Biomass of invertebrate bycatch on the East- and West-Greenland shelf during Walther Herwig III cruise WH379

The study on invertebrate communities in East- and West-Greenland shelf waters was embedded in a fisheries survey carried out during the 379th expedition of the German fisheries vessel Walther Herwig III of the Thünen Institute of Sea Fisheries, Hamburg, Germany. The aim of the study was a coarse classification of the bycatch comprising macrobenthic organisms. On the one hand the marine ecosystem of this area provides food for commercially valuable fish stocks and plays, potentially an important role in the remineralisation of nutrients. On the other hand it experiences stress by traditional bottom trawling as well as anthropogenic and natural climate variability. As a consequence the study can provide a baseline to detect further changes in the composition of this component of a sub-arctic marine ecosystem.

Groundfish survey data from the German Bight from 1902-08, 1919-23, and 1930-1932 and ICES International Bottom Trawl Survey (IBTS) quarter 3 data from 1991 to 2009

Groundfish survey data from the German Bight from 1902-08, 1919-23, and 1930-1932 and ICES International Bottom Trawl Survey (IBTS) quarter 3 data from 1991 to 2009 were analysed with respect to species frequencies, maximum length, trends in catch-per-unit-effort, species richness parameters (SNR) and presence of large fish (Phi40), the latter defined as average presence of species per haul with specimens larger than 40 cm given. Four different periods are distinguished: (a) before 1914 with medium commercial CPUE and low landings, Phi40 approx. 2, high abundance in elasmobranchs and SNR conditions indicating highly diverse assemblages, (b) conditions immediately after 1918 with higher commercial CPUE, recovering landings, Phi40 at > 4 in 1919, and SNR conditions indicating highly diverse assemblages, (c) conditions from 1920 to the early 1930's with decreasing commercial CPUE, increased landings, decreasing Phi40, SNR conditions similar to later years indicating less diverse assemblages, and a decrease in elasmobranchs. In the IBTS series (d), Phi40 remains low indicating an increased rarity of large specimens, and SNR characteristics are similar to the third period. Dab, whiting and grey gurnard have increased considerably in the IBTS series as compared to the historic data. Phi40 is suggested an alternative indicator reflecting community functional diversity when weight based indicators cannot be applied.