Tees Seals Research Programme

Monitoring Report No.27

(1989 – 2015)

Compiled by Ian Bond

Contents

Summary 3

1. Introduction 4

2. Seal Identification 4

3. Behaviour 6

4. Monitoring Methods 6

5. Results of the 2015 Seal Monitoring Season

5.1. Low tide haul out behaviour at Greatham Creek 7

5.2. Haul-out behaviour at Seal Sands 9

5.3. Birth and Survival of Harbour Seal pups 13

5.4. Maximum Count of Seals at Seal Sands 13

5.5. Mean Count at Seal Sands 14

6. Discussion

6.1. Haul-out Behaviour 17

6.2. Birth-rate of Harbour Seal pups 17

6.3. Seal Numbers 18

6.4. Disturbance 19

6.5. Deaths 19

7. Acknowledgement 19

Appendix 1 – Teesmouth Area 20

Appendix 2 – Seal Sands Haul-out Sites 21

This report has been produced to show the status of the Tees Seals colony as part of the Tees Seals Research Programme. It is not to be used for any other purpose nor relied upon by any third party.

Unless otherwise stated, the images displayed in this document are INCA copyright or reproduced with permission of the copyright holder. The images are not to be reproduced without the express permission of INCA. Any maps or location plans in this document have been reproduced in accordance with INCAs licence from the Ordnance Survey.

Summary

The 2015 season was the 27th year during which seal monitoring has taken place at Seal Sands. The first pup of the season was born unusually early but unfortunately didn’t survive, being found dead on 5th June. In total, 19 Harbour Seal pups were born, of which 18 survived to weaning, both figures being the same as in 2014.

Overall, Harbour Seal numbers in 2015 were broadly in line with those in 2014. August was again the peak month with average numbers for that month being around 91, i.e. 11% higher than in 2014 however average numbers for both July and September were down on 2014.

Harbour Seal numbers built to a daily maximum of 114 on 16th August 2015. This is less than a 4% increase on 2014 nevertheless it represents the highest count for Harbour Seal on the Tees Estuary to date.

Grey Seal numbers were at their maximum on the first day of monitoring, the 15th June, when 49 were counted. This is somewhat lower than last year’s record count of 59 but is still the second highest maximum for any year. However, outside of the formal seal monitoring programme, 82 Grey Seals were counted on Area D on 13th July. This represents a further 39% increase on last year’s maximum count, which was in itself a 37% increase on the previous maximum. Nevertheless mean numbers of Grey Seals were down overall on 2014. This was because the high mean numbers for June and September 2014 weren’t replicated this year, with each monthly average being more or less in line with the years in the earlier part of this decade.

Monitoring of disturbance caused to seals is part of the remit of the Tees estuary seal monitoring project. A total of 15 disturbance events were recorded in 2015, seven of these at Greatham Creek. This figure is down slightly on 2014.

1. Introduction

The Tees Seals Research Programme was initiated by the Teesside Development Corporation to monitor the effects of the 1988 phocine distemper virus outbreak. Since 1989 the programme has been managed by INCA in order to observe the status of the seal colony at Seal Sands as a general indicator of the health of the River Tees and its intertidal area.

Seals have lived at the mouth of the River Tees for many hundreds of years, but declined rapidly by the late 1800s. A number of factors were probably responsible:

 Industrial use of the estuary increased.

 Large areas of habitat were lost due to land claim of parts of the estuary.

 Increasing volume of shipping led to further habitat loss due to dredging.

 Industrial pollution led to the demise of the once-thriving Tees salmon population.

 Fishermen mistakenly blamed the seals for the salmon decrease, persecuting the already low numbers of animals present.

As a result of a combination of these factors by the 1930s seals had totally disappeared from the Estuary.

The mid 20th century saw old-style steel and coke plants being replaced by newer, less polluting works. Reclamation of the lower estuary restricted river access and probably reduced disturbance to the seals. From the early 1970s there began a concerted effort by regulators and industry to reduce the pollution load discharged to the estuary. Eventually Harbour Seals began to re-appear and by the mid 1980s there was again a resident population.

