Differential population dynamics of a coastal porpoise correspond to the fishing effort in a large estuarine system. Issue 2 (22nd January 2019) - Lin, Wenzhi
Abstract: The finless porpoise (genus Neophocaena ) is susceptible to fishery‐caused mortality, and its numbers are thought to be in decline across its entire range. However, population demographics have rarely been quantified for this genus, with a few exceptions of the narrow‐ridged form ( Neophocaena asiaeorientalis ) in waters off Japan, Korea, and in the Yangtze River of China, all of which show a drastic decline in recent decades. Similar analyses have not been performed for the Indo‐Pacific (known also as the wide‐ridged) finless porpoise ( Neophocaena phocaenoides ) that inhabits (sub‐)tropical waters; thus, reliable risk assessments are lacking. The demographic dynamics of the Indo‐Pacific finless porpoise in the Pearl River Delta (PRD) region were investigated by analysing 307 cases of beached carcasses that were recovered between 1996 and 2014. The mean instantaneous rate of increase r indicated a declining trend of 3.6% loss per annum during 1996–2005, and a subsequent recovering trend with 0.76% increase per annum during 2006–2014. The individual‐based Leslie matrix model constructed with the most up‐to‐date demographic parameters suggests that the conservation status of the finless porpoise in the PRD region corresponds to Near Threatened (NT) according to the International Union for the Conservation of Nature criterion A3. This temporal demographic change may be due to changes in fishing effort, which has been declining locally since the late 1990s. Although more quantitative evidence is needed, it is shown that regulated management of coastal fisheries can serve as an effective tool in securing the long‐term persistence of Indo‐Pacific finless porpoise in the PRD region, which likely applies also elsewhere in the genus/species' range where coastal fisheries overlap with the porpoise habitat. Results provide baseline ecological indicators that can facilitate further monitoring of the population status and trend.