Size selection and exploitation pattern of diamond mesh codends with different mesh sizes in demersal trawl fishery for banded scad (Caranx (Atule) kalla) in the South China Sea

Effects of Codend Mesh-Shape and Size on the Size Selectivity of Demersal Trawl Targeting Banded Scad (Alepes djedaba) in the Beibu Gulf, South China Sea

“…The trials took place in the Beibu Gulf in the northern SCS (Figure 1). This fishing area was selected according to the information of the previous experiment by Yang et al [9] to ensure sufficient catch data for the species investigated. To mimic a commercial fishing condition, the fishing practice was kept identical to that of commercial-fishing trawlers.…”

“…In order to mitigate the by-catch of undersized individuals in trawl fishery, one simple modification would be to increase the mesh sizes of the codends. This modification has been proven to have positive effects on improving the selective properties of demersal trawls targeting Banded Scad in some previous studies in the SCS [8,9]. For example, the selective properties were better if the codend mesh-size increased from 25 to 30 mm.…”

“…For example, the selective properties were better if the codend mesh-size increased from 25 to 30 mm. When the mesh size further increased to 40 mm, however, negative effects were demonstrated by Yang et al [9], as CIs in the selectivity parameters and selectivity curves became wider and the loss of marketable individuals of Banded Scad became of concern. Thus, other alternative modifications need to be considered to optimize the selective properties of trawl codends for this species.…”

“…For instance, the results of a study by Yang et al [8] showed that the D25 codend was so unselective that nearly no escape of Banded Scad was observed. More recently, another selectivity experiment was conducted by Yang et al [9] to test the legal D25 codend in an otter-board trawl fishery. Their results were much better, obtaining two selective parameters: L50 (the length with 50% probability of retention) and SR (selection range) at 6.99 and 1.94 cm, respectively, however, their confidence intervals (CIs) were relatively wide at (0.10-9.22) and (0.10-6.41) cm, respectively [9].…”

“…More recently, another selectivity experiment was conducted by Yang et al [9] to test the legal D25 codend in an otter-board trawl fishery. Their results were much better, obtaining two selective parameters: L50 (the length with 50% probability of retention) and SR (selection range) at 6.99 and 1.94 cm, respectively, however, their confidence intervals (CIs) were relatively wide at (0.10-9.22) and (0.10-6.41) cm, respectively [9]. Moreover, their results showed 2 of 11 that the exploitation pattern of the D25 codend was undesirable, as more than 20% of undersized Banded Scad was retained in the SCS.…”