was observer capture fisheries in major reservoirs

was revised.

1.4.2.
Reservoir Fishery in Sri Lanka

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In Sri Lanka reservoirs mainly
constituent with ancient reservoirs and new reservoirs constructed primarily
for two major economical purposes, including irrigation and generation of
hydroelectricity. Generally reservoirs are rarely or
never created for fishery as a primary purpose. As a secondary purpose the
impounded waters used for fisheries as a secondary purpose is becoming an
increasingly important activity particularly in the Asian continent. The total
extent of reservoirs of the country is included 155,000 ha (MoFARD, 2015).

The
extant reservoir density is about 2.7 ha per square kilometer, which is highest
reservoir density in the world.
The fish production in Sri Lanka reservoirs was 55,000 MT in 2003, contributing
for 11% of the total fish production in country. Medium and large perennial reservoirs (> 250
ha) are provided more than 80% of the inland fish production. Generally
tropical reservoirs are highly productive with annual average yield of 283 kg
ha-1 (De Silva, 1988; Fernando, 2000). In Sri Lanka culture based fishery activities are
conducted in the seasonal tanks, while the perennial reservoirs are important
in capture fishery. Characteristics
of reservoir fishery in Sri Lanka

Three
characteristics can be observer capture fisheries in major reservoirs of Sri
Lanka, a) the fishers use of non-mechanized fiberglass outrigger canoes,
approximately 5-6m in length operated by one or two persons; b) gill nets used
as an exclusive fishing gear by fishermen, 6-20 net pieces per craft and mesh
sizes ranges more than 8.5 cm; and c) the catch is predominant with exotic cichlid species Oreochromis
mossambicus and Oreochromis niloticus (De Silva, 1988). 85 native freshwater fish species
are reported in Sri Lanka is belongs to 19 families and 24 exotic fish species
have been introduced since late 19th century. Reservoir fish communities are not
essentially identical to the fish communities recorded in rivers and streams,
due to the differences in habitat preferences of them (Pethiyagoda, 2006).

The
restrictions on gears and regulations of mesh sizes of gill net fishery
imposing the minimum permissible mesh size 8.5 cm, resulted in incomplete
utilization of fishery resources including most of indigenous fish species. Be that as it may, the fishery potential in tropical
reservoirs isn’t completely utilized because of the deficiency of methodologies
for scientific administration (De Silva et al. 1991; Amarasinghe & De
Silva, 2015)   Furthermore, due to the
presence of submerged tree stumps use of wide variety of gear types are limited
or impossible in many reservoirs (Jayaginghe et al,
2017). Due to this gear regulation and high consumer demand Oreochromis
mossambicus and Oreochromis niloticus contributing over 90% of total
fish landing in reservoirs (Ajith &
Amarasinghe,2008).

1.4.3.1.
Ecological Aspect of Reservoirs

Generally
reservoirs are presence of intermediate characteristics between rivers and lakes,
consisting riverine zone close to the inflow area, lacustrine or lentic waters
close to the dam bund and intermediate zone between these two extremes. (Thornton
et al. 1990). Therefore, reservoirs can refuge wide variety of fish species
ranging from those adapted to riverine habitats and those adapted to lacustrine
habitats. In tropical region of Asia, less number of fish species adapted to
lacustrine habitats. Naturally indigenous fish species are preferable to
colonized in limnetic zones of the reservoirs, because food resources are
constantly available with slow flowing habitats (Yap,
1999). Due to the complex interaction of several factors which is
influenced to biological productivity of reservoir, the differences in annual
fish yield in reservoirs cannot be easily understood  (De Silva & Amarasinghe, 2009).

The ecology of
reservoirs plays an important role with determining the habitat quality and the
carrying capacity level for fish harbor in the reservoirs and provides the
basis for fishery activities and socio-economics of riparian fishing
communities. Perspectives of fisheries