14 sighting of two otters together in a period of ten days, this has been ignored as it is less likely to be a family group.

Minsmere Family Sightings - Cameras and Log book

January February March April May June July August Sept October November December

2014 2 Started on 14th March 2014 3 4 2015 2 ! 3 !! 4 2016 2 Key 3 - 2 Otters. (assumed mother +1 cub) !! - simultaneous sighting 2 families 4 - 3 Otters. (assumed mother +2 cubs) ! - new sighting mother + 1 cub - 4 Otters. (assumed mother +3 cubs)

i. Key dates in this period were as follows:  March to June 2014 – a mother and single cub were seen regularly at Island Mere and as June progressed less regular views and an increase in vocal activity and interactions between individual otters were noted.

 September 23rd 2014 first sighting of a mother with two cubs

 March 14th 2015 a simultaneous sighting of two groups of a mother with 2 cubs at opposite ends of Island Mere. (!! on chart)

 At the end of September 2015 a mother with a young cub was picked up on camera. No more sightings of mother and two cubs were made. (! on chart)

 February 23rd 2016 mother and three cubs seen and picked up on camera. A plaintive, rather sickly cub was recorded on camera on 10th March and from then on just a mother and one was recorded. It was assumed she had lost two of her cubs.

 April 5th 2016 mother and 2 cubs were seen in front of Island Mere hide.

The following issues have been taken into account in calculating the minimum number of family groups at Island Mere Minsmere:

 Cubs stay in the maternal holt for 12 weeks, so the earliest we would see a family group is when the cubs are 3 months old. Other studies have found that cubs stay with their mother until a year old, so we are unlikely to see a family group together for longer than nine months.  We do not know what triggers oestrus. Mating could take place before the cubs have been cast adrift. The gestation period is nine weeks and there is no delayed implantation in this species of otter.  Cub mortality is high. So we should not be surprised if the number of cubs in a family group reduces with time.  As the cubs get older and more independent they spend an increasing amount of time at a distance from the mother. Seeing just one or two otters does not mean that this is definitely the full family group.  Estimating the age of cubs has proved surprisingly difficult. In Loch Sunart on the west coast of Scotland where most of our other experience of watching otters comes from, the dives of adult otters often last for 25 seconds and it takes the cubs some time before they can stay

15 under for a similar amount of time. At Minsmere the water is so shallow that dives are frequently only a few seconds, so as soon as the cubs can dive they can stay under for the same length of time as the mother.

ii. Calculation of Minimum Numbers. In the 25 months from the start of observations we have:  the mother and one cub Spring 2014;  the two families of mother and two cubs present Summer 2015;  the mother and one cub that appeared September 2015;  the mother and three cubs that appeared 23rd February 2016;  and the mother and two cubs that appeared 5th April 2016 This gives a minimum total of 6 sets of cubs born to at least two females.

iii. Productivity. We do not know how many of our cubs reached independence. If we do not include the mother and 3 cubs from Feb 2016 - only the single cub we think survived - then this gives us an average of 1.3 cubs per female. This is low compared with the Shetland average of 1.8 and averages of 2.3 to 2.8 for ‘various inland studies’ (Chanin 2013). We do not always know whether the figures from these published studies are cubs born or cubs reaching independence. Philip Wayre found that the average for his captive otters was 2.4 cubs at birth but down to 1.8 by the time they became independent. It seems as if productivity per Minsmere female is low compared with other published studies. It may be that the density of otters at Minsmere increases the potential for otters to interact with one another, with resulting conflict and stress. Vic Simpson discovered that between 1996 and 2003, as the otter population was recovering, his post mortems (mostly from road casualties) recorded an increase in the wounds that could be attributed to other otters - with both males and females affected. (Chanin, 2013) In 100s of watches at Island Mere we have only once heard a full blooded fight.

