Tallulah Gorge

I visited Tallulah Gorge a few years before I started writing this blog, so at the time I didn’t think to write down my observations.  I can’t remember where I put the photos I took of that trip or if I even took any.  However, I found plenty of Tallulah Gorge photos online.  I do remember walking down a long flight of manmade stairs to the bottom of the gorge and on the way down coming face to face with a black vulture that was perched on a ledge.  I saw blueberry and blackberry growing on the canyon wall.  And I recall swimming in a very cold reservoir nearby.  Lately, I’ve been reading a new book, Roadside Geology of Georgia, by Pam Gore and William Witherspoon.  Their page on Tallulah Gorge reminded me of my trip there.  I didn’t realize Tallulah Gorge had such a fascinating geological history.

Location of Habersham County.  Tallulah Gorge is in this county.

The headwaters of the Tugaloo River eroded backwards upstream from the Tugaloo and captured the Tallulah and Chattooga Rivers both of which formerly flowed into the Chattahoochee River.

Tallulah Gorge is the 4th deepest gorge east of the Mississippi.

Tallulah Falls.  The sudden drop in elevation when the Tugaloo River eroded backward into the Gainesville Ridge created these falls.

The Gainesville Ridge separates the Chattahoochee River drainage from that of the Savannah River.  All streams on the west side of the ridge empty into the Chattahoochee River, while all streams on the east side of the ridge flow into the Savannah River or its tributaries.  Formerly, the Chattooga and Tallulah rivers were tributaries of the Chattahoochee River.  But the headwaters of the Tugaloo River eroded upstream into the Gainesville Ridge capturing the Tallulah and Chattooga Rivers.  These 2 rivers changed course making a sharp right angle turn through the Tugaloo River which empties into the Savannah River.  It’s a classic example of what geologists refer to as stream capture.  Geologists believe this stream capture event occurred “recently”, but I haven’t been able to find any studies of the exact age of the event, and  I think scientists have not determined the exact timing of this dramatic occurrence. Recently in geological time could be 10 million years.  Nevertheless, scientists believe the steepness of the gorge is evidence the stream capture occurred relatively recently.  Some of the cliffs are 600 feet high.  Geologists believe the gorge is geologically young because not enough time has passed for the high cliffs to erode away.  In older river and stream incisions, water eventually erodes the sides back, creating broad gently sloped valleys.  But at Tallulah Gorge, not enough time has passed for this to happen.

The rock along Tallulah Gorge is made of erosion resistant quartzite which is sandstone that has been metamorphized.  There is no Chattooga River gorge because the rock along that river is less resistant to erosion.  When the Tugaloo River eroded backwards and captured these 2 tributaries, the elevation suddenly lowered, creating the falls.  This change in elevation is the reason the Chattooga river is known for its white water rafting.

There are 2 types of environments in the vicinity of the Tallulah Gorge.  The cliffs provide nesting habitat for many species of birds (See https://markgelbart.wordpress.com/2013/05/19/piedmont-cliff-ecology/).  In pre-Columbian times bald and golden eagles and peregrine falcons likely nested here.  An acidic pine/oak woodland and forest grow on the rim of the gorge.  Plant species composition includes white pine, Virginia pine, table mountain pine, pitch pine, shortleaf pine, southern red oak, rock chestnut oak, scarlet oak, blackjack oak, red maple, sourwood, persimmon, mountain laurel, rhododendron, blueberry, and greenbrier.  This is the southernmost range limit of the Carolina hemlock.  Monkey-faced orchid and persistent trillium are rare plants that favor this moist, water-splashed environment.

The Soque River may be a remnant of the Chattooga and Tallulah Rivers before they were diverted from the Chattahoochee River Drainage to the Savannah River Drainage.  This is a beautiful small river with little public access.

