Deteriorating Habitats and Conservation Strategies to Repopulate the Endangered Indus River Dolphin (Platanista gangetica minor); a Lesson Learned From the Conservation Practices of the Yangtze Finless Porpoise (Neophocaena asiaeorientalis)

The Indus River dolphin (IRD; Platanista gangetica minor) is an endangered and blind freshwater cetacean, endemic to the Indus River system of Pakistan and India. This review article provides detailed information about the major challenges IRDs are facing, and their possible consequences on the population dynamics of the IRD. Furthermore, we have suggested future conservation strategies for the IRD based on the lesson learned from the conservation of the Yangtze finless porpoise (YFP; Neophocaena asiaeorientalis), a Critically Endangered freshwater cetacean. The major challenges for IRDs are habitat degradation, habitat fragmentation, and several types of industrial and agricultural pollutants. Worsening climatic changes, illegal fishing, and overfishing are additional threats. The construction of several barrages has fragmented the population into several short segments, some of which are too small for the IRDs to survive. In some segments, the population status of the IRD is unknown. In the remaining populations, genetic inbreeding, water shortage, canal entrapment, and altered ecological environment are potent negative factors for the survival of the IRD. Conservation strategies including fishing bans, translocation, and future research (tagging, periodic health assessments, necropsy and virtopsy, understanding the reproductive biology, and genomics) are possible recommendations. Very serious conservation efforts are needed to save the IRD from decline keeping in view the water shortage, pollution, lack of health assessment studies, and habitat degradation and fragmentation.


INTRODUCTION
The primary drivers of the loss of biodiversity worldwide are habitat loss and degradation (Sala et al., 2000;Newbold et al., 2014;Arroyo-Rodríguez et al., 2017;Fink et al., 2017;Nabi et al., 2017c). In fact, there are only a few places on earth that remain free of human influence (Kareiva et al., 2007). It is believed that biodiversity is more at-risk in freshwater systems than in other systems (Allan and Flecker, 1993;Master et al., 1998;Ricciardi and Rasmussen, 1999;Aloo, 2003;Schelle, 2010).
The Indus River dolphin (IRD; Platanista gangetica minor) is a freshwater cetacean, endemic to the Indus River of Pakistan and India (Braulik et al., 2015a). Due to highly fragmented populations and an 80% reduction in its distributional range, IRDs are listed in the International Union for Conservation of Nature (IUCN) Red List as an endangered species (Braulik et al., 2015a). In 2006, the meta-population estimates of IRDs were in the range of 1,550-1,750 (Braulik et al., 2012a). In 2011, the population declined to 1,452 (Noureen, 2013), but surprisingly increased to approximately, 1,816 in 2017 (WWF, 2017). Although, a recent survey showed an increase in the IRD population (WWF, 2017). However, still, they are exposed to several overwhelming potential threats including worsening water pollution, stranding in irrigation canals, dams and barrages construction, accidental capture in fishing nets, loss of genetic diversity, drying rivers and lakes, altered Indus River ecological conditions, conflict with India about the Indus River discharge, climatic changes, and illegal and overfishing (Braulik et al., 2012a,b;Mirza and Mirza, 2014;Nabi et al., 2019a). Although, being a top predator, information about the IRD basic biology is limited (Braulik et al., 2015b). Furthermore, there are few comprehensive review articles that have highlighted several major challenges that the IRDs are facing (Waqas et al., 2012;Braulik et al., 2015b). However, based on the lesson learned from the conservation practices of the critically endangered freshwater cetacean, the Yangtze finless porpoise (YFP; Neophocaena asiaeorientalis), we have listed several threats, their consequences, and strategies for the conservation of IRD population (Wang, 2009(Wang, , 2015. Both the IRDs and the YFPs are exposed to various anthropogenic stressors (Wang, 2009;Afzal et al., 2012;Braulik et al., 2014Braulik et al., , 2015b. Similarly, dolphins and porpoises are warm-blooded, air-breathing, give birth, nurse their young with milk, consume some of the same common foods, and use echolocation for navigation, communication, escape from predators and finding food (Berta, 2015). Both belong to the same order "Cetacea" however, porpoises belong to family "Phocoenidae" and dolphins to family "Delphinidae" and have some morphological and anatomical differences (Berta, 2015). The average declining rate of YFPs was first estimated 6.06% per year (Mei et al., 2012). However, later, the average declining rate per annum was increased and estimated doubled (13.73%) to the previous study (Mei et al., 2014). To conserve the YFPs, scientists at the Institute of Hydrobiology (IHB), University of the Chinese Academy of Sciences, Wuhan, China has used several conservation practices and have fruitful results (Wang et al., 2005;Wang, 2015). Therefore, based on the lesson learned from the conservation practices of YFPs, the aims of the present article were to highlight the key threats that the IRDs are experiencing and suggest strategies and research direction for the IRD conservation.

