1.0 Introduction
1.1 Background of the Study
Nigeria is a maritime country with tremendous aquatic and fisheries resources that make significant contributions to livelihood, food security and the overall economy of the nation. The country's fresh water and marine fisheries resources are enormous with tremendous opportunities for fish production through capture and cultured fisheries (fig.1).
The country's freshwater bodies (Table. 1) was estimated about 14 million hectares, comprising of seasonal and perennial rivers, lakes, reservoirs and dams (Table.1). While the coastal waters (creeks, lagoons and estuaries) housing most aquaculture cover about 37, 934km2, with an undisputed marine jurisdiction over the physical, chemical and biological resources exploitation within a distance of 320 km nautical kilometers (853 km2) into the Atlantic Ocean (FAO, 2014).
Most fisheries exploitation in freshwaters and coastal waters are carried out by artisanal (small scale) fishermen, employing simple fishing gear and equipments. This subsector employment, according to FDF (2008) has over 8 million fishermen, with another 18 million people engaged in fish processing, distribution and marketing, thereby accounting for a well over 80% of the total annual domestic production of the country.
While, the industrial fishing sub-sector dominate the Atlantic Ocean, especially as the country's portion of the Atlantic is not an isolated entity (Ipinjolu et al. 2014) [24]. While several studies have implicated climate change on rapidly changing physical, chemical and biological properties of known water bodies to sea level, with significantly impacts on fisheries; a subsector known to contribute about 4% Nigeria annual domestic fish production, are made up of significant few large-scale investors.
The climatic and geomorphic characteristics of Nigeria has placed the country among vulnerable and one of the most threatened countries globally. Although, these impacts are widely reported as direct and indirect or positive and negative consequences, including in aquaculture; their impacts are becoming more evident. However, the country's highest contributions to global fisheries estimated in 2014 was from inland aquaculture, in line with the 2008 Central Bank of Nigeria Statistics office (fig. 2) (FAO, 2014), and believed to be most threatened by changing climate.
According to FAO (2008) [16], climate change impact is expected to cut across ecosystems, societies and economics, livelihood and food supplies in West and Central African countries most vulnerable due to their fragile ecological and geological formation (WorldFish Centre, 2007) [37], coupled with their climate characteristics. In climate change scenario, fisheries and aquaculture are particularly vulnerable because aquatic habitats directly absorbed and store part of the solar energy, especially as most fish species are cold blooded, except Pangasius species with ability to thrive in both tropical and temperate environment; a concern for top producing countries like Vietnam and China.
Climate change impact directly on water quality by changing the physio-chemical conditions through temperature increase, and consequently on other important assessment which can increase the risk indices for aquatic lives. Several empirical studies have been conducted to investigate the different impacts of climate change on Nigeria fisheries and aquaculture which includes the work of Idowu et al. (2011) [19] on the Impact of climate change in Nigeria; Ipinjolu et al. (2014) [24], the potential impacts of climate change on fisheries and aquaculture in Nigeria; Anyanwu et al. (2015) [3], climate change, effects and mitigation strategies on aquaculture: a review; Essam and Senebe (2013) [15]; Impacts of climate change on fisheries: implications for food security in Sub- Saharan Africa; Aphunu and Nwabeze (2012), Fish farmers' perception of climate change impact on fish production in Delta State, Nigeria (Leon and Antonio, 2015).
According to these authors, climate change scenario especially through temperature and carbon dioxide increase will continuously warm the earth with resultant effects on fisheries and aquaculture, and that Nigeria vulnerability is high. Leon and Antonio (2015) asserted that warming has increased thermal stratification, reduction in surface water cold and warm mix thereby preventing upwelling effects of nutrients, and consequently affect primary productivity, the distribution and fecundity of marine fishes.
Surprisingly, it was also observed that changing climate through temperature will temporarily increase dissolved oxygen in water which will deplete afterwards due to increase in biochemical Oxygen demand; a natural phenomenon in water noted to regulate water quality. This have been observed to increase nutrient content of water bodies causing algal bloom, thus eutrophication of waters in Netherlands (Verweij et al., 2010) [35].
Increase in temperature can adversely increase food consumption by fish, especially small sized fishes, and resultantly increase the cost of inland aquaculture. Consequently, increase biological oxygen demand (BOD), deplete available dissolved oxygen (DO) and thus, pollution of water bodies and death in some cases. The quality of a water body is key to the survival of fish life, which is an important consideration for both marine and inland aquaculture assessment.
1.2 Statement of Problem
Changes or poor water quality has been reported to result to large scale fish death in ponds or marine ecosystems, especially as fish and shellfishes known to have suitable environmental conditions to thrive in some of these aquatic systems. In Vietnam for example, the 2008 Vedan factory pollution incident and 2016 large scale surface water pollution was reported to cause ecosystem damage and unquantifiable fish kill (Ngoc, 2008 and Vietnam News).
Although aquaculture have been reported to contribute to greenhouse gas emission and thus global warming (a phenomenon associated with temperature increase from normal); the contribution is still at minute level, when compared to other anthropogenic sources. Increase in carbon dioxide will lead to acidification of waters and decalcification of shell fishes and complete change in ocean chemistry occur. The influence of climate change on surface water is very striking and should be studied in-depth to provide improve information in assessing water quality.
Climate change through temperature increase will temporarily increase dissolve oxygen concentration; consequently increase biochemical oxygen demand (BOD), which will deplete the available oxygen causing an anoxia in water bodies. Increases in dissolve oxygen (DO) have been observed to regulate water quality by reducing carbon dioxide concentration in waters (Verweij et al. 2010) [35].
The livelihoods in Nigeria lies between longitudes 2°49' E — 14°37E and latitudes 4°16N'13° 52N and with two distinctive seasons (dry and wet) suitable for agricultural production, with an average rainfall above 2800mm and high relative humidity of about 80 — 92%.
The aim of this paper is to highlight some of the attendant impacts of changing climates and strategies for adaption to sustain an industry contributing to National and livelihood development in Nigeria.
1.3 Research Objective
The objective of this study was to evaluate impact of climate change on fisheries and aquaculture.
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