Species Endangered (MS-Blog Series from) XIII / 09

Ganges Gharial

(Gavial)

Class: Reptile

Order: Crocodylia

Latin name: Gavialis gangeticus

Range: India, Nepal (Survives in scattered populations at some larger rivers; mainly the Ganges, Brahmaputra and Indus) – Earlier also at Bangladesh, Bhutan, Myanmar, Pakistan, but these populations now probably lost or nearly so.

IUCN: CR (Critically Endangered) / CITES: Appendix I

(about a 2008 situation)

Crocodiles from outer appearance are large aquatic (predatory) animals with strong bite and powerful armor. Because of that, the adult specimen have few potential threats at the nature, except that of man. In during the past decades(/centuries), the hunt for fx crocodile leather used in the various manufactures has taken it's toll on wild populations. More recently additional threats have emerged, as they also suffer from increased pollution of waters, ao.

In lack of any especial knowledge from that (ie hunt of crocodiles in the pasts, which probably was at most intensive before 20th century) it's noticed many of them been classed for the threatened already at 1970s. Actually, in that recent past, most/all of the species were found endangered, nowadays some are considerably better and only about a one third are more severely threatened. By very brief look one can also notice captive-breeding and farming of captured animals been sometimes found having had positive effect, although usually in the cases when crocodiles have been of some use/benefit for humans (in purposes of crocodile leather and meat production, etc). Because many of the species also mature rather young, the releases of the captive-bred animals have sometimes been of effective help in recovery of the wild populations.

As a group, the crocodiles are often said little changed during their long history, belonging for the most distant of surviving animals – kind of summarizing that, Halliday-Adler book mentions the Crocodylia having “Seen the Dinosaurs come and go” (in during about 150-65 Million year in the past). In overall (on the basis of fossil record), crocodylia at first raised as animal order about some 240 Myr ago. They are estimated have separated for their main lineages (commonly known Alligatoridae and Crocodylidae), around the Cretaceous (roughly before 65 Myr ago). After that, in later periods are the currently extant species evolved. The 3^rd from main lineages (the Gavialidae), separated of its own around Paleocene (around 50 Myr), perhaps even already during preceding Cretaceous. It is also considered more closely related for the crocodilians than alligatoridae. According to the traditional categorization Gharial (Gavialis gangeticus) is the sole extant species left in group, others having gone extinct well before the Pliocene (ca 5-2.5 Myr). (There's closer to 30 different Crocodylian species in the main order, if the some recently divided (sub-)species are counted as species on their own.)

Like the reptiles usually, crocodiles also give birth by laying clutches of eggs that hatch outside females body (so called oviparous form of reproduction). More especial for the crocodilians (and perhaps even surprising it being so) is their long period of parental care, which for some species lasts several months - Since less usually the reptiles fx guard their nests and more commonly juveniles just develop on their own once hatched. But in the crocodiles the parent (usually the mother) even helps the juvenile to hatch and carries recently born at its mouth. (As well, loosely related to previous perhaps, but according the book mentioned above the crocodile eggs are predated by various species ranging from ants to bears. But, like said, the adult specimen rarely have any natural enemies.)

More typical to reptile/not so unique for the crocodiles, is fx so called TSD (Temperature dependent sex determination). It's been shown that TSD imposes the sex ratio in many reptiles, but it is the sole governing factor for that in the Crocodylia, Tuatara and in some of the Turtles – The mammals, birds, frogs, etc generally instead have GSD (Genotypic sex determination). The latter probably is more recently evolved mechanism, supposedly. For the lizards and in some of the turtles (acc. to my understanding) both mechanisms are found in use; TSD appearing generally more common for the turtles, while (vice versa) GSD is more usual in the lizards.

In practice this means that from a complete clutch of eggs once laid by 'TSD-parent', the reptile juveniles born are usually of the same sex - However, the eggs laid on different levels (under the sand, fx) may develop in the varying temperatures and as result both male/female juvenile may develop. Generally, in case of the (many) turtles low incubation temperatures produce males and higher the females. At the crocodylia, this largely goes similarly like in the example from Nile Crocodiles, from which the book mentions study showing that incubation temperatures above 34.5 and below 31.7 (C) mostly resulted for female offspring, while in the intermediate temperatures male offspring was dominating. (For the crocodiles, TSD is likely universal – and no GSD is found to affect for their reproduction). (Halliday-Adler, p. 116-7; 215) To make things more complicated, however, various things have effect for the incubation, and not solely it is left for the surrounding temperatures to 'decide'; fx some turtles seem to select nesting locations favorable to particular sex ratios. As well, some of turtles - and perhaps other reptiles too - may even be able to manipulate their sex ratios (ie sex of their offspring) by altering level of hormones they allocate to their egg yolk, like also is mentioned. Even in case of crocodiles, hormones play some part in the process, especially at the transition temperatures that usually produce both male and female. All in all, the process (TSD) in the reptiles isn't yet completely understood; fx some lizards are known to have GSD, but certain temperatures in spite of that seem to favor producing merely females, the other males.(Halliday-Adler 2002, p. 116-7; 215) (And from the reason that any general source – as usual here - doesn't seem to show us any additional information, we can leave the subject for these brief simplified and very concise remarks.)

