Assessing the information-content of messy data to reconstruct population recovery dynamics for the world's rarest primate.

Understanding the dynamics of population recovery in threatened species requires robust longitudinal monitoring datasets. However, evidence-based decision-making is often impeded by variable data collection approaches, necessitating critical evaluation of restricted available baselines. The Hainan gibbon, the world's rarest primate, had possibly declined to only seven or eight individuals in 1978 at Bawangling National Nature Reserve but has experienced subsequent population growth. Past population estimates lack detailed reporting of survey effort, and multiple conflicting estimates are available, hindering assessment of gibbon recovery. We investigated all reported estimates of Bawangling gibbon population size from 1978 to 2022, to evaluate the biological signal of population trends and the extent to which noise associated with varying survey effort, reporting and estimation may mask or misrepresent any underlying signal. This longitudinal dataset demonstrates that the Bawangling population experienced a series of bottlenecks and recoveries, with three successive periods of growth interspersed by population crashes (1978-1989, 1989-2000 and 2000-2022). The rate of gibbon population recovery was progressively slower over time in each successive period of growth, and this potential decline in recovery rate following serial bottlenecks suggests that additional management strategies may be required alongside "nature-based solutions" for this species. However, population viability analysis suggests the 1978 founder population is unlikely to have been as low as seven individuals, raising concerns for interpreting reported historical population counts and understanding the dynamics of the species' recovery. We caution against overinterpreting potential signals within "messy" conservation datasets, and we emphasise the crucial importance of standardised replicable survey methods and transparent reporting of data and effort in all future surveys of Hainan gibbons and other highly threatened species.

Functional extinction of dugongs in China.

Dugongs (Dugong dugon) experienced a serious population decline in China during the twentieth century, and their regional status is poorly understood. To determine their current distribution and status, we conducted a large-scale interview survey of marine resource users across four Chinese provinces and reviewed all available historical data covering the past distribution of dugongs in Chinese waters. Only 5% of 788 respondents reported past dugong sightings, with a mean last-sighting date of 23 years earlier, and only three respondents reported sightings from within the past 5 years. Historical records of dugongs peak around 1960 and then decrease rapidly from 1975 onwards; no records are documented after 2008, with no verified field observations after 2000. Based on these findings, we are forced to conclude that dugongs have experienced rapid population collapse during recent decades and are now functionally extinct in China. Our study provides evidence of a new regional loss of a charismatic marine megafaunal species, and the first reported functional extinction of a large vertebrate in Chinese marine waters. This rapid documented population collapse also serves as a sobering reminder that extinctions can occur before effective conservation actions are developed.

The medium over the message: Differential knowledge of conservation outreach activities and implications for threatened species.

Conservation outreach is regularly conducted to increase support for conservation by altering local awareness and attitudes about species or environmental issues. However, there is often little assessment of the effectiveness of these activities. We investigated knowledge of past conservation outreach in 26 villages adjacent to Bawangling National Nature Reserve, Hainan, China, which contains the last population of the Hainan gibbon (Nomascus hainanus). The medium of past outreach activities was reported most frequently by interviewees, followed by who delivered them and the outreach topic, with the fewest interviewees reporting the specific messages being communicated (the consequences of following conservation management policies). Negatively-framed messages, emphasizing prohibited activities and associated punishments, were reported more than positively-framed messages that aimed to foster conservation support. Male interviewees and those with higher education levels reported more aspects of past activities. The Hainan gibbon had higher salience than other threatened native species, and reporting the occurrence (but not necessarily the content) of past outreach was associated with increased likelihood of knowing that gibbons were threatened. These findings highlight the need for conservation outreach to increase both exposure and retention of key messages among target audiences. Meaningful and concrete conservation benefits should be communicated to local communities, and the effectiveness of outreach using a flagship species could be expanded to also improve awareness of other conservation-priority species within the same landscape.