Harbour Porpoise And Seabird Survey At Point Lynas Biology Essay

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Harbour porpoises (Phocoena phocoena) have short, bodies and are the smallest size group of Cetaceans; adult female harbour porpoises reach 160cm and males slightly smaller at 145cm. Mean mass is 60 kg and 50 kg, respectively (Bjorge and Tolley, 2009). They are grey in colour, dark at the top  graduating to a light belly and have a dark grey stripe which runs from mouth to flipper on either side of the body. The  dorsal fin is small and triangular and its characteristic swimming pattern has several short, rapid surfacings, moving with a wheel-like motion through the water, followed by an extended dive of several minutes.  It is limited in distribution to the continental shelves in cool temperate and subpolar waters of the Northern Hemisphere (Jefferson et al. 1993. Goodwin and Speedie, 2007).

Harbour porpoises (Phocoena phocoena) along with other cetaceans face many threats to their coastal habitats. Overfishing, pollution, climate change and human activities all impact on the life and environment of the harbour porpoise. For this reason this species is listed in Annex 2 of the Habitats Directive as a species that warrants the designation of Special Areas of Conservation for its protection. However, identifying significant areas of the marine environment that could serve to protect this sparcely distributed mobile species is not an easy task. Distribution and abundance data of populations is important for conservation of the species. However, collection of  data presents many problems due to the complexity of coastal habitats (Dawson et al., 2008).  Populations can vary in size and distribution over time for a number of different reasons. Monitoring spatial and temporal variations in abundance and  identifying the causes for  any changes are very important if  conservation is to be achieved. 

Point Lynas in Anglesey, North Wales has been identified as an important foraging habitat for harbour porpoises (Weare, 2003). Here high tidal streams help to aggregate prey. This attracts seabirds and harbour porpoises. (Shucksmith et al., 2009).

 

Aims:

To conduct a survey off Point Lynas in order to asses the abundance and distribution of harbour porpoise and record the bird speces associated with the coastal environment in this area.

Methods:

Visual surveys from boats have the advantage of being able to cover areas further from the coast and have the potential for close encounters with the observed species. However, horizons are limited by the elevation of the boat as well as weather conditions and sea state. Observations are generally conducted from the highest convenient vantage point on the vessel which can be variable and need to be planned to take in the whole horizon. Scanning can be predominantly conducted with the naked eye. for first sightings of single individuals or a group of animals, and binoculars (7x50) can be used to clarify identification, groups or behaviours in the same way as land based scans. A logical sequence of watches varying the observations can be rotated for example every 30 minutes. The bearing and heading of animals can be recorded in relation to the vessel using angle boards mounted at each observation station, a hand bearing compass or binoculars with an internal reticule Environmental data such as sea state (Beaufort scale), swell height (m), visibility (poor -excellent), cloud cover and precipitation (none - heavy) is generally recorded and updated as it changes. The presence, number and type of other vessels in the vicinity are also generally recorded and updated as they change.

 

Line transect surveys represent one of the most common and efficient way of estimating cetacean population abundance (Dawson et al 2008). Surveys can be designed  to maximize  cover over depth and slope gradients, as these sort of features are considered to be important in influencing distribution (Thomas and Williams, 2007).The primary data required for estimating the abundance of cetaceans using line transect sampling are the extent of the searched distance along the transect and the perpendicular distance to and size of each detected school of the target species. In visual shipboard surveys, perpendicular distance is usually calculated from radial sighting distance and angle. In addition, other important variables such as sea state, sun glare and visibility are collected and later incorporated as parameters affecting the detectability function for the species. Detection rates are  optimal in summer when the weather can be more favourable for observation but seasonality may effect actual distributions that are not reflected in detection rates. The idea behind line transect sampling is to estimate the density of the target species in strips sampled by surveying along a series of transects, and to extrapolate this density to the entire survey area. The calculated number is therefore an estimate of abundance in a defined area at a particular time.

