Underwater sound recordings of the narwhal from northern Baffin Island are analyzed and described. Frequency ranges of pulsed and pure tone vocalizations are found to be somewhat greater than previously observed. An earlier report that narwhals generate exclusively narrowband sounds is confirmed. Narwhal pulses appear to have a potential function as both orientation and communication signals. Pulse series having irregular repetition rates resemble the echolocation clicks of captive delphinids, and it is suggested that they serve a similar purpose. Pulse series having regular changes in repetition rate and distinct aural tones probably serve as social signals. The regular recurrence of a number of recognizably distinct pulsed tones suggests that the narwhal has 'signature' calls similar to several other odontocetes.
An account is given of the known records, distribution and migrations of the smaller Odontocete whales occurring in eastern Canadian waters, with measurements of specimens obtained of the rarer species. The distribution of the abundant pilot whale Globicephala melaena (Traill) has been studied in most detail. The species' summer range includes both the offshore waters of the Labrador Sea and the coastal waters around Newfoundland. The coastal population feeds only on the squid Illex illecebrosus (LeSueur) and its movements inshore in spring and offshore in autumn follow those of the squid over the southwest Grand Bank. In some years a failure of the squid to move shorewards results in a failure of the fisheries for both squid and pilot whales in Newfoundland. The species is known to winter in an oceanic area southeast of the Grand Bank.The white-sided dolphin Lagenorhynchus acutus Gray associates with the pilot whale and apparently inhabits the same climatic zone in these waters, while the white-beaked dolphin L. albirostris Gray is found in somewhat colder waters. The killer whale Grampus orca (L.) migrates northwards in spring along the Newfoundland and Labrador coasts, its migration coinciding with that of the rorquals.New records for the waters of eastern Canada, extending the known range of each, are given for Mesoplodon bidens, Tursiops truncatus, Lagenorhynchus albirostris and Lagenorhynchus acutus.
We have studied the comparative anatomy of arterial plexuses (retia mirabilia) related to supply of the central nervous system in two closely related species of toothed whales - narwhal (Monodon monoceros) and beluga Delphinaterus leucas). In both species, retia originate from major vessels in the neck, thorax, and lumbar regions, then extend into the neural canal and cranium to supply the spinal cord and brain. The system generally consists of arteries embedded in á matrix of fatty connective tissue. Constituent vessels are only occasionally reated to veins or venous sinuses. Though retial anatomy is similar in the two species, there are two related features that appear species specific: (1) amount of retia originating from the supreme intercostal arteries and (2) thoracic retial size. Both are larger in the narwhal, as are values for hematocrit and hemoglobin concentration, which, in this study, we use as indices of diving ability. Our data are consistent with the hypothesis that the retia are in some way linked to diving ability. The nature of this link is not known; however, we discuss our results in the context of the most popular hyotheses of retial function.
The structure of the retina of the harbour seal, Phoca vitulina richardii, is described. It is shown that the retina of the harbour seal is similar to that of the harp seal, in that it shows little zonation of the inner nuclear layer, possesses large horizontal cells, and has similar nuclear densities within the different retinal layers throughout the retina. The outer nuclear layer is also the thickest of all the retinal layers. Two types of photoreceptor cell, types B and C, were observed with a ratio of roughly 1:23 respectively. This ratio, along with a well-developed and extensive tapetum, indicates a highly light-sensitive retina. The existence of retinal folding in marine mammals is also questioned and discussed.
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