The large fish indicator (LFI) is a size-based indicator of fish community state. In the North Sea, the LFI is already established as the fish community's Ecological Quality Objective (OSPAR-EcoQO). The LFI has also been proposed as an indicator for food webs and for monitoring of biodiversity in European regional seas. The LFI was developed based on the entire North Sea fish community, which ignores the differences between the southern and the northern fish communities from the International Bottom Trawl Survey (IBTS) data. In this study, we have calculated LFIs based on IBTS and the Beam Trawl Survey (BTS), which target different components of the fish community and we test whether the LFI responds to changes in fishing pressure. The results did not confirm our expectation of a negative correlation between the pressure and state. We found a positive relationship between the IBTS-based LFI and the roundfish fishing mortality as well as an inverse relationship between the BTS-based LFI and the flatfish fishing mortality. The differences in the relationships between the IBTS- and BTS-based LFI and the respective roundfish-averaged and flatfish-averaged fishing mortality confirmed the spatial differences between the North Sea roundfish and flatfish fish communities. Although previous relationships between the LFI and the fishing pressure involved lengthy time-lags (10-12 years), we found shorter responsiveness of the LFI of 1-2 years. Further understanding of the ecological, environmental and anthropogenic factors affecting the LFI is required before ecosystem objectives can be set within the MSFD. |