MATERIALS AND METHODS
We reviewed published peer-reviewed books, journal articles, theses, as well as magazines, and newspapers in English and Chinese related to the IRD and YFP through the Thomson Reuters "Web of Science" and "Google Scholar" databases. We refined our review article by using the following keywords in different combinations: threats, anthropogenic activities, habitat quality, pollution, population status, conservation practices, conservation physiology, reproductive biology, and molecular biology. The review article is organized as follows: (1) background information of the IRD and YFP (2) threats and challenges to the IRD and their consequences, and (3) future conservation strategies and research direction for the IRD.

MAJOR CHALLENGES
The IRDs face a lot of threats and challenges. These challenges are discussed individually below and summarized in Figure 1.

Barrages
The Indus basin irrigation is the largest irrigation system in the world, consisting of 19 irrigation barrages and a series of gates (Braulik et al., 2015b). The purpose of the system is not to store water, but to divert water into lateral canals (Braulik et al., 2015b). These barrages have fragmented the dolphin population into 17 small sections. In some sections, their status is currently unknown (Braulik et al., 2014). In the Indus River, historically, dolphins were found throughout in the approximately, 3,400 km main channel and tributaries (Braulik, 2006). To date, they are only found in approximately, 1,000 km stretch of the downstream reach of the main channel, with 99% of the population confined to a 690 km linear segment (Braulik, 2006). The IRD is now divided into five subpopulations which are bounded by the Kotri, Sukkur, Guddu, Panjnad, Taunsa, Chashma, and Jinnah barrages while one population is found in Beas River India (Figure 2; Braulik et al., 2015b). In fact, approximately, 70% of the dolphin population is found in a short 190 km section of the Indus River between the Sukkur and Guddu barrages (Braulik et al., 2015b). These barrages isolate different dolphin populations which are detrimental in several ways such as:

Loss of Genetic Variability
The species reproductive biology is also affected by habitat fragmentation (Yates and Ladd, 2005). The most immediate effect of habitat fragmentation/isolation is inbreeding in a population (Barrett and Kohn, 1991). The inbreeding further reduces the frequency of heterozygotes and increases the frequency of recessive, deleterious traits (Charlesworth and Charlesworth, 1987). Inbreeding often results from a population bottleneck (Charlesworth and Charlesworth, 1987;Barrett and Kohn, 1991). As a result, the risk of population extinction increases. Therefore, for long-term population survival, a continuous gene flow is crucial through functional connectivity between habitat patches (Melissa et al., 2003). It has also been known that species with low reproductive rates require more habitat area, and thus are more prone to extinction, than species with high reproductive rates (Melissa et al., 2003). Unfortunately, the majority of IRDs are confined to a small 190 km section of the Indus River (Braulik et al., 2015b). In past, the population has been declined (Braulik, 2006;Noureen, 2013), which could in part be due to lower reproductive output. Furthermore, the lack of knowledge of reproductive biology and the minimum habitat requirement for the IRD further complicate the conservation efforts. With only two dolphins living between Jinnah-Chashma Barrages and 18 dolphins living between Sukkur-Kotri Barrages (Braulik, 2006), loss of genetic diversity due to inbreeding can occur as observed in the populations of YFPs (Chen et al., 2014).

