posted by Pete McIntyre (U of Wisconsin)
One of the most intriguing species endemic to Lake Tanganyika is the water cobra, an aquatic cobra that seems to feed exclusively on fish. It hunts underwater, systematically probing under rocks until it can corner some hapless cichlid.
For years, there has been some concern that water cobras could be imperilled by getting tangled up in fishermen's nets. Along much of the lake shore, there probably have not been enough gill nets used to have a major impact on the cobras. However, those of us working near Kigoma have noticed a distinct drop in the number of cobras we see while working in the nearshore zone over the last decade.
The last time that I had seen a water cobra was 2002, so I was thrilled (in multiple senses) to see a monster today. When I met up with the team this afternoon after counting fish at other nearby sites, George told me that he had seen a large cobra about 100m up the shore. I was relieved to hear that the snakes are still present in at least small numbers, but we had little time to talk about it because we needed to turn to catching the last few fish needed for the day. George quickly got two Neolamprologus toae, and I found a third to complete the collection. On my way to shore to hand the fish off to Ben and Ellen, I saw a tree branch among the rocks that I hadn't noticed before. Then it moved!
The cobra was by far the largest I have ever seen. I am confident it was nearly 3m long, perhaps more. I didn't get a look at the head, but the neck had 7 black bands compared to the 2-4 that i have seen on smaller cobras. Its girth was shocking--the size of my upper arm--and more than a bit intimidating.
Thankfully, these beautiful snakes rarely if ever bite anything but fish. This one vanished among the rocks, and we did not see it again. It was heartening indeed to come across my first water cobra in a decade, suggesting that they have not been extirpated from our study area. Alas, as we left the site an hour later, a fishermen was deploying a gill net in exactly the area where we saw the snake. We can only hope that it can continue to elude these inadvertant death traps. Indeed, these marvelous predators may now be sensitive indicators of the few remaining sites where nearshore fishing pressure has not yet intensified... . Long live the water cobra!!!