Ceton 12/2019 (IESSNS 2019)
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | Ceton (26AS) |
| Cruise identifier | 12/2019 (IESSNS 2019) |
| Cruise period | 2019-07-02 — 2019-07-12 |
| Status | Completed |
| Port of departure | Skagen Havn, Denmark |
| Port of return | Hirtshals Havn, Denmark |
| Purpose | Research |
| Objectives | The main objective of the IESSNS (International Ecosystem Summer Survey in the Nordic Seas) is to estimate mackerel abundance per age class, but also CTD and plankton samples are being collected. The survey is carried out during July and a special designed gear, the Multipelt 832 pelagic trawl with Dynema warps, is used to catch the mackerel. The trawl fishery takes place at a combination of fixed and non-fixed stations located along transects, and fishing depth is form surface to about 30 - 35 m depth. Even though the importance of the IESSNS survey for the mackerel assessment has recently increased, one criticism of the survey that has been raised several times is that the survey does not cover the southern edge distribution. Only samples taken north of 60° N are included in the index, thus the entire North Sea, Waters around the British Isles and the Bay of Biscay are not sampled. There are two reasons for that. First, the survey is designed and performed by Norway, Iceland, Faeroes and Greenland with focus on their waters. Secondly, there is concern to what extend the survey design are applicable in more shallow areas like the North Sea. The reason for this concern is the absence of a thermocline in the southern and shallower waters, which is dividing the water column into a warmer upper layer and a colder deeper layer. The presence of a thermocline in the northern waters (at around 30 m depth) is believed to limit the habitat of the mackerel, as the fish are unlikely to cross the thermocline and dive into the cold deeper waters. If such a thermocline is not present then the depth range of the mackerel south of 60°N is larger extending beyond the layer fished by the trawl. Despite the concern about the applicability of the survey design south of 60°N, there appears to be a potential in expanding the survey as this might improve the index, especially for the younger year classes which are expected to be located more southerly than older and larger individuals. With this background, Denmark joined the IESSNS in 2018 using a commercial vessel in order to investigate whether the applied methods in the IESSNS would also work for the North Sea. Based on the positive results from 2018 the survey was conducted again in 2019 using the same vessel and methods but with a slightly changed layout of the sampling locations based on a request from the IESSNS coordinator. |
| Chief scientist | Kai Wieland (Technical University of Denmark, National Institute of Aquatic Resources) |
| Cruise report |  (1.13 MB) |
| NPRC | (0.35 MB) |
| Ocean/sea areas | |
| General | Skagerrak North Sea |
| Specific | Skagerrak and northwestern North Sea |
