By William Cheung, Nereus Director (Science)

A range of human pressures is threatening the sustainability of marine fisheries. Amongst those, overfishing, partly driven by Illegal, Unreported and Unregulated (IUU) fishing, is a major stressor. Thirty percent of global fish catch goes unreported, found a recent studyby Nereus Program collaborator Sea Around Us.

But the relationship between IUU fishing and climate change is a new topic. I speculate that climate change impacts on fisheries may indirectly increase IUU fishing.

How climate change is affecting who fishes what

Increases in greenhouse emission concentrations in our atmosphere contributes to ocean warming, decreases in oxygenation levels and ocean acidification. Ocean acidification is the decrease in the pH of oceans due to the absorption of CO2; it affects calcifying organisms, like oysters, clams and corals, which have difficulties building their shells in more acidic water.

Fish stocks are also shifting tens of kilometers per decadetowards the poles or into deeper waters in response to ocean warming. Globally, potential fisheries catches are projected to redistribute to high latitude regions, with a large reduction in potential catches in the tropics, of up to 30 percent in some regions. The tropic is amongst the areas where communities are most dependent and vulnerable to fisheries resource depletion. If traditional fisheries resources decrease because of climate change, fishers may need to shift their fishing grounds, or engage in alternative fishing methods to compensate for their lost. Shifts in distribution of fish stocks may also destabilise existing fisheries management, such as bycatch quotas, or bi-/multi-lateral agreements on straddling fish stocks. Moreover, fish stocks shifting to new habitats may create opportunities for new fisheries that do not yet have management and reporting frameworks, such as fisheries in the Arctic. Climate change impacts on vulnerable communities may also drive migration and increase pressure of coastal fisheries resources. All these factors could increase incidences of and complicate measures to combat IUU fishing.