Table 1 : Sightings per month 2006-2008

	2006	2007	2008	Average
January	3	5	12	7
February	2	21	5	9
March	4	12	20	12
April	13	46	89	49
May	13	88	63	55
June	115	87	27	76
July	108	46	21	58
August	58	38	20	39
September	40	30	13	28
October	10	58	0	23
November	23	30	6	20
December	1	0	19	7
Total	390	461	295	382

Table 2 : Percentage of each year’s total sightings per month

Species Breakdown

Table 3 : Number of sightings per species per month

Table 4: Number of Individuals per month of the 3 main species

Tables 3 and 4 show, as expected, that the Harbour Porpoise was the most commonly seen and most numerous cetacean throughout 2008. There were also a high number of Risso’s dolphin sightings and individuals particularly in April and May. Notably there was also a large number of Risso’s dolphins in August, predominantly due to two very large groups. Also noticeable are the lack of Minke whale sightings throughout the year (n=18 in 2008, n=74 in 2007, n=96 in 2006) and the relatively high number of bottlenose dolphin sightings in the winter months.

Species Distribution

In this section, distribution maps are shown for the three most frequently seen cetacean species in Manx waters; Harbour Porpoise, Risso’s dolphin and Minke Whale. There are four plots per species for 2008, representing “Spring”, (March to May), “Summer” (June to August), “Autumn” (September to November) and “Winter” (December to February) and the respective plots for 2006 and 2007 combined for comparison. Please note there is no “Winter” plot for Minke Whales as there were no winter sightings in 2008.

Harbour Porpoise :

Overall, the spatial distribution of Harbour Porpoise sightings is similar in 2008 compared to the previous two years, with sightings from all round the island throughout the year. Overall, there were far less sightings of Harbour Porpoise in 2008 than in the previous two years, particularly in autumn. This is likely to be due to appalling weather conditions in autumn 2008, making spotting the small and elusive Harbour Porpoise very difficult, as opposed to any change in their temporal distribution.

However, a total of 535 sightings, comprising 1588 individuals, over the three years of opportunistic sightings highlight the importance of Manx waters for Harbour Porpoise. Of the 535 sightings, 80 were reported to contain calves, around 15%. Any individual spotted that is significantly smaller than a porpoise adult will be less than 9 months old, as porpoise reach nearly adult size at only 1 year old. Since such size of porpoise have been reported, this suggests that Harbour Porpoise breed in Manx waters, making Manx waters vital for this species.

Risso’s Dolphin :

The plots for 2006 and 2007 combined showed two clear patterns in spatial distribution of the Risso’s dolphin in Manx waters; firstly, that the majority of the sightings throughout the year are on the east coast and secondly a southerly shift in distribution between spring and summer. There also appeared to be temporal aspects to the sightings, with very few sightings in autumn and spring (n=5 and n=5 respectively) compared to spring and summer (n=60 and n=76 respectively).

In winter and autumn of 2008, sightings of Risso’s, both in terms of spatial and temporal distribution, are comparable with 2006/2007, with sporadic sightings from no particular area of Manx waters. 2008 is also comparable to the previous two years in spring, with large numbers of sightings around Douglas head and very few on the west coast. Although 5 out of the 8 Risso’s sightings in the summer of 2008 were in the south, this is not a big enough sample to be able to make any conclusions about whether their distribution had shifted south in the summer as in the previous two years. Hopefully the weather will allow more effort to be carried out in 2009 to see whether a southerly shift in the summer months is the norm for Risso’s dolphins in Manx waters.

Of the 86 sightings in 2008, 11 (12%) were reported to contain calves. Furthermore, sexual type behaviour was reported in one sighting suggesting that the Risso’s dolphins breed and calve in Manx waters. For a predominantly offshore cetacean species, this is rare hence making Manx waters a critical area for Risso’s dolphins.

Minke Whale :

As has been previously been discussed, there were only a fraction of the number of sightings of Minke whales in 2008 (n=18) that had been reported in the previous two years (n=96 2006, n=74 2007). There are several possible reasons for this. It could be due to a lack of effort being spent looking for Minke whales, poor weather making them un-spottable or a change in the distribution of the herring stock which the whales follow, caused by a change in position of the Irish sea front or a combination of the three. The publication of data on the Irish sea front and on the landings of herring in the northern Irish Sea may provide an answer.

