CLIMATE CHANGE — IMPACTS ON FISHERIES AND AQUACULTURE

BIPUL PHUKAN¹, ANKUR RAJBONGSHI², SANGIPRAN BAISHYA³ & RANJIT BORDOLOI⁴

^{1, 3, 4}College of Fisheries, Assam Agricultural University

²NAIP cell, Assam Agricultural University

¹ Corresponding Author: bipul_phukan@yahoo.co.in

Introduction:

The study, "Climate change implications for fisheries and aquaculture", is one of the most comprehensive surveys to date of existing scientific knowledge on the impacts of climate change on fisheries and aquaculture. There is no doubt that fisheries are already a vulnerable sector facing widespread and often profound changes. Marine and freshwater ecosystems are profoundly affected by processes like ocean acidification, coral bleaching and altered river flows with obvious impacts on fisherfolk. But it is not just about what happens to fish. Fishing communities are vulnerable to sea level rise and their livelihoods are threatened by storms and extreme weather. Meanwhile, the social and economic context of fisheries will be disrupted by impacts on security, migration, transport and markets. Fisheries are already rapidly evolving due to over exploitation and globalization. They will suffer from a wide range of different impacts from climate change which may be unpredictable and surprising. The poorest will be least able to adapt to these impacts.

Marine capture fisheries already facing multiple challenges due to overfishing, habitat loss and weak management are poorly positioned to cope with new problems stemming from climate change. Some 520 million people depend on fisheries and aquaculture as a source of protein and income. For 400 million people of the poorest of these, fish provides half or more of their animal protein and dietary minerals. Inland fisheries 90 percent of which are found in Africa and Asia — are also at risk, threatening the food supply and livelihoods of some of the world's poorest populations. Warming in Africa and Central Asia is expected to be above the global mean, and predictions suggest that by 2100 significant negative impacts will be felt across 25 percent of Africa's inland aquatic ecosystems.

Fish farming will also be affected. Nearly 65 percent of aquaculture is inland and concentrated mostly in the tropical and subtropical regions of Asia, often in the delta areas of major rivers at the mid to upper levels of the tidal ranges. Sea level rise over the next decades will increase upstream salinity, affecting fish farms.

Contribution of Fisheries to Food Sector:

Aquaculture earned its fame as a fast growing food sector which continues to grow more rapidly than all other animal food producing sectors, with an average global growth rate of 8.8 percent per year since 1970, compared to 2.8 percent for terrestrial farmed meat production systems. If growth in aquaculture can be sustained, it is likely to fulfill the increasing demand for aquatic food supplies by supplying more than 50 percent of the total aquatic food consumption by 2015. The fisheries and aquaculture sector contribution to Gross Domestic Product (GDP) typically ranges from around 0.5 to 2.5 percent, but may exceed 7 percent in some countries, which often compares very significantly with agricultural sector GDP. Aquatic foods have high nutritional quality, contributing 20 percent or more of average per capita animal protein intake for more than 2.8 billion people, mostly from developing countries. Millions of people around the world depend on fisheries and aquaculture, directly or indirectly, for their livelihoods. Worldwide, fish products provide 15% or more of the protein consumed by nearly 3 billion people and support the livelihoods of 520 million people, many of them women (FAO 2009, The World Fish Center 2008). Currently, an estimated 42 million people work full or part time as fishers and fish farmers, with the great majority in developing countries, principally in Asia. Hundreds of millions of other people work in the sector as occasional fishers or in associated activities including supply and post-harvest services, marketing and distribution. Growth in sector employment, largely outpacing that of agriculture, has been mainly in small scale fisheries and in the aquaculture sector in the developing world where it has important seasonal income, food supply and security impacts. (FAO, 2008).

Climate change and its impacts on Fisheries and Aquaculture:

Oceans are warming in the 0-300 m layer, which is the zone where most of the world fisheries exist. It is predicted that the Mean Sea Level would rise between 10 and 90 cm in the 21^st centaury. Changes in ocean currents, as well as having a substantial influence on the worlds climate, may have significant direct effects on aquaculture through changes in temperature, primary productivity and hence food availability, and distribution of disease toxic algae blooms and predators (Handisyde et al, 2008 ). The vulnerability of fishery and aquaculture to climate change is complex, reflecting a combination of all factors associated with production. Lakshmi, A. & Ramaya, R.( 2009) has illustrated this complex i.e.,

Temperature:

Average temperature, is predicted to rise between 1.4 and 5.8°C between 1990 and 2100 with changes most likely to be in the 2 - 4.5°C range. It will have a direct impact on all other factors responsible for production. There are likely to be influences on other factors such as oxygen levels, toxic algal blooms, and the prevalence of pests, diseases and predators. Temperature may influence in both ways i.e., positively or negatively. It increases the growth rate, thus it would increase the per unit area production but temperature above 30°C stops feeding and slows the growth rate (McCauley and Beitinger, 1992). It will enhance Net Primary Productivity (NPP) to benefit production of filter feeders. It is predicted that it may lower natural winter mortality.