Deep Creek and the Soque River are likely remnants of the Chattooga and Tallulah Rivers before they were diverted from the Chattahoochee River Drainage.  There are many species of mussels common to both the Chattahoochee and Savannah Rivers.  The Tugaloo stream capture event must explain how bivalves from the Chattahoochee Drainage colonized the Savannah.  For a while during this stream capture event, water must have flowed from the Savannah to the Chattahoochee as well because mussels originating from the former also made it to the latter.  However, it’s not clear how thie mussel exchange from the Savannah to the Chattahoochee occurred.

Sturgeon and Lamprey

The destruction of the sturgeon population mirrors the devastation of southeastern primeval forests.  Both of these astonishing natural resources have been utterly obliterated.  In a previous blog entry from about a year ago, I excerpted William Bartram’s 18th century description of a magnificent forest in Georgia consisting of trees with diameters 8-12 feet thick.  I drove through the same area last summer and was hard pressed to find a single tree greater than 1 foot in diameter.  The story of Georgia’s most impressive river fish follows the same plotline.

 

 

 

 

 

Man Alive!  Look at the size of this Atlantic sturgeon.  There used to be so many of these fish in our southeastern rivers that they posed a navigational hazard.  Now, they are almost extinct.

The sturgeon run in southeastern rivers began in mid-May.  For the first month of the run most of the spawning sturgeon averaged 3-4 feet in length, but beginning in mid-June and lasting until mid-September sturgeon averaging 6-9 feet in length were common.  Captain John Smith, founder of the Jamestown colony, caught 62 sturgeon in 1 haul of a net, though that take was extraordinary, even for that time.  More often, netting would yield 7 or 8 large sturgeon in a few hours.  The schools of sturgeon “clogged” the river and made for a dangerous navigational hazard that could upturn boats.  Occasionally, the giant fish even jumped into a boat.  John Lawson, an early naturalist who traveled and settled in North and South Carolina circa 1704, wrote that he saw hundreds of sturgeon every day. (He also mentioned pulling 300 chain pickerel from 1 fish trap in a single day.)  Now, sturgeon are almost extinct.  There is a tiny breeding population in Georgia’s rivers but none of the rare sturgeon found in mid-Atlantic rivers breed there.  About 1850  men began overfishing sturgeon which formerly were considered trash fish.  This decimated the population, but dams and muddy erosion from agriculture blocked and smothered much of their former spawning grounds–perhaps the final death blow.  Sturgeon need shallow water with gravel bottoms for spawning, but instead, if the spawning fish themselves are not blocked by dams, the gravel bottoms have become covered in mud, making them unsuitable.  The sturgeon eggs need to adhere to gravel.

Three species of sturgeon, all endangered, live in Georgia.  The Atlantic sturgeon (Acipenser oxyrhincus) reaches the most spectacular size, obtaining a maximum length of 9 feet and a weight exceeding 800 pounds.  The adults live in the lower stretches of the river and near offshore ocean water, but they used to spawn as far as 300 miles up the river.  The juveniles stay in the river until they’re about 7 or 8 years old before they migrate to the ocean.  They return when they reach breeding age which isn’t until they’re between 10-30 years old, explaining why it’s so difficult to bring back sustainable population levels.  They feed on the bottom by scooping out depressions and lying in ambush nearby.  Smaller fish and invertebrates carried by the current fall into these saucer-shaped traps next to where the hungry sturgeon awaits.  The short-nosed sturgeon (Acipenser brevirostrum) is similar in habit to the Atlantic sturgeon, but it is smaller in size reaching 4-5 feet in length and just 50 lbs in weight.  A landlocked population of lake sturgeon (Acipenser fluvescens) lived in the Coosa River  until 1965.  In 2003 biologists reintroduced them to the Etowah River.  The Coosa River lake sturgeon must have been a relic population that some how made their way from the Mississippi River system, perhaps from a chain of wetlands that existed during the Pleistocene in northern Alabama.  Floods between river basins must have facilitated the spread of this species.

Sturgeon piccatta, broccoli, and stuffed squash blossoms.  I’ve never eaten fresh sturgeon.  I think I’ve had smoked but it’s been so long I can’t remember for sure.  I’ve had caviar…tastes like fish guts.

