Abstract
Swimming trajectories of Calanus euxinus Hulsemann in the Black Sea were studied using an echosounder at 120 and 200 kHz. C. euxinus were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. Species became torpid in water with DO values <0.5 mg l−1. The time spent swimming under DO conditions between 2 and 5 mg l−1 was insignificant, and varied greatly from the 10% to 25% of total time spent swimming under normoxic conditions (5–10 mg l−1). C. euxinus formed a concentration layer in the water of 1–3 m thickness. Upward migration was completed in about 3.5 h, starting 2.5 h before and ending 1 h after sunset (average rate: 0.95 cm s−1) in summer. Species ascended discretely from the suboxic to the lower boundry of the cold intermediate layer (CIL) at 0.82 cm s−1, and passed up the CIL and thermocline fast (2.3 cm s−1). Downward migration took less time (2 h), starting ~1 h before and ending ~1 h after sunrise. Swimming speed within the thermocline and CIL was 2.7 cm s−1; copepods subsequently returned to daylight depth at a sinking speed of 0.57 cm s−1. Total time for C. euxinus to settle to their nocturnal depth layer was about 5 h.
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Acknowledgements
This work was carried out within the NATO TU-Fisheries and Black Sea projects; the IMS-METU was funded by the Scientific and Technical Research Council of Turkey (TUBITAK), by the Scientific Affairs Division of NATO as part of the Science for Stability program, and by a project (METU-AFP-99-06-01-01) linked with other programs of TUBITAK/Turkey and NATO-SfP. The hydrographical data were obtained from the Physical and Chemical Oceanography Dept. of the IMS-METU. I thank the crew of R.V. "Bilim" for assistance at sea.
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Communicated by O. Kinne, Oldendorf/Luhe
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Mutlu, E. Acoustical identification of the concentration layer of a copepod species, Calanus euxinus . Marine Biology 142, 517–523 (2003). https://doi.org/10.1007/s00227-002-0986-3
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DOI: https://doi.org/10.1007/s00227-002-0986-3