鯨豚受海洋廢棄物影響之亞洲案例與臺灣二十一年鯨豚擱淺資料分析

Abstract

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Cetaceans are widely regarded as sentinel species of marine ecosystem change and health, and continuously monitoring their welfare should therefore be of high conservation concern. However, several cetacean species are threatened by various anthropogenic pressures worldwide, including marine pollution, fishery activities, and concurrent habitat degradation. The threat of marine debris pollution has in particular gained increasing scientific attention due to emerging evidence of its detrimental welfare impacts on cetaceans. In light of such emerging concerns, the first part of this thesis – Chapter 2 – investigates various cetacean – marine debris cases from across Asia, with a focus on macro-debris interactions. The cases are synthesized and discussed along with a review of the primary biological and ecological impacts on cetaceans reported to date. In doing so, this chapter addresses the urgent knowledge gap prevalent in Asia regarding the welfare threat of litter pollution on cetacean populations. Interactions with litter were recorded in 86 individuals, comprising 27 identified and 6 unidentified species of 6 families of Cetacea; Balaenopteridae, Delphinidae, Kogiidae, Phocoenidae, Physeteridae, Ziphiidae. Interactions thus occurred in a large number of species with different foraging strategies and habitat preferences. In total, 89% documented ingestion of anthropogenic materials, primarily various plastic-derived items, 9% of cases documented entanglement involving fishing gear, and 2% recorded both ingestion and entanglement interactions. However, due to logistical and resource constraints in several monitoring locations, there is presumably a high prevalence of undetected and unrecorded cases, meaning that the full extent of interactions occurring in Asia needs further investigation. Furthermore, due to the natural mobility and ranges of cetaceans, these species are notoriously hard to study and collect continuous data of. However, examining stranding data can help overcome such inherent methodological challenges, and provide valuable insight into species occurrences, disease, population trends, and indicate overall population health. Therefore, the second part of this thesis – Chapter 3 – focuses on descriptive and spatio-temporal analyses of long-term stranding data from Taiwan during 2000 to 2020. The analyses of stranding records show a clear increase in strandings, with a total of 1439 stranding events recorded, comprising 23 odontocete and 4 mysticete species. A high cetacean species diversity (n = 27) is confirmed in Taiwanese waters, consistent with previously published records. Clear seasonal patterns were also identified, with most incidents occurring during “cold season” (December – April), and fewest during “warm season” (May – August). Such patterns may be indicative of season-specific abundance or habitat use, or possibly season-specific anthropogenic pressures such as fishery activities. Additionally, the most frequently stranded species, finless porpoises (Neophocaena spp.), pygmy killer whales (Feresa attenuata), and common bottlenose dolphins (Tursiops truncatus), are all particularly vulnerable to various human activities. While the cause of increase in strandings, seasonality patterns, and variability in species’ susceptibility to strand, needs further investigation, these findings provide critical knowledge of cetacean occurrence, vulnerable populations, and stranding hotspots around Taiwan – which is essential information for conservation management. Additionally, evidence of human interactions (HI) in strandings were investigated and detected in 8.6% individuals (63 out of 735), and primarily included interactions relating to fishery gear. However, this number should be interpreted with caution as several limiting factors exists in terms of detecting and reporting HI, thus contributing to the low detection rate presented here. Overall, there is an apparent need for continued research efforts to expand on the current state of knowledge regarding cetacean welfare status in Asian waters. Regional cooperation and data sharing would greatly enhance future cetacean monitoring and assessment of human impacts on cetaceans. Additionally, methods to respond to and investigate cetacean strandings would benefit from becoming further standardized and should preferably include dedicated protocols for detection of HI. Such improvements will greatly improve our knowledge of cetaceans in Asian waters and will also allow for collection of better-quality data for future analyses.