Variation in Foraging Behaviour of Sperm Whales - Essay Example

VARIATION IN FORAGING BEHAVIOUR OF SPERM WHALES (PHYSETER MACROCEPHALUS) IN SCOTLAND Lecturer Variation in Foraging Behaviour of Sperm Whales (Physeter Macrocephalus) In Scotland Introduction Scotland is one of the regions making up the United Kingdom. Others are the United Kingdom, Wales and Ireland. Scotland itself is an Ireland with a long coastline. Besides, it lies within the European continental shelf with two oceans meeting at its coasts. These are the Atlantic Ocean to its west and the North Sea to its east. The Scottish coast, estimated to be roughly less than 12,000 km, is rich in flora and fauna. It boasts of a number of whale types such as the Minke whale and the Humpback whale which are the majority and easy to site (Whitehead, 1996). Other whale types which do exist but are area to site include the sperm whale, killer whale and the fin whale. Sperm whales are famous for their massive heads and rounded foreheads. It is believed that they are rare because of intense hunting. However, data on the exact population of whales at the Scottish coast is hard to come by given that little research has been carried out to estimate their numbers (Clark, 1997). Some of the reasons for this state of affairs are the little research which has been carried specifically on this marine mammal. This may be explained by the fact that the United States has been keen to end the practice of whaling which kills whales for the sake of it. Therefore, a lot of research on whales has tended to be in waters around where the practice is prevalent such as Japan (Au, 2003; Griffin, 1998; Elnser, 1999). Industrialization and development around the Scottish coast is believed to have significantly led to the pollution of waters around the coast, compromising the quality of ecosystems these whales enjoy. This is because uncontrolled dumping of waste into the sea has negative effects on the environment, affecting the food chain in the process. Human activity along the coast has been increasing over the decades, increasing the frequencies with which accidents involving whales and other marine animals attack people. Sperm whales are known to dive to deeper levels in search of food. Even though their environment might have been affected, it is expected that still some would be around, assuming that their deeper diving can compensate for the declining food supply due to pollution. This is because pollution starves the plants and other marine animals such as fishes and seals fed on by the sperm whales of the oxygen and other nutrients needed for their nourishment (Elsner, 1999). Essentially this means that the whales are likely to have faced a drop in their food supplies. On the other part, such levels of pollution also have the effect of making the ecosystem for the whale untenable, forcing them to move to safer areas. Otherwise, ingestion of contaminated water with industrial effluent may lead to incapacitation and even deaths of the animals. It is thus expected that the sperm whales could also move look for better quantities of food further away from the polluted zones (Foote, 2011). These movements out of polluted zones of the Scottish coast will essentially have the impact of affecting the frequency of the sighting of the whales. Elnser (1999) observes that the whales, just like any other aquatic animal feed under water. This means that they only come on the surface to breathe and strategies on how to dive again with better precision so that they get food in better quantities. Therefore, Ellis (1999) notes that the diving of the whales, and the duration within which they remain under water is very key in determining the quantities of the food eaten by the whale. Incidentally, this also requires a lot of strategy on the part of the whale especially given that other organizations eaten by the whales such as fishes are also in motion and running away from the whales to save their lives. This paper is going to focus on the foraging behavior of the sperm whales especially with regard to changes taking place around the Scottish coast. As noted earlier, the foraging areas are undergoing changes chiefly because of the the pollution from industrial activity. Another factor must be the climate change which is believed to be making the coast warmer and altering the traditional supply of food to the whales. Some varieties of plants and animals are declining in supply or disappearing while others are appearing or supply is increasing. This study will focus on the foraging areas based on distance from land of the sperm whales along the coast of Scotland. This study hypothesize that there will be a difference in distance of sighting of the whales from land. This study also seeks to explore how local habitats and constraints they impose affect the foraging behavior of the Sperm whales. Method