Block Migration
Dams and other barriers disrupt the river's continuity and retard the free movement of aquatic organisms to their breeding as well as feeding grounds (Lucas and Baras, 2001). Curtailing the long-term upstream and downstream movements of the river can negatively affect the long-term population viability by reducing the effective breeding of the population which can affect population abundance (Morita et al., 2009). In the Indus River, within the barrages gate, turbulence and water velocity is very high, which allows only downstream rather than upstream movements. This leads to downstream migratory attrition of upstream subpopulations (Reeves, 1991;Reeves et al., 1991). Based on a single individual with radio-tagged, dolphin either moved up and down or trapped downstream (Toosy et al., 2009;Braulik et al., 2012a). However, the design and operation of each barrage is different (Braulik et al., 2015b) and there is no detail study to prove a regular upstream and downstream movement across the barrages. If the movement of individuals is primarily in one direction, this would be another important factor to consider in the IRD population dynamics.

Alteration in Ecological Environment
Barriers cause an alteration in water velocity, discharge, siltation and suspended solids, riverbed movement, dissolved oxygen, temperature (Crisp, 1993), stream habitat, and biogeochemistry (Larinier, 2001). These factors further compromise different biotic compositions, de-synchronize aquatic species life history categories, and break longitudinal and lateral hydraulic connectivity (Bunn and Arthington, 2002). Additionally, the decline in water flow during a dry season can affect the dolphins by increasing water temperatures and reduce the average water depths, the water velocity, and the physical space available to them (Nilsson et al., 2005;Xenopoulos and Lodge, 2006). Indirectly, flow regulation could affect dolphins by increasing the success of invasive species, the dominance of generalist fish species, and the decline in fish diversity (Nilsson et al., 2005;Xenopoulos and Lodge, 2006). As the Indus River runs through semi-desert land, the river is naturally highly turbid, broad, shallow and braided, sand-bedded, and is constantly eroding its bed and banks (Braulik et al., 2015b). Furthermore, little vegetation and an extreme rise in temperature (Braulik et al., 2015b) can create a worse scenario for the IRD survival. Therefore, based on the historical pattern of decline, IRDs are most likely to disappear in the future from locations with a low river discharge (Braulik et al., 2014).

Low Socialization/Group Cohesion
Cetaceans are social animals (Peter and Raga, 2001). Social living has many advantages such as communal care, especially of calves, defense from predators, co-operative feeding, the formation of breeding coalitions and a variety of forms of social organization, and adapted to different environmental conditions and lifestyles (Peter and Raga, 2001). This social cohesion is not only crucial for an individual's own survival, but also for the survival of the entire group. By remaining connected, the knowledge collectively held by the group, especially by more mature members, can be used to enhance survival (Whitehead and Rendell, 2015).

Entrapment
Occasionally, IRDs close to the irrigation barrages enter irrigation canals and remain either close to the river or travel hundreds of kilometers (Bhaagat, 2002;Khan, 2005). Each year, all canals are drained for over several week periods (Waqas et al., 2012), which can cause mortality and morbidity for entrapped stressed dolphins (Waqas et al., 2012). A total of 34 recorded entrapped dolphins died between 1992 and 2014 (Waqas et al., 2012). Furthermore, the lack of monitoring the number of dolphins entering the canals and how and when they traverse the gates (Braulik et al., 2015b) further complicate their survival.

