Archive for the ‘Ichthyology’ Category

Tuna- The Superfish

June 24, 2020

Most people think of tuna as just some fish in a can that is an ingredient in tuna salad.  They don’t appreciate what a spectacular animal it is.  Biology books state that fish are cold-blooded, but tuna are an exception to this rule.  Tuna are actually a warm-blooded fish, and this physiology enables them to swim at ultra high speeds of up to 47 mph.  That is faster than most boats.  However, their warm-blooded physiology has a greater temperature range than those of mammals and birds.  Their blood temperatures do vary, while mammal and bird temperatures generally stay constant, unless they are sick.  The video below shows off the impressive speed of this animal.  They swim with dolphins for protection against sharks, explaining why dolphins can get caught in nets intended for tuna.

 

Tuna are large predatory fish that can swim up to 47 mph.

There are 15 species of tuna within 5 genera including the Allothonnus (thunder tunas), the Auxil (frigate tunas), Euthynnus (little tunas), Katsunnus (skipjacks), and Thunnus (true tunas).  Bonitos are considered a sister species to the tunas, and both are part of the mackerel sub-group.  4 species of tuna overwhelmingly make up the tuna found in supermarket cans and at fish markets and sushi restaurants.  These include bluefin, yellowfin, skipjack, and albacore.

Tuna did not become a popular food fish until well into the 20th century, but now every grocery store in the U.S. stocks tuna.  It doesn’t seem likely to me that this can go on forever.  Eventually, wild tuna populations will become too depleted to support this fishery.  The future of tuna remaining a staple in our diet is aquaculture, but tuna fish farming is in its infancy.  Some Japanese have had experimental tuna fish farms for decades, but the 1st tuna farm in America just opened business last year in San Diego.  Tuna fish farming, unlike tilapia, catfish, and salmon aquaculture, has a long way to go.

There is evidence from Indonesia that humans caught tuna as early as 42,000 years ago. (See: https://markgelbart.wordpress.com/2011/12/07/deep-sea-fishing-42000-bp/ ) It’s surprising some primitive people had deep sea fishing technology that early, though tuna swam closer to shore during the Pleistocene because land extended over the continental shelf and deep waters were located closer to the coast then.

Albacore - Wikipedia

The most common species of tuna found in a can–albacore.

Giant Bluefin Tuna Sells for $3.1 Million in Tokyo | Fortune

500 pound tuna are worth over 3 million dollars to sushi chefs.

1 of my favorite summer dishes is tuna noodle salad and it is very easy to make. Mix a 12 oz package of tuna with the juice of a lemon.  Add a 16 oz box of cooked macaroni, mayo to taste, a can of peas, chopped celery, chopped Vidalia onion, and couple of chopped hard boiled eggs. Stir it up and serve it warm or cold from the refrigerator.

This is my tuna noodle salad.  It’s great warm or straight out of the refrigerator on a hot summer’s day.

Don’t Believe it when People or Books Refer to Some Species as Trash Fish

January 24, 2020

I often found it hard to believe books or people who refer to some species of fish as trash. I think some reject eating certain fish based on their ugly appearance or difficulty in cleaning and dressing.  However, I don’t get to fish much because my wife is disabled, and I’ve had to give her 24 hour care for 24 years.  I never had the chance to prove these claims wrong.  Recently, I discovered a youtube channel produced by a man who does just that.  He has videos of hundreds of outdoor recipes including a series entitled “Fish: Trash or Treasure.”  His youtube channel is The Backwoods Gourmet.  https://www.youtube.com/channel/UCZlbqHy8lvGjryf2A-XT4ag

In the first episode I watched he prepared 2 species of saltwater catfish by frying them with a cornmeal coating.  Many books about fishing refer to them as “trash.”  Though they were a “pain to clean,”  the backwoods gourmet discovered hardhead catfish tasted just like freshwater catfish, and sailfin catfish tasted like sea trout.  Whoever labeled them as “trash” were wrong.  In another episode he prepared chain pickerel.  This is the 2nd species of fish I ever caught.  I was 10 years old, visiting my grandfather in Inverness, Florida, when he showed me how to set a pole out over night.  I jumped up and down in excitement upon awakening in the morning to find a pickerel on the line.  But my grandfather told me we couldn’t eat it because it was too bony.  The backwoods gourmet was able to filet 2 boneless backstraps from a chain pickerel, and he pronounced it delicious.  John Lawson, an early settler of North Carolina, once found 300 chain pickerel in his fish trap circa 1710.  (See: https://markgelbart.wordpress.com/2012/07/27/john-lawsons-voyage-to-carolina-1700-1711/ )

The backwoods gourmet tried bonita, a species of tuna thought of as trash.  He blackened some and smoked the rest, and said it tasted as good as restaurant tuna.  He also fried black drum, and sheepshead roe.  The black drum was good, and he enjoyed the creamy sheepshead roe.  I boiled freshwater bream roe and discovered they tasted just like bland chicken eggs.  But to me, store bought caviar pretty much tastes like fish guts and needs to be mixed with cream cheese to get it down.

Sea robins are a bizzare-looking fish that the backwoods gourmet fileted and sautéed in garlic butter.  He called it “amazing.  Another really strange-looking fish he tried was remora.  This interesting species has a sucker on the top of its head that attaches to a shark’s body.  When the shark is feeding, the remora detaches itself and feeds on the scraps.  The backwoods gourmet said they tasted like red snapper.

Backwoods gourmet shows how to clean and cook a remora fish.