Data Collection Data for this study was obtained by the Society for Marine Mammology in a study conducted in from October 2010 to November 2011. This data was collected through the use of satellite tagging technology. This data comes from various studies done of the tagged animals such as the distance covered while foraging, number of days spent foraging and the depth dived. The area of study covered four sites within the Scottish coast which were chosen based on factors such as depth, nearness to deep waters, presence of rocks and gradient into the sea. The data set called Regional trip distance and duration by sex was downloaded from the Public Library of Science Website (Plusone.org). Spatial Analysis The data derived was exported into the the ArcGIS to be analyzed. The first task was to plot the data using its specific coordinates in terms of longitudes and latitudes. On the ArcGIS, this was done by the option ‘Select Display XY data’ tool. The Euclidean distance tool was then used to divide the distance measured from the shore into ten equal intervals, with each range being assigned a different colour. This was done so that they could easily be distinguished. This made it easy to extract the distances for each sighting made from coastline and convert them into meters. Values obtained above were then imported into the SPSS software for purposes of carrying out a number of tests to be carried out. The first test was done to establish whether the data obtained fulfilled the criteria for a parametric test. To do this, a test of normality was done by the use of a shapiro-wilk test. Results Distance Travelled There were significant disparities in terms of distances travelled by the whales to outside locations in search of foraging sites. In particular, whales tagged at sites A, B and D recorded longest average distance. Whales tagged at point A had an average distance of 5703 m. Those tagged at point B had an average of 10,982 m while those tagged at point D had an average of 7327 m. Whales tagged at point C had the shortest average distance of 250 m. The difference in distances between the highest and the lowest was in excess of 9,000m, meaning that some whales were very faithful their their forage area and almost never left these areas in the course of the study. Looking at the means of the distances travelled by the whales in search of food, it is important to note that whale from site B and D covered longest distances, above the means score. Table 1: Showing average distances travelled by Sperm Whales from different sites It has to be noted that variability in trip distance cannot be captured by averages alone. In some instances, individual whales made very long distances in search of forage, yet the average from their locality was still low. A good example is site D, where we had some animals making distances of over 15,000 m, yet its average stood at 7,327 m. Another example is a bull tagged at A, travelled from his site to another site outside the study area and in the process accumulated more than 20, 000 m. The maps below shows the distances covered by various seals under the study plotted. The distances were measured from the shore at locations where the whales were tagged. Figure 1: Individual maps showing Average Distance Travelled by Sperm Whales in the Scottish coast, measured with equal distance intervals dividing the distances from shore (Bands 1 – 10). Distance (Metres) Antarctica Band 1 - 0 - 160,000 From the individual performance, it is clear that most seals are falling between the second and fifth band. Hence, most of the whales were moving slightly out of the areas in which they were tagged. Number of Sightings Apart from distance, the whales were also observed with regards to the sighting. The sighting of whales was done at all the four locations. There were more sightings of whales at site A compared to other locations. With 156 sightings, site A had almost twice the number of sightings made at site C which was the second location with 72. There were also 58 sightings at site D compared to 34 sightings at B. The sighting of whales in site A was important because it may be an indication of the popularity of the place, may be due to the amount of food, necessary to support the huge population. The low numbers of sighting at B is an indication of low numbers of whales at this site. Depth of Dive Maximum average depth dived by whales within the duration of the trip was also observed. This was computed by looking at the various bands and depth dived within those bands. On this indicator, whales that recorded the highest depth were tagged at sites A, B and D. Whales tagged at site C recorded an average depth of 82 m while those tagged at A dived a depth of 153 m. Whales tagged at D recorded an averaged dived length of 147 m while those tagged at B dived a depth of 164 m. Discussion One strong