Cetacea: Whales & Dolphins

At least 19 species of cetaceans are regularly found in the seas surrounding the British Isles.


DOLPHIN OBSERVATIONS IN
SUSSEX SEAS
by Steve Savage (Sea Watch Foundation)

Off the coast at Brighton is one of the most least likeliest places that you might expect to see dolphins. Not only is the coastline extensively developed, there is also a large amount of boat traffic.

 However, since I started the 'Dolphin Watch' project in 1991, Bottle-nosed Dolphins, Tursiops truncatus, have been observed by myself and a small network of observers at three key sights between Brighton and Hove (English Channel coast). Details of my observations were sent to Dr Peter Evans, Director of Research for the Sea Watch Foundation. Earlier this year, I became a Regional Co-ordinator for the South-east (Sussex and Hampshire) and I am in process of building a network of volunteer observers. Unfortunately, this year the sightings of dolphins have been disappointing. The reasons for this will be discussed later.

Project Aims

When I started recording cetacean sightings in 1991, I set out several aims for the project. My first aim was to identify that had been reported on various occasions by the media. From my observations and photographic evidence, the species was identified as the Bottle-nosed Dolphin.

 The next step was to collect as many sightings as possible and to help with this I set up a small network of interested locals. The aim is to discover which months the dolphins were in the area and the frequency of their visits. It was also possible from this data to plot the movement of the dolphins within the observation area.

Resident Group

It appears that the dolphins are a resident group that live in the English Channel and their movements bring them into the observation area at certain times of the year. The largest number recorded at one time is ten dolphins, the smallest number was a single animal. It appears that they may be same animals returning each year, but further study is needed to be certain. The main way that this can be done is to photograph these marine mammals close up and record any natural markings that can be used to identify an individual animal. The photographs can be compared to see if any subsequent observations are the same or a different animal.
 The Common Porpoise, Phocoena phocoena, has been recorded but they usually stay further out to sea and are only occasionally involved in inshore sightings.

Feeding

Feeding can take place close to the shore or out in deeper water. The dolphins have on occasions been seen to herd fish close to the shore and take it in turns feeding (e.g. in July 1991, a group of dolphins at Brighton were observed herding fish using the marina wall and land as a barrier). In deeper water, dolphins may use the surface of the sea as a barrier by driving fish towards the surface. This feeding behaviour sometimes attracts sea birds and they can be seen diving to catch these fish (e.g. May 1993 at Brighton). When dolphins are hunting for fish, they often swim side by side several dolphins abreast. This allows them to scan a wider area with their echolocation.

Playing and Swimming

Dolphins are very playful animals. They are also very inquisitive and often approach boats, particularly yachts. On several occasions, dolphins have been observed playing around yachts and sometimes motor boats, swimming underneath the vessel from one side to the other (e.g. May 1992 at Littlehampton and July 1993 at Christchurch), or occasionally bow-riding.
 Dolphins have been observed either solitary animals or small schools swimming past, exhibiting no other behaviour. These observations should not be confused with porpoise sightings which are regular a few miles offshore of Sussex.

Photograph by E. Mitchell
 
 
 

Inshore Sightings

Inshore sightings usually coincide with high tide, when the coastal water are at their greatest depth. This is also when the maximum number of invertebrates and fish are inshore and the dolphins have been observed feeding (e.g. August 1992 at Hove). Inshore sightings usually occur from May to October. However, this year, five dolphins were observed off the coast at Shoreham-by-Sea on the 8 April 1993. The sea temperature was 6.70C (440F). (This seems a bit low). All previous inshore sightings occurred when the sea temperature was at least 100C. A fishermen contact informed me that the mackerel were around earlier this year, so this may explain this early sighting. Many of the inshore sightings are the result of timed systematic observations from particular areas of the coast.
 

Bottle-nosed Dolphin off Worthing, West Sussex.
 

