Variation in Foraging Behaviour of Harbour Seals at the Antarctic - Coursework Example

VARIATION IN FORAGING BEHAVIOUR OF HARBOUR SEALS (PHOCA VITULINA VITULINA) AT THE ANTARCTIC. Lecturer Variation in Foraging Behaviour of Harbour Seals (Phoca vitulina vitulina) at the Antarctic. Introduction Harbour seals are one of the most widely distributed species of the seals. They are to be found in the temperate as well as the subarctic coastal areas within the north Atlantic and the north pacific areas (Thompson and Harkonen, 2008) which also include the coast of Antarctic. According to the Seal conservation Society (2011), there are five known species of the harbor seal which include the eastern Atlantic harbour seal (Phoca vitulina vitulina), the western Atlantic harbor seal (Phoca vitulina concolor), Ungawa seal (Phoca vitulina mellonae), the eastern Pacific harbour seal (Phoca vitulina richardii) and western Pacific harbor seal (Phoca vitulina stejnegeri). Antarctic is one of the coldest and driest places on earth and it is estimated to contain almost 90 per cent of the earth’s ice. Harbour Seals is just one of the many types of seals living in the Antarctic. Others include the Weddel seals, Southern Fur seal, South Elephant Seal and the Crabeater seal. Harbour seals like living in shallow waters from where the haul-out to rest on the beach. Brasseur et al. (1996) observes that harbour seals are opportunistic predators and primarily consume bottom dwelling and schooling prey. All that said, adult seals eat molluscs, crustaceans, octopus, squid and a variety of fish such as hake, salmon, herring, perch and rockfish (Hall, Watkins, and Hamond, 1998 and Fichter, 1990). The diet of the harbour seal tends to vary with food availability and the region and thus seal from different areas are likely to show a significant difference depending on the season and abundance of prey (Fichter, 1990; Payne and Selzer, 1989 and Olesiuk, 1993). Sharples et al. (2012) notes that these variations in region and season also largely impacts on foraging behavior and movements as the seals move to obtain their prey. Data on the exact population of seals is hard to come by but various reports agree that the population of seals across the world is declining though the main cause of this decline remains largely unknown (Thompson and Harkonen, 2008). However, there is a possibility that changes within the foraging areas brought by the warming of climate and industrial activity may be a likely reason. This study will focus on the foraging areas based on distance from land of the seals within the Antarctic. In this study hypothesize that there will be a difference in distance of sighting of the seals from land. This study also seeks to explore how local habitats and constraints they impose affect the foraging behavior of the seals. Method Data Collection Data for this study was obtained by the Society for Marine Mammology in a study conducted in from November 2001 to October 2006. 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 travelled while foraging, number of days spent foraging and the depth dived. The area of study covered seven sites within the Antarctic 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 seals to outside locations in search of foraging sites. In particular, seals from longer distances compared to animals from other regions under study. Seals tagged at sites A, B and D recorded shortest average distance. Seals tagged at site A had the lowest average distance of 551 m while those tagged at B were second with an average of 847 m. On the other hand, those from sites G and F recorded longer distances on average as they went foraging. Seals tagged at site G recorded 54,231 m while those tagged at F accumulated 10, 632m on average. The difference distances between the highest and the lowest was in excess of 53, 000m, meaning that some seals were very faithful their their forage area and almost never left these areas in the course of the study. Calculating the mean of these distances gives us 10,810 m meaning that seals tagged at G covered more distances as they are the only ones who were above the mean distance covered. Table 1: Showing average distances travelled by tagged seals from different sites Site Average Distance Covered (m) A 551 B 847 C 1,250 D 860 E 7,300 F 10,632 G 54,231 It has to be noted that variability in trip distance cannot be captured by averages alone. In some instances, individual seals made very long distances in search of forage, yet the average from their locality was still low. A good example is site C, where we had some animals making distances of over 8,000 m, yet the average stood at 1250 m. Another example is a female seal tagged at E, travelled from her site to another site outside the study area and in the process accumulated more than 22, 000 m. Still we had a male seal travelling from B where it was tagged and spend several months between site D and another site outside the study area and in the process accumulated more than 