Teesmouth is the only known estuary in Europe where Harbour Seals have re- colonised as a direct result of environmental improvements and the colony is once again breeding. This report details the situation in 2015.

2. Seal Identification

At Seal Sands the species present are the Harbour or Common Seal (Phoca vitulina) and the Grey Seal (Halichoerus grypus). Grey Seals are much larger than Harbour Seals.

Male Grey Seals (bulls) are up to 2.7m in length and 230kg in weight. The females (cows) are smaller, rarely exceeding 1.7m long and 150kg in weight. Grey Seals have a ‘Roman’ nose and vertical nostrils which are set further apart and parallel.

Harbour Seal males can be up to 1.9m long and weigh up to 170kg, while the females are around 1.5m long and weigh up to 100kg. Harbour Seals have a smaller, more rounded head, with smaller V-shaped nostrils.

Figures 1 and 2 show the two species described.

Figure 1: Harbour Seal (Phoca vitulina)

(courtesy: John Bridges, www.northeastwildlife.co.uk)

Figure 2: Grey Seal (Halichoerus grypus)

(courtesy: John Bridges, www.northeastwildlife.co.uk)

3. Behaviour

3.1. Haul-out

At Seal Sands the two species of seal generally haul-out in separate groups. Harbour Seals tend to leave a significant amount of space between individuals in the group, whereas Grey Seals haul-out in a tightly-bunched group and do not mind being in close proximity to each other. Occasional confrontations do occur when Harbour Seals attempt to haul-out close to a group of Grey Seals.

All seals moult once a year. They haul-out in groups as they moult and are often seen to be very irritable and listless during this period. For Grey Seals, moulting occurs between January and March, compared to August for Harbour Seals.

3.2. Breeding

Harbour Seals usually have their pups between late June and early July. The pups are very small when born, being around 0.7m long and 10kg in weight. They appear very dark in colour, almost black from a distance. Pups are taken into the water only hours after birth, remaining with their mother constantly. The mother/pup relationship is critical in ensuring that the pup is cared for and is not malnourished or abandoned. Typically, a pup will need to feed for at least 10 minutes in every hour to wean successfully and there is a four week lactation period during which the pups more than double their birth weight.

The Grey Seal does not breed at Seal Sands, as conditions are unsuitable. New-born Grey Seal pups, which are born around October and November, are fur-covered at birth and cannot swim. Therefore, Grey Seal cows haul-out above the high water mark for long periods of time during and after giving birth. This is not possible at Seal Sands, as haul-out sites are inundated at high tide. The Grey Seals at Teesmouth probably originate from the large colonies at the Farne Islands or Donna Nook on the Humber. Towards the end of the year, some Grey Seals are assumed to leave the River Tees to return to their breeding sites. This takes place between September and December. However a number of non-breeding seals, particularly juveniles, remain at Seal Sands.

4. Monitoring Methods

Appendix 1 shows the main areas of the River Tees which the seals frequent, while Appendix 2 shows the specific haul-out sites used at Seal Sands.

In 2015, monitoring at Seal Sands was carried out between mid-June and mid- September, which includes the period in late June and early July when the Harbour Seals give birth and the period in August and early September when they gather to moult.

At each daylight low tide period, monitoring was undertaken from the observation hide on the sea wall above Greenabella Marsh, which is approximately 250m from the most regularly used haul-out site.

Monitoring took place 2 hours either side of low tide, using a 60X magnification telescope to record the following observations:

 Total population of each species.

 Variation in the number of seals which had hauled out on each low tide.  Areas used as haul out sites and the changes in site usage.  Number and health of pups.  Disturbance to the colony and other potential problems, such as injuries and indications of pup desertion.  Inter- and intra-species behavioural interaction. This included feeding observations, porpoising activity, play and aggression.

In addition, weather observations and the extent of low tide were made at the time of seal monitoring.

