Fishing under Climate Change Conditions: Local Constraints at the Waterhole of Rouafi, Konni (Niger)

In Niger, the fishing sector supports the needs of communities for their income as well as to meet their nutritional needs for protein. The present work focused on fishing on the Rouafi waterhole, rural community of Bazaga, Konni department. The main objective of this work is to examine the evolution of fishery products in a climate change context. The methodology used in this study is based on the processing of meteoro-climatic data, data on the quantities of fish caught in the Rouafi watherhole, and the identification and mapping of the space occupied by cryptocoryne. The results show that climatic parameters (rainfall and maximum ambient temperature) do not directly influence the quantities of fish caught in the Rouafi waterhole. On the other hand, in parallel with the decrease in the quantities of fish caught, Cryptocoryn spiralis, an aquatic plant species, developed strongly.


Introduction
The major droughts of the 1970s and 1980s, soil erosion and high anthropogenic pressures have caused accelerated environmental degradation in the Sahel (Rishmawi & Prince, 2016). This degradation has caused not only the reduction and decline of the productive potential of the "natural resource capital", but also the disarticulation of the centuries-old systems of production and management of natural environments (Mahé and Paturel, 2009; Moussa Issaka, 2014; Karimou Barke et al., 2018). This is the case of wetlands, which are confronted, among other things, with invasive plant invasions (Amani and Barmo, 2010). Among the effects of this trend, from which communities are already suffering, are the decline of fisheries, water pollution, the proliferation of toxic algae and, above all, the erosion of biodiversity (Youssoufa, 2004;Walther, 2016).
In Niger, before the great droughts of the 1970s, fish catches were around 11,000 tonnes, of which 7,000 tonnes were caught in the Niger River and 4,000 tonnes in the various water bodies. In the following years, catches plummeted to their lowest level in 2009 with 1,469 tonnes, including 900 tonnes for the Niger River and 569 tonnes for the various water bodies (DPA, 2011). While, fishing brings together nearly 50,000 people and generates a turnover of more than 40 billion CFA francs (MHE, 2012).
In Konni Department, fishing is practiced around some 17 ponds and reservoirs. All these ponds and reservoirs have benefited from fish stocking operations and fishermen's equipment, which are organized in cooperatives. The Rouafi pond (rural commune of Bazaga) is one of them. It has a permanent water regime and covers an area of more than 36 ha. The pond has been stocked three (3) times (1984; 1994 and 2014) but yields are constantly decreasing. It is in this context that this study, which concerns fishery products (fish) from the Rouafi pond, is being conducted.
The general objective is to examine the evolution of fishery products in the context of climate change. Specifically, the aim is to compare the evolution of the quantity of fish caught according to climatic parameters (rainfall and temperature); and to discuss the evolution of the quantity of fish caught according to Cryptocoryne spiralis.

Study area
The waterhole of Rouafi, is located in the village whose name it bears. Rouafi is in the rural commune of Bazaga (4°59'4'' -5°11'04'' E and 13°44'33'' -13° 56'00'' N), located 15 km west of the capital of Konni department (in central-western Niger) ( fig. 1). Its average depth is 1.5m in low water and exceeds 3m in high water (DDE/Konni, 2018). The hydrographic network of the waterhole of Rouafi is essentially composed of temporary watercourses that only operate during the rainy season. The water that is collected in the waterhole of Rouafi comes essentially from runoff after rain. This runoff originates on the one hand from the immense chain of hills that surround the reservoir and on the other hand from a few watercourses, the main one being the Maggia (DDP/Konni, 2018).

Google Earth Image
Google Earth images covering the waterhole of Rouafi are from the month of November, which corresponds to the period when the waters of the pond are clearer. The images are from 2010 to 2017 that is to say 8 scenes.

Evolution of the quantities of fish caught
Simple statistical calculations (sum, mean, standard deviation) are used to characterize the annual and seasonal evolution of the quantities of fish caught on the waterhole of Rouafi. This evolution was compared with that of the meteorological-climatic parameters to investigate the possible relations of temperature or rainfall on fish caught quantities. The comparison was made using the Pearson correlation.
The normalized values of this correlation provide a synthetic measure of the intensity of the relationship between two characteristics (Snedecor & Cochram, 1989).

Quantification of the surface occupied by cryptocoryne spiralis in the waterhole
On Google Earth images of the waterhole, some dark areas are visible. After identification, these areas correspond to the surface occupied by a cryptocoryne spiralis, an aquatic plant (Picture 1). These areas were delimited and their statistical variation were calculated on ArcGis software.   This year is also a deficit year in the CRU.TS series (Fig.3).

Evolution of fish production versus temperature
The evolution of the annual quantity of fish caught in the waterhole of Rouafi was compared with that of the maximum ambient temperatures (monthly) of the Konni station and the NCEP/NCAR reanalysis. In order to comply with the fishing schedule, this comparison will focus on the season when fishing is not carried out. This season is considered as the renewal period of the fish stock in the pond. The season runs from September to February (Fig. 4).   The expansion of Cryptocoryne spiralis could explain the decrease in fish catch observed at the waterhole of Rouafi (Fig. 6). Indeed, the Cryptocoryne spiralis serves as a shelter for fish and prevents some tools (gillnet and sparrowhawk net) from reaching the bottom of the pond. This species is less described in the water bodies of Niger. Rather, it is the plant species Eichornia crassipes or water hyacinth that is mainly described in the Niger River (Amani and Barmo, 2010; Mounkaila Ganda, 2015). This hyacinth causes an eutrophication of the environment that would explain the decrease in the fish population.
(Amani and Barmo, 2010). Cryptocorynus spiralis could have the same effects on the fish population of the waterhole of Rouafi.