However, as the case of sex determination appears a rather significant question, also the concerns from current climatic effects have been raised aforth; especially how might the warming influence the sex ratios in some (TSD-)reptiles (various already vulnerable as result of other reasons)? Whatever most likely, usually they're also mentioned having survived past somewhat resembling periods and changes through the millions of years. So – simplifying the matter a lot, making guesses – one could suppose that reptiles which evolved in times of the warmer global climates by origin, maybe also have some other effective 'mechanisms' to protect their continuation and sex ratios from consequences of (climatic) changes. Not the least because they 'get by' with such curious manners as using external heat sources for to behaviorally adjust their bodily temperatures (like do the ectothermic / poikilothermic species); and contain also others that reproduce via ovoviparous birth and parthenogenesis, (fx). Or at least so we could assume...

More worrying, probably, appears the problem from the human created chemical pollutants. There's reasons say that sheer speed of current changes and various threats affecting the sex ratios (in reptiles) may hold possibilities of more severe changes than usually believed. Some reptiles are been shown/found noticeably highly susceptible for hormone-mimicking chemicals, such as the breakdown products of some commonly used herbicides, (fx). Also some pollutants, (the DDT-derivatives mentioned) are known to have feminizing effects on alligators as well as the turtles eggs. (For the positive side it's also mentioned that using certain hormones in captive breeding for produce females may be of some help in conservation efforts.) But, as well book mentions studies from the chemical alteration and environmental contaminants as causes of reduced egg hatching and neonatal mortality in reptiles (Although the example is from some time past, 1980s Florida, where the alligator populations of some lakes were found with abnormalities in their reproduction and endocrine systems, probably as result of pesticides exposure and nutrient pollution.) In overall, during the 20^th century man-made chemical compounds have reached numbers of tens or hundreds thousands. Not all appear harmful by effect, but some very potentially can influence the biology of animals altering their endocrine system. More typically noticed are the effects from certain chemicals which are used on agricultural purposes, but also there's some other mentioned of little concern until recently; the “inert” chemicals contain such as plasticizers, surfactants, and flame retardants, whose impacts on reptiles and amphibians not adequately known or haven't been studied so far – recent studies also are mentioned to have found (ao) the polybrominated biphenyls (Pbb) ubiquitous pollutants and as powerful hormone system modulators. (Halliday-Adler 2002, p. 215; 222-223) No wonder there's arguments presented against the use of above mentioned every once in a while...And since we're basically altering ourselves to same compounds we're spreading for the nature, one could say that (some chemicals) probably have part on the male sex hormone declines and the reduced overall fertility, often more commonly noticed topics at the usual discussions.

But seriously, its by all means reasonable to notice that the possible impacts from many of these aren't probably at all sufficiently known. Also since some pollutants are been in use only for some decades until present, their long-term effects and consequences are still unknown. Even that a certain particularly harmful have been prohibited for some time, like the DDT. (In spite of that, it is also mentioned still used as a pest killer in some countries, usually in the tropical regions.)

Less especially a matter concerning the reptiles but many other animals as well, are problems from 'regular pollution' that contaminates many the larger river systems and small seas. Unfortunately, many species living in them are endangered/affected by various other factors - in addition to some most typical are the past and current hunt of animals, and the damming of the rivers (can have harm the animal reproduction success, survival, etc., although other aspects concerning the human water use are perhaps more often noticed.)

Anyway, the stress on river systems for uses of energies production is more likely to increase, than the reverse. According to World Development Report 2010, from planets freshwater only tiny small percentages are in the rivers and lakes, and further from that only about 10 per cent used in the renewable energies production (agricultural uses make the largest part, closer to 70 per cent – although these types of use aren't strictly comparable). But, about half of the total renewable electricity of the South Americas, fx, is mentioned produced with hydro, and in some other parts of the world where there's still 'unbuilt' water power (rivers) the use is expected to still increase. (Above information from various parts of the report; Overview, p 6.; Chapt. 1 and 3) Likely, the hydro remains a source for large part of renewable produced electricity in future. However, there's also various co-effects from the water power if it's built on riverine systems.

