Climate change and its impact on fish

Themshang Sasa *

mahseer (Ngara in Manipuri)

The climate of a place is the average weather that is experiences over a longer period of time. It is the natural phenomenon that has occurred throughout the history of the earth. Climate change is associated with higher temperature, altered rainfall, changes in the trend of relative humidity and higher level of atmospheric carbon dioxide and other greenhouse gases (GHGs) like methane, chlorofluorocarbons (CFCs), ozone (O3), water vapour, nitrous oxide. Climate change is due to natural variability or as a result of human activities. Human activities have altered natural climatic processes by booting atmospheric concentrations of several greenhouse gases (GHGs).

Scientists have reported a number of substantial evidences revealing consistent with global climate change. If we look at the Top 10 hottest years on record ever measured in the atmosphere record, they have all occurred in the last 14 years (1990, 1991, 1995, 1997, 1998, 1999, 2001, 2002, 2003, 2004 &2005) and the hottest of all was 2005. Greenland ice sheet lost two cubic miles of mass per year during 1993-1998.

Climate change is caused by two major categories, natural and man-made. Some of the natural causes of climate change are volcanic eruptions, tilting of earth axis and ocean currents. Ocean covers about 71% of the earth surface, and it has major influence on climate system. Ocean currents carry huge amount of heat and cold across the earth surface. The direction and speed of ocean current may change influencing the weather parameters of the regions. Much of the heat that escapes from the ocean is in the form of water vapour, the most abundant green house gas. Certain parts of the world are influenced by ocean currents more than others.

Ocean current may have great impact on climate in long run. Now the question arises about the causes of ocean warming. Human activities to meet modern life-style have increased GHS such as carbon dioxide, methane, nitrous oxide, water vapour that cause greenhouse effect is warming the ocean. This in turn is changing the course of ocean current that result in series of climatic events. The GHGs are now far about their natural concentrations in atmosphere.

Some of the human activities that produce GHGs are forest fire, industrial process, emission from power plant, motor vehicles, agriculture activities, dairy farming, explosion etc. Carbon dioxide is a good transmitter of sunlight but restricts infrared radiation from going back into the space and causes greenhouse effect that prevents drastic cooling of the earth during the night.

Currently, carbon dioxide is responsible for 57% of the global warming. Methane is another important greenhouse gas in the atmosphere which is emitted during the process of oil drilling, coal mining (through underground air circulation), incomplete combustion of fossil fuel. Methane is also emitted from the paddy field and other marsh area especially after flood.

A team of scientists from every corners of the globe got together under the Inter-governmental Panel on Climate Change (IPCC) has affirmed that the global warming is real, serious and accelerating. Permanent change in weather parameters triggers weather extremes such as high temperature, floods and droughts. Since the end of the 19th century the earth average surface temperature has increased by 0.3-0.6°C. Scientists estimated that man-made emission of greenhouse gases are likely to lead increase in global average temperature of between1.4°C and 5.8°C by another 100 years (IPCC, 2001).

Impact on Fish

Climate change can affect fish directly, by affecting their physiology, growth and behaviour and indirectly, for example, through affects on ecosystem structure and function. For poikilothermic (cold-blooded) animals like fish, warming will directly affect their metabolism. Growth rates in temperate (mild temperature) species are predicted to increase initially as temperature rise, but then decline as individual struggle to maintain cardiac function and respiration in the faces of increased metabolic demands. Researchers have provided evidence in consistent with this prediction for a marine fish Cheilodactylus spectabilis in Tasman Sea; one of the most rapidly warming regions of the southern hemisphere ocean.

When fish encounter water that is too cold for them, their metabolism slow down and they become lethargic. In contrast, as the surrounding water warms up their metabolism speeds up and they digest food more rapidly, grow more quickly, and eventually have more energy for reproduction. But fish needs more food and more oxygen to support this higher metabolism.

Global warming also means that some warm water fish species can be exploited (carp and other fish that are cultured in hot places) and cool water fishes would benefit from an increase in available habitat space at northerly latitudes, and some cool water species would gain access to higher altitudes and latitudes that are currently too cold to inhabit.

However, this shift would dramatically alter assemblage relationships with unknown consequences (Mandrak, 1989). Cold water fish species will probably be both replaced and displaced by warm water species especially, invasive generalists, accelerating the process of faunal homogenization. Any "gain" would be offset by an overall lost of genetic and species diversity, especially, because climate appears to be changing too quickly for genetic change to keep pace.

Researchers in ICAR, Manipur Centre, Lamphelpat, are now focussing on harnessing the beneficiary effect of higher temperature in some aquacultural fish. This ensures exploitative opportunities for some fish species and at the same time mitigation measures may be taken as climate change is likely to reduce the abundance of some species while increasing the abundance of others.

Some fish species fail to spawn successfully in lower temperature as they mature slower in low temperature regime. However, it is aware that fishes in warmer temperature tend to mature quickly but are often at the cost of smaller body size. 90% of aquatic animals like fish raised in warm water end up smaller than their peers raised in cooler temperature (Sullip K.M et al 2011).