b. Minsmere North Marsh. A camera has been in position on the North Marsh at Minsmere for the last year and although not always giving good results, because of rapid bracken growth during the summer, a mother and cub were occasionally picked up on the camera throughout the summer and autumn of 2015. Rather surprisingly when the two lots of mother and two cubs were active elsewhere on the Reserve they were never picked up on this camera. It is only about 2 km, as the otter swims, from the camera position to Island Mere. They need to cross the North Wall but this is a well-used sprainting place and otters are often observed crossing the wall at the sluice so it does not create a barrier. On the last day of April this year a mother and 3 cubs were picked up on this camera and have been recorded three times since, and yet they have not been recorded elsewhere on the Reserve. Although they turned up six weeks after the mother and three had disappeared from Island Mere they seem too small to be the same ones. The North Marsh itself is not very large, there is no stream outlet at the western end, and the 2013 electro fishing results were not very good. It seems inconceivable that a family has a range this small. We have recently positioned a camera at the eastern end of the Reserve to see if this sheds any light on this issue.

16 North Marsh camera

Island Mere

e. The Alde/Ore. At Stanny Farm, Iken eight cameras have been in position on regular runs and sprainting places throughout the period. A mother and two cubs were recorded between end of December 2014 to mid- March 2015 and then a mother and one cub from mid-April 2015. At Orford Ness cubs were recorded early in 2015 and then a mother and 2 have been seen since mid- December 2015. At Boyton a mother and two cubs were recorded from mid-January to mid-March 2015 but the camera has not been operational since then. None of the mother and cubs’ videos from the early part of 2015 were recorded at the same place on the same day/night so, in theory at least, they could be the same family. On the Alde/Ore the number of camera hits per month is substantially less than are recorded at Minsmere, and the number of family groups are less. Whether this is a reflection of the density of otters present in the area may be a conclusion too far at this early stage.

7. Footprint Study. One of the objectives of this project, is to try to find simple methods that might identify individual otters. These might include: facial recognition from still photos or videos and DNA analysis from spraint. Another method is footprint analysis. We are working with an American not-for-profit group, WildTrack (www.WildTrack.org), who have developed a Footprint Identification Technique (FIT), which has proved successful with various large mammals such as black rhino, white rhino, Bengal tiger, Amur tiger, and Polar bear. It is a non-invasive, cost-effective and sustainable method which is now an accepted way of identifying species, individuals, by sex and age, all by using digital images of the animal’s footprints. 17 The technique requires images of individual footprints, taken according to a standardised method. These images are then reviewed using the FIT algorithm, which has been designed for the purpose. It is analogous to the technique used to identify finger prints.

Play sand is used and spread out in a rectangle 1 metre wide by three or four metres long and sited in a place where the otter is likely to pass by. After photographing any prints, the whole sand trap is smoothed flat and clean ready for new prints.

At present we have volunteers regularly visiting our ‘sand traps’, to see if new prints have been produced. The images we take are sent to Germany where a PhD student has the software and is able to run the algorithm of the FIT analysis. Later this year (2016) we hope to be given a copy of the software for us to carry out the procedure ourselves. A full report of the technique has been published in the journal Endangered Species Research. Alibhai, S.K., Jewell, Z.C. & Law, P.R. (2008) Identifying white rhino by a footprint identification technique, at the individual and species level. Endangered Species Research 4:219-225

8. Behavioural Observations Grooming. All our cameras are set up at sprainting points. Some shots are fleeting but it is not unusual to get two or three videos consecutively of otters in front of the camera. These frequently involve what we assume is grooming, pushing their neck through the grass, rubbing their undersides on the grass and rolling over.

Aggression. An otter was seen to pursue a fox on one video and seeing off a badger on another. In contrast to this assertiveness against other carnivores, on one video an otter seemed to be petrified by a pheasant and once by an approaching red deer.

Hunting behaviour 1. A video was taken by Meg Amsden of an otter on the mud flats at Blythburgh. There was a thin layer of water over much of the mud and the otter seemed to be pushing through the top layer like we would push a shrimping net. www.nutmegpuppet.co.uk/october-otter-2/

Hunting Behaviour 2. An otter was watched zig-zagging backwards and forwards in water about 50mm. deep just behind the hide at Island Mere. The area was used by Springwatch for filming stickleback breeding activity. Nothing was seen to be consumed but the activity continued for a few minutes.