It’s hard to believe the early settlers considered sturgeon a trash fish and fed the flesh and caviar to the hogs and dogs.  Sturgeon flesh when dressed correctly is reportedly supposed to be mild and durable and an acceptable substituted for boneless chicken breasts or veal in recipes.  Caviar, of course, is considered a delicacy but in my opinion tastes like fish guts.  Mixed with cream cheese, it’s palatable.  In my fantasy Pleistocene world, I’d definitely be harvesting and eating the sturgeon.

Sea lampreys parasitize fish, latching on and ingesting blood.  Sea lampreys no longer occur in the Savannah River, but they used to.  They must have been dependent on the large sturgeon population.

Sea lampreys (Petromyzon marinus) are no longer recorded from the Savannah River, but there is a historical record of 1 from the upper part of this river where Clark Hill Reservoir now inundates.  John Lawson mentions sea lampreys as a fish the Indians refused to eat (though the French consider them a delicacy).  This anectodal evidence suggests sea lampreys used to be fairly common in southeastern rivers.  They’ve likely disappeared from the Savannah River because they depended upon sturgeon for sustenance and now that the sturgeon are all but gone, so are the lampreys.  It’s no coincidence that sea lamprey spawn in the same habitat as sturgeon–shallow water with gravel bottoms.  The larva move downstream after hatching, then burrow into sandy or muddy bottoms and become filter feeders, living on detritus and algae until they grow into their parasitic phase.  When they reach this stage they actively attack fish as depicted in the figure above.  I suspect sturgeon were their primary prey/host in southeastern rivers.  Striped bass and swordfish have been recorded as preying on sea lampreys, but probably any large predatory fish will eat them.

At least 3 other species of lampreys inhabit Georgia’s rivers–the southern brook lamprey (Ichthyomyzon gagei), the American brook lamprey (Lampetra appendic), and the least brook lamprey (Lampetra aegypidtra).  The former occurs in the Chattahoochee River, and the latter 2 live in north Georgia rivers.  None of these have a parasitic phase and they live as filter feeders burrowed in mud for most of their lives, except when they spawn.  They all have rasping mouths, however.  This is evidence they evolved from parasitic species.

Sturgeon are an ancient family of fish.  Fossils of sturgeon dating to the Cretaceous prove they swam when dinosaurs roamed the earth.  Lampreys long ago evolved to exploit this once abundant food source.  It’s a shame both of these remarkable fish have nearly vanished in the last 150 years in the wake of man’s environmental destruction after they’d successfully survived natural ecological changes for over 100 million years.

How far South did Brook Trout (Salvelinus fontinalis) Range in Georgia during Ice Ages?

Illustration of a Brook Trout from Cornell University.

No scientist has ever studied this topic, so my blog post is the first of a kind.  Scientists are limited due to a lack of data–no trout fossils have ever been found in the region.  There’s also a lack of interest, probably because I’m the only person in the world who daydreams about what it would be like to live in Georgia 37,000 years BP.  I want to know, if I traveled in a time machine to live then and there, whether or not brook trout would get caught in fish traps I would place in the Broad River.  I’ve concluded that it’s possible, maybe probable, that they did occur in the Broad River during stadials and even interstadials because summers were cooler then than they are today, an age within a full blown interglacial with hot summers.

Present day Georgia brook trout range map.  Map from the University of Georgia Museum of Natural History.

Today, brook trout are the only native species of trout in Georgia, and as the above map shows, their natural range is restricted to the extreme northeastern region of the state with a few outlying disjunct populations, suggesting formerly a  wider, more continous distribution.  Temperature is one obvious limiting factor in their present day range.  Brook trout suvive best in waters with temperatures between 55-65 degrees F.  They can withstand water temperatures between 32-72  F, however, they can only live in warm waters of up to 78 degrees F for a few hours.  Stocking trout in waters with temperatures greater than 70 degrees F generally fails in the long term.  The temperature of the Savannah River near Augusta, Georgia on June 13, 2011 was 73 degrees F.  (Modern reservoir temperatures are much warmer.)  Water temperatures this warm and warmer are common during summer months in southeastern rivers, making them unsuitable for trout.

