독도 연안역 어류상 장기변동과 먹이망 구조 계절변화 = Long-term Changes in Fish Assemblages and Seasonal Food-Web Dynamics in the coastal waters around Dokdo

다국어 초록 (Multilingual Abstract)

This study hypothesizes that the intensification of oceanic turbulence and alterations caused by the cold current flows in the Dokdo region are driving to increase sea surface temperature. These environmental changes are expected to induce structural shifts in local fish assemblages, transitioning from temperate-dominated communities toward mixed assemblages that include tropical and subtropical species. Consequently, feeding strategies and trophic structures within these assemblages are anticipated to be reorganized, reflecting the ecological impacts of climate-driven oceanographic variability. Fish assemblages were investigated through multi-year surveys （2008–2024） using SCUBA diving and commercial gill nets. Species were classified according to year and seasonal water temperature. Their feeding ecology, trophic levels, and food web structures were also analyzed using both stomach content and stable isotope methods. During SCUBA surveys （2008–2020）, 109 species belonging to 47 families and 12 orders were identified. Perciformes accounted for the largest proportion, reaching 77.8% in 2012 and declining to 53.7% in 2018. Scorpaeniformes showed the opposite trend, comprising 34.1% in 2018 compared to 11.1% in 2012. Tetraodontiformes reached their highest proportion （15.0%） in 2017 and the lowest （6.1%） in 2013. In gill net surveys （2020–2024）, 35 species from 17 families and 6 orders were recorded, with Perciformes dominant. Seasonal variation in water temperature strongly influenced fish species composition around Dokdo Island. During the high-temperature period （August–October）, when the average water temperature was over 20°C, a total of 109 species were observed, consisting of 38 temperate species （35%）, 38 tropical species （35%）, and 33 subtropical species （30%）. In contrast, during the relatively low-temperature season （May–June）, when the average water temperature was below 17°C, only 54 species were recorded, comprising 26 temperate species （48%）, 13 tropical species （24%）, and 15 subtropical species （28%）. Thus, the number of species observed during the low-temperature season decreased by 50.46% compared to the high-temperature season. These findings highlight the significant role of seasonal water temperature in shaping fish assemblage composition in the Dokdo region. Based on similarities in prey composition, fish species were classified into three major feeding groups. The first group, the crustacean feeders, included Sebastes inermis, Sebastes joyneri, and Ditrema temminckii, which consistently relied on crustaceans as their primary food source and exhibited high dietary similarity, representing typical crustacean specialists. The second group, the fish feeders, comprised Sebastiscus marmoratus, Sebastes zonatus, and Hexagrammos otakii, which showed a piscivorous tendency by consuming fish as the dominant prey item, clearly separated from the crustacean feeders. The third group, the omnivorous feeders, included Thamnaconus modestus and Oplegnathus fasciatus, which displayed non-specific feeding behavior by consuming a mixture of crustaceans, fish, echinoderms, and other taxa. These results highlight distinct trophic strategies among fish assemblages in the Dokdo region, differentiating ecological adaptations to prey availability. Feeding ecology analyses demonstrated diverse trophic niches. Predators such as Hexagrammos otakii and Seriola dumerili occupied higher trophic levels, whereas herbivorous species including Thamnaconus modestus and Stephanolepis cirrhifer were positioned at lower levels. Integration of dietary and stable isotope analyses enabled reconstruction of seasonal food web structures, suggesting differences between cold and warm seasons. This research examined patterns of trophic niche overlap and resource partitioning among dominant fish species in the coastal ecosystem of Dokdo through stable isotope analysis. The ecological niche breadth, expressed as standard ellipse area （SEA）, varied across species: Oplegnathus fasciatus （9.93）, Sebastiscus marmoratus （9.92）, Sebastes zonatus （9.61）, Sebastes inermis （8.15）, Ditrema temminckii （8.22）, Hexagrammos otakii （6.55）, Thamnaconus modestus （5.97）, and Sebastes joyneri （1.05）. Among these, O. fasciatus and S. marmoratus exhibited the widest trophic niches, while S. joyneri showed the narrowest. The dominant species displayed substantial niche overlap, with S. zonatus sharing more than 93% of its dietary sources with all other major species, indicating high potential for interspecific competition. In contrast, S. joyneri maintained a distinct trophic position, overlapping most with T. modestus （32.53%） but showing minimal overlap with H. otakii （1.73%）. Notably, O. fasciatus overlapped almost completely with S. joyneri （99.3%）. These findings suggest that while generalist species such as O. fasciatus and S. marmoratus exploit diverse food resources, specialist species like S. joyneri occupy unique trophic niches, thereby reducing direct competition. Overall, the coexistence of generalist and specialist feeding strategies highlights the complex trophic interactions and resource partitioning that structure the fish community in the Dokdo coastal ecosystem. This study provides fundamental baseline data on the structure and temporal dynamics of marine ecosystems around the Dokdo Island. The findings can be contributing to trophic dynamic, marine biodiversity conservation, and sustainable fisheries management in the context of climate change. Further multidisciplinary research to support these results will be needed.

