Pensi (Corbicula Moltkiana, Prime 1878) Population At Lake Maninjau In Related To Its Exploitation And Cage Aquaculture Activities.
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Pensi (Corbicula moltkiana, Prime 1878), a species of molluscs (bivalves) of Lake Maninjau, have become one of the local fishery commodities. Cage aquaculture (CA) activity in Lake Maninjau has led to deterioration of pensi habitat and also by ongoing pensi exploitation severely threatened its population. Until now the availability of pensi in Lake Maninjau has not been measured, while the population pressure on either exploitation or environmental degradation continue to take place. Thus the purpose of the research is to study the influence of pensi exploitation and CA activity on pensi population in order to formulate a management plan for pensi utilization in Lake Maninjau. Cage activities in Lake Maninjau spread throughout the shores with the density between "scarce" (<225 units.km-1), "dense" (225-675 units.km-1) until "crowded" (> 675 units.km-1). Sediments substrate in the northern and eastern part of the lake was composed of sand and a mixture of sand and mud; while that in the southern and western part was composed of gravel and rocks. Cluster analysis to anthropogenic parameter water quality show that the conditions throughout the stations were similar (Similarity> 85%). Based of water quality cluster analysis, the CA density were grouped into two levels: "Low" (<675 units km-1) and "High" (> 675 units km-1). T- test to anthropogenic parameter of water quality results levels of COD on Low CA density area were lower than that of High density. However, the levels of other parameter have no significant differences. Level of CA density ("Low" and "High") and the sediment fraction character were set as criteria for pensi population analysis and resulted in three categories of regions: I) High CA density; Soft substrate; II) Low CA density; Soft substrate; and III) Low CA density; Hard substrate. Annual average of pensi abundance was 148-3,994 ind.m-2, the highest were at a depth of 1 m and 3 m, on sandy, and in Low CA density area. The annual production [P] of pensi between 216 - 799 g AFDM m-2 year (y)-1, biomass [B] was 91 – 214 g AFDM m-2 and P/B ratio ranged from 2.02 to 3.73 y-1. The highest production was in Region II, while the lowest production was in Region I. Region I also has the highest coefficient of total mortality (Z) indicated high environmental stress on the pensi population and show high utilization rate or overfishing (E> 0.5). The other regions have a utilization below of its sustainability potency (E < 0.5). Exploitation rate of pensi the whole weight was 42 kg d-1 equal to 12.4 g AFDM d-1 per fishermen. Total exploitation yield of pensi was 111 tons AFDM y-1. Seeing as the potential pensi available was 425 tons AFDM y-1, the utilization rate was lower than sustainably potency (26%). The recruitment of new pensi populations in Lake Maninjau takes place throughout the year in line with frequent findings mature until spawning stage gonad and small size of pensi (<2.5 mm).
- DT - Fisheries