Table 5 : Yearly comparison of land based effort

Year	Effort (hours)	Sightings
2006	118	174
2007	72.75	86
2008	87.75	55

There are clearly less sightings per unit effort (a unit is one fifteen minute interval) in 2008, than in 2007 or 2006. This is probably due to more effort being carried out in the winter months (November to April) in 2008 (see figure 5), when there are less sightings. As a comparison, 59% of effort in 2008 was carried out in winter, compared to 19% in 2007 and 10% in 2006. As can be seen from figure 6, there are many more sightings per unit effort in the summer months compared to during the winter. Indeed, the highest sighting rate occurs in July, when there is a sighting every 28 minutes.

It is hoped that after several more years of effort, there will be sufficient data in all months allowing statistical comparisons to be made between months and sites. To avoid negative bias in terms of sightings rates, effort based watches are only carried out when the sea state is three or less and it is this that has prevented more effort being carried out.

Figure 5 : Graph to show monthly distribution of effort per year

 Figure 6: Graph to show sightings per unit effort throughout the year

The species composition and number of individuals of the effort based sightings can be seen in table 6. “Others” in the bottom row refers to seals, basking sharks and sightings of unknown species.

Table 6 : Species composition of sightings

Species	Number of sightings	Number of individuals
Harbour Porpoise	24	52
Minke Whale	1	1
Risso’s dolphin	5	16
Common Dolphin	1	4
Others	24	68
Total	55	141

As would be expected, the most commonly seen cetacean species is Harbour porpoise. In common with the other types of data collected in 2008, there were surprisingly few Minke Whale sightings compared to 2006/2007 (n=29).

Effort based watches can also be used to compare different sites in terms of sighting frequency, which can be measured in cetacean positive intervals, the percentage of fifteen minute intervals in which at least one sighting of a cetacean was made. The data for 2008 can be seen in table 7. For comparison, the data from the same site from 2006 and 2007 combined can be seen in brackets.

The highest sighting rate, as in 2006/2007, was at Port St Mary, which equates to twenty five minutes of sightings per hour in 2008 compared to forty minutes per hour in 2006/2007. As mentioned earlier, this is likely to be due to more effort being carried out in winter. Niarbyl has the next highest sighting rate, which equates to eighteen minutes of sightings per hour.

Table 7 : Sightings rates per area

	Effort (hours)	% Cetacean positive intervals
The Calf	7.75	9.7 (11.2)
Douglas Head	19	10.5
Little Ness	8.5	0
Niarbyl	8	31.25 (28.3)
Port St Mary	17.5	42.8 (67.1)
Dhoon Bay	5	4

The continuation of effort based watches should lead to a data set with a much more even spread of effort throughout the year and a data set that is big enough to make statistically strong statements about hotspots for cetaceans as a whole and for individual species and the best times of year to see them. It may also provide even more fine scale information, such as the best state of tide for a particular species in a particular area.

2008 Manx Cetacean Survey – Boat based

Effort

Overall, 885 kilometres were completed during boat trips in 2008, all of which was on dedicated boat surveys. This compares to 2588km in 2007, which included 650km on press trips. This comprised the following effort types:

Table 8 : Breakdown of effort types in Manx Cetacean surveys

Effort Type	Distance (km) 2008	Distance (km) 2007
Casual Watch (no dedicated observers)	23.7	35.3
Dedicated Search (2 dedicated observers on fly-bridge, no independent observer)	623.5	956.1
Line Transect (2 dedicated observers on fly-bridge, 1 independent observer)	223.7	938.7
Photo Identification	14.0	7.6

As can be seen, the distance travelled overall was significantly less in 2008, particularly on effort type “Line Transect” from which the most useful data is derived. This was due predominantly due our average trip length being only 4hrs 25minutes, compared to 7hrs 30minutes in 2007. This in turn was due to the weather being so changeable in 2008. Most trips were planned to only take advantage of a small weather window during the day, which had to coincide with the tides being high enough to get in and out of port.

It was felt that doing dedicated photo-identification trips was a better usage of time than completing a quarter of a transect line. Only two trips were managed beyond three miles offshore, during which transect lines were followed and only a few kilometres of effort was carried out on the west coast.

 Sightings

 There were a total of 61 sightings in 2008 comprising 185 individuals. This equates to a sightings rate of 0.07 sightings per km or 14.75km travelled for every sighting. This compares to a sighting rate of 0.08 per km in 2007.

However, nearly 20%, or 172km, of all the effort carried out in 2008 was in a sea state of Beaufort 3, when sightings of delphinids and porpoise become unreliable. Since these make up the majority of sightings in Manx waters, effort in sea state 3 is excluded for analysis. This results in a sighting rate of 0.08 per km, compared to 0.10 per km when sea state had been taken into account in 2007. Despite the small sample sizes, especially in 2008, these figures are somewhat comparable.