18 Hunting Behaviour 3. We have watched otters on a number of occasions at Island Mere, most often in the side pond but also in the area immediately in front of the hide, leaping out of the water followed by rapid swims Pouncing hunting technique. underwater. This is repeated Photo: Dennis Brown in a frantic bout of activity until a fish is caught and eaten in the water or taken into the bank. The water is shallow, between 300- 450mm, and the substrate mud so the water must be murky. Small fish can often be observed leaping from the water immediately in front of the otter’s bow wave. More than one individual is involved and on one occasion it was a mother with 3 cubs on the bank.

Hunting Behaviour 4. As reported earlier, birds are sometimes taken by otters on Island Mere. Birds are very wary when otters are about and very often give us clues as to where to look. Sometimes it is complete panic at other times it is far more relaxed. The victims that have been observed by us are actually taken on the open water, involving a rapid underwater approach, usually in rough water. They include cormorant, shoveller, coot, and great crested grebe. There has been a report in the book of a grey lag goose being taken and also of a cormorant taken off the perch, which is 450mm above the water surface. They are taken into the reeds to be dealt with and as we never get primary feathers or beaks we assume that they concentrate on the breast.

Hunting Behaviour 5. In 2015 Springwatch had a camera on a redshank nest that recorded an otter poking its head into the nest but ignoring the eggs. Philip Wayre reports that his captive otters when offered eggs would play with them but not eat them. They would eat the contents if the eggs were broken. We have never found egg shells in any of our spraint.

Hunting Behaviour 6. A deer carcase under camera surveillance by RSPB at Havergate Island recorded an otter visiting the carcase on at least two occasions. Dead trout (Tesco special offer) were consumed enthusiastically by otters when left out as bait for photography purposes.

Mid-summer lull. Sightings on Island Mere seem to be much reduced during mid-Summer. Some of this is due to the abundant reed growth in front of the hide but we do not think it is the whole reason. Spraint deposition seems to be reduced as well but this may be partly due to the density of the vegetation making it more difficult to find.

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9. Recommendations for Future Action Priorities. (NB not in priority order!) 1. Sites. Valuable insights can be gathered by comparing and contrasting behaviour between sites. We will continue with work at RSPB Minsmere; the Alde/Ore; the Blyth Catchment. Studies will be extended onto the River Deben. 2. Camera Network. We need to refine our camera networks at sites to ensure optimum coverage and identification of different family groups. 3. Spraint Collection. We will continue spraint collection at the Minsmere; Blyth; and Alde/Ore and extend studies to include the River Deben to study any patterns of geographical or seasonal differences. 4. Spraint Analysis. We will continue and refine spraint analysis to gain insights into diet; foraging areas; and any seasonal changes. 5. Identifying Individuals. We will continue to explore techniques to identify individual otters including footprint recognition, photographic techniques using recognition software; and DNA. 6. Freshwater and Estuarine Ecology. We will carry out further investigation into otter prey species in estuaries and freshwater habitats. We will try and assess the impact of tides on otter behaviour in estuaries. 7. Further afield. Contact will be made with projects/people working on otter ecology in other parts of the country to share and collect information. This could lead to a weekend event held at Stanny during the autumn of 2016. 8. People. Otters are loved or hated. We will establish links with fisheries and fish farms to gather information on actual and perceived predation. Examine any impacts from different types and levels of disturbance.

10. Acknowledgements This report is the result of a lot of people’s hard work especially all the Team at Stanny Farm, Rodney, Maggie, Gill and Mike. To the Staff and Vols at RSPB Minsmere especially David for his dedication to spraint collection. The Spraint Appreciation Group especially Mark for leading us to where we are today. The Blyth Otter Group especially Dale and Nicky. Dennis for his early morning company at Island Mere and his excellent photos. Reg for his work at Boyton and Jamie for photos and a growing list of other things. Much appreciated financial support has been provided by the Amenity and Accessibility Fund from the Suffolk Coast and Heaths AONB and the Paul and Louise Cooke Endowment Trust.

11. References Kruuk, H.(1995) Wild Otters, Predation and Populations. Oxford University Press. Chanin, P. (2013) Otters.. Whittet Books. Conroy, JWH et al. (2005) A Guide to the Identification of Prey Remains in Otter Spraint. Mammal Society. Wayre, P. (1979) The Private Life of the Otter. Batsford

Richard Woolnough, July 2016

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