Monday, August 12, 2013

Cottonmouths in the Ocean: Fact or Fiction?

           We know that some reptiles love the water. Alligators, turtles, snakes, the swamps are crawling with them. But what about the ocean? Are there any reptiles that use saltwater habitats?

            Of course. Sea turtles are well-known for spending their lives in the ocean (aside from their brief trips to the beach to lay eggs). Not technically a sea turtle but another turtle also using the sea is the Diamondback Terrapin (Malaclemmys terrapin). Several species of crocodiles frequent salty habitats: the Saltwater Crocodile (Crocodylus porosus) comes to mind. There are a handful of Sea Snakes that are adapted to ocean-life, they feed on marine fish. Finally, don't forget marine iguanas. Brackish habitats, those areas where swamps and rivers meet the sea that are not quite freshwater but not quite saltwater either, may contain many more reptiles than the open ocean.

            But overall, few reptiles use salty areas. Why is that? Saltwater habitats are stressful environments. The biggest problem is the lack of drinking water. Just like us, animals needs water. And, just like us, salt water is not exactly thirst quenching. Because salt water is so…salty, most vertebrates are simply not equipped to process it physiologically; it can be very hard on the kidneys. 

           Vertebrates that live in the ocean don't have it easy. Some seals either rarely drink water or eat snow instead. We don’t even have a very good understanding of how whales and dolphins manage to get the water they need. So, it should not be too much of a surprise to hear that many species of wildlife, reptiles included, avoid these saltwater environments.

            Cottonmouths (Agkistrodon piscivorus) are an example of a water-loving species that can sometimes be found in brackish and estuarine habitats. If freshwater isn't available to drink, it’s likely that they can extract enough water from the other animals they eat. But pure saltwater is too much for Cottonmouths to handle and they do not live in the ocean.

            Or do they? A reader (thanks Shawn O.) sent me the following picture of a Cottonmouth floating in what appears to be the open ocean. Rumor has it that the picture was taken 65 miles (105 km) offshore of Alabama (let’s assume that’s true). Are Cottonmouths ocean dwellers after all? I doubt it. 

           Any animal on the open ocean is vulnerable, to the sun and to marine predators like sharks; most animals you see floating in the open ocean or either just popping up for a breath or can fly away. Cottonmouths are not deep-divers and they can’t fly either (although some commenters might disagree) so I think it is safe to say that this animal is out of its element. I think that this unlucky Cottonmouth had taken an exploratory crawl around the beach and got swept away by a wave.  Right now, it looks like it’s just floating around and not under its own power, just like the balloon next to it. Currents are probably controlling the movement of the Cottonmouth, just as they are controlling the movement of the balloon. I think this Cottonmouth’s days are numbered.

            So, what was the snake doing on the beach in the first place if the ocean is such an inhospitable place? We can look to some very interesting research conducted on the Cottonmouths of Seahorse Key, Florida for the answer. Seahorse Key, a small island off the shore of Florida and in the Gulf of Mexico, contains a very unusual population of Cottonmouths. Although the species can be found on many islands, there is no fresh water on Seahorse Key, and the Cottonmouths there are considered terrestrial.

            The Cottonmouths on Seahorse Key rely heavily on large colonies of nesting birds. When the adult birds feed fish to their young, some of the fish fall to the ground, where they are consumed by waiting snakes. This is a very seasonal resource, of course, and when there are no nesting birds, the Cottonmouths are left looking for something else to eat. During these times, the snakes may wander to the intertidal zone searching for dead fish that have washed onto shore. Because the species does it there, they probably do it elsewhere from time to time too. Cottonmouths generally don’t crawl around on the open beach or enter the ocean, they are too vulnerable to predators there. But, perhaps they are also vulnerable to being hit by a rogue wave? I suspect at least one was.

        Ever seen an animal in the ocean that did not belong there, such as a Cottonmouth? Let us know below.

Want to read more?

H.B. Lillywhite, C.M. Sheehy III, & F. Zaidan III (2008). Pitviper scavenging at the intertidal zone: an evolutionary scenario for invasion of the sea BioScience, 58 (10), 947-955 DOI: 10.1641/B581008

Rasmussen AR, Murphy JC, Ompi M, Gibbons JW, & Uetz P (2011). Marine reptiles. PloS one, 6 (11) PMID: 22087300

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