Habitat preference of the Yangtze finless porpoise in a minimally disturbed environment
Introduction
Distribution pattern of animals, including the extent of occurrence and core-habitat selection, relates to the complex and dynamic functions of habitat selectivity, accessibility of preys, social interactions, predator-prey interactions and inter-habitat mobility (Wilson et al., 1997, Heithaus, 2001, Davis et al., 2002, Torres et al., 2008, Garaffo et al., 2011, Braulik et al., 2012, Wang et al., 2015a, Wang et al., 2015b, Wang et al., 2016), which discloses ecological niche of animals in their living environment (Guo and Liu, 2010, Baird et al., 2013, Merow et al., 2013). Analysis on the animal distribution and habitat characteristics provides a valid approach to identify key features that define core habitats of animals (Skov et al., 2008, Garaffo et al., 2010, Garaffo et al., 2011). In conservation, these kinds of studies provide insights into population status, key habitat identification and action planning of habitat protection, management and restoration (International Union for Conservation of Nature IUCN, 2001, Wilson et al., 2004, Cañadas et al., 2005, Garaffo et al., 2011, Choudhary et al., 2012, Harihar and Pandav, 2012, Zhao et al., 2013, Wang et al., 2015a, Wang et al., 2015b, Wang et al., 2016). Distribution patterns disclosed from field surveys are often regarded as baselines of the habitat preference and selection. The habitat preference and selection analyses substantially depend on the sighting records of animals in field surveys (as in Baird et al., 2013), which are generally assumed at neutral status. The patterns of animal distribution and habitat preference, however, frequently fluctuate with biotic and abiotic status of the habitat environment (Rayment et al., 2010, Fury and Harrison, 2011, Cox et al., 2016, Wang et al., 2016), especially the anthropogenic activities. In areas where anthropogenic activities are frequent and intense, the change in distribution patterns and habitat preference can be substantial (Buckstaff et al., 2013, Huang et al., 2013, Huang and Karczmarski, 2015) and can reshape the population social structure and habitat preference (Wang et al., 2015a, Wang et al., 2015b). However, studies in the habitats where anthropogenic activities are frequent and intense may identify a misleading ‘baseline’ which actually represents a shifted status rather than a baseline representing the original habitat status. Conservation decisions based on a shifted ‘baseline’ can jeopardize the effectiveness and efficiency of conservation management. Analysis of animal distribution in a neutrally or minimally interrupted habitat can provide a natural state baseline that is essential for identifying key habitat characteristics and planning habitat protection and restoration measures.
The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), which is an endemic odontoceti in Yangtze River, China, is now critically endangered (Mei et al., 2012, Mei et al., 2014a, Mei et al., 2014b, Wang et al., 2013, Huang et al., 2016). Current conservation managements include enactment of a number of in situ and ex situ reserves, four months fishing ban and a captive breeding population (Mei, 2013, Huang et al., 2016). Since 2015 ex situ conservation measures such as establishing ex situ reserves receives more attention; and many local governments are seeking to establish their own ex situ ‘reserve’. There has been a long-standing debate over whether ex situ conservation measures are sufficient to preserve the critically endangered Yangtze finless porpoise (Huang et al., 2016). The latest modeling analysis of population dynamics demonstrated the necessity to implement and strengthen ex situ measures to preserve a number of viable porpoise populations for future reintroduction (Huang et al., 2016). However, the question of selecting adequate sites for ex situ reserves remains insufficiently answered, since knowledge of the baseline of habitat preference with little or no human disturbance for the porpoise are generally lacking.
The pervasive anthropogenic activities in the nature habitats of the finless porpoise, including the Yangtze River and the adjacent Dongting Lake and Poyang Lake, present a major challenge to acquire the baseline of habitat preference (Wang, 2009, Mei, 2013, Wang et al., 2013, Mei et al., 2014a, Mei et al., 2014b). It becomes extremely difficult and impracticable to find a site in natural habitats with little or no human disturbance. In contrast, the ex situ reserves provide a suitable environment where anthropogenic activities are minimal or controlled. Inside the reserve vessel traffic, fishing and behaviors likely polluting water quality are not allowed. Anthropogenic activities such as livestock breeding, farming and tree planting, on the other hand, shall be hold at least 200 m away from the reserve. Within a confined habitat, the extent of occurrence and distribution pattern can be used to extrapolate fundamental habitat requirements for the Yangtze finless porpoise in the wild.
A new ex situ reserve was enacted at He-wang-miao oxbow in 2015. This oxbow connects with the main stem of Yangtze River while earlier study indicates a water environment that is suitable for the Yangtze finless porpoise (Mei et al., 2014a, Mei et al., 2014b). We conducted a survey of the occurrence of the Yangtze finless porpoise and measure the habitat characteristics including bathymetry, benthic slop and fish resources in the ex situ He-wang-miao reserve, aiming to approach the baseline of habitat preference. We analyzed the correlations between porpoise occurrence and the three habitat characteristics. Based on above analysis, we discussed the habitat preference of the Yangtze finless porpoise, and the proxy to select adequate sites to enact ex situ reserves. These results shed a light to action planning of key-habitat protection and habitat restoration for the porpoise in the wild.
Section snippets
Study site
The He-wang-miao oxbow (112.983°N, 29.708°E), which is 33 km in length and 46.7 km2 in coverage, located in Hubei Province, China (Fig. 1), is currently an ex situ reserve of the Yangtze finless porpoise established in March 2015. A small channel at downstream connects the oxbow to the mainstream of the Yangtze River. A total of eight finless porpoises were translocated into this reserve in March 2015 (two females and two males) and December 2015(two females and two males) respectively.
Two
Distribution pattern and core habitat identification
Total 245 sightings of finless porpoise were recorded from April 2015 to July 2016 (Fig. 2). The MCP outlining all sighting records was 4.328 km2 area and 10.442 km in the maximal diameter (Table 1). Upon these sighting records, the 50% KDE was plotted at two dis-adjoining sites (Fig. 3) and 3.003 km2 area in total (Table 1). The 75% and 95% KDE were 5.797 km2 and 9.532 km2 respectively (Fig. 3).
Habitat preference analyses
Relation between probabilities of finless porpoise distribution (measured by kernel density estimate,
Discussion
The seasonal immigration and emigration of individuals between habitat patches can change local abundance and distribution of animals (Wilson et al., 1997, Chen et al., 2010, Toth et al., 2011), which further alters their distribution and habitat use patterns (Wang et al., 2016). For free-living cetaceans that have wide moving ranges, the geographical range of study region is often unable to cover actual home-range of the studied animals. In this condition, the MCP and KDE measured from field
Acknowledgements
This work was supported by grants from the National Natural Science Foundation of China (Nos. 31430080, 31500456), the National Key Programme of Research and Development, Ministry of Science and Technology (2016YFC0503200), the Knowledge Innovation Programme of the Chinese Academy of Sciences (No. KSCX2-EW-Z-4). We sincerely thank Mr Jinzhou Shi and Mr Jinfang Liu for their joining our field surveys. All authors declare no conflict of interest.
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