Water Shortage
The Indus Basin Irrigation System (IBIS) has reduced the annual downstream water flow from greater than 150 billion m 3 to less than 45 billion m 3 (Inam et al., 2007) due to its extensive use for agriculture (95%), industry, sanitation, and drinking (Kamal, 2008). Especially during the dry season, the IBIS severely affects the water flow to such a level that the river virtually ceases to flow (Dudgeon, 2005), causing habitat degradation, reducing physical space, and a decline in the range of the IRD (Braulik et al., 2014(Braulik et al., , 2015b. Therefore, to increase the chances of foraging opportunities and decrease the risk of being isolated in a small pool, the dolphins will move and congregate in a relatively deep area (Braulik et al., 2012b). However, the congregation can increase the chances of negative interactions with humans (Braulik et al., 2012b). Furthermore, with an expanding agriculture and economic sector, there is an increased demand for more cultivable land. A conflict with India about the Indus River discharge and the newly planned and under constructed hydropower stations, river linking projects, barrages, and dams are additional potent threats to IRDs (Asian Development Bank, 2010).

Industrial Pollution
Due to rapid industrialization and urbanization, water pollution has significantly increased in Pakistan (Qadir et al., 2008). More than 90% of the municipal and industrial effluent from paper factories, sugar mills, tanneries, wood mills, jute mills, textile mills, and distilleries enter the lakes and rivers, causing chemical pollution (World Bank, 2005;Directorate of Land Reclamation Punjab, 2007). Streams of sewage just upstream of the Sukkur Barrage and the dumping of the waste into the Indus River (Gachal and Slater, 2003) further amplify the water pollution problem. Various industrial pollutants such as cadmium, lead, mercury, copper, and arsenic were recorded in higher concentrations in the Indus River as well as in the tissue samples of fish (Gachal et al., 2006a,b;Humerah et al., 2011;Afzal et al., 2012). Since fish tend to accumulate heavy metals in their body (Jia et al., 2017). Dolphins are at the top of the food chain and can, therefore, accumulate high metal loads from their prey (Aguilar et al., 1999). The large quantity of prey consumed, and the long lifespan of dolphins further enhances their capacity to accumulate metals (Aguilar et al., 1999;Bowles, 1999). Like other cetaceans, several toxic pollutants have been reported in the various tissues of YFPs (Xiong et al., 2019). Though not specifically studied in detailed in the IRD, the bioaccumulation of metals could cause higher mortality, morbidity as well as could negatively compromise reproduction, putting the population health and growth atrisk (Aguilar et al., 1999;Murphy et al., 2015). Chemical pollutants can affect the cetacean immune system in several ways including alterations in the immunoglobulin production, cytokine gene expression, hematology/circulating immune cell populations, and cytotoxicity (Desforges et al., 2016;Nabi et al., 2020b). Chronic exposure to immunotoxic pollutants may have population-level consequences and can cause infectious disease outbreaks which typically occur near heavily urbanized and polluted areas (Duignan et al., 2014).

Agricultural Pollution
The plain areas of Pakistan are intensively cultivated with rice, wheat, sugarcane, and cotton (World Bank, 2005;Ali et al., 2016).
To combat pests, about 25,000 tons of pesticides and chemical compounds are used with an annual 6% increase (Memon, 2004;World Bank, 2005;Humerah et al., 2011). Commonly used pesticides include Endosulfan, Cypermethrin, Chlordanes, Heptachlor, Hexachlorobenzene, Hexachlorocyclohexane, DDT, and several others (Sultana et al., 2014;Ali et al., 2016). These pesticides are sprayed on crops using irrigation water. The water containing the chemicals leaches through the soil and enters into various water sources (Ali et al., 2016). Some of these chemicals have also been found in the tissue of three dead IRDs (WWF-Pakistan, 2011). Analysis of water samples indicates heavy organic pollutants and tissue samples of different fish species indicate a heavy fertilizer load (Gachal et al., 2006a,b). Some fishermen use poisonous pesticides in the Indus River to maximize their fish catch (Waqas et al., 2012). All these pesticides both directly and indirectly, through prey consumption, affect the IRD. Similarly, YFPs exposed to heavy pesticides load showed elevated levels of liver enzymes in the Tian-E-Zhou Oxbow (Nabi et al., 2017a). Furthermore, the slow degradation of pesticides and accumulation in different biotic and abiotic matrices (Yang et al., 2013) can increase the pesticide load, and possibly can lead to carcinogenesis, immunological disorders, reproductive disorders, and finally death of the animals (Sanpera et al., 2003).

