Crocs Afar

Repost from gregladen.com

One day, about six thousand years ago (or more like 15 thousand … the timing of this is disputed) a volcano in the vicinity of Mwea, Uganda blasted a huge volume of stuff into the air, covering the surrounding landscape and choking off most of the life forms living in a nearby lake. (A very nearby lake … the current configuration of the lake suggests that the volcano may have actually been beneath the lake at the time of the eruption).


Over a very short period of time, we can presume that the land animals that would have been wiped out by this eruption returned to the area, following the quick colonization of the ashy surface by grasses and other plants. The fish diversity in the lake is still very low … one of the lowest of all of the major African lakes. The primary fish that live here now are lungfish (likely survivors of the blast), tilapia (cichlid fish that are very good at colonizing new lakes … hitching rides on duck feet and such) and various fish that would have come in from nearby streams and rivers. Also wiped at the time were the crocodiles. The crocs appear in the fossil record here before the blast, but not after. From that day until the time I visited Lake ex-Edward, on the Congo/Uganda border, no crocs had been seen, and the people living along the lake were very happy about this.

Then, one day, there were crocs … short ones, maybe 60 to 80 cm. in length … sighted here and there along the banks of the river. In the absence of any competition form other crocs, these animals grew very quickly to reach two meters long in less than two years. Who knows how big they are now?

Rumors abounded that German Scientists working on the Uganda side of the lake had planted crock eggs in the sand. I’m sure similar, but converse, rumors were being spread on the Uganda side about what was going on over in Zaire. It is not at all unreasonable that someone planted eggs, because otherwise, why would we see only baby crocs? How would they get there? On the other hand, 98 percent of this lake’s shoreline is in National Parks, with no settlement, and much of that is in very difficult to access terrain. There is a huge part of the lake, on the southern end, that is not even visited by the local fishermen because navigation there is too dangerous … the surface only barely covers a veritable forest of boulders, all ready and willing to poke a hole in your boat, foul your nest, or break your prop. A croc could easily live in that area without notice for many years.

It has long been suspected that crocs have the capacity to move over great distances between suitable habitats. But a recent study has provided better-than-ever quantification of this. Here is the abstract from “Satellite Tracking Reveals Long Distance Coastal Travel and Homing by Translocated Estuarine Crocodiles, Crocodylus porosus” recently published in PLoS:

Crocodilians have a wide distribution, often in remote areas, are cryptic, secretive and are easily disturbed by human presence. Their capacity for large scale movements is poorly known. Here, we report the first study of post-release movement patterns in translocated adult crocodiles, and the first application of satellite telemetry to a crocodilian. Three large male Crocodylus porosus (3.1-4.5 m) were captured in northern Australia and translocated by helicopter for 56, 99 and 411 km of coastline, the last across Cape York Peninsula from the west coast to the east coast. All crocodiles spent time around their release site before returning rapidly and apparently purposefully to their capture locations. The animal that circumnavigated Cape York Peninsula to return to its capture site, travelled more than 400 km in 20 days, which is the longest homeward travel yet reported for a crocodilian. Such impressive homing ability is significant because translocation has sometimes been used to manage potentially dangerous C. porosus close to human settlement. It is clear that large male estuarine crocodiles can exhibit strong site fidelity, have remarkable navigational skills, and may move long distances following a coastline. These long journeys included impressive daily movements of 10-30 km, often consecutively.

This tells us not only that, for salt-water crocodiles at least, long distances are not really a problem. It also tells us about apparently uncanny homing skills in this species!

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