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Spatial variability in long-term changes of climate and oceanographic conditions in Korea.
The Academy 2008 Journal of environmental biology Vol.29 No.4
<P>I evaluated long-term changes in hydrological conditions (temperature, salinity and dissolved oxygen) in Korean sea waters in relation to the regional land climate change (air temperature and precipitation) based on available meteorological and oceanographic data. Regression analyses, spatial patterns and cross-correlations on the climatologic and hydrological factors suggested that industrialization processes and related urban heat-island effects during the past 37 years from 1968 to 2005 in South Korea have increased land surface temperatures by 1.267 degrees C, at least for the urban areas, and subsequently increased sea surface temperatures by 0.975 degrees C and decreased salinities by 0.229. The influence of land surface temperature on the sea water temperature reached at least 75-m depth. Regarding the causality in the land-ocean climate changes, air-temperature changes preceded sea water temperature change by 0-2 months in spring and summer; but the sequence could be reversed, possibly because of potential heat held by the ocean. This study demonstrated that human factors have been driving warming influences on regional sea waters, impacting marine ecosystems and changing dominant fish species in commercial fishery catches of Korea.</P>
모의실험을 통한 한국 연근해 고등어(Scomber japonicus)의 가입당 생산 분석
이경환 ( Kyunghwan Lee ),고성길 ( Seonggil Go ),정석근 ( Sukgeun Jung ) 한국수산과학회(구 한국수산학회) 2018 한국수산과학회지 Vol.51 No.3
Chub mackerel Scomber japonicus is an economically important pelagic species in the western North Pacific. In the last 50 years, the annual total catch in Korean waters showed large fluctuations, ranging from 100 to 420×10<sup>3</sup> tons. To provide a biological reference point for management of chub mackerel, we applied a simulation-based yield-per-recruit (Y/R) model that considered both temperature-dependent growth and size-dependent mortality. We estimated the fisheries yield with respect to varying biological reference points and environmental conditions, including 1) the instantaneous rate of fishing mortality (F), 2) length of fish at first capture (L<sub>c</sub>), and 3) water temperature. The result of our analysis showed that the Y/R could be greatest when the L<sub>c</sub> ranges from 19-27 cm and F ranges from 1.48-2.00 yr<sup>-1</sup>. Y/R increases with increased water temperature between 15 and 23℃. We suggest targeting an L<sub>c</sub> of 17 cm (age=0.6 years) under the assumed current of F=0.48 yr<sup>-1</sup> for maximizing the chub mackerel harvest. Further analysis considering spawning and recruitment processes are required to provide biological reference points to ensure the sustainability of chub mackerel fisheries in Korean waters.
Observed Pattern of Diel Variation in Specific Gravity of Pacific Mackerel Eggs and Larvae
Lee, Hwa Hyun,Kang, Sukyung,Jung, Kyung-Mi,Jung, Sukgeun,Sohn, Dongwha,Kim, Suam Korea Institute of Ocean ScienceTechnology 2017 Ocean and Polar Research Vol.39 No.4
Although Pacific mackerel (Scomber japonicus) is an important commercial species in Korea, its recruitment mechanism remains largely unknown. Diel vertical positioning of larvae in the water column, which is affected by their specific gravity and the surrounding water density, may help to provide an understanding on recruitment success through predator avoidance and prey availability. The specific gravity measurement on Pacific mackerel eggs and larvae would seem to be essential information necessary to learn about the transport process from spawning to nursery grounds, and consequently the recruitment success. Eggs were artificially fertilized, and larvae were fed with rotifer when their mouths opened 3-4 days after hatching. We conducted the experiment using a density gradient water column to measure the ontogenetic changes in specific gravity from fertilization to 10 days after hatching. Egg specific gravity was stable during most of the embryonic period, but a sudden increase to $1.0249g\;cm^{-3}$ happened just before hatching. However, the specific gravity of newly hatched larvae was much lighter ($1.0195g\;cm^{-3}$), and specific gravity tended to increase continuously after hatching. Comparison of specific gravity with seawater density reveals that eggs and newly hatched larvae can float in the surface layer of the ocean. For the later period of the experiment, the specific gravity showed a cyclic diel pattern: the highest in the evening while the lowest at dawn. The fullness of larval stomach may be responsible for the observed differences in specific gravity, because stomach fullness was lower (40-60%) at midnight, and higher (80-85%) in evening. The diel pattern of specific gravity might provide clues regarding how larvae match the diel vertical migration of prey organisms.