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

Renouf, Deane (1972) Orientation and navigation of harbour seals (Phoca vitulina concolor) in their overland migrations on Sable Island. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (7MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

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 displaced. -- (6) Zastruga, often prominent on the sandy plain separating the lakes from the sea, were not a necessary cue for the seals' orientation. -- (7) Adults which were captured enroute to one of the lakes, and displaced 1500 yards to the east or west, either went to the sea upon release, or corrected for their displacement and continued their journey to the lake. This correction was made in the absence of landmarks, and did not appear to be related to sun and wind conditions. -- (8) The provenance of the sound of the surf did not appear to be related to the initial heading or to the bearing which a seal maintained during a spontaneous crossing. However, two adults which were relocated, and travelled to the lake upon release, may have been maintaining a bearing by listening to the sound of the surf. Weaners which were released at various points around Sable Island appeared to home on the sound of the surf when they were set free under unusually confined conditions. -- The results of a T maze experiment, in which pups were given a choice between approaching and avoiding surf noise are discussed. The limitations imposed by field conditions are set forth, and suggestions for future research are made.

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