In 2015 the programme continued to monitor seals hauling out on Greatham Creek to the west of the A178 road bridge. This took place over the 2 hours preceding and 2 hours following low tide so that the combined effect of seals hauling out simultaneously at Seal Sands and Greatham Creek could be assessed.

The methods employed were similar to those at Seal Sands, except that binoculars were employed at Greatham Creek due to proximity of the seals to the observer.

Monitoring was not carried out by INCA at Billingham Beck and at the Tees Barrage in 2015.

5. Results of Seal Monitoring in 2015

5.1. Low Tide Haul-out Behaviour at Greatham Creek

One of the objectives of ongoing seal monitoring is to ascertain the contribution of Harbour Seals hauling out at Greatham Creek to the Teesmouth total. The low tide haul out frequency at Greatham Creek for June to September 2015 is displayed in the tables which follow. Occasions when seals hauling out at Greatham Creek contributed to the daily maximum number of Harbour Seals in the estuary are noted in red.

June 2015

Date Low Number of Harbour Seals at Greatham Creek (GC) Contribution of GC Tide seals to daily max. LT- LT- LT- LT- LT LT+ LT+ LT+ LT+ 2h 1.5h 1h 0.5h 0.5h 1.0h 1.5h 2.0h 15.6.15 1.0m 8 4 3 3 2 2 2 0 0 2 (LT+1h) 16.6.15 0.8m 7 1 0 0 0 0 0 0 0 17.6.15 0.8m 7 0 0 0 0 0 0 0 0 18.6.15 0.7m 0 0 0 0 0 0 0 0 0 19.6.15 0.8m 2 0 0 0 0 0 0 0 0 20.6.15 0.9m 8 0 0 0 0 0 0 0 0 21.6.15 1.1m 24 19 4 3 4 0 0 0 3 22.6.15 1.3m 11 2 0 0 0 0 0 0 3 23.6.15 1.5m 36 37 31 17 0 0 0 0 0 17 (LT-0.5h) 24.6.15 1.7m 54 41 39 2 0 0 2 2 2 39 (LT-1h) 25.6.15 1.8m 66 66 52 45 24 10 0 0 0 66 (LT-1.5h) 26.6.15 1.8m 44 36 34 9 7 1 0 0 0 44 (LT-2h) 27.6.15 1.7m 73 59 24 10 4 4 3 8 8 73 (LT-2h) 28.6.15 1.9m 8 4 4 2 0 0 0 0 4 4 (LT+2h) 29.6.15 1.6m 19 17 20 6 1 0 0 0 3 3 (LT+2h) 30.6.15 1.4m 13 9 0 0 0 0 0 0 1

July 2015 Date Low Number of Harbour Seals at Greatham Creek (GC) Contribution of GC Tide LT- LT- LT- LT- LT LT+ LT+ LT+ LT+ seals to daily max. 2h 1.5h 1h 0.5h 0.5h 1.0h 1.5h 2h 1.7.15 1.1m 7 2 0 0 0 0 0 0 0 2.7.15 0.9m 14 3 2 2 0 0 0 0 1 1 (LT+2hr) 3.7.15 0.7m 39 42 30 6 1 0 0 0 0 30 (LT-1hr) 4.7.15 0.6m 17 2 1 1 0 0 0 0 0 5.7.15 0.6m 15 0 0 0 0 0 0 0 0 6.7.15 0.6m 21 12 2 0 0 0 0 0 0 7.7.15 0.8m 8 0 0 0 0 0 0 0 0 8.7.15 1.2m 28 17 0 0 0 0 0 0 0 9.7.15 1.2m 44 13 0 0 0 0 0 0 0 10.7.15 1.4m 54 23 13 1 1 1 1 1 1 11.7.15 1.5m 50 6 0 0 0 0 0 0 0 50 (LT-2hr) 12.7.15 1.6m 13 7 4 0 0 0 0 0 0 13.7.15 1.4m 10 3 0 0 0 0 0 0 0 14.7.15 1.2m 12 1 2 0 0 0 0 2 2 15.7.15 1.0m 25 7 0 0 0 0 0 0 0 16.7.15 0.9m 0 4 0 0 0 0 0 0 0 17.7.15 0.8m 13 0 0 0 0 0 0 0 0 18.7.15 0.9m 12 7 7 7 7 7 7 7 7 7 (LT+1hr) 19.7.15 0.9m 21 2 0 0 0 0 0 0 0 20.7.15 1.1m 42 14 0 0 0 0 0 0 0 21.7.15 1.2m 42 13 2 0 0 0 0 0 0 22.7.15 1.4m 45 28 0 0 0 0 0 1 1 23.7.15 No data 24.7.15 No data 25.7.15 2.0m 55 47 47 37 6 7 5 11 16 55 (LT-2hr) 26.7.15 1.9m 50 15 4 2 0 0 0 1 2 50 (LT-2hr) 27.7.15 1.8m 20 18 19 9 9 1 0 0 0 9 (LT) 28.7.15 1.8m 4 3 6 1 1 0 0 2 2 29.7.15 ? 36 40 31 11 7 7 7 5 7 5 (LT-1.5hr) 30.7.15 Void incomplete data 31.7.15 0.8m 28 18 7 2 0 0 0 0 0

