Primary productivity demands of global fishing fleets

Abstract

To be sustainable, the extractive process of fishing requires biomass renewal via primary production driven by solar energy. Primary production required (PPR) estimates how much primary production is needed to replace the biomass of fisheries landings removed from marine ecosystems. Here, we examine the historical fishing behaviour of global fishing fleets, which parts of the food web they rely on, which ecosystems they fish and how intensively. Highly mobile European and Asian fleets have moved to ever more distant productive waters since the 1970s, especially once they are faced with the costs of access agreements for exclusive economic zones (EEZs) declared by host countries. We examine fleet PPR demands in the context of large marine ecosystems (LMEs), which are frequently fished with PPR demands well above their average primary productivity (PP). In some cases, this was mitigated by subsequent emigration of fleets or by management intervention. Fleet movements, however, have stressed additional marine areas, including the EEZs of developing countries. This suggests the potential for spatial serial depletion, if fishing capacity is not reduced to more sustainable PP removal levels. Fundamentally, fishing is limited by solar‐powered PP limits. Fishing beyond solar production has occurred, but in the future, marine systems may not be as forgiving, especially if overfishing and climate change compromise their resilience.

High fishery catches through trophic cascades in China

“…Reducing trophic levels by only 14% for secondary consumers and above can bring fisheries in balance with primary productivity (reproducing ref. 46; SI Appendix); our model predicted changes in trophic level of up to 27% for species like largehead hairtail from those used in Watson et al (46). If China's fishery catch data are roughly correct, they appear to have, perhaps unwittingly, performed the world's largest experiment in marine predator removal with the result of increases in harvestable biomass.…”

“…For example, it has recently been suggested that the catch extracted from the East China Sea exceeds the potential of the input primary productivity (46), which implies unsustainable fishing at the ecosystem level. The age structure for most fished populations in the East China Sea consists largely of 1-y-olds and exploitation rates in the fisheries appear to be very high (47), which suggests decreasing harvest rates could result in large benefits [from the perspective of single-species assessment methods (48)].…”

Reconciling fisheries catch and ocean productivity

“…Although fishing has expanded offshore in recent decades, degrading a number of high value stocks (54), catch outside LMEs remains below 9% of the global total in all years. Offshore effort and ecosystem-level exploitation per area also generally remains far less than in coastal regions (55,56). This is in part a reflection of the high capital cost of high-seas fishing that restricts this activity to a select subset of nations (57).…”

Communities and change in the anthropocene: understanding social-ecological vulnerability and planning adaptations to multiple interacting exposures

“…Overfishing alters marine population demographics (removal of older individuals), spatial dynamics (changes in spawning grounds) and species abundance and thus reduces the ocean's ability to provide food, maintain water quality and recover from perturbations (Worm et al 2006;Rockström et al 2009a;Watson et al 2014). Historic exploitation of sea otters in the Aleutian Islands removed the primary predator of sea urchins, resulting in massive deforestation of kelp forests via an unregulated sea urchin population (Steneck et al 2002).…”