As a companion to the IPCC Special Report on Climate Change and Land, discussed in my last editorial, a recent Special Report on the Ocean and Cryosphere in a Changing Climate has been released. Regarding the oceans, warming, deoxygenation and acidification are the major concerns. Overall, from the perspective of coastal aquaculture, the world’s oceans are becoming less hospitable places to grow fish. The report flatly states that “over the 21st century, the ocean is projected to transition to unprecedented conditions.”

About 90 percent of the excess heat in the climate system is taken up by the oceans. Thermal expansion of ocean water and melting of polar ice has caused sea levels to rise by about 15 cm over the last century and a further rise of 25-60 cm by 2100 is expected, depending on emissions scenario. The frequency of marine heatwaves has doubled since 1982 and have lasted longer and are more intense and widespread. As a harbinger of the future, a prolonged period of unusually warm water temperatures and related low oxygen conditions were responsible for the death of about 2 million salmon in net pens in Newfoundland this past September.

For fisheries, ocean warming will likely cause expansion in the spatial range of some species, contraction in others. In general, ocean warming is expected to decrease catch potential of fisheries by more than 20 percent by the end of the 21st century relative to the present day. Obviously this will affect the income, livelihoods and food security of coastal communities.

In early December, the International Union for Conservation of Nature (IUCN) released a report at the recently concluded global climate change summit (COP25) called Ocean Deoxygenation: Everyone’s Problem that explicitly links nutrient pollution and carbon emissions from human activities with ocean deoxygenation. Oxygen is less soluble in warmer water and greater water column stability (stratification) is limiting ventilation. Deoxygenation is also caused by eutrophication from nutrient pollution from various sources, including aquaculture.

Low oxygen areas of the ocean have expanded from only 45 sites 60 years ago to 700 in 2011. Eutrophication of estuaries from agriculture and urban development since the 1970s have led to an increase in the number and area of low oxygen in coastal areas. What is new in the IUCN report is the focus of reduced dissolved oxygen concentration in vast areas of the open ocean.

Ocean deoxygenation in hypoxic zones is also a consequence of harmful algal blooms (HABs), stimulated by nutrient runoff and pollution (eutrophication) and ocean warming. The prevalence of HAB events has been increasing in frequency and range in coastal waters since the 1980s. The increase in HAB events has been most apparent in Asia, including China, Japan, Korea, the Philippines and Malaysia, all important aquaculture producing nations.

There are numerous examples of HABs negatively impacting aquaculture operations, going back to the 1970s. In 2016, two successive outbreaks of red tide in Chile killed 39 million salmon in net pens. Smaller fish kills occurred there in 2017 and 2018. This past May, more than 8 million salmon (more than 13,000 t) were killed by a toxic algae bloom in Norway. Such blooms are normally infrequent there. Marine Harvest reported that HABs killed around one million fish in Scotland in 2018. There were relatively small kills of salmon in net pens in British Columbia from a HAB in November. The risks and economic losses from HABs to aquaculture are expected to increase. At minimum, monitoring programs and early warning systems are needed for coastal areas at risk for HABs.

HABs are also a feature of so-called eastern boundary upwelling systems, such as the Humboldt Current that is critical for the Peruvian anchoveta fishery. These upwelling systems are highly productive but are imperiled by reduced oxygen levels associated with high-biomass HABs and by ocean acidification. The forage fisheries based on these upwelling systems are critical for aquafeeds. Future fluctuations in supply as well as a long-term decline in catch potential seem likely.

The recently concluded climate change summit can rightly be considered a failure because there were no new pledges for emission cuts and there were disagreements over rules for carbon markets and compensation for the developing nations bearing the brunt of the effects of climate change. However, one encouraging sign has emerged from a recent business collaboration between Tesco, Nutreco and Grieg Seafood. These companies have banded together to contribute money to a fund that will create incentives for “zero deforestation soy” production in the Cerrrado, one of Brazil’s most biodiverse regions. Direct financial payments will reward soy farmers who plant on existing agricultural land and preserve native plants on their farms.

This is another example of so-called “non-state environmental governance,” most often manifest as ecolabelling certification programs, that has been in vogue for the last 25 years. Corporate social responsibilities and more widespread scaling of such partnerships can perhaps pick up some of the slack in reducing emissions. This is also an example of how actors in aquaculture value chains can collaborate to address biodiversity conservation and greenhouse gas emissions within their areas of influence.

A recent paper published in Global Environmental Change by a group of 12 contributors led by Michael Tlusty argues that the framing of the role of sustainable seafood in promoting ocean health, with a focus on fisheries and aquaculture producers, especially those in developing countries, is too narrow and needs to be broadened to focus comprehensively on the whole value chain, especially the downstream stages. In so doing, decisions can be made on parts of the chain that provide greater returns in terms of improving ocean health rather than a narrow focus on improving the sustainability of producers. Taking a “seafood systems approach” that includes traders and consumers can then begin to address the ongoing challenges to ocean health.
— John A. Hargreaves, Editor-in-Chief