August 2015 Date Low Number of Harbour Seals at Greatham Creek (GC) Contribution of GC Tide LT-2h LT- LT- LT- LT LT+ LT+ LT+ LT+ seals to daily max. 1.5h 1h 0.5h 0.5h 1h 1.5h 2h 1.8.15 0.4m 9 6 6 6 6 6 6 6 6 6 (LT+0.5hr) 2.8.15 No data 3.8.15 0.3m 14 0 0 0 0 0 0 0 0 4.8.15 0.4m 15 4 0 0 0 0 0 0 0 5.8.15 0.6m 24 13 0 0 0 0 0 0 0 6.8.15 1.0m 45 17 3 1 0 0 0 0 0 7.8.15 1.3m 71 40 2 1 1 1 1 1 1 71 (LT-2hr) 8.8.15 1.7m 84 70 20 1 1 1 1 0 0 84 (LT-2hr) 9.8.15 1.8m 74 70 66 38 23 20 20 0 0 74 (LT-2hr) 10.8.15 1.8m 74 46 24 20 1 1 0 0 0 74 (LT-2hr) 11.8.15 1.6m 64 45 19 6 4 0 0 0 0 64 (LT-2hr) 12.8.15 1.3m 14 4 0 0 0 0 0 0 0 13.8.15 1.1m 8 2 0 0 0 0 0 0 0 14.8.15 1.0m 80 5 1 1 1 1 1 1 6 80 (LT-2hr) 15.8.15 0.9m 29 14 4 4 0 0 0 0 0 4 (LT-0.5hr) 16.8.15 0.9m 22 10 1 0 0 0 0 0 6 17.8.15 0.9m 39 7 1 0 0 0 0 0 0 18.8.15 1.0m 12 2 2 1 0 0 0 0 1 19.8.15 No data 20.8.15 1.4m 65 25 1 1 1 1 1 1 13 65 (LT-2hr) 21.8.15 1.6m 56 37 20 3 2 2 2 2 10 2 (LT+1hr) 22.8.15 1.8m 84 67 70 16 10 8 0 3 21 21 (LT+2hr) 23.8.15 2.0m 84 81 80 62 2 3 7 9 0 84 (LT-2hr) 24.8.15 2.1m 86 89 90 90 80 44 44 47 - 90 (LT-0.5hr) 25.8.15 2.0m 106 97 76 73 39 34 36 - - 106 (LT-2hr) 26.8.15 1.8m 40 27 10 9 2 2 2 3 10 10 (LT+2hr) 27.8.15 1.4m 18 11 4 1 1 1 1 10 42 42 (LT+2hr) 28.8.15 1.0m 29 16 0 0 0 0 0 0 0 29.8.15 0.6m 9 0 0 0 0 0 0 0 0 30.8.15 0.3m 11 3 3 2 2 2 0 0 0 2 (LT+0.5hr) 31.8.15 No data