Apart from these it may pose huge negative effects i.e., decreasing dissolved oxygen, increasing harmful algal blooms that release toxins in the water and increase fish kills increasing in infestations of fouling organisms, pests, nuisance species etc. Portner, O.H. and Knust, R (2007) have reported that, the eelpout, Zoarces viviparus, a bioindicator fish species for environmental monitoring from North and Baltic Seas (Helcom), that thermally limited oxygen delivery closely matches environmental temperatures beyond which growth performance and abundance decrease. Direct effects of climate change affect the physiology and behavior of fish. The distribution of fish is controlled by water temperature as fish are cold blooded (poikilotherms), unable to maintain their body temperature. Therefore, increasing water temperatures make the fish move to waters more suitable to them.

Alteration in Water level:

One of the certain outputs of the climate change is mean sea level rise and changes in current patterns. Mean sea level rise would take place over a long time period scale. Though it is difficult to forecast the consequent changes due to both of this two factors, it is assumed that it may effect distribution of fish stocks and migration patterns. Sea level rise and the increased penetration of seawater is believed to be preferentially increasing the halo-tolerant mangroves in the Sunderban. This could result in an increase in the brackish water fish and a decrease in the freshwater fish.

For inland waters, climate change will bring alterations to the evaporation and precipitation cycles that may well be much more serious and take place much more rapidly than for the case of salt water aquaculture. Although one may be able to predict temperature rise due to climate change, the evaporation and precipitation will be much more variable and difficult to forecast. The former will depend on cloud cover and windiness in addition to temperature, while the precipitation climate is not only expected to change, but may increase or decrease depending on the region concerned. So the major concern in some areas would be water supply.

Net Primary Productivity

Net Primary Production of any water body regulates the production system and very importantly in coming years a good assessment of NPP in relation to climate change may forecast the future trend of oceanic production. The productivity of water body depends upon phytoplankton populations which depend on the availability of light and nutrients, which in turn are governed by runoff, atmospheric dust deposition, ocean mixing processes, cloud cover, and the solar cycle. Satellite measurements of ocean color over the past two decades show changes in global NPP but with large regional differences that can be related to changes in upper-ocean temperature gradients, wind stress, and atmospheric iron deposition (Behrenfeld MJ et al, 2006). It is assumed that temperature may alter the thermal stratification of the water body which may affect the net exchange of gases and nutrients at the water surface that in turn may cause an alteration of the primary productivity and as a result it could seriously bring the changes in the food chain and food web that could eventually result in alteration of species assemblages because of changes in food availability, species specific differences in thermal tolerances, disease susceptibility and shifts in the competitive advantage of species. There is also evidence from both the Pacific and Atlantic that nutrient supply to the upper productive layer of the ocean is declining because of reduced meridional overturning circulation, increased thermal stratification, and changes in windborne nutrients (McPhaden Mj et al 2002 and Curry, R. & Mauritzen, C. 2005).

Alteration in Supporting Ecosystems

Some important marine ecosystems such as mangroves, sea grass and coral reefs, that are hugely under stress due to habitat destruction by human interference, pollution etc, climate change may add more stress to it and may completely bring the structural and behavioral change in the ecosystem. Lakshmi, A. & Ramaya, R. (2009) has reported that Climate change is also expected to increase the number of extreme events such as tropical cyclones. For example, tropical cyclone Nargis reportedly caused the destruction of some 17,000ha of natural forest. It is predicted that ecosystem changes would be rapid in coming times. Brander, K.M. (2007) has cited three reasons i.e. (i) the rate of future climate change is predicted to be more rapid than previous natural changes; (ii) the resilience of species and systems is being compromised by concurrent pressures, including fishing, loss of genetic diversity, habitat destruction, pollution, introduced and invasive species, and pathogens; and (iii) rising CO₂ levels are lowering the pH of the oceans, with consequences that are largely unknown.

Impacts on Economics and Community:

Perhaps the grave concern about climate change would be regional climate variability. Productivity and specific species resources in the region may be varied. That eventually may decrease the catch per unit effort and compel to go further for harvest which would demand more effort and cost. Moreover changing environmental conditions i.e., cyclones, rough weather will make the whole scenario more risk prone. Allison et al. (2009) used an indicator based approach to compare the vulnerabilities of 132 nations to potential climate change impacts on their capture fisheries. They found that countries in central and western Africa as well as some in Asia were most vulnerable. Indirect economic impacts will depend on the extent to which local economies are able to adapt to new conditions in terms of labor and capital mobility. Change in natural fisheries production is often compounded by decreased harvest capacity and reduced access to markets (FAO, 2006).

Conclusion:

Fisheries and Aquaculture continues to be the fastest growing animal food producing sector and to outpace population growth, with per capita supply from aquaculture increasing from 0.7 kg in 1970 to 7.8 kg in 2006, an average annual growth rate of 6.9 percent. Gradually it's drawing attention in the international arena about the potential impact due to Climate Change. Several reports have been placed already and created a mixed response in both a detrimental and beneficial way but, as the ocean ecosystem is very complex, the exact outcome seems very unpredictable to coin. As Asian countries mainly dominate the fisheries and aquaculture sector and this is the region where greater poverty and aquaculture related livelihood prevails, it should draw attention of policy makers and world aquaculture fisheries authority to take the matter seriously and find out remedial measures or policy to cope up with Global Climate Change.

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