Table 9: Species breakdown of sightings on Manx Cetacean surveys 2008

Species	Number of Sightings	Number of Individuals
Harbour Porpoise	38	116
Minke Whale	5	5
Risso’s Dolphin	2	16
Atlantic Grey Seal	4	4
Common Dolphin	2	31
Basking Shark	9	13

As would be expected from opportunistic and effort based sightings from land, Harbour porpoise were the most commonly seen cetacean on boat surveys, making up 63% of all sightings. The breakdown of sightings in 2008 is quite different to 2007, with a far smaller percentage of both basking shark and seal sightings. For both species, this is due to very little effort being carried out in the inshore south and west of the island, areas which both species tend to favour. The distribution of all cetacean and basking shark sightings can be seen in the following plot.

Figure 7: Distribution of sightings from Manx Cetacean Surveys, 2008

Unfortunately, with the lack of sightings and very little effort being carried out on the west coast, it is not possible to draw any real conclusions regarding distribution of sightings. Although hard to draw any conclusions from, the huge cluster of sightings in the left hand corner of the plot (between 7 and 11 miles offshore) is worth mentioning.

The cluster of sightings were all seen within two hours of each other having covered a distance of 50km and comprise seventeen harbour porpoise sightings, of around 74 individuals and one common dolphin pod of twenty five individuals.

Although this area was covered during Manx Cetacean Surveys in 2007, it did not result in such a huge number of cetacean sightings. It is likely that this aggregation of cetaceans was caused by a temporary aggregation of a favoured prey item in the area, possibly herring or whiting. This area will be covered in future surveys so it can be assessed whether this was an anomaly or a common phenomenon.

The first abundance estimate for harbour porpoise was derived from Manx Cetacean Surveys in 2007, but having a too small sample size has meant this has not been possible for 2008. There were only 21 harbour porpoise sightings were made on-transect in 2008, which would result in a very statistically weak estimate. The lack of temporal or geographical spread of the data is also problematic. The data can be incorporated into future abundance estimates however.

Boat Numbers

As in 2007, the numbers and types of boats were recorded whilst surveying. In 2007, the average number of boats seen was 2.5 per hour, whilst in 2008 this had increased dramatically to 4.4 per hour. The breakdown of the main types of boats can be seen in table 10 below.

Table 10: Numbers of each type of boat in both years

Although clearly a lot less time was spent surveying in 2008 (40.3 hours compared with 119.3 hours in 2007), the higher rate of boats per hour, along with the huge increase in numbers of motor boats is noteworthy. However, it should not be assumed that this purely represents a huge increase in number of boats. There is likely to be a weather element to these figures, with pleasure boats also only able to take advantage of limited opportunities to go out, and therefore many more being out on the few occasions Manx Cetacean surveys were also able to be out.

Photo Identification (ID)

Photo ID work, started in 2007, was very successfully continued in 2008, despite the lack of opportunities for boat based work. Not only was the Risso’s dolphin catalogue progressed, but catalogues were also started for Bottlenose dolphins, Common dolphins and Minke whales. It is hoped that, as with the Risso’s dolphins, these catalogues will allow us to determine any patterns of site fidelity to Manx waters as well as potentially offer information on social associations and comparisons with other populations around Britain.

Risso’s dolphins

We had two Risso’s dolphin encounters from our dedicated boat surveys in 2008 and a further three casual encounters (one from Douglas Head and two from photos submitted by MWDW observers). These resulted in the identification of 1 new ‘well marked’ individual, 2 new ‘left’ individuals and 1 new ‘right’ individual. The catalogue therefore now contains 21 ‘well marked’, 6 ‘left’ and 8 ‘right’ individuals.

The average percentage of well marked animals in a group can be used to provide a crude estimate of the overall population size. From all our encounters, the average percentage of the group that are well marked is currently 42%. Since there are now 21 well marked individuals, it can be said that these represent 45% of the population. It can therefore be calculated that 100% of the population would be 47 individuals. Using this same method, 50 was the minimum population size calculated at the end of 2007. Although this is only a basic inference, it does give a general idea of the size of population we have in Manx waters.

However, it is thought that there are still a number of individuals yet to be identified. This can be presumed from the discovery curve of identifications, as shown in figure 8 below.

Figure 8: Risso’s dolphin Discovery curve. ‘Catalogue Size’ only increases when an ‘Identification’ is of a new individual.

As discussed in previous reports, when the curve is still increasing, new animals are still being discovered and added to the catalogue. Only when the curve consistently levels out can it be concluded that all the individuals in a population have been identified. Although the discovery curve above has flatter sections, it is still principally increasing. It is therefore highly likely that the number of animals utilizing Manx waters is higher than currently recognised.