The porpoise survey was undertaken on 27th April 2009.Weather conditions were Beaufort 2-3 occasionally 4 with visibility moderate to excellent. There was no swell and  boat speed was 6-13 knots. Effort was increased to maximise possible sightings by zigzaging around Lynas point. This should be more efficient in estimating densities (Palka and Pollard, 1999). Transects sampled deep and shallow water from 5m to 32m.

The bird survey was made on the cliffs in the same area on 7 May 2010. The weather conditions were good visibility, no precipitation, Beaufort 5-6. Birds were observed with the naked eye, binoculars and bird watching telescope.

Results

Total number of porpoises sighted were approximately 17 over the 4 hours 20 minutes survey. There were two groups of 3, a group of 5 and two sighted individually. All were reported to be adults.

Non parametric Spearman Rank Correlation of porpoise sightings per unit effort with tidal heights showed no significant correlation.

Table 1 Bird sightings 7 May 2010

Species

Number

Vernacular

Scientific

Shag

Phalacrocorax aristotelis

15

Chough

Pyrrhocorax pyrrhocorax

2

Black Guillemot

Cepphus grylle

1

Northern Fulmar

Fulmarus glacialis

1

Lesser Black Backed Gull

Larus fuscus

4

Great Black Backed Gull

Larus marinus

3

Herring Gull

Larus argentatus

53

Northern Wheatear

Oenanthe oenanthe

2

Sandwich Tern

Sterna sandvicensis

3

Arctic Tern

Sterna paradisaea

1

Oystercatcher

Haematopus ostralegus

3

Northern Gannet

Sula bassana

25

Kittiwake

Rissa tridactyla

3

Razorbill

Alca torda

1

Discussion

Distribution and diving behavior provides direct information on where porpoises feed (Otani et al. 2000). Most of the porpoises were seen around high water when the tide was fairly slack and starting to set in a westerly direction and four were seen around slack water when the tide has a very slight easterly set between 0.2 and 0.3knots. They were probably foraging. Most were diving in approximately 30m of water. One was in 5m and three were between 10 and 20m.  Johnson et al. (2005) using time-depth recorders attatched to harbour porpoises in the Bay of Fundy recorded foraging behaviour that was characterized by "flat-bottomed" dives with around one-third of the dive time being bottom time, which would be consistent with foraging at the sea bed.  Pierpoint et al. (1999) using acoustic data loggers, recorded  harbour porpoise echolocation activity on the Welsh coast and found that  activity was highest during the ebb tide and at night. Preference for foraging in areas of high tidal stream and during high tide  has been recognised in north west Scotland (Marubini, 2009).

The life history of harbour porpoises is unique among cetaceans in having a very short nursing period (generally less than one year). They attain  sexual maturity  at around the age of three years and there is a very short resting period between pregnancies, with females often giving birth each year. Females can often be pregnant and lactating at the same time. (Read et al. 1997).  This factor combined with their cold water habitat imposes high energy demands and  their small size means that they cannot store as much reserves as other cetaceans  making them particularly dependent on a year-round proximity to food sources (Santos and Pierce, 2003).

Harbour porpoises eat a wide variety of fish and cephalopods, and the main prey items vary on regional and seasonal scales (Jefferson et al. 1993, Reyes, 1991). However, porpoises in any one area tend to have a diet of two to four main species for example whiting Merlangius merlangus and sandeels Ammodytidae in Scottish waters  (Macleod. et al 2006) Individual items of prey range in length from 10cm to 30cm and are mostly less than 40cm and are probably taken on or close to the seabed (Santos and Pierce, 2003). Large scale fisheries operating in the North Sea have depleted herring stocks and still target species  such as whiting which are important prey items for harbour porpoises. In targeting the same species as fishermen the harbour porpoise are brought into contact with the threat of fishing nets which can have serious impacts on the species (Northridge and Hammond 1999). In the northeast Atlantic anthropogenic effects of over-fishing may have produced  a longterm shift from a diet of clupeid fish, mainly herring Clupea harengus to sandeels and gadoid fish (Santos et al 2004). Stable isotope data from harbour porpoise tissues collected in the North Sea indicates that they are now feeding at a lower trophic level than during the last century (Christensen et al. 2008).  Changes in prey can alter the nutritional quality of the diet  and could subsequently have consequences for population status.

