Kd. Friedland et al., Open-ocean orientation and return migration routes of chum salmon based ontemperature data from data storage tags, MAR ECOL-PR, 216, 2001, pp. 235-252
Temperature data storage tags were applied to maturing chum salmon Oncorhyn
chus keta in the Bering Sea during summer 1998, 5 of which were recovered i
n the coastal waters around Japan. These tags recorded water temperatures e
xperienced by the fish for periods of 62 to 118 d at resolutions of 15 to 3
0 min, We considered fine-scale aspects of the data by analyzing diel tempe
rature patterns in regard to the migration behavior and orientation of the
fish. During the night, temperatures experienced by the fish changed little
, and were among the highest temperatures experienced whereas daytime tempe
ratures often showed dramatic changes as the fish changed depth. We analyze
d a time series of temperature differences between sunrise and sunset as an
indication of progress made by the fish against horizontal thermal gradien
ts, which was assumed to represent changes in latitudinal position. Daytime
differences were positive when the fish were migrating to warmer waters, w
hereas night-time differences were zero or slightly negative, This suggests
that the fish made more progress migrating during the day than at night. W
e also considered large-scale aspects by examining oceanographic data in re
lation to the temperatures recorded by the tags. Analysis of possible migra
tion routes based on large-scale patterns of sea surface temperature distri
butions suggests that zonal (east-west) routes are preferred. These data su
pport the hypothesis that chum salmon utilize orientation cues associated w
ith the sun during open ocean migration. However, whether salmon also utili
ze additional orientation or navigation mechanisms remains to be determined
.