Scientists predicted that many fish will also have less off-spring as temperatures rise, and some may not be able to reproduce at all and become permanently sterile. This was drawn from the fact that the testis and ovary recovered from fishes reared in comparatively higher temperature have shrunk, devoid of germ cells and become sterile, contrarily, fish reared in ambient (immediate natural condition) condition have thick germ cell population that make them sexually more competent .

Temperate species like trout (Sana nga in Manipuri) and salmon cannot spawn at all if winter temperatures do not drop below a certain level. In Manipur and other north eastern region, climate change will threaten the sustainability of hill stream fishes that is economically important species like mahseer (Ngara in Manipuri)and other hill stream fish like Botia spp. (Sareng koiba), baril (Ngawa) etc. due to rising water temperature and reduced river flow. Fish may not have enough oxygen to breathe as water grows warmer.

The amount of oxygen dissolved in water decreases as temperature rise. So, many fish will experience stress due to oxygen deficient environment. With increase in temperature, metabolic rate of fish increases. They will need more oxygen to support their elevated metabolisms but they may not be able to get it from the warmer oxygen-poor water around them.

As global temperatures rise, some fish may be able to shift locally by moving deeper or by heading upriver towards cool water. Now in north eastern hill region of India fishes like golden mahseer once abundantly distributed in streams located at low altitude( < 500 m above MSL) are no longer available in the said altitude. Probably these fishes have headed toward high altitude or cooler water zone. Unfortunately this migration is obstructed by dams or reservoirs artificially generated by man.

As our water bodies are warming up, many parasites and microbes that cause fatal fish diseases will grow faster and become more virulent. So, more fishes will be infected. If harmful microbes and parasites become more numerous fishes which are already stressed by warm water, low dissolved oxygen (due to rise in temperature) will become even more susceptible to diseases. Consequently fishes will die massively.

It is paramount that concerted effort be made by individual, club, organization and government agencies locally and globally to cut down greenhouse gas emission, particularly carbon dioxide as obliged under Kyoto protocol to cut CO2 emission to pre-industrial CO2 level. To stay below 2øC danger threshold, the industrialised countries must reduced their emission by 60-80% . While meeting the developmental goal, working on the possible remedial and alternate perspective to be able to shift to alternate technologies to clean and sustainable technologies is the need of the hour all over the world.

Our state should declare aquatic protected area for a globally threatened species of fish. Some rivers, their tributaries and their beds should be designated as 'National Park'.

Wildlife and fisheries department should go to the extent of creating aquatic national park and not confined only in production of fish for commercial purpose. Indigenous hill stream fishes need to be protected by creating hill stream fish national park as it is necessitated by the threat to the mahseer species and lots of other fishes that play pivotal role in the maintenance of biodiversity and ecological balance.

The Golden Mahseer, scientifically known as Tor putitora is the largest fresh water fish on earth found in many of the rivers originating from Himalayas. The Mahseer fish inhabits the southern watersheds of the Himalayas and live in lakes, dams or man-made impoundments but migrates upwards to the tributaries to locate the shallow, gravel stream beds where it breeds each year.

Fishing during monsoon time should not be allowed as this is the fishes spawning period and it is important they are not disturbed during this time when they travel far upstream in search of spawning sites. The Mahseer which is found in some districts of Manipur like Ukhrul and Tamenglong (Chindwin and Barak drainages) is a super streamlined carp/barbel family member and can grow in excess of 80 lb (36.288kg) and 6ft in length or more. Other spectacular hill stream fish in hill region of Manipur include Neolissochilus hexagonolepis, Neolissochilus stracheyi and Tor tor (All of them locally known as Ngara in Manipuri).

Unsustainable commercial over-fishing, uncontrolled subsistence angling using poisons, electrical devices and explosives, uncontrolled fishing in the breeding season and destruction of the spawning habitat by extraction of gravel and sand seriously threaten the population of Mahseer river system.

Gradual decline in the population of threatened species was a matter of grave concern not only for Manipur and concern authorities but also for the conservationists across the globe, Therefore declaration of rivers as national park would help arrest all such activities that is detrimental to ecological balance and fish fauna in particular. Concern authorities should formulate legislation that prohibits activities that threatened hill stream fishes in river system concern and would be liable to punishment, including imprisonment or fine or both, under such Act or the existing Act should be exercised.

However, a community mobilisation programme may also be launched in cooperation with the rural support programme for the benefit of the communities dwelling near the river and its tributaries and dependant on them for livelihood. These communities may be involved in a participatory conservation programme and may be entitled to 80 per cent of the revenue generated from the protected area in future.

Supports from the World Wide Fund for Nature (WWF), Himalayan Wildlife Foundation (HWF) Programme etc. may be obtained for both fund and technical part in conservation and management of aquatic life in hill stream of Manipur.