Microbial Pollution
Analysis of the Indus River water showed a heavy load of total coliform and thermo-tolerant coliforms bacterial pathogens (Humerah et al., 2011). These bacterial pathogens are not limited to fecal sources but also are commonly found in sugar beet processing wastewater, cotton mill effluents, textile processingplant effluents, and pulp and paper mill effluents (Dufour, 1976) which are discharged into the Indus River. However, a detailed study of the micro biota of the Indus River is lacking. There is a great possibility that there are a number of bacterial, fungal, and viral pathogens as well as parasites in the Indus River which pose a serious health risk to the IRD.

Acoustic Pollution
The Indus River is not immensely used for traffic because of several barrages, but still, vessels are present in the form of motorized or oar-powered ferries and fishing boats (Braulik et al., 2015b). Dolphins use sound for prey localization, escape, navigation, and communication, because their vision is limited underwater (Nabi et al., 2018c). Aquatic animals are also exposed to natural noises such as wave noise and rainfall and lightning strikes on water, but over the evolutionary time, they genetically adapted (Rabin and Greene, 2002). However, noises from anthropogenic sources are recent additions which pose a serious survival risk to animals (Rabin and Greene, 2002;Mei et al., 2021). Acoustic pollution can cause death (Claridge, 2006), and a variety of health issues such as physiological stress, behavioral alteration, cardiovascular collapse and hemorrhages in the subarachnoid, cochlear duct, lungs, kidney, and intracranial areas (Balcomb and Claridge, 2001;Freitas, 2004;Cox et al., 2006;Miller et al., 2008;Nabi et al., 2018a). Noise can affect reproduction in all marine animals regardless of their age (Wright et al., 2007) by directly suppressing the hypothalamic-pituitarygonadal (HPG) axis (Rengarajan and Balasubramanian, 2008) or through hypothalamic-pituitary-adrenal (HPA) axis activation (Rolland et al., 2012). The indirect effect of noise is hearing loss (Cox et al., 2006).

Dolphin Hunting
For a long time, IRDs were hunted by different indigenous groups (McNair, 1908) using well-equipped boats for their capture (Pilleri, 1972). The meat was used for food by the highly marginalized communities. The oil was used as fuel in lamps and for medical purposes (Braulik et al., 2015b). The hunters then moved to the Punjab province of Pakistan after the enforcement of a ban on dolphin hunting in Sindh province . Currently, there is no evidence that IRD hunting has continued anywhere in Pakistan since then (Braulik et al., 2015b), however, still, overfishing and using illegal fishing gears are potential threats for the IRD population (WWF-Pakistan, 2011).

Illegal Fishing
The irrigation canals are heavily fished, and, therefore, net entanglement of dolphins is very common (Khan, 1947) which poses risks to the IRD survival. In 2011, within the protected area, six dolphins were killed by insecticides dumped into the river to increase fish catch (WWF-Pakistan, 2011). Furthermore, with the increased use of the Indus River by unskilled fishermen, an increase in dolphin mortality has been observed (Waqas et al., 2012). There is also a possibility of using others harmful, illegal, and non-selective methods for fishing such as gill nets, rolling hooks, and electrofishing which was one of the factors in the extinction of the Lipotes vexillifer (Turvey et al., 2007).