September 2015

Date Low Number of Harbour Seals at Greatham Creek (GC) Contribution of GC Tide LT- LT- LT- LT- LT LT+ LT+ LT+ LT+ seals to daily max. 2h 1.5h 1h 0.5h 0.5h 1.0h 1.5h 2.0h 1.9.15 No data 2.9.15 No data 3.9.15 No data 4.9.15 No data 5.9.15 1.5m 60 53 29 6 5 4 5 4 8 60 (LT-2hr) 6.9.15 1.9m 79 53 41 37 9 6 3 2 6 6 (LT+2hr) 7.9.15 2.1m 74 65 46 27 31 19 20 20 22 74 (LT-2hr) 8.9.15 2.0m 66 70 35 27 23 - - - - 70 (LT-1.5hr) 9.9.15 1.6m 11 5 0 0 0 0 0 0 4 10.9.15 1.4m 35 14 13 4 0 0 0 0 9 11.9.15 No data 12.9.15 1.0m 17 2 2 1 1 1 1 1 1 1 (LT-0.5hr & -1hr)

5.2. Haul-out Behaviour at Seal Sands

The following data give a summary of monthly mean numbers of both Harbour and Grey Seal observed over the four hour low tide period at each of the haul-out sites on Seal Sands and is discussed in Section 6.1. The named sites (Site ‘A’, ‘B’, etc) are shown in Appendix 2. Monthly means were obtained using the maximum numbers of seals present on each site during each low tide period on the days where monitoring took place. Comparative data from the period 2007 to 2014 is shown in the figures which follow in order to place the 2015 data into context. The bar charts below show blue columns corresponding to the average number of Harbour Seals, while red columns correspond to the number of Grey Seals.

5.2.1. ‘Site A’

Figure 3a: June 2007-2015 Figure 3b: July 2007-2015

Figure 3c: August 2007-2015 Figure 3d: September 2008-2015

Figure 3: Incidence of seals using ‘Site A’ between 2007 & 2015

5.2.2. ‘Site B’

Figure 4a: June 2007-2015 Figure 4b: July 2007-2015

Figure 4c: August 2007-2015 Figure 4d: September 2008-2015

Figure 4: Incidence of seals using ‘Site B’ between 2007 and 2015

5.2.3. ‘Site C’

Figure 5a: June 2007-2015 Figure 5b: July 2007-2015

Figure 5c: August 2007-2015 Figure 5d: September 2008-2015

Figure 5: Incidence of seals using ‘Site C’ between 2007 and 2015

5.2.4. ‘The Spit’

Figure 6a: June 2007-2015 Figure 6b: July 2007-2015

Figure 6c: August 2007-2015 Figure 6d: September 2008-2015

Figure 6: Incidence of seals using the ‘Spit’ between 2007 and 2015

5.2.5. ‘The Wall’

Figure 7a: June 2007-2015 Figure 7b: July 2007-2015

Figure 7c: August 2007-2015 Figure 7d: September 2008-2015

Figure 7: Incidence of seals using the ‘Wall’ between 2007 and 2015

5.2.6. ‘Site D’

Figure 8a: June 2007-2015 Figure 8b: July 2007-2015

Figure 8c: August 2007-2015 Figure 8d: September 2008-2015

Figure 8: Incidence of seals using ‘Site D’ between 2007 and 2014

5.2.7. ‘Site E’

Figure 9a: June 2007-2015 Figure 9b: July 2007-2015

Figure 9c: August 2007-2015 Figure 9d: September 2008-2015

Figure 9: Incidence of seals using ‘Site E’ between 2007 and 2015

5.3. Birth and Survival of Harbour Seal Pups

A total of 19 pups were born in 2015, of which 18 are thought to have survived to weaning. Figure 10 shows the birth and survival rates of Harbour Seal pups at Seal Sands since inception of the seal monitoring project.

Figure 10: Harbour Seal Birth Rate (1989 – 2015)

5.4. Maximum Count of Seals at Seal Sands / Greatham Creek

Data recorded for 2015 are contrasted with that from previous years in Figure 11.

