2050 – Will There be Fish in the Ocean?

Will there be fish in the ocean in 2050? Opinions differ and many fear that our impact is so devastating that all fish supporting fisheries will be gone by 2050. Such statements create headlines, but how founded are they in reality? Alternative interpretations of data conclude that conditions are improving and we see improvements in fish populations. Music in managers’ ears, but is it the Titanic’s orchestra? With this in mind, we set out to make a global assessment of how fish biomass has changed over the last hundred years. We built on more than 200 data-rich, quantified descriptions of marine food webs representing marine ecosystems throughout the world from 1880 to 2007, and all constructed based on the same approach. We performed a standardized assessment wherein we ran the quantified food webs through a spatial model that distributed the biomass of their components based on habitat preferences, ecology, and feeding conditions. We extracted more than 68,000 estimates of fish biomass (for predatory and prey fishes, separately) distributed over time and space, and subsequently used multiple regression techniques to predict the biomass distribution as a function of year and environmental parameters. The regressions were highly significant and predict that the biomass of predatory fish in the world oceans has declined by two-thirds over the last hundred years.  This decline is accelerating, with 54% having taken place in the last 40 years. We also found that the biomass of prey fish has more than doubled over the last hundred years, likely as a consequence of predation release. Jointly, these findings allow us to predict that there will be fish in the ocean in 2050, but they will be mainly of small prey fish. Our study also addresses the controversy whether ‘fishing down the food web’, often based on the relative contributions of high vs. low trophic-level fish in fisheries catches, is a phenomenon actually occurring in nature or a sampling artifact due to catches not representing relative abundances in ecosystems. We note that our study is based on ecosystem models not on catch time series, and more generally, on data derived from commercial fisheries. Given our finding that predatory fish have decreased globally while prey fish has increased, our study strongly indicates that the impact of fisheries has caused fishing down the food web of ecosystem resources at the global level.