No abstract

This study investigated the food quality characteristics of mottled skate Raja pulchra including the proximate composition, taste, color, flavor and texture as affected by area caught (Heuksando and Daecheongdo), sex and fish weight (heavy, intermediate and light grades). Based on viable cell counts, all of the mottled skates studied remained fresh. The moisture and protein contents of the mottled skate did not differ by the area caught and fish weight, but differed by fish sex. The taste of mottled skate was affected only by fish weight. The texture of the mottled skate differed according to fish sex and fish weight. The odor intensity did not differ for the three parameters.

Catches, CPUE, fishing season, disc width composition and fishing ground were studied to rebuild skate ray, Raja pulchra resource by the offshore longline fishery in Heuksan-do, Korea. Annual catches and CPUE of skate ray were increased from 2003 to 2010 (CPUE: from 2007 to 2010) continuously. The main fishing season of the skate ray was from December to next May. Disc width at 50% maturity for Raja pulchra by sex were estimated to be 65.83cm, 57.01cm by female and male respectively. The range of disc width was 22.3-112.0cm and the average disc width was 66.9cm, 60.0cm by female and male of Raja pulchra respectively during 2007-2010. Annual average of disc width of female skate ray was decreased from 2007 to 2010. The fishing grounds were formed from the coastal water off Hong-do to the coastal water off Gyeogyeolbiyeol-do, Korea. The center of fishing ground in October was formed in the northwestern coastal water off Gyeogyeolbiyeol-do and separated from that of the other months.

To estimate the impact of aggregate mining on a marine ecosystem, fish assemblages and phytoplankton communities were analyzed using environmental DNA metabarcoding. Metabarcoding analysis revealed 152 fish amplicon sequence variants (ASVs) (88 in September and 118 in February), which were assigned to 29 orders, 62 families, 104 genera, and 114 species (73 in September and 89 in February). Heatmap analysis showed that the fish assemblages in the mining area clearly differed from those in the surrounding area and that Pagrus major, Lateolabrax japonicus, Zeus faber, and Eopsetta grigorjewi were significantly more abundant there than in the surrounding area. In the phytoplankton community in September, the phyla Cyanobacteria and Haptophyta differed significantly between the mining area and its surroundings. By contrast, no such significant differences were identified in February, presumably due to the low temperature impeding phytoplankton growth. Taking these findings together, mining activities clearly affect fish and phytoplankton communities, but further long-term study is required to assess their impacts on marine ecosystems.

The forming of fishing ground and the population ecological characteristics of yellowtail, Seriola quinqueradiata, in the coastal waters off Gim-nyeong of Jeju Island were investigated. The stock of yellowtail, Seriola quinqueradiata, between Jeju Island and coastal areas of the East Sea is probably the same. Water temperature probably is a major factor for controlling distribution of yellowtails in deeper, offshore areas off Jeju Island. However, the major factor that determines aggregation of yellowtails in coastal areas of Jeju Island, especially off Gim-nyeong is probably strong tidal currents driven by distribution of yellowtails rather than hydrological conditions such as Yellowtails collected off Jeju Island were from 1 to 4yrs old and about 50% of them were 1 -yr old, probably indicating overfishing. Jack mackerel was the major prey item for yellowtails off Gim-nyeong from October to March, suggesting concurrence of the two species.