Ocean productivity index for fish in the Arctic Ocean : initial assessment of satellite-derived plankton-to-fish productive habitats

The JRC explores the potentials of a satellite-derived index (the Ocean Productivity index for Fish - OPFish) at large scale to represent the production of high tropic level communities (fish) and its variability after currently observed climate change during the period 2003-2016 in the Arctic Ocean. The OPFish uses the daily detection of productive oceanic features (chlorophyll-a [CHL] fronts) from ocean colour satellite sensors at 1/24-degree resolution as a proxy for food availability to fish populations. These productive features, such as eddies or gyres, were shown to attract fish and top predators as they are active long enough (from weeks to months) to allow the development of mesozooplankton populations. Potentially eutrophic waters are excluded by removing high daily levels of surface chlorophyll-a contents (daily surface content above 10 mg CHL.m-3). The satellite monitoring of productive fronts associated with day length in the OPFish formulation provide insight on the overall capacity of the marine environment to sustain high trophic level communities. Time-series and trends of OPFish identify current climate change impacts on potential fish productivity, including seasonal deviations, which may affect fish growth and recruitment. The annual climatology levels of OPFish between 2003 and 2016 were assessed setting zero value in months of permanent night (mostly from November to February) and monthly means of index values for periods of long-day duration (mostly from May to September) filtering out low coverage of CHL due to low-light levels, ice and clouds. The climatology of OPFish in the ice-free of the Arctic Ocean, an area mostly over the continental shelf and shelf-break, displayed lower levels and more uneven distribution than in temperate shelves (e.g. North-East Atlantic) with absolute values ranging from 20 to 50% compared to 45-55% respectively. The trends of OPFish on the 2003-2016 period showed about four-fold higher regional variability and levels in the Arctic compared to the North-East Atlantic shelf area. The general OPFish trend of the Arctic Ocean is the highest observed among the regional oceans, with +2.9% per decade (in absolute value) compared to +0.5% per decade for the global ocean. In relative change, this increase translates into +16% per decade in the Arctic compared to +2.1% per decade for the global ocean. The OPFish is a plankton-to-fish index that represents the potential distribution of high trophic level (fish) productivity. Despite a necessary ongoing validation process using zooplankton and fisheries data in the Atlantic Ocean, the moderate absolute level of OPFish in the Arctic Ocean compared to temperate shelves and the substantial positive trend over 2003-2016 provide useful baseline information for future fisheries management. The high geographical disparities of level and trend of the potential fish productivity also emphasizes the necessity to take into account the spatial dimension when planing a sustainable exploitation of natural living resources.