A no-take zone and partially protected areas are not enough to save the Kattegat cod, but enhance biomass and abundance of the local fish assemblage

Abstract

Abstract To supplement catch and effort regulations with the purpose to rebuild the cod (Gadus morhua) stock in Kattegat, Sweden and Denmark established a large (426 km2) year-round no-take zone (NTZ) surrounded by partially protected areas (PPAs) in 2009. The purpose of these spatial regulations was to prohibit cod fishing on the spawning grounds and to displace fisheries bycatch of cod from areas where mature cod aggregate in the Kattegat. The aim of this study is to evaluate the effects of the established NTZ and PPAs on the local fish assemblage, including cod. Based on a spatially high-resolution bottom trawl survey in the Kattegat (covering 2008–2021), multivariate analyses revealed significant shifts in the fish assemblage. A closer analysis indicated that six to seven fish species, including cod increased in the NTZ relative to control areas depending on if abundance or biomass was used as dependent variable. Univariate analysis showed that two flatfish species dab (Limanda limanda) and lemon sole (Microstomus kitt), and Norway lobster (Nephrops norvegicus) significantly increased in biomass in the NTZ, and turbot (Scophthalmus maximus) in the PPA relative to the control areas. These results suggest that the NTZ protected even relatively mobile species in an open sea system, such as the Kattegat. However, neither cod abundance nor biomass showed a significant increase as an effect of the NTZ and PPA despite two relatively strong year classes in 2012 and 2013, which possibly would have helped the recovery of the cod stock. As assessed by the International Council for the Exploration of the Sea in 2022, Kattegat cod continuously suffer from being severely overfished with low recruitment, and high discard rates in the mixed N. norvegicus fishery, is considered the major driver behind the reinforced depletion of the stock.