Figure 11: Maximum Number of Seals Recorded Per Day (1989 – 2014)

As for the previous two years, the maximum data recorded for Harbour Seal in 2015 were a result of pooling numbers simultaneously hauling out at Seal Sands and Greatham Creek.

The daily maximum count of 114 Harbour Seal on 16th August 2015 is the highest recorded for this species since the monitoring project began and is around a 4% increase in the 2014 total, which represented the previous highest maximum. The last six years have all resulted in an increased maximum daily count of Harbour Seals.

The maximum Grey Seal numbers for 2015 that were recorded as part of this study were down somewhat on 2014, with the highest count being 49 on 15th June, the first day on which monitoring took place this year. However a count, unrelated to this programme, recorded 82 Grey Seals on Area D one hour after low tide on 13th July. This represents a further 39% increase on last year’s maximum count, which was in itself a 37% increase on the previous maximum.

Harbour Seals continue to use Greatham Creek in large numbers. On the 26th August, at 2 hours before a 2m neap low tide, the entire Teesmouth population of 106 Harbour Seals were counted at Greatham Creek. This is the highest number of seals recorded at Greatham Creek at low tide to date.

Grey Seals were recorded at Greatham Creek on 10 of the 76 survey days in 2015, with a mean daily number of 0.47 individuals for the entire survey period and a maximum number of 10 on 6th September. While this is still relatively infrequent usage these figures represent an increase of 50% and 100% on the respective 2014 figures and it will be interesting to see if this increased usage continues in future years.

5.5. Mean Count at Seal Sands / Greatham Creek

The mean number of seals present during 2015 was calculated for the four months of the year during which the survey was conducted (June, July, August and September).

5.5.1. Harbour Seal

The mean number of Harbour Seal observed was 58.2 for June (cf 53.9 in 2014; 39.7 in 2013; 39.6 in 2012; 49.5 in 2011); 63.4 for July (cf 68.9 in 2014; 63.7 in 2013; 51 in 2012; 54.1 in 2011); 90.6 for August (cf 81.3 in 2014; 73.9 in 2013; 63.3 in 2012; 56.8 in 2011) and 70.1 for September (cf 72.3 in 2014; 50.6 in 2013; 57.8 in 2012; 44.2 in 2011). As in previous years mean numbers were at their highest in August and the August 2015 figure was 11% higher than the previous highest monthly mean however mean numbers were slightly lower in July and September than the corresponding months in 2014

Figure 12 shows the mean numbers of Harbour Seal which have been observed in previous years. Note: data are not available for June in years prior to 2005 or September for years prior to 2008.

Figure 12: Mean Harbour Seal Count from June to September (1989 – 2015)

The mean number of seals hauling out at Greatham Creek at low tide has also increased markedly in recent years. For August, the month when Harbour Seals numbers are consistently at their highest, the mean of the maximum daily count over the four hour low tide period is shown in Figure 13. Numbers were fairly consistent from 2010 to 2012 but have increased annually over the past three years with the mean number recorded in 2015 being 43.4, almost double that in the period 2010- 2012.

Figure 13. Mean Harbour Seal Count at Greatham Creek (2010-2015)

5.5.2. Grey Seal

The mean number of Grey Seal observed was 15.1 for June, 16.8 for July, 16 for August and 11.7 for September.

Mean numbers of Grey Seals were down overall on 2014. This was because the high mean numbers for June and September 2014 weren’t replicated this year, with each monthly average for 2015 being more or less in line with the respective months in years in the earlier part of this decade.

Figure 14 shows the mean numbers observed in the years 2005 to 2015 for which there are available data.

