UTILIZATION PATTERN AND POTENTIAL FACTORS OF THE YANGTZE FINLESS PORPOISE IN AN ISOLATED HABITAT PATCH

Habitat loss and fragmentation caused by various types of human disturbance pose significant threats to the population of Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) inhabiting the Yangtze River mainstream. Studies on utilization patterns of fragmented habitat patches surrounded by human activities by Yangtze finless porpoises can provide valuable insights into their response to human disturbance and aid in targeted habitat conservation efforts. Hejiazhou water in Ma'anshan section of the Yangtze mainstream is an excellent habitat for the Yangtze finless porpoise because of the well-developed shallow waters. However, Hejiazhou water is encircled by shiiping, large ports and channel regulation engineering, causing this water body into an island-type habitat patch for the Yangtze finless porpoises. Visual observation and acoustic monitoring were both used in this study to survey seasonal and diel activities of finless porpoises in two sites of Hejiazhou water and in one site of Niutun Beach water, a natural near-shore water of the Yangtze River. Detection rates were compared between these two different habitat patches to reveal utilization patterns of the island-type habitat patches by Yangtze finless porpoises and to analyze potential influencing factors. The results revealed that porpoises primarily concentrated in Hejiazhou water and Niutun Beach, with an average sighting of (10.00±2.35) and (15.60±8.17) individuals during the wet and dry seasons, respectively. No significant difference was detected in sightings between the two seasons. Porpoises were detected nearly every day in Hejiazhou and Niutun Beach waters during both seasons. During the wet season, detection rates of porpoises in shallow water and confluence area of Hejiazhou, as well as Niutun Beach water, were 0.377, 0.06 and 0.140, respectively. During the dry season, these rates were 0.137, 0.216 and 0.495, respectively. Porpoises showed randomness in diel pattern. Although statistically significant differences were detected in some sites and seasons, these rates varied only slightly in numerical terms, indicating the utilization rate of finless porpoises in Hejiazhou water was nearly equally between daytimen and nighttime. These results suggest that finless porpoises continue to display a high utilization rate of the Hejiazhou waters, which are encircled by high dense human disturbance, particularly during the wet season. However, during the dry season, due to combined pressures from low water levels and shipping occupation, the utilization rate of the Hejiazhou shallow waters by porpoises was significantly reduced. On account of high utilization rate of porpoises in Hejiazhou waters and the surrounding human disturbance, this study suggests that avoidance and protection of migration corridors should be strengthened.