READ and GASKIN: RADIO TRACKING HARBOR PORPOISES 



study do not support previous contentions that the 

 metaboHc requirements of harbor porpoises (see 

 Kanwisher and Sundnes 1965) are such that in- 

 dividuals must spend a large proportion of each day 

 engaged in foraging behavior (Smith and Gaskin 

 1974; Watson and Gaskin 1983). 



Herbers (1981) has hypothesized that behavioral 

 inactivity is a product of predation efficiency. As 

 predation efficiency increases, less time is spent 

 searching for and capturing prey, and more time is 

 available for other behavior, including inactivity. 

 Therefore, if harbor porpoises are efficient predators, 

 it seems reasonable to suggest that only a small por- 

 tion of their day would be spent engaged in foraging 

 behavior. 



Many other mammalian predators are inactive for 

 large portions of the day. For example, Serengeti 

 lions, Panthera leo, are inactive for about 85% of 

 each day (Schaller 1972). Similarly, spotted hyaenas, 

 Crocuta crocuta, are inactive for 84% of the day 

 (Kruuk 1972). Even the sea otter, Enhydra lutris, 

 with a metabolic rate 2.4 times that predicted for 

 a terrestrial mammal of equal size (Costa and 

 Kooyman 1982), spends only 34% of each day for- 

 aging (Loughlin 1979). 



The ventilation sequences recorded from RT-2 and 

 RT-4 suggest that these harbor porpoises restricted 

 the majority of their activity to daylight and even- 

 ing hours (Tkble 2). If a circadian pattern of activity 

 exists, it may be related to the schooling behavior 

 of prey species. The structure of herring schools 

 breaks down after dusk, as the visual cues used to 

 maintain school structure become inoperative 

 (Brawn 1960). Thus, the fish exhibit a dispersed 

 distribution at night, presumably limiting prey cap- 

 ture by predators such as the harbor porpoises, 

 which rely on dense schools to maintain maximum 

 capture efficiency. 



Other odontocete species exhibit various circadian 

 patterns of activity. Observations of captive bottle- 

 nose dolphins indicate that, like the harbor porpoise, 

 Tursiops is relatively inactive at night (McBride and 

 Hebb 1948; McCormick 1969; Saayman et al. 1973). 

 In contrast, Hawaiian spinner dolphins, Stenella 

 longirostris, rest during the day and feed almost ex- 

 clusively at night (Norris and Dohl 1980). The prey 

 of spinner dolphins undertake extensive vertical 

 migrations (Perrin et al. 1973) and may be more 

 available to the dolphins at night. 



We were interested in observing the nocturnal 

 behavior of harbor porpoises (when they were 

 presumably relatively inactive) under conditions of 

 strong winds and heavy seas, when surface resting 

 was not possible Ventilation data recorded from RT-7 



during a 5-h period (0000-0500, 5 September 1982) 

 of heavy seas consisted almost exclusively of Pattern 

 B sequences. Watson and Gaskin (1983) have sug- 

 gested that this ventilation pattern is expressed 

 primarily by foraging porpoises, but it seems unlikely 

 that RT-7 (a calf) was foraging for 5 consecutive 

 hours at night. An alternative explanation is that the 

 porpoise was resting underwater and rising to the 

 surface for a series of breaths (see similar observa- 

 tions by McBride and Hebb 1948; Layne 1958; 

 McCormick 1969; Condy et al. 1978). It is possible, 

 therefore, that harbor porpoises engaged in diverse 

 behavioral activities may exhibit similar ventilation 

 patterns. 



During the period of reduced activity (from 0000 

 to 0600) radio-tagged porpoises were often located 

 in open water some distance from shore This may 

 reflect a tendency for porpoises to rest in areas 

 where the hazards of swift currents and shallow 

 waters are minimized. Observations made in the in- 

 shore waters of the Deer Island region confirm that 

 porpoises seldom rest at the surface in nearshore 

 environments (Watson and Gaskin 1983). 



ACKNOWLEDGMENTS 



We thank W. Kozak and the members of the Fundy 

 Weir Fishermen Association for their assistance in 

 this study. Sterling field assistance was provided by 

 C. Thomson and members of the Fundy Cetacean 

 and Seabird Research Group. Constructive criticism 

 of earlier versions of this paper were provided by B. 

 Braune, L. Murison, P. Watts, L. White, and two 

 anonymous reviewers. This research was supported 

 by Joint Contract UP-G-152 (Departments of Sup- 

 ply and Services and Fisheries and Ocean Canada). 

 Harbor porpoises were tagged under a permit issued 

 by Fisheries and Oceans Canada. 



LITERATURE CITED 



Amundin, M. 



1974. Functional analysis of the surfacing behaviour in the 

 harbour porpoise, Phocoena phocoena (L.). Z. Saugetierkd. 

 Bd. 39:313-318. 

 Andersen, S., and A. Dziedzic. 



1964. Behaviour patterns of captive harbour porpoise Pho- 

 coena phocoena L. Bull. Inst. Oceanogr. Monaco 63(1316): 

 1-20. 

 Anonymous. 



1982. Canadian tide and current tables. Vol. 1. The Atlantic 

 coast and Bay of Fundy. Department of Fisheries and 

 Oceans Canada, Ottawa. 

 Bailey, W. B., D. G. MacGregor, and H. B. Hachey 



1954. Annual variations in temperature and salinity in the Bay 

 of Fundy. J. Fish. Res. Board Can. 11:32-47. 



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