Ring-net Landings at Galle fishery Harbor, at South Coast of Sri Lanka with Special Reference to Trigger Fish Catches (Canthidermis maculatus)
Ring- net fishery which is mainly targeting medium sized pelagic fish has become popular in the south coast of Sri Lanka As no studies have been carried out to study the fishery and biology of trigger fish species in Sri Lanka, this study aims to evaluate the variations in ring net catch rates, total catch and length frequency distribution of Canthidermis maculatus landed at Galle fishery harbor from August to November 2017. Catch and effort data on ring net fishery were collected by making fortnightly field visits to the Galle fishery harbor. Trigger fish samples were collected randomly from the unloaded ring - net landings to estimate the morphometric parameters and length weight relationship. Monthly, as an average of 15 multiday boats operating ring- nets are landing at Galle fishery harbor. In ring- net caches Thunnus albacares, Decapterus russelli, Katsuwonus pelamis, Canthidermis maculatus were predominant. Ring- net catch rates variation ranged from 678.75 – 2872.6 kg per boat per trip while catch rates of C. maculatus were in the range from 89.37- 424.41 kg per boat per trip. The total ring net landings at the Galle harbor during the study were 855.8 tonnes of which contribution of C. maculatus was 197.37 tonnes. Decapterus russelli (Linna) showed the highest contribution (51%) to the total ring - net landings followed by Trigger fish (23.06%). Length and weight of C. maculatus ranged from 20.1 cm to 32 cm and 200.4 g to 600.1g, respectively. More than (75%) C. maculatus landed by ring- nets belonged to the length group of 25 – 30 cm. C. maculatus exhibits isometric growth (b=2.91). The observed variations in ring- net catch rates and contribution of C. maculatus to the fishery may be due to several reasons including the variations in number of multiday boats operated for ring net fishery, shifting of fishing grounds and seasonal variations in aggregation of these schooling fishes. This study indicates that C. maculatus is the second dominant species in the ring net catches landed at Galle fishery harbor.
Catch Rates, Galle Fishery Harbor, Ring Net, Trigger Fish, Sri Lanka
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