An overall indicator for the good environmental status of marine waters based on commercially exploited species

Abstract

An indicator is presented to assess and monitor the good environmental status of national marine waters based on the status of commercially exploited marine fishes and invertebrates, including fully-assessed as well as data-limited stocks. The overall-indicator consists of one number per year. It summarizes the following sub-indicators: the stock size relative to the size that can produce the maximum sustainable fishing yield; the mortality caused by fishing relative to the natural rate of mortality; the mean length in the catch relative to the length where 90% of the females reach sexual maturity; and the abundance in national waters relative to mean abundance in the time series. For the example of German marine waters, the overall-indicator shows that only 3 of 19 stocks (Baltic Sea dab, North Sea plaice and North Sea sprat) were above the limit reference point for the overall indicator in 2011. North Sea herring was close to reaching the threshold, but most other stocks were still far below. Apparently fishing mortality was too high to allow recovery of more stocks to levels capable of producing the maximum sustainable yield. The chosen indicators and reference points may prove useful to other scientists tasked with assessing the environmental status of their national waters.