One of the most useful applications of photo ID is in the determination of site fidelity of animals to an area. In 2008, four well marked animals which were first identified in 2007 were re-sighted. Additionally, two individuals have now been seen five times, across the two years and in five different months (April – August inclusive). This shows that the same animals are using Manx waters consistently, year on year, and that the same individuals remain in the area for significant periods of time. This strongly suggests that Risso’s dolphins do not simply pass through Manx waters, but that the waters around the Isle of Man are a vital habitat for supporting and sustaining this population.

Work is currently underway to create a wider ranging catalogue, to try and identify whether any of these individuals have been seen in other areas of the west coast of Britain.

Bottlenose Dolphins

The end of 2008 saw a fantastic number of sightings of large groups of Bottlenose dolphins. Although we were unable to collect any images ourselves, we were very grateful to receive a number of images from Bob Taylor, of Gemini, who had a large sighting off Port St Mary. From this one encounter, we have identified 12 ‘well marked’ individuals, 3 ‘left’ and 4 ‘right’ individuals. This is the first catalogue of Bottlenose dolphins from around the Isle of Man and is an important start for establishing the patterns of these winter visitors.

It has long been thought that the Bottlenose dolphins that are seen around the Isle of Man in the winter months are part of the same population that spend the summer months in Cardigan Bay, Wales. Until now, there have been no images from Manx waters which would confirm whether this is the case. However, from this one encounter, four individuals have now been matched to the catalogue from Wales. Interestingly, only one of these four has been seen in the northern waters of Cardigan Bay and none of them have been seen on the north coast of Wales.

Although this is based on only one encounter, there is now substantial evidence that the dolphins which spend the summer as residents in Cardigan Bay, are much more widely ranging in the winter months. Not only does this give us a great deal more information about the individuals which are using Manx waters, but it also has significant conservation management implications.

It is hoped that in the future, more images will be able to be matched to other populations, both in Wales and Scotland, to gain a more comprehensive picture of Bottlenose dolphin movement and site fidelity patterns.

Common Dolphins

Although sightings of Common dolphins were scarce in 2008, we were lucky enough to have an encounter with a group of around 30 individuals, about 10 miles south west of the Calf. From this encounter, 6 ‘well marked’ individuals have been identified. As with the Bottlenose dolphins, this is the first catalogue of Common dolphins to be created from around the Isle of Man.

Common dolphins are not widely studied through photo ID techniques, for various reasons. They often appear in large numbers and it is therefore nearly impossible to photograph the whole group, meaning social association studies are not generally possible. Their high speed movements also tend to make photography difficult and they are typically not as well marked as other cetacean species which are studied with photo ID.

Nevertheless, having a catalogue of recognisable individuals can still provide useful information. With a general decline in Common dolphin numbers throughout Europe, any information with which they can be studied is both rare and invaluable. With a catalogue in place, we are now at least in a position to try and determine whether the same individuals come back year on year. It may also be possible to compare the individuals seen in Manx waters with others throughout Europe.

Minke Whales

Again, despite a poor year for Minke whales, we managed to have 2 encounters which each yielded one identifiable individual. Additionally, we have received images of a third individual from Chris Sharpe, which date back to July 2006. Therefore there is now a first Minke whale catalogue from around the Isle of Man, containing 3 well marked individuals.

As with the other species, hopefully this will allow us to determine patterns of site fidelity to Manx waters, as well as potential comparisons with other populations. 

Conclusions

The work carried out by MWDW continues to play a vitally important role, both in the understanding of cetaceans in the Irish Sea and in raising awareness and understanding about cetaceans amongst the general public. Despite the well documented poor weather in 2008, there were still over 200 sightings on the public sightings network (1 every day and a half) and a further 74 people registered on the website.

The information gained from the sightings network continued to provide useful information regarding the temporal and spatial distribution of cetaceans around the island. This information is vital both in a conservation sense and in terms of informing the public about where to see cetaceans around the island from land at different times of year.

Much progress was also made regarding photo-identification, with three new catalogues being created. Furthermore, re-sightings of Risso’s dolphin individuals first seen in 2007, suggests that some individuals are showing a degree of site fidelity to the island. This again is vitally important information on what is a little understood cetacean species.

All cetaceans are in the IUCN Red list and hence any information about their numbers and movements is vital for their conservation and survival. As was shown in 2008, there can be huge differences between years when studying marine megafauna and hence only long term study will be useful in providing accurate information from which management decisions can be made.