7923 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 seals were tagged. Figure 1: Individual maps showing Average Distance Travelled by Harbour Seals in the Antarctic, 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 seals were moving slightly out of the areas in which they were tagged. Trip Duration Apart from distance, the duration of the trips out of location from where the seals were tagged was also looked at in this study. This went hand in hand with the trip distance. Thus, seals tagged at sites E, F and G tended to stay out for longer duration compared to those tagged at AT sites A, B and C who made shorter trips. Average durations ranged from 0.78 at site A to 8.73 days at site G. Another thing to be noted is that there was no significant difference between duration stayed out of the tagging site for both male and female. This in essence rules out gender as a potential determinant to foraging behaviour. At site F, only male seals were tagged, hence the lack of female values for this indicator. Region Trip duration (days)   Male SD Female SD A 0.78 1.87 2.60 3.62 B 1.53 1.60 1.45 1.73 C 2.59 2.60 2.45 1.34 D 1.31 1.51 1.50 1.74 E 3.99 4.25 2.62 3.38 F 5.90 0.97 - - G 8.73 5.33 4.50 5.14 Depth of Water Maximum average depth dived by seals 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, seals that recorded the highest depth were tagged at sites D, F and G. Seals tagged at site G recorded a depth of 163 m while those tagged at D recorded a depth of 102 m. Seals from site A recorded the lowest depth of 33 m while those tagged at site B recorded a depth of 50 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 seals. For example, looking at the difference in distance travelled and foraging duration, seals tagged at sites A, B and D made short foraging trips of between 551 and 860 m within shorter duration. 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. This was further backs up by the fact that those seals who made longer foraging trips of up to 500 km were basically migrating to over-wintering conditions (Lesage, Hammill and Kovacs, 2004; McConnell et al., n.d.). We cannot however deduce that seals foraging trips would largely be determined by the weather patterns given the difference telemetry used in these studies. However, it gives us an indication that such weather seasonal variations may indeed have a bearing to the foraging behaviour of seals. Apart from weather, it should also be noted that there was a large topographical variability between the regions under review. For instance, sites A, B and D were which are very close to the deeper waters while sites E, F and G 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). In most cases therefore, the seals 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. The only glaring exception to this trend is perhaps site C whereby despite the fact that it is a gently sloping areas into the sea, the seals travels a shorter distance with short foraging durations. However, it can be inferred that the suite, being poor in forage, may have had limited number of seals who could be comfortably be supported by the available food resources without the need to travel further (Revilla and Wiegand, 2008). Bibliography 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. Brasseur, S., Creuwels, J., Werf,B. & Reijnders, P. (1996). Deprivation indicates necessity for haul-out in harbor seals. Marine Mammals Science 12(4):P. 619-624. Fichter, G. (1990). Whales and other Marine Mammals. Wisconsin, Golden Press. Hall, A.J., Watkins, J. and Hamond, P.S. (1998). Seasonal variation in the diet of harbour seals in the southwestern North Sea.  Marine Ecology Progress Service 170: p.269–281.  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. Olesiuk P.F. (1993) Annual prey consumption by harbour seals (Phoca vitulina) in the Strait of South Georgia, British Columbia. Fishery Bulletin 91(3):p. 491–515 Payne P.M. & Selzer L.A. (1989) The distribution, abundance and selected prey of the harbor seal, Phoca vitulina concolor, in southern New England. Marine Mammal Science 5: p.173–192. 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. Revilla E, Wiegand T. (2008) Individual movement behaviour, matrix heterogeneity, and the dynamics of spatially structured populations. Proceedings of the National Academy of Sciences of the United States of America 105: p.19120–19125. Seal conservation Society (2011). Harbour Seal. Available from http://www.pinnipeds.org/seal-information/species-information-pages/the-phocid-seals/harbour-seal [Accessed November 16, 2014]. Sharples R.J, Moss S.E, Patterson T.A & Hammond P.S. (2012).Spatial Variation in Foraging Behaviour of a Marine Top Predator (Phoca vitulina) Determined by a Large-Scale Satellite Tagging Program. PLoS ONE 7(5): p.3721- 3771 Vincent C., McConnell B., Delayat S, Elder J. & Gautier G (n.d.) Winter habitat use of harbour seals (Phoca vitulina) fitted with Fastloc GPS/GSM tags in two tidal bays in France. NAMMCO Scientific Publications Read More