So the holidays took their toll on us modelers, but we're back in full form and ready to write again.  As a reminder, this slimy segment to the blog is dedicated to our friends under the water.

For this segment, a day late I know, I want to revisit Eels for a cool life history story as well as a prime example of how a life history can potentially throw off how we determine distributions and go about modeling them.  

First, a wiki reference for a description of the American Eel: "The American eel, Anguilla rostrata, is a catadromous fish found on the eastern coast of North America. It has a snake-like body with a small sharp pointed head. It is brown on top and a tan-yellow color on the bottom. It has sharp pointed teeth but no pelvic fins. It is very similar to the European eel, but the two species differ in number of chromosomes and vertebrae."  Here's a pic:

So even thought this critter has been researched to hell, with almost 10,000 publications and studied by Aristotle and Freud, we still know little about it.  And this is due to its crazy life!  The thing is, scientists and anglers never caught baby eels. Not until about 1900 did it come together.

You see, eels spend almost their entire life in freshwater. So it was a big surprise when scientists were raising these tiny transparent 2-inch worm-like things in captivity when they turned into juvenile eels.  At the time, these "glass eels" were considered their own species, Leptocephalus brevirostris.  To this day the larvae are called leptocephalus (should that be italicized when its a Latin common name??).   

So whats the story!  Quote from the interweb: "The eel lives in fresh water and only leaves this habitat to enter the Atlantic ocean for spawning.  The female can lay up to 4 million buoyant eggs, but dies after egg-laying. It takes 9 to 10 weeks for the eggs to hatch. After hatching, young eels move toward North America and enter freshwater systems to mature."

So that states it mildly.  These fish swim from sometimes hundreds of miles inland, to the middle of the Atlantic ocean, the Sargasso sea, breed and then die (much like Salmon but the opposite, sort of). The larvae hatch, then being 2-3 inches, swim back to land and up streams, growing into juveniles by the time they reach adulthood.   

There's much more to this eel story, they're economically important and threatened from dams and overfishing, but the main reason for this post is to bring up the point of the importance of life history when understanding distributions.  Just because habitat might be marginal to one life stage, doesn't mean another stage doesn't completely rely on it for various reasons. My research right now is being complicated with decisions on ecologically relevant thresholds, so the perspective of habitat utilization among and between life stages is important.

Ben Labay is a "fish-geek" and research associate for the Texas Natural History Collections at UT Austin

See his fish art at: www.inkedanimal.com