Systematic sightings from vantage points on the shore (the higher up the greater the view) are made on a regular basis and the reports are filed whether the cetaceans are sighted or not. This information is just as important as actual cetacean sightings, as it helps to build up a picture of where cetaceans are seen and when. The data is added to the national records kept and analysed by Dr Peter Evans (Director of Research).

Offshore

Offshore sightings are usually made by yachtsmen (an women) and fishermen. On most occasions, these vessels travel to different areas each time they put to sea and the observations are on more of a casual basis. Reports are made only if cetaceans are actually sighted.

Boat Traffic

Due to the increase in boat traffic (pleasure and commercial), it has been suggested that dolphins are avoiding areas where they were once common. For this reason, we are monitoring the movement of vessels in local waters to assess any possible impact that boats may have on populations and movements of both dolphins and porpoises.
 There has always been a large volume of boat traffic in this area, but there appears to have been an increase from previous years. Motor vessels are the greatest threat to dolphins. Although there is some danger of collision (a dead Striped Dolphin, Stenella coeruleoalba, was washed ashore in 1990 with signs of propeller damage) the biggest danger is that dolphins will avoid the area because of noise pollution. Dolphins have sensitive hearing and the sounds produced by motor vessels, particularly jet-ski and wet-bikes are at the level where dolphin hearing is most sensitive.

 Sailing yachts present little impact on dolphins, although the larger vessels sometimes use an engine when leaving port, or when there is insufficient wind. Dolphins often approach and play around single yachts, although large numbers of yachts (in excess of 30) were recorded at Brighton Marina on 27 June 1993. It is difficult to assess whether these large congregations of yachts have any impact on the dolphins. They are likely to detect the presence of the yachts and avoid the area in advance.

Coastal Developments

One possible reason for the poor record of observations in 1993 could be the work carried out by Southern Water at Worthing (Long Sea Outfall) and adjacent to Brighton Marina (Storm Drain).

 At Worthing, Southern Water have been working on a 2 mile long sewage discharge pipeline. Noise produced during the dredging and from chains, cables and anchors could have cause the dolphins to avoid this area. This may have temporarily caused them to stay further west. None of the crew of these vessels noticed any dolphins around the immediate area. The work should be completed by the end of October.

 At Brighton, a storm water tunnel is being built that will enter the sea near Black Rock (west side of the Marina). This project commenced in May 1993. The tunnel is being constructed to divert sewage from flowing into the sea from existing storm water outlets. The sound of the work can be heard at least half a mile away. The sound would travel much further through water and this could cause the dolphins to avoid this area. It will be interesting to see if the dolphins return next year after the work is completed.

1993 Sightings Records

The lack of sightings from June onwards has been confirmed by the Beach Superintendent from Hove. This year, neither they or the lifeguards have observed cetaceans since May, and the Brighton observers also reported no observations.
 Fishing vessels inshore could also cause dolphins to avoid the area.  I only started monitoring fishing vessels this year, so I have no past records to compare observations. However, it is a basis of study in future years. The fishing boats I have observed this year have been present close to the shore when conditions have been for inshore movements of cetaceans, based on past observations. Dolphins were sighted on a few occasions in May (consistent with past records 1991-2), after which sightings suddenly ceased. It is hoped that the work undertaken by Southern Water has caused a temporary change in the dolphin movements.

  •  We will continue to monitor coastal vessels during 1994, as well as the rise and fall of the sea temperature throughout the year. We will plot the dolphin sightings against the sea temperature and weather conditions. 

  • For enquiries and survey forms please write to:

    Steve Savage
    Sea Watch Foundation
     (Sussex Area)
    51 Eastbrook Road
    Portslade
    East Sussex.
    BN4 1LN
    Tel: 01273 424339

    Steve Savage previously worked at Brighton Aquarium & Dolphinarium and is the author of the book "Endangered Species - Dolphins & Whales".

    Cetacean Page
    Cetaceans in British Seas
    SEAQUEST SW REPORTS
    Sussex Dolphins 1998
    Sussex Dolphins 1999

    Sussex Cetaceans 2001
    Sussex Sea Watch Foundation News 2001
     

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