Overfishing
More than 180 fish species are found in the Indus River (Mirza and Mirza, 2014). However, they are exposed to various threats such as the westward shifting of the river's course, global warming, extensive deforestation, illegal hunting of fish, pollution, and most importantly overfishing (Mirza and Mirza, 2014). At the Taunsa Barrage, fish diversity is poor as compared to other rivers in Asia such as the Yangtze River, the Yellow River, the Mekong River, the Salween River, the Brahmaputra River, and the Ganges River (Muhammad et al., 2016). Much stress has been placed on commercial fish species due to overfishing (Muhammad et al., 2016). Commercial exploitation of fishes, poverty, and illegal fishing not only leads to a reduction in prey for the IRD, but also a scarcity of food (WWF-Pakistan, 2011;Waqas et al., 2012). Poor nutrition in cetaceans can affect immunity and reproduction (Beineke et al., 2010;Murphy et al., 2015). Furthermore, maternal body condition can alter the sex ratio of the offspring (Wiley and Clapham, 1993). if the uneven birth sex ratios in an endangered population persist for a long time, it can hamper the conservation efforts (Wiley and Clapham, 1993;Saragusty et al., 2009).

Climatic Changes
Climate changes can cause a dramatic alteration in ecosystems and can negatively impact freshwater cetaceans (Smith et al., 2010). Alteration in the thickness of glaciers (Hewitt, 2007), seasonal snow melting, rainfall (Archer et al., 2010), an increase in temperature (Hijioka et al., 2014), and the lack of water conservation practices results in the deterioration of the ecosystem where the IRD dwell in. The IRDs, through the passage of time, have evolved the ability to adapt to the rising temperature (Braulik et al., 2015b). However, an increasing global temperature and other climatic changes which affect biodiversity, and the ecosystem can negatively affect cetaceans (MacLeod, 2009). Although cetaceans in response to adverse climatic changes can change their geographical range (MacLeod, 2009), but unfortunately, the IRDs are restricted to a 190 km stretch of the Indus River (Braulik et al., 2015b). Therefore, exposure to adverse climatic conditions can potentially have life-threatening consequences.

FUTURE CONSERVATION STRATEGIES
After the extinction of the Yangtze River dolphin in 2006, YFPs are the only fresh-water cetacean, endemic in the Yangtze River, Poyang, and Dongting Lakes of China (Turvey et al., 2007;Mei et al., 2014). Like IRDs, YFPs are also exposed to a variety of anthropogenic factors, and declining continuously (IUCN, 1996;Wang et al., 1998Wang et al., , 2000Wang, 2009). Due to a tremendous decline in population, YFPs are further reclassified as critically endangered cetacean (Wang et al., 2013). Various conservative approaches are used for YFPs conservation, some of which have fruitful results. For example, the first freshwater cetacean birth in captivity and the higher fecundity and a net increase of 108% in the population of Tian-E-Zhou Oxbow (Wang et al., 2005;Wang, 2015). Based on our experience with the YFPs conservation, we have suggested the following strategies for the IRD conservation, summarized in Figure 3.

Translocation
There are various goals which can be achieved by using a translocation program such as speeding the recovery of a species after habitat restoration, establishing satellite populations, and bolstering genetic heterogeneity (Griffith et al., 1989). The subpopulation of the IRD between Sukkur and Guddu is relatively large (n = 1289) (Braulik et al., 2012a). This is compared to the few dolphins found at Jinnah-Chashma, the 96 animals living at Chashma-Taunsa (Noureen, 2013), and the 10 animals living in the Beas River (Behera et al., 2008). Furthermore, these animals, due to downstream migration are declining continuously and are concentrating between the Sukkur and Guddu barrage (Braulik et al., 2015b). To prevent the extirpation of these small subpopulations, translocation of animals, especially those trapped in irrigation canals, may provide a better solution. The translocation of the IRDs from an area of low population to an area of high population through well-trained staff could help the conservation of specie in several ways. For the conservation of YFPs, porpoises have been translocated either to new habitats or other reserves to boost the genetic diversity of existing population, and ultimately, save them from extinction (WWF, 2015).