Figure 14: Mean Grey Seal Count from June to September (2005 – 2015)

6. Discussion

6.1. Haul-out Behaviour

6.1.1. Studies at Greatham Creek

Simultaneous monitoring of seals over the low tide period took place through the 2015 season at both Seal Sands and Greatham Creek. Section 5 shows the results of monitoring from the period June to September 2015. The frequency of occasions when the daily maximum number of Harbour Seals in the estuary was supplemented by the seals hauling out at Greatham Creek is summarised as follows:

 June – 50%  July – 28.6%  August – 60.7%  September – 71.4%

Numbers of Harbour Seals at Greatham Creek contributed to the estuary daily maximum count on 48% of the total monitoring days. This compares to 50% and 46% of the available days through the survey season of 2013 and 2014 respectively. As in 2014 seals hauled out very close to the seal observation area and the road at Greatham Creek, both on the northern and southern sides of the Creek. This apparent habituation may explain why the numbers of Harbour Seals using Greatham Creek at low tide have increased markedly. At present there is no data on numbers present at Greatham Creek at high tide although anecdotally this appears to be increasing as well.

While seals are observed to enter the Saltern Wetlands managed realignment site on spring high tides, the levels of inundation experienced across the site do not appear to be sufficient to make this area generally suitable for seals and to date the seal monitoring project has not recorded any seals hauling out in this area.

6.1.2. Seal Sands

Appendix 2 shows the key haul-out sites used at Seal Sands. Site ‘A’, ‘B’, ‘E’ and the ‘Wall’ are used mainly by Harbour Seals, while Site ‘D’ is used by Grey Seals. Site ‘C’ and the ‘Spit’ are used by both species.

Site usage is dependent upon the height of the low tide. The position of Site ‘A’ is relatively high in comparison with most of the other haul-out sites (except Site ‘D’, which is exposed for most of the tidal cycle). Site ‘B’, Site ‘C’, the ‘Spit’ and the ‘Wall’ are only 2.3m above the Lowest Astronomical Tide (LAT), so they are often mostly covered by water on neap tides. Seal Sands haul out data from 2015 are shown in Section 5.2. Relative use of the various haul out sites by Harbour Seals remained fairly constant throughout this survey season. Site ‘A’ was the most well used supporting around twice the number of seals in each month as Site ‘C’ the next most frequently used haul out site.

6.2. Birth-rate of Harbour Seal Pups

The 2015 season saw the birth of 19 pups, of which 18 were thought to have survived to weaning. This is identical to the situation in 2014. The first pup of the season was born unusually early but unfortunately didn’t survive, being found dead on 5th June.

The first live birth of the season was noted on 19th June 2015, while the last births occurred on 15th July 2015. This is a slightly extended birthing period to the typical situation, which normally spans less than three weeks and may be related to the cool, windy spring and summer weather this year.

6.3. Seal Numbers

As noted above, 2015 saw a continuation of the year on year trend of new records of the maximum daily number of Harbour Seals that has occurred since 2010, albeit in this case a relatively minor increase. The mean monthly total for August 2015 was the highest monthly total for Harbour Seal since the seal monitoring project began. However, overall, Harbour Seal numbers were roughly in line with the 2014 numbers.

The importance of Greatham Creek to Harbour Seals continues to increase. It is noticeable that seals are hauling out closer to the seal hide and the road than they did in previous years and also using the north side of the Creek more frequently although, to date, counts have not differentiated between the different haul out areas on Greatham Creek. As in 2014 this doesn’t appear to be in response to any changes on Seal Sands. It may simply be that Greatham Creek is generally a more suitable haul out location as it offers a wider range of elevations with respect to the tidal cycle than Seal Sands and that seal numbers are increasing there as they become more habituated to people and traffic.

Both the mean and the maximum numbers of Grey Seals recorded as part of the Seal Monitoring Project were down in comparison to 2014. However a casual record of 82 Grey Seals on 13th July was much higher than any previous counts and crucially was much higher than the count for Site D made at the exact same time as part of the Seal Monitoring Project. A similar discrepancy occurred on a casual count on 30th June, when the numbers of Grey Seals differed from those recorded from the Seal Monitoring Project. The two casual counts were made from Seaton Snook which is directly opposite the haul out at Area D. This highlights the difficulties in counting seals on Area D from the usual observation point, something that was commented on by members of the survey team this year. It also means that the numbers of Grey Seals in the estuary are likely to be under recorded to some degree.

