MEPS 324:1-17 (2006)  -  doi:10.3354/meps324001

ABSTRACT: Dosidicus gigas is a large and powerful oceanic squid that is economically valuable and ecologically important in the eastern Pacific Ocean. We employed electronic tagging methods to provide the first long-term monitoring of the natural behaviors of D. gigas in its mesopelagic habitat. Seven pop-up satellite tags logged depth and temperature for a total of 842 h, and a conventional archival tag yielded 780 h of continuous time-series data. Horizontal movements of nearly 100 km over 3 d were observed, and these were temporally associated with an established trans-Gulf migration. Squid consistently spent most daylight hours at depths >250 m, the approximate upper boundary of a midwater hypoxic zone termed the oxygen minimum layer (OML). A diel migration brought squid to near-surface waters at dusk, but a highly variable amount of diving back into the OML occurred throughout the night. Rhythmic vertical movements within the OML often occurred, and sojourns of up to 6 h in this hypoxic zone below 300 m were observed. Laboratory experiments revealed a high resting rate of oxygen consumption under normal conditions, but this rate decreased drastically under hypoxic conditions such as would be associated with the OML in nature. These findings suggest that D. gigas has physiological adaptations that permit constant foraging in both oxygenated near-surface waters and within the OML.

KEY WORDS: Squid · Electronic tagging · Oxygen minimum layer · Migration · Diving · Hypoxia · Gulf of California