Gannets, sula bassana, feeding offshore from the cliffs suggest shoals of small fish are present in the area such as are prey for harbour porpoises. The importance of sandeel in harbour porpoise diets

is shared with a large range of other predators, for example, whiting (Daan 1989) which is also an important prey species of the harbour porpoise. Bird species which prey on sandeels include Arctic tern Sterna paradisaea and Sandwich tern Sterna sandvicensis (Monaghan et al. 1989), puffins Fratercula arctica, guillemots Uria aalge, razorbills Alca torda (Harris & Riddiford 1989), kittiwakes, Alca torda (Furness 1987), shags Phalacrocorax aristotelis (Harris & Wanless 1991) and black guillimots, Cepphus grylle (Ewins, 1990). The bird survey identified the presence of Sterna paradisaea, Sterna sandvicensis, Uria aalge, Alca torda, Phalacrocorax aristotelis and Cepphus grylle in this coastal habitat. Alththough adults of  most of these birds consume a variety of fish and some invertebrates, sandeels are particularly important in feeding their young. Their presence in the area at this time of year suggests the presence of sandeels.

Climate change is known to negatively effect sandeel populations. Porpoise diets from spring 2002 and 2003  in Scotland were compared to baseline data from 1993-2001. During the spring of 2002 and 2003 the diet was found to be substantially different, with a significant and much smaller proportion of sandeels being consumed and during this time 33% of dead, washed up porpoises died of starvation  compared to only 5% during the baseline period. (MacLeod et al. 2007)

Negative effects of pollution in the form of persistent organic contaminants in food sources can also have serious impacts on harbour porpoise populations(Santos et al. 200). Pesticides, plasticisers, trace metals and flame retardants such as PBDEs BPA and HBCD accumulate to harmful levels in predators at the top of the food chain. This can negatively effect reproduction rates (Borjesson  and Read, 2003). Contaminant levels in harbour porpoises often vary geographically and as well as being potentially harmful to the porpoise may serve as useful markers in studies of population structure (Koschinski, 2002).These and genetic analysis has demonstrated limited low level connection of harbour porpoises across the Atlantic  and  harbour porpoises from West Greenland, the Norwegian West coast, Ireland, the British North Sea, the Danish North Sea and the inland waters of Denmark  are all genetically distinguishable from each other (Andersen et al. 2001). Because of this limited connectivity betweeen groups of harbour porpoise it is particularly important to monitor distribution and abundance with the aim of conserving all of these groups.

The anthropogenic affects of increased shipping traffic and associated sonar, marine exploration and the construction of offshore wind farms have noise levels which are a potential  threat to harbour porpoises and may  affect the behaviour and distribution of the species.(Koschinski et al. 2003). 

Identification and monitoring of  high-use, important habitats such as the waters off Lynas Point is necessary for conservation management. However. limiting conservation efforts within a small spatial area which is not representative of the total foraging movements does not give a complete picture and it is important to understand the extent of individual porpoise movements in UK waters possibly through telemetry (Evans et al 1969).

Around Anglesey the most likely sources of disturbance are recreational activities and increased development of  wind farms. Recreational activities increase during the summer months. This coincides with the harbour porpoise calving/breeding season which extends from May  to  September (Borjesson & Read, 2003).

The limitations of this particular survey are that it took place over a very short period of time and as such is only a snapshot of harbour porpoise activity in this area. The data would need to be combined with other surveys to produce a long term data set which could be used to more accurately monitor adundance and any changes. Status of harbour porpoise in British waters needs to be monitored carefully to asses the impacts of anthopogenic affects (Parsons et al, 2006, Hammond et al 2002 Evans and Wang, 2002). Interpretation of long term data for for the area could be used in developing management strategies to give protection at critical times of the year and identify and protect sensitive areas for harbour porpoise survival such as feeding grounds and calving or nursery areas.

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