Wednesday, October 21, 2015

"Poisonous" Sea Snake Surfaces in California – Is it that Big of a Deal? --Guest Post---

Image courtesy of Will Flaxington.
   You've probably seen the headlines, a Yellow-bellied Sea Snake (Pelamis platura) was recently found along the California coast at Silver Strand Beach in Ventura County. This is a rare and interesting find given the waters along the western coastline of the United States are colder than where the species is usually found. 

    But, it’s not completely surprising given that the northeastern extent of the range extends north of the Baja peninsula. So, while although this record is extremely rare along west coast waters, Yellow-bellied Sea Snakes are actually part of the native herpetofauna in California. Globally, this species has a very extensive range and is native to tropical waters from the east coast of Africa to the west coast of North and South America.

Range of the Yellow-bellied Sea Snake. Map courtesy of IUCN Red List Spatial Data.

    Yellow-bellied Sea Snakes (also known as the Pelagic Sea Snake) are relatively large-bodied snakes (50 – 80 cm) and have a generally flattened body profile and a large paddle-like tail. The snakes are dark above and bright yellow underneath and  and. This species spends a majority of its life at sea although they sometimes give birth to their live young in tide pools. One of the most interesting aspects of this species is its ability to drift in the open seas far from shore. This species will often congregate in large numbers to form large rafts that are believed to imitate driftwood or large mats of seaweed. Yellow-bellied Sea Snakes will prey on fish and other aquatic prey that choose to seek shelter under this floating snake raft. I imagine that a large raft of snakes might be most folk’s worst nightmare, but it sounds pretty amazing to me!

    As most have probably noticed, many headlines described the Yellow-bellied Sea Snake as a “poisonous snake.” Being the literal person that I am, I got very excited thinking that the writer had either found an introduced Rhabdophis tigrinis (Tiger Keelback) or was describing the discovery of a new snake species to the US that causes death of predators upon ingestion. As Yellow-bellied Sea Snakes envenomate their prey via fangs, they are indeed venomous, not poisonous. There are snake species that are both poisonous 
and venomous, but that’s for another blog post.

    Sea snakes are part of the family Hydrophiidae and have a similar fang structure to snakes in the family Elapidae, which includes the oft-feared cobras and mambas. Collectively, snakes in these two families are equipped with stationary fangs that are used to deliver a rather potent dose of neurotoxic venom, which they primarily use on their aquatic prey (mostly fish).

    Fixed fangs differ greatly from the retractable fangs of the pit viper species we encounter in the United States in that venom essentially trickles through hollow fangs rather than being injected. Envenomations of humans by Yellow-bellied Sea Snakes are extremely rare (none have been recorded in the US); fishers that encounter this species as by-catch are most likely to suffer bites.

    Some of the articles about the snake that was found in California suggest that the larger-than-normal El Niño weather pattern is to blame for this rare encounter. Given that the distribution of Yellow-bellied Sea Snakes falls within the tropical waters of the Pacific and Indian Oceans, it’s completely conceivable to think that weather patterns that result in increased warming of ocean waters will lead to the occasional expansion of a species out of its normal tropical environment. Similarly, there have been lots of observations lately of many different species experiencing shifting geographic patterns due to climate change. So, although this rare encounter of a Yellow-bellied Sea Snake in the continental United States is interesting, we will likely experience similar weird occurrences of vagrant species in the future given the long-term predicted impacts of climate change.

Bill Sutton is an Assistant Professor of Wildlife Ecology at Tennessee State University in Nashville, Tennessee. Bill’s research interests include understanding the impacts of human disturbances, such as climate change and landscape disturbances, on wildlife populations.  Check out more of Bill’s research here.

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