Essential Fish Habitats for commercially important marine species in the inner Danish waters

Abstract

The aim of this project is to map Essential Fish Habitats (EFH) for ten of the commercially most important species in the inner Danish waters. New data were collected to supplement existing data to better describe seasonal differences in distribution. The spatial overlap between habitats of the different life stages is evaluated as well as the degree of overlap between EFH and existing management areas such as Natura 2000 areas and fishery management areas. The EFH maps will be incorporated into Maritime Spatial Planning to ensure that fish species can complete their life-cycle and thus preserve, improve or restore important habitats, essential for the development of a species. The species studied are: Atlantic cod Gadus morhua, European plaice Pleuronectes platessa, common sole Solea solea, turbot Scophthalmus maximus/Psetta maxima, European flounder Platichthys flesus, Atlantic herring Clupea harengus, European sprat Sprattus sprattus, European eel Anguilla anguilla, lumpfish Cyclopterus lumpus and Norway lobster Nephrops norvegicus. Apart from using existing time-series data from national and international fishing surveys, new data were collected. An additional Kattegat Survey (KASU) survey was conducted during summer 2016 (Q3) using the same methods and visiting the same stations that KASU surveys conduct in Q1 and Q4 every year. Summer feeding grounds were identified with the new data. These summer feeding grounds were significantly different to overwintering (Q1 and Q4) areas or spawning areas (Q1). This was true for cod, plaice, flounder and sprat. The EFH maps showed the degree of overlap between juvenile and adult habitats for those species where distinction could be made between adult and juvenile fish (cod, plaice, sole, flounder and herring). Spawning grounds were identified for cod, plaice and flounder that spawn in the winter season (Q1) but could not be identified for sole and turbot that spawn in May/June (Q2) due to lack of seasonal overlap between spawning season and timing of survey. The surveys do not cover coastal areas and thus coastal habitats could not be mapped. This was the case for example for herring that spawns in shallow coastal areas. New data was also collated through a juvenile fish survey that sampled 146 stations in the inner Danish waters. Habitat quality maps were developed using fish abundance data and growth data obtained from otoliths for Young-of-the-Year (YOY) of three flatfish species, plaice, flounder and sole. This work is reported in a separate paper intended for peer-review (Brown et al. 2019). This survey covered the coastal areas in the inner Danish waters and excluded fjord systems, which can be essential growth or spawning areas for several species. Interviews with fishermen provided information on presence for the 10 species. Since particular information on spawning or juvenile areas for individual species was too sparse to produce separate maps, composite maps were produced on fish presence per species as provided by the fishermen. EFH maps were produced for the focus species from existing data and the newly obtained data from the surveys in this project. The data was used to develop statistical models on the relationship between fish abundance and environmental variables such as temperature, salinity, depth and sediment type. The best fitting model was then used to predict potential fish habitats within the whole study area. The yearly survey data were used to map the general fish distributions over the years during different seasons and different life-stages (adult, spawning, juvenile). Maps for juvenile and adult cod, plaice, sole, flounder and herring were developed. Also maps for turbot and sprat are shown. Error maps were developed to provide information on the “uncertainty” of the estimations. For the remaining species data was insufficient to produce maps. For some species presence maps only were available from the fishermen interview data. As seasonal maps were produced, it was possible to identify spawning areas, feeding grounds or overwintering grounds for the different species. Spawning areas can only be identified when spawning time and survey timing coincide. Peer-reviewed literature field studies were used to validate the interpretation of the predictive maps. Maps produced from the fishermen interviews (Støttrup et al. 2019) were also used to validate interpretation. A workshop dedicated to cod allowed for the discussion of the cod maps and exchange of relevant information. several subsequent short meetings were held with colleagues who had specific expertise on some of the species. The aggregated maps of the individual species distributions highlighted hot-spot areas for multiple commercially important fish species. Not surprisingly, a poor overlap was found between the aggregated maps and a map of the Danish marine Natura2000 sites, since the latter are generally designated for other purposes than fish protection. The overlap with the fisheries management area just north of the Sound, “kilen”, coincides with the spawning area for cod and provides some protection for other species, but does not capture the important multiple fish habitats captured in this study.