I get asked often about this issue… A truly complicated topic I know very little about (and I believe not many people do really know a lot about it). Its really complex and truly interesting, since it adds a full new set of variables to fisheries management, which is per se already multifaceted.
A few years ago, SPC published an interesting book (Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change), that in my opinion still leads the pack and what is (could?) be happening.
The build-up of greenhouse gases in the atmosphere is acting in two major ways that are ultimately expected to affect fisheries and aquaculture in the tropical Pacific.
First, the accumulation of greenhouse gases is trapping more of the heat that would normally escape from the Earth, leading to an overall increase in global surface Temperature. The oceans have absorbed almost 80% of the additional heat, acting as a buffer against more rapid atmospheric warming. However, the continued uptake of this extra heat has wide-ranging implications for marine resources.
Generalised effects of increased greenhouse gases on oceanic and coastal ecosystems in the tropical Pacific
Thermal expansion of the ocean, together with melting of land ice, is resulting in rising sea levels. Increases in ocean temperatures are also changing the strength and direction of currents, and making surface waters more stable, reducing vertical mixing and the availability of nutrients in the upper layer of the ocean. Reductions in the supply of nutrients usually limit the primary production at the base of the food chains that support fisheries.
Warmer oceans also cause changes in atmospheric circulation patterns, giving rise to regional changes in climate. In the tropical Pacific, greater evaporation and moisture availability are expected, leading to an intensification of the hydrological cycle, and a pole ward expansion and possible slow down of the Hadley circulation. As a result, rainfall is projected to increase in tropical areas of the Pacific and decrease in subtropical areas, although there is still considerable uncertainty about the regional pattern of projected changes. There is also the possibility that warmer conditions may result in more intense cyclones and storms, resulting in rougher seas, more powerful waves and greater physical disturbance of coastal environments.
The second way that increasing greenhouse gases are expected to affect fisheries and aquaculture is through changes to oceanic concentrations of CO2 and the resulting effect on ocean acidity. The ocean has absorbed more than 30% of human CO2 emissions since the beginning of the industrial revolution and it is now more acidic than at any time during the last 800,000 years.
This effect is largely independent of global warming but also has grave consequences for marine ecosystems. The dissolved CO2 reacts with sea water to form weak carbonic acid, which reduces the availability of dissolved carbonate required by many marine calcifying organisms to build their shells or skeletons.
There is serious concern that continued emissions of CO2 will drive sufficient gas into the sea to cause under-saturation of carbonate in some areas of the ocean this century. Where this happens, the environment will favour dissolution rather than formation of carbonate shells and skeletons.
Nature of effects of climate change on fisheries and aquaculture worldwide
The basis of tuna production in the Western and Central Pacific Ocean, and the main methods used to harvest tuna
We already know that variations in climate on time scales of years to decades can cause significant changes in fisheries production. For example, catches of Peruvian anchovies have varied between < 100,000 tonnes and > 13 million tonnes since 1970 as a result of changes in ENSO46,47. The different phases of the ENSO cycle also determine the distribution of skipjack tuna in the Western and Central Pacific Ocean – the fish move further east during El Niño events and further west during La Niña episodes ( I wrote about this here and here)
Over and above normal year-to-year variations, longer-term changes in physical oceanography and biology, known as regime shifts, can have major consequences for the species composition and productivity of fisheries. Some heavily fished stocks have collapsed due to the additive effects of environmental and fishing stresses.
However, the effects of such changes in climate have not always been negative. For example, a period of ocean warming around Greenland starting in 1925 resulted in a northern extension in the range of cod by > 1000 km and the creation of an international fishery of up to > 400,000 tonnes per year.
Questions abound for fisheries management. Will the species that currently support substantial harvests still be available as climate change continues? If not, which types of species are most likely to replace them? For those species that continue to support fisheries, will climate change reduce the capacity for replenishment and production, and increase the risk of overfishing? How should managers and policymakers respond to the projected changes to maintain sustainable benefits from fisheries? How will fishers perceive and react to the risks associated with projected changes? Will fishing at sea become more hazardous? How much will it cost to adapt?
Potential impact of climate change on fisheries and aquaculture in the tropical Pacific
The range of coastal fisheries activities in the tropical Pacific, and the habitats that support them.
All fisheries and aquaculture activities in the region are likely to be affected by climate change. The distribution and abundance of tuna, which dominate oceanic fisheries and are the mainstay of the economies of some smaller PICTs1, are influenced largely by water temperature and the availability of nutrients.
The coastal fisheries that currently provide much of the animal protein for Pacific islanders14, and the contribution of aquaculture to the economies of French Polynesia and Cook Islands, are based largely on coral reef habitats. These habitats are threatened by changes to water temperature, acidification of the ocean and sea-level rise, and possibly more severe cyclones and storms.
The freshwater fisheries of PNG have evolved in a climate of heavy rainfall and any major alterations in precipitation can be expected to change the nature of these resources, on which hundreds of thousands of people rely.
Preliminary analysis has already identified the following possible effects of climate change on fisheries and aquaculture production in the tropical Pacific from climate change:
Changes to the distribution and abundance of tuna: Alterations in ocean temperatures and currents and the food chains that support tuna, are projected to affect the location and abundance of tuna species21,48. In particular, the concentrations of skipjack and bigeye tuna are likely to be located further east than in the past. This has implications for the long-term management of the region’s tuna resources, and for the development and profitability of national industrial fishing fleets and canneries in the western Pacific.
Decline in coral reefs and coastal fisheries: Rising sea surface temperatures and more acidic oceans are projected to have direct impacts on coral reefs and the habitats and food webs they provide for reef fish and invertebrates. Degraded coral reefs are likely to support different types of fish and lower yields of some species. Reduced catches of reef-associated fish will widen the expected gap between the availability of fish and the protein needed for food security.
Difficulties in developing aquaculture: Changing patterns of rainfall and more intense storms could flood aquaculture ponds more regularly in some places, and make small pond farming for food security impractical in others due to more frequent droughts. There could also be higher financial risks associated with coastal aquaculture as a result of (1) greater damage to infrastructure and equipment from rising sea levels and the possibility of more severe cyclones and storms; and (2) the effects of higher water temperatures, ocean acidification, reduced salinity and increased incidence of disease on the growth and survival of shrimp, pearl oysters, seaweed and ornamental specimens90.
Increased operating costs: Projections that cyclones and storms could possibly become progressively more intense would involve increased risk of damage to shore-based facilities and fleets for domestic tuna fishing, and processing operations. Fleets operating within the cyclone belt may need to be upgraded to provide improved safety at sea. Rising sea level may eventually make many existing wharfs and shore-based facilities unusable. Taken together, increased costs associated with repairing and relocating shore-based facilities, and addressing increased risks to occupational health and safety for fishers, may affect the profitability of domestic fishing operations. Such increased costs will need to be taken into account by PICTs when planning the optimum mix of developing local industries for tuna and providing continued access for DWFNs.
Reality is that the main findings are mixed – there are likely to be winners and losers – underscores the importance of this vulnerability assessment. Practical adaptations, policies and investments are now needed to reduce the threats of climate change to the many fisheries and aquaculture activities that are part of the economic and social fabric of the region. Adaptations, policies and investments are also needed to capitalise on the opportunities.
Otherwise we will keep running behind the ball (as usual)… unfortunately I don’t see that happening.