FLOOD AND FISHERY RESOURCES OF ASSAM

Dr. Ranjita Bania

(Assam Tribune_21May-2013)

Assam is endowed with rich inland water resources in the form of ponds, beels, streams, lakes, reservoirs, natural wetlands and gurgling rivers. No doubt, river provides food and habitat for a diversity of life, ranging from a tiny freshwater fishes to the giant human beings. Especially in Assam, river becomes the lifeline for the communities residing on the bank particularly for the fisher. At the same time it brings gloom for human life too. Flood damages not only the property but also the agricultural crops of the victims. It was observed that the impact of flood in 2012 was virtually more on paddy because paddy seeds were just sown at the time of flood and paddy seedlings were lost in more than 44,000 ha area due to flood which would have cover an area of around 4.5 lakh ha of crop land in the entire state.

Historically, riverine flooding was considered to be a nuisance. Flooding was thought to negatively impact flora and fauna, and be potentially hazardous to humans. Recent studies, however, have demonstrated that flood is a specific characteristic of a riverine ecosystem Further, a regular annual flood is of particular advantage to aquatic systems along large floodplain rivers. Aquatic fauna, in general, are adapted to this annual flood pulse, and many of them colonize the floodplains at rising and high water levels because of breeding and feeding opportunities that arise. In floodplain rivers, the recession of the annual flood delivers high levels of dissolved organic carbon and detritus to the main channel.

In a state like Assam, 4-5 times typical monsoon flood is common phenomena as the state falls under the heavy and prolonged rainfall zone, which leads to very high flood in the flood plains of Brahmaputra. This in tern creates huge fisheries resources for consumption and sports. This flood water ensures availability of nutrient rich food supply to the organisms including fish. The amount of available feed also increases with flood. Most of the fishes breed in the early monsoon i.e. April to June.  After the receding flood though feed resources are available, it decreases comparatively opening the golden chance for the anglers. No doubt, flood act as catalyst for sport fishing accelerating the growth of fish.

Variation in water level influences riverine systems. Rising water levels not only increase the wetted surface of the channel and eventually of the floodplain, but at the same time influence the exchange between groundwater and surface water either by allowing an up-welling of groundwater or by forcing a down-welling of the surface water into the aquifer vertically and laterally. Dynamics of water flow and nutrient status of floodplain habitats is very important for the early life history stages of riverine fishes.  According to Low Flow Recruitment Hypothesis unpredictable flooding and decoupling of the flood pulse from the temperature pulse leads to low temperatures during floods and high temperature that triggers spawning of some fish species during low water level. However, large rivers derive most of their animal biomass from the floodplains. Without the flood pulse, production within the river ecosystem is drastically reduced, and community composition and energy pathways are radically changed. Similarly, disturbances also play a critical role in organizing communities and ecosystems.

Eventhen, flood in Assam has never been taken as a positive indication for large breeding ground of fish in numbers and size. With the onset of flood and monsoon the naturally available feed resources increases many fold, leading to fast growth and size. In Assam every year flood brings miseries to the people but it also brings a many fold blessing for fishery resources. Assam has the largest potential for recreational sports fishing for its large water bodies including wastelands, beels, ponds and of course the mighty Brahmaputra and its tributaries.

            During the monsoon months the flood water inundates the open beels and there is virtually no demarcation between river and the connected beels. The aquatic fauna of the beels get the chance of feeding as well as breeding that arises along with the flood pulse. The flood water also carries a large number of adult brooders to the connecting beels. In fact these beels are the spawning grounds for many of the riverine species which form the bulk of the capture fishery. As the flood recedes, these fishes return to the main river. Major carps and giant catfish (Sperota, Bagarius, Pangasius, Silondia etc.) migrate to the upstream during monsoon/rainy season as do many other species presumably for spawning purpose. This annual inundation has both positive as well as negative impacts.  Though it helps in auto stocking of ichthyofauna at the same time it carries silt to them which now a days become a severe problem in many of the beels of Assam as in Dibru Saikhowa destructing the suitable productive habitats to a comparatively less productive ones. Mobile organisms such as fish actively seek floodplain carbon in mass migrations as soon as flooding begins in order to feed in the floodplain.

            However, the abundance of large sized fish species in a river stretch depend on adequate cover such as pools and deeply undercut banks, which these fish can use to avoid the predators. Increased frequency of flood substantiates the fact that water holding capacity of river is considerably reduced. Due to this large fish migrate upstream during flood but take reverse direction as flood recedes. Thus flood act as boon for both anglers as well as for the sport fishery. The intensity of fishing is also closely associated with the flood regime of the river. The riverine fishes march into new areas, creeks, channels, flood plain lakes and other water bodies at the time of high flood. However, as the flood subsides, the fish return to the main river. This is why there is high intensity of fishing just before and after the flood.  In spite of these vast potentialities the pressure on the wild riverine fish stock is very high but the production from the same is not fitting to the total catch statistics of Assam. Fish production data of 2011-12 shows lowest productivity of riverine fishery i.e. 190 kg/ha among the various water resources of Assam. No doubt, wild collection data is not recorded properly, though it occupies a lion share of catch. That is why it is not reflected in national economy. A proper estimate of riverine production in terms of fish catch statistics for the main rivers viz. Brahmaputa and Barak and its major tributaries is an immediate necessity which may contribute to establish the authentic riverine production scenario of Assam.