Fishing Ban
The conversion of a fishing system in Sindh province from contract to license has resulted in an exploitation of fish resources and an abrupt increase in the use of illegal fishing practices, such as fishing without a legal permit, pesticide use, and overnight netting (WWF-Pakistan, 2011;Waqas et al., 2012). Furthermore, many local and native peoples depend on the Indus River as a source of subsistence. All these activities have adversely affected the fish resources of the Indus River (Waqas et al., 2012). As a result, the IRDs travel into water channels and lakes due to high fish availability. Unfortunately, in these environments, they are exposed to many negative anthropogenic activities (Waqas et al., 2012). There is an intense need to enforce ban on the illegal fishing and using harmful fishing gears in the Indus River and its adjoining lakes. The Pakistani government needs to provide jobs or facilities for fish farming, cattle farming, agriculture, and other alternative facilities for the local people who depend on the Indus River. Furthermore, there is also a need to investigate fisheries resources in the deteriorating habitats of the Indus River. To save the YFPs and other biodiversity in the Yangtze River from extinction, Chinese government first initiated an annual 3 months fishing ban in 2002, then 4 months in 2016, and in January 2020, China instituted a 10-year ban on fishing in the Yangtze River and its adjoining lakes (Mei et al., 2020). This new ban is estimated to affect more than 110,000 fishing boats and approximately, 280,000 fishermen in ten provincial regions along the Yangtze River. However, the government has promised to provide vocational training, financial support, and social security services for fishermen who have to find new ways of living (Xinhua, 2020).

Future Research Recommendations
Tagging Tagging is an essential research tool that permits tracking species survival, growth, migration, and reproduction (Nielsen, 1992). Instead of group tagging, nowadays individual tagging in the form of passive integrated transponder (PIT) is effectively used in different species, (Baras et al., 2000) including YFPs. The PIT tag has not only a vast number of individual code combinations but also operates for an unlimited period of time (Baras et al., 2000). The use of PIT tagging in IRDs will help in identifying each individual. In addition, PIT tagging can be used to monitor canal entrapment, survival, growth, disease, behavior and downstream migration of the dolphins.

Periodic Health Assessment
For the assessment of animal health, several different assessments such as physiological, disease, blood, and biochemical are very crucial for making management and treatment decisions for the animals (Moore et al., 2007). Furthermore, physiological indices such as fats reserves, body growth, hematological, and biochemical parameters can be used to rank habitat quality indirectly (Nabi et al., 2017a). Several studies regarding different marine mammals including YFPs have been performed to investigate population health for effective management and conservation and have focused research on understanding the implications of stressors such as infectious diseases, marine toxins, and pollutants on the health of marine mammal populations (Wells et al., 2004;Fair et al., 2006;Goldstein et al., 2006;Nabi et al., 2017bNabi et al., ,c, 2018bNabi et al., , 2019bNabi et al., , 2020aNabi et al., , 2021. In the light of the above studies, an annual periodic health assessment is needed for the IRDs in order to understand their growth rate, fertility, and the diseases which cause morbidity and mortality.

Necropsy and Virtopsy
Most of the literature suggests that the worsening ecological environment is the causative factor for the IRDs decline (Braulik, 2006;Noureen, 2013;Braulik et al., 2015b). However, it is unknown how these various environmental factors can cause morbidity or mortality. Therefore, it is very crucial from a conservation point of view to identify the exact cause of illness or death using necropsy, virtopsy, pathology, histopathology, microbiology, and biochemistry techniques. All this information will guide the conservationist in designing conservation strategies.