While recording as part of this project only occurs from mid June to mid September, it is known that seals are present in some numbers throughout the year. To date there has been no systematic recording of seal numbers outside of the project however a series of 27 ad hoc counts of seals on Area D were undertaken by the author and by Mike Leakey, the Teesmouth National Nature Reserve manager and Vicky Rae, the Teesmouth EMS officer, from November 2014 to April 2015. In line with observations from the seal monitoring project, these were almost exclusively Grey Seals. The counts were undertaken at various stages of tide. Across all counts there was a mean of 10.6 seals, with a maximum count of 35. For the eight counts that occurred within 2 hours either side of low tide the mean number of seals was 11.6. Each of these counts represented a single point in time and it is possible that had there been several counts over part of the tidal cycle, as in the Seal Monitoring Project, that higher numbers of seals may have been recorded. In any case, this is higher than recorded for any of the four months of the Seal Monitoring Project and may again indicate that the numbers of seals on Area D is being under recorded. Alternatively it may be that Grey Seal numbers at Teesmouth are higher during winter.

6.4. Disturbance

The term ‘disturbance’ relates to any observed reaction of seals to a stimulus, in particular of seals taking to the water. It is important to limit disturbance experienced by seals during the summer period when mothers are suckling pups as this can influence the ability of pups to survive their first winter.

In 2015, 15 instances of disturbance to seals were recorded, which is down slightly from 2014 when there were 18 occasions where disturbance to seals was observed. Twelve of the disturbance events in 2014 were at Greatham Creek but in 2015 this was reduced to eight occasions. Of those eight, three were from people approaching the seals and a fourth from people standing on the A178 road bridge. The other four disturbances were perhaps unavoidable, e.g. from traffic standing on the road bridge, a dog barking etc.

Of the seven disturbance events on Seal Sands, three were related to noise from piling from Able UK operations and a fourth from a siren. The extent to which these caused disturbance wasn’t recorded, however it was noted that piling by Able UK occurred on several occasions without causing any disturbance. The remaining three disturbance events were caused by boats moving up the channel and on each occasion most or all of the seals left their haul out sites and entered the water.

6.5. Deaths

There were two reported Harbour Seal deaths in 2015. The first was the pup found at Greatham Creek on 5th June. From the vet’s synopsis it appears to have been one to three days old. The lack of subcutaneous fat raised some questions relating to the nutritional status of the mother and the vet concluded that the mother either had been unable to produce milk or had abandoned the pup. It is possible that it had been stillborn but the vet was unable to check this hypothesis as the lungs had been scavenged.

An immature Harbour Seal was found dead at Crimdon Dene on 31st July. It was a fresh corpse and had a bloodied nose and mouth but was otherwise intact. However it could not be recovered for post-mortem.

A dead Grey Seal was photographed under the Town Wall at Hartlepool Headland and reported on the Teesmouth Bird Club website on 30th August. There was some speculation that it was a Bearded Seal, Erignathus barbartus, however from the photo it could be identified as a Grey Seal.

7. Acknowledgements

This ongoing project would not have been possible in 2015 without funding provided by The Crown Estate. Huntsman Pigments also provided ongoing support in provision of the observation location at Seal Sands and giving access to this site.

The raw data for this report is collected by a dedicated set of monitors. Particular thanks are due to Linda Watson, the co-ordinator of the group. In addition to Linda in 2015 they were Claire McCarty, Zoe Fraser, David Laing, Dave Miles, Dave Thew, Paul Thomson, Dez Watson, Mel Watson and Terry Wells.

APPENDIX 1: Locations within the Tees estuary

Greatham Creek (including ‘managed realignment scheme’)

Seal Sands

Bailey Bridge

APPENDIX 2: Location of haul-out sites on Seal Sands ¯

Observation Point

Site D

The Spit

Site C

Site B The Wall

Site E

Site A

210 105 0 210 Meters