A unique view of recent trends in the species abundance

A large part of Skagerrak, particularly its deep-sea areas, is not covered by the international bottom trawl survey (IBTS). To produce a comprehensive overview of trends in species abundance in Skagerrak, we therefore combined data collected from the IBTS (quarter 1) and the lesser-known Norwegian northern shrimp survey in a statistical model and estimated standardized catch rates for the period 2013–2022. The trends in the survey catch rates provide an indication of recent trends in species abundance (hereafter referred to as abundance indicator). By combining these two surveys, we achieved extensive and unique coverage of Skagerrak, except for near-shore, coastal areas. The trends in the abundance indicators were compared to trends in the combined commercial landings from Denmark, Norway, and Sweden (for the same period) and to the international and national red list status. An overview is provided in Table 1.

Skates and rays were excluded from the analysis because they are often not identified to species level as well as being wrongly identified in some cases.

Table 1: Overview table showing trends in total (DK, SE and NO) official landings over the period 2013–2022, trends in abundance modelled from scientific surveys (also for the period 2013-2022), and red list status from IUCN ratings (Europe), and national lists (green = least concern, grey = data deficient or not relevant, and red = near threatened, vulnerable, endangered, or critically endangered) vertical arrow pointing up = strong positive trend, vertical arrow pointing down = strong negative trend, diagonally arrow pointing up = weak positive trend, diagonally arrow pointing down = weak negative trend, horizontal arrow = no trend.