Understanding Reproductive Biology of the IRDs
Escalating anthropogenic activities are the major drivers for animal extinction, and therefore, to conserve and manage wild species, basic and applied knowledge about their reproductive biology is essential (Comizzoli and Holt, 2019). Unfortunately, for most of the wild endangered species including the IRDs, very little is known about their reproductive biology (Frankham, 2008;Comizzoli and Holt, 2019). Unlike YFPs, IRDs do not have a specific breeding season and can breed at any time of the year (Dolphins-World, 2017). However, the low reproductive rate of the IRD warrants further investigations (Khan, 2016). Although cetacean chasing, catching, and handling is difficult and there are several logistics, ethical, and physiological issues (Nabi et al., 2018a). However, the IRDs in the irrigation canals and during the rescue operations could provide an opportunity to study them for a while (for example mother and calf interaction, lactation, parental care, and sexual behavior). These opportunities could also help us to record the sex ratio and anthropometric measurements. Blood, milk, and blowhole samples collected can be used to assay various reproductive parameters. Furthermore, studying the fresh carcasses could also provide a unique opportunity to understand the basic reproductive biology of the IRDs (Xiao et al., 2018;Ji et al., 2019). In 2005, the first YFP was born in captivity at the Baiji Dolphinarium, located in Wuhan, China (Wang et al., 2005). The long-term objective of this natural captive breeding program is to establish a colony of animals in which some can be released into the wild (Wang et al., 2005). The birth in captivity of this first ever freshwater cetacean not only indicates the success of the natural breeding program, but it also provides hope for other freshwater cetaceans which could potentially be bred naturally in captivity. Furthermore, reproductive biology of the YFP is studied both in the captive and free-ranging populations (Zeng et al., 2017(Zeng et al., , 2018Hao et al., 2019). The IRD, unlike, YFP is not critically endangered and due to several other reasons, it is very early to start a captive breeding program like started for several other animal species (Suresh et al., 2010;Sandler, 2012). However, understanding the basic reproductive biology will help the natural or artificial breeding programs whenever it is applicable. Furthermore, attention from national and international organizations for funds and collaboration with international institutions for technical aid is needed to understand the reproductive biology of IRD.

Genomics
Advancement in molecular technologies including genetic engineering and advanced genomics can help conservation researchers and provide important scientific information to policy makers and managers (Supple and Shapiro, 2018). These techniques can help in identification and enhance the expression of the genes responsible for adaptation and increase our understanding about micro-evolution. Tools can be developed which are essential for the advanced monitoring of endangered biodiversity . Genomics studies provide information about speciation time, recombination rates, origin, relationships, estimation of the current and the ancestral effective population size (Wilding et al., 2001;Locke et al., 2011), the genetic architecture of inbreeding depression, and genetic mechanisms including epistasis, over-dominance, and gene-environment interactions (Steiner et al., 2013). Genomewide association studies (GWAS) (Charlier et al., 2008), gene expression profiles (Paige, 2010), and genomic sequencing (Charlesworth and Willis, 2009) are broadly used to identify inbreeding depression related loci. Advanced genomics can more effectively detect relevant susceptible genes and can provide a better comprehension into protective and pathogenic mechanisms and can determine new molecular targets for therapeutic and prophylactic interventions (Hill, 1999).

CONCLUSION
The conservation status of the IRD is not as serious as the status of the YFPs. However, still, it is one of the world most endangered mammals. The Indus River is highly polluted and fragmented by several barrages. In addition, fisheries resources are exploited, and climatic changes have had a negative impact. Furthermore, the shortage of water and the decreased level of the Indus River due to agriculture, installation of new hydropower projects, and a conflict with India have complicated survival of the IRD in the long term. Despite such major challenges, the current conservation progress and practices are not enough, and it seems that its conservation status will be drastically compromised in the future. We have suggested translocation and fishing ban practices for the conservation of IRD. These practices have significantly contributed to the conservation of YFPs. Furthermore, we have suggested several future research directions for IRDs conservation including genomics, tagging, necropsy and virtopsy, periodic health assessment, and to understand basic reproductive biology of the IRD. These research studies have played an important role in the conservation of YFPs.

AUTHOR CONTRIBUTIONS
GN conceived and drafted the manuscript. ShA, RM, YH, NA, and MK critically reviewed and edited the manuscript. DL, SK, SaA, and WU polished the manuscript. DL funded the study. All authors contributed to the article and approved the submitted version.

FUNDING
This study was conducted with the support of the National Natural Science Foundation of China (NSFC, 31971413), the biodiversity investigation, observation, and assessment program (2019-2023) of the Ministry of Ecology and Environment of China, and the Natural Science Foundation of Hebei Province (NSFHB, C2020205038) to DL.