목차 (Table of Contents)

• 1장. 연구개요 1
• 1.1. 종합서론 1
• 1.2. 연구해역 6
• 1.3. 연구동향 11
• 1.4. 연구목적 16
• 2장. 독도 연안역에 출현하는 어류의 종 조성 19
• 2.1. 서론 19
• 2.2. 재료 및 방법 24
• 2.2.1 과학잠수 조사 24
• 2.2.2 어획 조사 27
• 2.2.3 자료 분석 29
• 2.3. 결과 30
• 2.3.1 과학잠수 조사로 확인된 어류 종 조성 30
• 2.3.2 어획 조사로 채집된 어류 종 조성 52
• 2.4. 고찰 59
• 2.4.1 독도 어류 종 조성（과학잠수 조사） 59
• 2.4.2 독도 어류 종 조성（어획 조사） 61
• 2.4.3 과학잠수 조사와 어획 조사 간 비교 63
• 3장. 독도 서식 어종 간 먹이자원 섭식 분할 관계 68
• 3.1. 서론 68
• 3.2. 재료 및 방법 70
• 3.2.1 상대성장（체장-체중 관계） 70
• 3.2.2 소화관 내용물 조사 71
• 3.2.3 자료 분석 73
• 3.3. 결과 74
• 3.3.1 주요 어종의 체장분포 74
• 3.3.2 주요 어종의 체장-체중 관계 및 비만도 변화 80
• 3.3.3 주요 어류의 소화관 내용물 조성 및 성장, 계절 변화 90
• 3.3.4 주요 어종의 영양단계 비교 및 먹이섭식관계 131
• 3.4. 고찰 137
• 4장. 주요 어종 간 먹이망 구조 및 생태적 지위 분석 142
• 4.1. 서론 142
• 4.2. 재료 및 방법 146
• 4.2.1 탄소 및 질소 안정동위원소 조사 146
• 4.2.2 영양단계 및 먹이망 구조 조사 147
• 4.2.3 자료 분석 148
• 4.3. 결과 149
• 4.3.1 탄소 및 질소 안정동위원소비 값 149
• 4.3.2 안정동위원소비 값의 계절변동 154
• 4.3.3 안정동위원소비 값의 성장에 따른 변화 162
• 4.3.4 어류군집의 안정동위원소비 값의 시기별 비교 164
• 4.3.5 주요 출현종 먹이분할 관계 및 중복도 166
• 4.3.6 어류 분류군의 영양단계 비교 170
• 4.4. 고찰 171
• 5장. 종합고찰 175
• 5.1. 독도 표층수온 변화와 어류상 장기변동 175
• 5.2. 주요 어종의 계절별 먹이원 변동 182
• 5.3. 주요 우점종 간 먹이분할 관계 192
• 5.4. 독도 연안역 계절별 먹이망 구조 199
• 5.5. 정책제언 203
• 5.6. 결론 206
• 감사의 글 208
• 참고문헌 210
• Appendix 238