Small scale distribution of zooplankton, suitable as cod larval prey, off Vesteralen, northern Norway

• Main Author: Wittwer, Claudia
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: Lofoten; Norway; Calanus finmarchicus; Gadus morhua; Northern Norway
• Online Access: https://oceanrep.geomar.de/id/eprint/20166/; https://oceanrep.geomar.de/id/eprint/20166/1/Dipl.%202012%20Wittwer,%20C.pdf

The area off Lofoten and Vesterälen is an important spawning ground and first feeding area for cod (Gadus morhua). Major prey of cod larvae is the nauplii of Calanus finmarchicus. The distribution pattem of Calanus nauplii was studied in April of 2010 and 2011, the main spawning time of cod. Sampling took place on 400m scale, as it suggest that small scale high concentration peaks are important for the survival of cod larvae. With a WP2 net (200μm) and with a handnet (lOOμm) investigation on the nauplii C.finmarchicus, other nauplii and their predator fish larvae, especially cod larvae could be made. Main hypothesis was that Calanus nauplii have a patchy distribution on small scale. The results confirmed this and showed that there is a heterogeneous distribution of nauplii with significant patchiness on small scale. The distribution of Calanus nauplii did not correlate with hydrography or cod larvae on small scale, suggesting the patchy distribution was the result of currents, wind or spawning patches of females of Cfinmarchicus. Nauplii of other species, were less abundant, but showed also a patchy like distribution. These nauplii, were larger and showed in some cases significant correlation to the distribution of fish and cod larvae. The study pointed out that prey of cod larvae showed small scale high concentration peaks, which are important for the survival of cod larvae. lt can be suggested that older cod larvae concentrate for feeding on the larger nauplii, while younger first feeding larvae, which feed on the smaller Calanus nauplii are maybe not able to actively search for and stay in this nauplii patches.