Marine Biology Story of the Day #6:
Well happy belated 4th to my fellow Americans--all though, I don’t feel particularly patriotic this year (huh, I wonder why). So I decided to take this time to talk about the biodiversity of this great continent to get my mind off of all of the bad shit that we are staring down right now.
Today we are going to talk about the wonderful world American freshwater fish biodivesity.
So, one geologic quirk of this continent is the eastern half is much “older” than the western half--the western half is still building up, creating the rocky mountains, whereas the eastern half has been worn down for millions of years--this means that freshwater fish have had semi stable rivers to live in for millions of generations. This rivers are often separated by land, and only meet other bodies of water at tributaries and at the sea. This allows fish to be separated for millions of years, and therefore spectate. Which means we have a lot of cool freshwater and estuarine fishes.
After I got my masters, my first job was as a summer hire on the juvenile striped bass seine survey at the Virginia Institute of Marine Science.
Basically, we sampled stations along Virginia rivers with seine nets, which basically collect fish in a “purse” along the shore line, with one person dragging the net out in the water, and the other holding the other end standing on the shore. While this survey focused on Striped Bass, a popular recreational fish in the area, we got a chance to sample a HUGE variety of species.
above: seine net at work.
take a look at some of the colorful freshwater fish we collected:
Pumpkinseed and blue spotted sunfish (Top): these are both part of the sunfish family, which includes freshwater bass. They are closely related to bluegill, a popular sportfish.
American Eel (middle left): The only freshwater eel species in the eastern united states. Are becoming threatened because they are sold on the Asian market as food fish--I will probably do an entire post about these guys later.
Sheapshead minnow (middle right): small baitfish, the males turn blue when it’s mating season. They are also salt tolerant and are often found closer to the coast.
Channel catfish and madtom catfish (bottom): both native species are being out-competed by the blue catfish in this region.
Because the rivers in this part of the country are so ancient, we also caught these prehistoric fish as well:
Bowfin (right): This fish is the only remaining fish in the Order Amiiformes. They are considered a “primitive fish” and they can actually gulp air if water conditions are too hypoxic.
Longnose Gar (Left): Closely related to other gar species (like the massive alligator gar), these fish have armored platelets along their entire body and wicked sharp teeth. And like the bowfin, they too can breath oxygen.
Now, the sections of the rivers we sampled ranged from completely freshwater to almost full salt water. These parts of the rivers are considered estuaries, and they include fish that can withstand a wide range of salinities, and stretch for hundreds of miles. They are often prime nursery habitat for young saltwater species as there are less predators due to the variable salinity.
Above: Map of the region sampled
There are a few of my favorite estuarine fish:
Northern Puffer (top left): self explanatory. Cute angri boi.
Spanish Mackerel (top right): these are very much offshore fish--we rarely see them this far inshore
Atlantic Spadefish (mid left): one of my favorites, they are so darn TINY when they are babies but they grow to be three feet long.
Black Drum (mid right): Another saltwater sport fish that can grow to be 100 lbs in weight. They also grow the cutest whiskers on their chins.
Blue Crab (bottom left): this one is a teeny baby, probably hatched that spring.
Tautog (bottom right): another coastal sport fish, these guys like to hang around oyster reefs and are so colorful as babies!
But these ecosystems are fragile--they are often in areas with high human population. Climate change can screw up conditions as juveniles enter the estuaries--which can make them more vulnerable to mortality. Invasive species are eating these young fish, and out completing other adults in the same niche. Freshwater flow in these rivers is being limited, as we draw out more freshwater to feed our fields. Oyster reefs are disappearing as fertilizer clouds up the Chesapeake bay and it’s tributaries. And there’s always overfishing.
So, this 4th, while we continue struggle to protect the human diversity that has actually made this country great, I hope you remind you that our amazing biodiversity needs protection too. Our natural resources in this country are so unique, and they are quickly slipping through our fingers.
As always, if you have any questions about the research, PLEASE do not hesitate to ask.