Population Viability Analysis Revealed the Vulnerability of Yangtze Finless Porpoise (Neophocaena asiaeorientalis) in Poyang Lake

Comments 1: This manuscript presents and discusses the results of an analysis, via simulation software, of the threats to an isolated population of Yangtze finless porpoises and what might happen

to this population. Considering increasing habitat degradation and declining genetic

diversity, the population faces a very serious threat of extinction. The study is fairly

straightforward. The manuscript is clear and easy to read.

Response 1: Thank you. We agree with this comment.

Comments 2: Obviously, the citations/references will need to be converted—either by the authors or editorial staff—to the format used by this journal and other MDPI journals of numbered references instead of how they are given here (as parenthetical in-text citations and an alphabetical listing of references at the end).

Response 2: Agree. We have, accordingly, modified.

Comments 3: I am unfamiliar with VORTEX software. Is the name an acronym? I appreciate the citation (for Lacy, 2000) but the authors should name the publisher or owner of the software.

Response 3: Agree. We have added a sentence in the article to clarify the publisher and owner of the software. The software is developed and recommended by the Conservation Breeding Specialist Group (IUCN/SSC/CBSG), and its owner is the Species Conservation Toolkit Initiative (SCTI) project under the Species360 organization.

Comments 4: For all three figures, the legends (explanations of the colored lines) are extremely small—too small to read unless magnified greatly. These should be presented in a larger font size to aid readers, which should be very easy for the authors to fix.

Response 4: Agree. We modified the legends of all 3 figures.

Comments 5:In line 39, the YFP is described as a “relatively small” species. How small? Please give an average body length and citation.

Response 5: The maximum weight of the YFP is 78.5 kg, with an average of 39.1 kg. The maximum body length is 1.77 m, and the average is 1.30 m（Gao，1995）. 

Gao AL. 1995. Geographical variation of external measurements and three subspecies of Neophocaena phocaenoides in Chinese waters. Acta Theriol Sin.. 15:81-92.

Comments 6: Line 47: please cite one (or more) references regarding the current population estimates for this species.

Response 6: The results of the 2022 scientific expedition show that the population of Yangtze finless porpoises has reached 1,249, an increase of 237 compared to 2017（Li, Mei, et al. 2022）.

 Li, Mei, et al. A Comprehensive Analysis of the Increase in Yangtze Finless Porpoise Population: From the 2017 - 2022 Scientific Research Data. Marine Biology Research. 2023, 19(3): 245 - 258.

Comments 7: Line 56: YFP is described as “the most successfully protected natural population,” but it is unclear what the authors mean. Most successful relative to what? The most successfully protected of all species in Lake Poyang? The most protected of all endangered mammals, or odontocetes, etc., anywhere in the world? Please clarify!

Response 7: The Yangtze finless porpoise (YFP) is described as the "most successfully conserved natural population" relative to its own previous endangered status and in comparison with other endangered species.

Changes in its own population

Due to human activities, fishery exploitation, ship disturbances, etc., the YFP population once declined sharply. The 2017 ecological scientific survey concluded that its population was critically endangered. However, with the implementation of conservation policies such as the Yangtze River's ten-year fishing ban, the 2022 scientific survey showed its population increased to 1,249 individuals, a historic rebound of 237 individuals compared to 2017.

Comparison with other endangered species

Compared with rare species in the Yangtze River basin like the Chinese paddlefish (extinct) and the Yangtze river dolphin (functionally extinct), the YFP has achieved more significant conservation outcomes. Although the Chinese sturgeon has been protected for years, researchers have not detected its wild natural spawning for six consecutive years, and its survival remains highly threatened. Against this backdrop, the YFP's population increase makes it stand out as a "most successfully conserved natural population".

Comments 8: Line 68: A map (even a simple line drawing) showing the contours of the lake, and the region where the study area is located, would be very helpful to readers. Please strongly consider adding one.

Response 8: Agree. We added schematic Diagram of the Location and Water System of Poyang Lake Area.

Comments 9: Line 142: Concerning the location of the two bridges relative to the lake and river (and other nearby bodies of water)—again, a map would be very useful.

Response 9: Agree. We added schematic Diagram of the Location and Water System of Poyang Lake Area.

Comments 10: Line 150: The font size is much larger for a sentence here (which was presumably added during editing). Same for a citation in line 268.

Response 10: Agree. We made modifications as required.

Comments 11: Line 157: When was the YFP population threatened (starting what year?), or do the authors mean that it is currently threatened since [year]?

Response 11: The results of the 2017 ecological scientific survey of Yangtze finless porpoises organized by the Ministry of Agriculture and Rural Affairs showed that the population of Yangtze finless porpoises was approximately 1,012, of which about 457 were in Poyang Lake. We set this year as the starting year for evaluating population viability. The 2022 data can be used to verify which simulation scenario is closer to the real population dynamics.

Comments 12: A strength of this manuscript is that the writing is concise and crisp; the authors do not waste words. The final section, which includes their recommendations for action, is no exception. It says a lot with few words. I find that their conclusions concerning the need for YFP interchange (to maintain genetic diversity) as well as habitat protection, restoration, and expansion, are important and backed up by the findings of this analysis. The only things they might add to this section are more information about where (or what

populations) they recommend other YFP individuals be exchanged from—for example, from

far downstream? Are there other populations that are more genetically distinct from the

Lake Poyang population? Also, is the habitat degradation directly causing problems with

these porpoises, or indirectly, by harming its food supply?

