The ascent migration of Calanus finmarchicus from overwintering depths in the Faroe–Shetland Channel

• Published in: Fisheries Oceanography
• Main Author: Heath, M.R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1999
• Subjects: Arctic; Norwegian Sea; Calanus finmarchicus; North East Atlantic; Copepods
• Online Access: http://dx.doi.org/10.1046/j.1365-2419.1999.00013.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-2419.1999.00013.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2419.1999.00013.x

The Faroe–Shetland Channel is an important overwintering area for the copepod Calanus finmarchicus in the north‐east Atlantic. Stage V copepodites descend to depths of greater than 600 m, where they remain in an arrested development state (diapause) until the following spring. The ascent of the copepods back to the surface waters in the spring was investigated by six surveys in the Faroe–Shetland Channel between October 1993 and May 1995. In February, the first animals emerged from diapause and moulted to become stage VI males; these ascended to depths of 300–500 m. Females constituted a higher proportion of animals that emerged later in the season and these ascended through the layer of males, presumably mating on the way, and proceeded to the upper 100 m to begin spawning in March. Emergence was not synchronous in the population, and was estimated to occur over a 60–70 day period beginning around 10 February. The mean ascent rate of individuals was estimated to be 15–20 m day –1 , so that for any individual the ascent from a mean overwintering depth of 800 m to a depth of 100 m took between 35 and 47 days. The ascent migration resulted in the mass transfer of the C. finmarchicus stock from its overwintering habitat in the cold southerly flowing Norwegian Sea Deep Water of Arctic origin to warm northerly flowing Atlantic water masses. The extent of asynchrony suggests that emergence is probably not triggered by environmental cues. An alternative hypothesis for regulation of the life cycle is proposed that involves reduced development rates during the winter.