Mesh selectivity of encircling gill net for gizzard shad Konosirus punctatus in the coastal sea of Korea

ABSTRACT:   Fishing experiments were carried out in Yeongil Bay, Korea using an encircling gill net with four different mesh sizes and two different hanging ratios to measure the mesh selectivity for gizzard shad Konosirus punctatus . Twenty-six trials were conducted giving a total catch of 485 gizzard shad. The 'share each length's catch total' (SELECT) analysis with maximum likelihood method was used to fit the different functional models, the normal, lognormal, and bi-normal model, for a selectivity curve to the catch data. In addition, two cases in which the relative fishing intensity was either estimated or fixed were compared. The bi-normal model with the fixed relative fishing intensity was found to fit the data best. For the selectivity curve on the bi-normal model, the relative length (the ratio of fish length to mesh size) with the maximum efficiency was obtained as 3.70. From this, the focal fish lengths in the commercial encircling gill net, with mesh size ranging from 5.0 to 6.0 cm, were inferred to be 18.5–22.2 cm.     

Analysis of the green fraction of humic acids

The green fraction of humic acids (HAs), Pg, was fractionated by gel chromatography on Sephadex G-50. Repeated chromatography of the crude Pg obtained by the first chromatography of HA yielded a sharp peak (G₁) and two broad bands (G₂) of purified Pg. The recovery of Pg in G₁ and G₂ as percentages of the total Pg content of the HA were 16.2 and 14.5%, respectively. Distinct peaks were detected at 615, 570, 450 and 280 nm in the UV-visible spectra of both G₁ and G₂ in alkali solutions. Estimates of weight-average molecular weight were 9.7 * 10³ for G₁ and 1.23 * 10⁴ for G₂. In the ¹H-NMR spectra the percentage of hydroxyl groups of 4,9-dihydroxy-perylene-3, 10-quinone (DHPQ) nuclei, which are known to be the chromophore of Pg, was 4.1 and 4.5% of the total H, respectively. Based on these values and the H/C ratios, DHPQ-C was estimated as 28% of total C. ¹³C-NMR spectra obtained using inverse-gated decoupling yielded 40–41% aromatic C, which suggested the presence of aromatic rings other than DHPQ. All of the IR, ¹³C- and ¹H-NMR spectra indicated that the two purified Pg samples largely differed from each other in their contents of alkyl and polysaccharide components.