Response 12: Agree. Individual exchange conservation actions for the Yangtze finless porpoise can be carried out between the two natural populations in Poyang Lake, Dongting Lake, and the Yangtze River mainstream, as well as between the Poyang Lake population and the four ex-situ conservation areas: Hubei Shishou Yangtze Tianezhou Dolphin National Nature Reserve, Anhui Tongling Freshwater Dolphin National Nature Reserve, Hubei Jianli Hewangmiao/Hunan Huarong Jichengwan Yangtze Finless Porpoise Provincial Nature Reserve, and Anhui Anqing Xijiang Yangtze Finless Porpoise Municipal Nature Reserve.

In November 2022, the Jiangxi Provincial Department of Agriculture and Rural Affairs organized the transfer of 111 YFP individuals from the southern sand pit of Songmen Mountain, including 66 male porpoises, 45 female porpoises, 11 mother-child pairs, 8 confirmed pregnant by B-ultrasound, and 7 suspected pregnant. As the population of YFP in Poyang Lake was about 492 in 2022, the rare drought that year put more than one-fifth of the Poyang Lake YFP in extreme danger (due to food shortage and increased stranding risks). "Protecting water means protecting the YFP in Poyang Lake" has become a national consensus.

Comments 1: In the title add Neophocaena asiaeorientalis (Pilleri & Gihr, 1972)

Response 1: Thank you for pointing this. We agree with this comment. Therefore, we have accordingly revised.

Comments 2: line 10: add Neophocaena asiaeorientalis after Yangtze finless porpoise

Keywords: the scientific name of the species i.e. Neophocaena asiaeorientalis  should be added

Response 2: Agree. We have, accordingly, done.

Comments 3: line 39:

change it to: (Neophocaena asiaeorientalis) YFP

Response 3: Agree. Therefore, we have accordingly revised.

Comments 4: line 76: add max lake depth, and average lake depth Please also include the average depth of other bodies of water frequented by the species i.e. Yangtze River, canals, etc., at least in the stretches adjacent to the lake 

Response 4: Agree. Poyang Lake is a "through-flow type" and seasonal freshwater lake, whose water level, area, and volume can vary significantly with seasons and years. Factors such as different measurement times, measurement methods, and the scope of the study area may also lead to differences in data on average water depth. Currently, when the water level of Poyang Lake is 21 meters (Wusong Datum), the north-south length is 170 kilometers, the maximum east-west width is 74 kilometers, the minimum is 3 kilometers, and the average width is 20.4 kilometers; the maximum water depth is 23.7 meters, and the average water depth is 5.1 meters; the water surface area is 3,960 square kilometers, and the volume is 26 billion cubic meters. YFP mainly inhabit waters with a depth of 2 to 9 meters. When the water depth exceeds 3 meters, the number of YFP decreases exponentially. They prefer relatively slow flow velocities, generally ranging from 0.3 to 1.2 meters per second.

Comments 5:line 228: Fig. 4 ???? What figure is this? I think it is Fig. 3. Check carefully and correct

Response 5: Agree. Figure 4 is a non-essential figure, which has been deleted to keep the paper concise, but due to our oversight, we failed to delete the annotations in text, which have now been removed, thank you.

Comments 6: In the discussion it should also be said what are the fish species preferred by the species and their consistency, at least in general terms, also because it could be a very important factor for the conservation of the species in the future. Are these prey fish fished professionally by humans, are some species decreasing? Furthermore, is human navigation with ships and boats present in the areas concerned? If so, does it have a potential disturb impact on the porpoise? 

Response 6: Agree. There is a strong coupling relationship between the YFP and the fish community in the Poyang Lake. The fishing yield and the population of the YFP showed a relatively high tendency of coincidence, that was, both of them first decreased, then increased, and had been stable and increasing since 2012. The areas with the high probability of YFP occurrence overlapped with the areas with high fish diversity index and catch per unit of effort. It is suggested that the YFP has a certain indicator function to fish diversity and fish density, and the higher fish diversity and density can ensure the nutrient balance and improve the feeding efficiency of the YFP. It is important to note that, the declining

trend of fish diversity in the Poyang Lake and its estuaries had not changed. The aggressive

predatory fish was recovering rapidly, while the survival of small fish was under great

pressure, seasonal and regional food shortages might be one of the limiting factors to the

recovery of the YFP population in the Poyang Lake. But the population

of Coilia nasus in the Poyang Lake was in an undeveloped state, and the population recovery

trend was obvious. This was good for increasing the source of food for YFP in the Poyang Lake. It should be noted in particular that the presence of ships was found to significantly alter the behavior patterns of YFPs. Specifically, the proportion of foraging behavior decreased from 48% to 33%, while the proportion of travel behavior increased from 32% to 43%. The distance between vessels and YFPs emerged as a critical factor influencing their behavioral responses. When vessels were positioned more than 300 meters away, YFPs exhibited a neutral response in 95% of the observed cases, with no discernible escape behavior. Conversely, as the distance closed to within 300 meters, the frequency of escape reactions among YFPs increased progressively, reaching approximately 30% when vessels were within 100 meters. In contrast, vessel type and cluster size of YFPs had only minor and statistically non-significant effects on their behavioral responses. These findings clearly demonstrate that the presence and proximity of vessels pose a substantial threat to the normal activities of YFPs. To safeguard the survival and well - being of this critically endangered species, it is imperative to implement strict regulations on navigation routes. In particular, maritime traffic should be restricted from traversing nearshore areas where YFPs are densely concentrated, thereby optimizing conservation efforts and enhancing the protection efficiency for YFP.