In addition to fx crocodiles, there's plenty unique large species that live in the rivers at various continent (or in the river deltas). The threatened (from various reasons, of course) contain fx most of the river dolphin species, like Yangtze river dolphin (CR - mentioned possibly extinct), Ganges river dolphin (Platanista gangetica, EN), Indus river dolphin (P. minor, EN), Amazon river dolphin (Inia geoffr., VU) and La Plata Dolphin (VU – appears on Amazon delta and/or some S.A. coastal shores). From the Crocodylia similarly threatened are at least the Philippines crocodile (Crocodylus mindorensis, CR, - probably rarest from crocodiles), Siamese crocodile (C. siamensis, CR, - equally rare) Orinoco crocodile (C. intermedius, CR), Mugger (marsh crocodile)(C. Palustris, VU), Cuban Crocodile (C. rhombifer, EN), Chinese crocodile (C. Sinensis, CR) - Listing based on information from Beer-Morris book, mostly, and not generally checked other sources for their more recent situation. Also there's various other; like many (larger) fishes (ao), from which the common knowledge also tells that in the past the fishes used to be not only more plenty, but also larger from size. (Again, possibly as much variety as river systems appears, some being at recovery from past effects, and some perhaps only recently have come under increases of waste and other consequences of human large-scale uses of land and waters.)

Gharial is an ancient species, and the young specimen at least appear very vulnerable to pollution (a serious concern hampering the recovery, like noticed in this news-briefing.) It is also been protected from since 1970s fx to prevent the poaching losses and there's been captive-breeding programs to aid its recovery for some time. India being a country with large population and a lot of poverty, it's mentioned that gharials earlier breeding areas have in time become occupied by human settlements. Decline at the latter part of the 20^th century was rather steep since still in the 1940s there probably was about 5000 – 10000 animals left in the wild - the page also lists some other reasons for decline like the humans collecting the crocodile egg, reduction of available diet (the fishes decline), and as well specimen harvested and killed for human uses, ao in the (traditional?) medicinery. (Also mentions from the establishment of Gharial Conservation Alliance, GCA). Additionally, fishers often regard gharials as direct competitors and destroyers of their nets. From other things, it's noticed that Gavials only lay their eggs on sandy shores of river (those are only places where they come ashore), but such peaceful breeding sites have become rarer too. Eggs are also often washed from the nesting areas by floodings, etc.

Crocodiles in general also suffer largely from being feared as threat to humans. Indeed they are effective predators that can attack any kind of suitable prey coming for river sands/water edges (But, just two species – the largest - are mentioned as reputable man-eaters; the Nile Crocodile (C. niloticus) and the Salt-water Crocodile, Estuarine.) But not the Gharial. Although they can grow about as large as the above mentioned species, they are almost exclusively fish-eating from diet. Larger individuals supposedly sometimes also eat smaller birds and reptilia. Although, they may scavenge anything found on the rivers, also perhaps remains from the corpses placed on river in funerals; But as result they're also believed as man-eaters.

So, more generally, in addition to hunt, pollution and changes of their natural eco-systems (among other things), there seems been various things causing it becoming conservation dependent and nowadays classed among the more severely endangered. The decline can be timed in the modern times, since traditionally they are mentioned been considered as sacred animals. However, since we find it rather recently classed as CR – downlisted from earlier status - but have no further information to present, it's better to check some other sources for additional information too, (fx) the links in the text. Not the least because our sources – as usual here at MSW – appear to present rather differing figures from the total amount of individual animals left in wild populations (;fx Beer-Morris book lists fewer than 2500, but often only 200 is mentioned.) So in this case, one who's interested can probably also check the species status from IUCN Red list (on Gavialis gangeticus) – as it also presents the information from amount of the adult breeding specimen, fx (and has also other more precise information from their current conservation status).

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Sources:

Beer-Morris, 2005, Encyclopedia of the endangered animals. Grange books.

Halliday, T. – Adler, K., [2002], The New Encyclopedia of Reptiles and Amphibians. N.Y.

[W.B's] World Development Report 2010: Development and Climate Change (2009); at http://go.worldbank.org/ZXULQ9SCC0 [ Pre publicat. version?? ; read pre 15th Oct.]

[Pics from Halliday-Adler : Above; Three Gavials on river bench , Below; Alligator juveniles, Florida]

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