Summer air temperatures in the southeast were much cooler during the last glacial maximum, and even during interstadials within the Ice Age, therefore water temperatures were as well.  Data from isotopic oxygen ratios of fossil foraminifera in the Atlantic Ocean suggest average annual summer temperatures were 9 degrees F cooler.  (See my May 15, 2011 blog entry for more detailed explanation of this.)  Taking the present day summer water temperature reading from the Savannah River near Augusta (73 degrees F) and subtracting it by 9 = 64 degrees F…within the brook trout’s comfort zone.  Potentially, trout could’ve lived as far south as what’s now Augusta.

Trout also prefer shallow fast moving water–fingerlings like water that’s just 16 inches deep, and adults prefer the water slightly deeper than that.  Trout stay in shallow water and avoid deeper water even if temperatures are cooler in the latter.  Much of the present day Savannah River, besides being too warm, is too deep, but during the LGM arid climate lowered the water table, creating more shallow fast moving streams for trout.  Suitable trout habitat likely existed in 2 notable streams that flow into the Savannah River: the confluence of the Broad River with the Savannah is only ~60 miles south of present day trout habitat, and the Little River’s confluence is only ~70 miles south.  The headwaters of the Broad River is just a scant few miles from present day trout habitat.  Both the Broad and the Little Rivers have the gravel and rocky bottoms brook trout prefer.  During cooler climate phases, there was no ecological reason brook trout couldn’t have expanded their range at least that far south.  The fossil record shows that many other species from northern climates extended their range farther south during the LGM including caribou, elk, woodchucks, bog lemmings, red backed voles, red squirrels, gray jays, pine siskins, wood turtles, and others.  So it’s not only possible but probable brook trout did too.  Unfortunately, finding Pleistocene fish bones in a region almost devoid of Pleistocene fossils is not likely, rendering my hypothesis difficult to prove.

A Review of Giants in the Storm by Mark Renz

There are so many fossil sites in Florida that academic experts don’t have the time and money to excavate the all.  Mark Renz, a professional fossil-hunting guide but not an academic expert, sought and gained permission to excavate 2 productive retention ponds in LaBelle, Florida.  Giants in the Storm is about his experiences spear-heading that effort.  His team found a truckload of fantastic fossils including lots of mammoth, mastodon, and horse material as well as specimens of llamas, flat-headed peccary, long-nosed peccary, white tail deer, Harlan’s ground sloth, saber-tooth, jaguar, bobcat, Armbruster’s wolf, alligator, and giant tortoise.  The site is unique because it dates to the middle Irvingtonian Land Mammal Age (~500,000 BP).  Though Florida has many fossil sites dating to the Rancholabrean Land Mammal Age (~300,000-~10,000 BP), and plenty from the late Pliocene/early Pleistocene (~2 million BP), the LaBelle fossil site is a rarity that helps fill in a gap in the fossil record, and it provides more specimens for comparison of the evolution of individual species.  The site is located in southwest Florida.  The types of mammals excavated here suggest the region was mostly grassland interspersed with riverine and lacustrine forests.

Like the other Mark Renz book I reviewed, Fossiling in Florida, the best thing about this book are the copious photographs of fossils that are useful for amateur  and serious fossil collectors.  Some of my favorites include parts of the anatomy that don’t automatically come to mind such as a mammoth’s calcaneum (heel bone) and an hyoid (tongue bone) from either mammoth or mastodon.  Of course, there were the usual proboscidean teeth, and spectacular fossils–a relatively complete mammoth skull and a 9 foot long, 300 pound tusk found in place but broken into 4 pieces.

Mr. Renz imagined a single dramatic event, a storm of great magnitude causing a flood, as an explanation for why these fossils concentrated here.  It gave him an excuse for a dramatic title for this book, but he concedes his title is a misnomer.  After consulting with Richard Hulbert, curator of the University of Florida Natural History Museum, he agrees with the conclusion that all the fossil specimens were accumulated here gradually over a long period of time.