. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 140 J. J. C. ROSENTHAL AND F. BEZANILLA A. 20 mV = 210us •' ms B (Q-F-cm) a 5 10 15 20 Temperature (C) 25 Figure 5. Product of resistance and capacitance changes seasonally. (A) Example of measurement. Dotted line is an action potential recorded at 10°C from a May axon; solid line is an exponential tit to the action potential foot. (B) Values of (/?, + Rt.)Cm vs. temperature for May (tilled triangles) and August (open triangles) axons. See text for derivation of (/?, + KelCm. Error
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 140 J. J. C. ROSENTHAL AND F. BEZANILLA A. 20 mV = 210us •' ms B (Q-F-cm) a 5 10 15 20 Temperature (C) 25 Figure 5. Product of resistance and capacitance changes seasonally. (A) Example of measurement. Dotted line is an action potential recorded at 10°C from a May axon; solid line is an exponential tit to the action potential foot. (B) Values of (/?, + Rt.)Cm vs. temperature for May (tilled triangles) and August (open triangles) axons. See text for derivation of (/?, + KelCm. Error bars represent the standard error of the mean; n = 6 for May and 5 for August. lower. Schopf (1967) reports the presence of thermoclines and maximum annual bottom-water temperatures of 13°C in the waters off Nantucket. The migration patterns of Loligo pealei are not well understood. On a seasonal basis this species is reported to winter near the break of the continental shelf where it can avoid temperatures below 8°C (Summers, 1969). In the spring these squid move inshore when waters warm past about 10°C (Summers. 1969; Mesnil, 1977). The first group to arrive are the 2-year-olds, normally in early May, fol- lowed by the 1-year-olds in June (Summers, 1971). This sequence of events probably explains the larger diameter of the May axons. Migration on a shorter time scale has not been reported for this species, and therefore it is unknown whether these squid migrate to colder oceanic waters on a daily basis. We consider such a migration unlikely for two reasons. First a substantial horizontal shift would be re- quired to reach deep oceanic waters (depending on the point of departure in Vineyard Sound). Second, the August squid were routinely captured during the day. In other cephalo- pods, daily migrations involve a nocturnal shift to shallow waters (Boyle. 1983; Hanlon and Messenger, 1996). There- fore it is likely that the squid spend a significant portion of their time a
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