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The real effect of uncontrolled and intensive small-scale fisheries, due to open-access and
common-property right nature, is rarely evaluated. Such a small-scale fishery is operated for
shrimpi; in shallow coastal waters off Jaffna using drag nets. The dragnet catches have been
observe id which comprise with large amount of very small blue swimming crabs (BSC) (Portunus
pefagicui). Therefore, this study aimed to analyse the non-targeted BSC catch and the effects of
this dr ig net fishery on BSC industry. Weekly samples of BSC which randomly collected from
dragnet landing were analysed from June to December 2015, the peak fishing period of dragnet.
Around 140 fishermen from Saanthai were found to be migrating 8-45 km daily to Ponnalai,
Velanc i and Punkuduthivu fishing grounds, which are abundant with sea grass beds and adjacent
mangdwe, to operate dragnet: 1.5 x 5 m long; 1.27 cm stretched mesh net piece connected to
strong! poles at either sides, and in between lighter vyooden poles to facilitate dragging by two
fished from both sides. At the fishing grounds 70 ± 3 gear units were operated per day. Catch
per uf it effort was 26.58 ± 9.62 kg per day. During the study period Shrimp: by-catch ratio
varied from 1:5 to 3:1, while Shrimp: BSC ratios were 3:4 to 95:1 in weight basis. O f BSC, 72 %
was smaller than the Lso, 7.68 cm carapace width which has been calculated by Sivanthan and
De Crx>s (2012). Among them, 40 % of BSC individuals were 5 times smaller than the Lsoin
number. Moreover, 60.5 % of BSC were immature individuals probably caught while migrating
towards sea from the nursery ground. Per day 23 % of these smaller BSC was discarded while
Seaweeds and sea grass discards were 33 %, indicating the damage caused on the important
nurserjy habitat for juvenile BSC. This study emphasises the importance of implementing and
monitoring BSC resource management regulations even on the other multispecies fisheries and
their fcy-catches.
