Orientation and navigation of harbour seals (Phoca vitulina concolor) in their overland migrations on Sable Island

• Main Author: Renouf, Deane
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1972
• Subjects: Departure Point; Phoca vitulina
• Online Access: https://research.library.mun.ca/7194/; https://research.library.mun.ca/7194/1/Renouf_Deane.pdf; https://research.library.mun.ca/7194/3/Renouf_Deane.pdf

During the spring and summer months on Sable Island, Nova Scotia, about 10% of the 1200 Harbour seals (Phoca vitulina) which are resident on the Island at this time, regularly migrates between the sea and three inland lakes. This necessitates an overland journey of often ½ mile or more, one which is undertaken by adult seals, and by newly weaned pups which have been born on the lakes and move to the sea for the first time. The results of the investigations described in this thesis enabled the following conclusions to be drawn about the nature of the overland journeys, and the orienting abilities of these Harbour seals in guiding themselves to the lakes and back to sea. -- (1) Both seabound and lakebound crossings were usually undertaken at sunrise and sunset. The peak number of crossings seemed to coincide with the pupping season in May and June, and the moult in late July. -- (2) The approximate bearing of the shortest path between the lake and the sea is 204°, and the average bearing adopted by seabound adult seals was 202°. The lakebound adults did not necessarily cross on a bearing which was perpendicular to the coast; they did, however, tend to take the shortest path between the point where they had hauled out on the coast, and the lake. The variability of the lakebound tracks did not differ from that of those heading toward the sea. -- (3) The journeys of both adults and pups were not impaired by either visibility being reduced to less than 100 yards in fog which completely obscured all landmarks, or by a 100% cloud cover, which, for the human observer, made the sun impossible to locate. -- (4) Many animals, both adult and newly weaned, having aborted their journeys, sometimes after having travelled more than 3/4 the way, were able to return to their exact departure point. Some did so when visibility was 1/4 mile or less. -- (5) There was no clear relationship between wind direction and the courses adopted by seals either spontaneously crossing between lake and sea, or travelling after having been ...