indicator coming out of the results of the study is that there exist strong differences in the regions in terms of the foraging behavior of the whales. For example, looking at the difference in distance travelled and foraging duration, whales tagged at sites A, B and D made longer foraging trips of between 5,703m and 10,982m. At C, shorter foraging durations were noted. This result is consistent to a different study carried out in both Canada at St. Lawrence River estuary also noted shorter foraging durations (Lesage, Hammill and Kovacs, 2004). In that study, the shorter foraging trips were linked to the wintering conditions. However, in this specific case, whales travelling for long distance show that the area where they were tagged is lacking in food and thus the need why the whales have to cover longer distances. This is conceivable due to increased pollution of the coast in the recent past. Given that whales are presumed to eat as they travel (Whitehead, 1996; Jones, 2013), the longer the distance means the more food searched and maybe eaten. Apart from weather, it should also be noted that there was a large topographical variability between the regions under review. For instance, site C is very close to the deeper waters while sites A, B and D were shallow but gently sloping into the sea. Animals in rocky areas but with close proximity to the sea tended to have shorter foraging trips and shorter durations compared to those from shallow undulating regions. A probable explanation may be that rocky areas are likely to provide prey with some sort of refuge thus slowing down the rate of depletion (Reder and Lydersen, 2003; Clark, 2009). In most cases therefore, the whales will have enough to eat and therefore there may be no need to travel further to look for food. This means that those seals from shallow gently sloping topography would need to travel further so as to get sufficiently productive areas to forage (Baxter, 2001) and in the process their trips also take longer durations. Another factor to consider is the depth dived by the whale. Deeper dividing as noted at sites A, B and D may be taken to mean that the area has less food resources (Berzin, 2010; Norton & Lucy, 2012). This therefore necessitates deeper diving so as to get more food resources to sustain the whales. Shallow diving is an indication of ample food supply. When food can easily be accessed on the surface, then there is no need to dive to deeper ends of the sea. On the other hand, it can be argued that this is not a conclusive evidence as the depth dived may be a factor of other things. For instance, a whale may dive in search of a particular food resource. This way, deeper diving is not an indication of lack of food at the surface (Butler, 2004). References Au, W. (2003). The Sonar Dolphins. New York: Springer- Verlag Inc. Baxter J.M. (2001) Establishing management schemes on marine special areas of conservation in Scotland. Aquatic Conservation: Marine and Freshwater Ecosystems 11(2) p. 261–265. Berzin, A. (2010). The Sperm Whale. Jerusalem: Israel Program for Scientific Translation. Butler, P. J. (2004). Metabolic Regulation in Diving Birds and Mammals. Respiratory Physiology and Neurobiology , 297-315. Clark, M. R. (2009). Observation on Sperm Whale Diving. Journal of Marine Biology Association in U.K , 809-810. Clark, R. (1997). Marine Pollution. Oxford: Clarendon Press. Durban, J., & Pitman, L. (2011). Antartic Killer Whales make Rapid, Round Trip Movements to Subtropical Waters: Evidence for Physiological Maintenance Migrations? Biology Letters , 8 (2), 274-277. Ellis, R. (1999). Whales and Porpoises. New York: Alfred A. Knopf. Elsner, R. (1999). Living in Water: Solutions to Physiological Problems. In J. E. Reynolds, & S. Rommel, Biology of Marine Mammals. (pp. 73-116). Washington: Smithsonian Institution Press. Foote, A. (2011). North Atlantic Killer Whales. The Top Top Predator , Journal of American Cetacean Society. Griffin, D. (1998). Listening in the Dark. Ithaca: Cornell University Press. Jones, E. (2013). Whale Shark Sightings Summary. Retrieved December 2, 2014, from http://www.usm.edu/gcrl/whaleshark/sightings_summary.php Lesage V., Hammill M.O. & Kovacs K.M. (2004) Long-distance movements of harbour seals (Phoca vitulina) from a seasonally ice-covered area, the St. Lawrence River estuary, Canada. Canadian journal of zoology 82 p.1070–1081. Norton .D, J., & Lucy, D. (2012). Vocal Behaviour of Male Sperm Whales; Why do they Click. Journal of the Acoustical Society of America , 2254-2259. Reder S.& Lydersen C., (2003) Haul out behaviour of High Arctic harbour seals (Phoca vitulina vitulina) in Svalbard, Norway. Polar Biology 27:p. 6–16. Whitehead H. (1996). Variation in the Feeding Success of Sperm Whales: Temporal Scale, Spatial Scale and Relationship to Migrations. The Journal of Animal Ecology, 65 (4), pp. 429-438 Read More