In another episode the backwoods gourmet prepares long-nosed gar.  This species was a favorite of the American Indian, and it is still popular in Cajun cuisine.  He had to use a pair of snippers to cut through the thick armor.  He said it tasted like alligator.  In the entire series the backwoods gourmet found just 1 species that he labeled trash–the ladyfish.  It tasted good but was just too full of bones to eat.

There are a couple additional aquatic animals the backwoods gourmet cooks on his youtube series.  Frog legs are not all that unusual and are considered a delicacy in France.  That’s why the French are sometimes known as “frogs.”  He turned soft-shelled turtle into grilled kabobs and said they were chewy and tasted like chicken.  The 1 time I cooked turtle, I was able to make the meat tender by pounding it with a meat mallet, and I thought it tasted like lobster.  On the 4th of July he staged a turtle egg-eating contest.  The white on a turtle egg never gets hard no matter how long it is boiled.  The 3 adults who tried the turtle eggs liked them but a kid almost gagged on it.

Pleistocene Puffer Fish (Spheroides maculatus)

June 16, 2018

Pier fishermen often catch what many consider to be “trash” fish.  Stingrays, eels, dogfish, and puffer fish are common in shallow coastal waters during the summer and readily take bait.  Although fishermen usually throw them back in the ocean, they are all good to eat.  Pieces of stingray wings cut with a cookie cutter are used to make mock scallops.  Eel is a delicacy I have enjoyed.  Dogfish, a small species of shark, really does taste like chicken when fried. During WWII when rationing made meat scarce, fishermen caught hundreds of thousands of pounds of puffer fish off Long Island and sold them in New York City fish markets under the name “sea squab.”  However, an important cautionary note needs to be made about consuming puffer fish–its flesh is toxic in some regions.  From researching this topic online, I’ve determined puffer fish caught from North Carolina to Massachusetts are safe to eat, but puffer fish caught from Florida south to the tropics are deadly.  It is against the law to consume puffer fish caught off Florida’s coast because it contains so much saxitoxin.  I have not been able to determine whether puffer fish caught in the border region in between Florida and North Carolina are safe, so I wouldn’t chance it.

 

Video of a man cleaning puffer fish caught off the North Carolina coast.  It yields a piece of fish about the size and shape of a chicken drumstick.

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Illustration of puffer fish before and after it blows up.

The northern Atlantic puffer fish, also known as a blowfish, is a member of the Tetraodontinidae family which includes 29 genera and 191 species.  Most of these species occur in tropical waters and are toxic.  The family includes the famous fugu fish served in Japan where specially trained chefs dress them in a way that makes them safe for human consumption.  Toxins are heavily concentrated in the liver and gonads.  Puffer fish inhale air or water when threatened, and they have prickly spines on their scales.  This makes them tough for predators to grasp or swallow.  Ospreys are unable to grab puffer fish.  This defense mechanism has helped this family survive for millions of years.  Definitive fossil evidence of species in the Tetraodontinidae family has been unearthed from strata dating to the Cretaceous over 100 million years ago, and some specimens that may belong to this family were found in Triassic deposits.

The northern puffer fish evolved to live in cooler waters than its tropical cousins.  Cooler ocean currents began to expand in circulation early during the Pliocene when Ice Ages began to occur.  This may be when the northern puffer fish diverged from the southern puffer fish (S. nephulus) which reaches its northern range limit off the coast of north Florida where the 2 species overlap.  In this area northern puffer fish inhabit deeper waters to avoid competion with S. nephulus.  Northern puffer fish move into shallow waters over most of the rest of their range during summer but move to deeper waters when the water temperature seasonally cools.  This pattern may have been disrupted following Ice Age Heinrich Events when  the Gulf Stream shut down due to influxes of glacial meltwater.  There is no known Pleistocene-aged fossil evidence of puffer fish, and scientists have not yet studied the Tetraodontinidae family genome.

Puffer fish prey on crustaceans (schools of puffer fish gang up on blue crabs), molluscs, worms, and sponges; and they consume seaweed and algae. The species of algae they eat in warmer waters is toxic, and this is how they acquire their toxicity.  This explains why the same species is safe to eat when caught from cold waters but toxic from warmer regions.  There is no antidote for this kind of nerve poison.  It shuts down the victim’s nervous system.  A victim may recover in a few hours or days or they may die from suffocation while wide awake as their lungs and heart cease to operate.

Banks, S.; and Anthony Pachee

“Biology and Fishing Data on Northern Puffer (Spheroides maculatus)

NOAA Report 26 1961

Gibbon, Euell

Stalking the Blue-eyed Scallop 

David Mackay Publishing 1964

Fish Nest Associates

May 6, 2018

The bluehead chub (Nocomis leptocephalus) is a keystone species in piedmont and mountain rivers and streams of southeastern North America.  Dozens of species of shiners spawn and lay their eggs in bluehead chub nests.  Without the existence of bluehead chubs most of these species would probably become extinct.  Bluehead chubs and shiners are members of the minnow family, known scientifically as the Cyprinidae, and bluehead chubs are 1 of the largest minnow species, growing up to 8 inches long.  Bluehead chubs make large gravel nests and aggressively protect their young.  They bury their eggs with large pieces of gravel and in the process bury and protect the eggs of other minnow species.  A complex ecosystem inhabits bluehead chub nests. Many macroinvertebrates live in bluehead chub nests alongside the minnow eggs.  Snails, clams, and the larval stages of dragonflies, dobsonflies, caddisflies, and beetles use the bluehead chub nests for shelter.  Salamanders and darters prey on the invertebrates entering and exiting the nests.  Scientists believe shiners and bluehead chubs both benefit from the congregation of eggs and hatchling fish, referring to the relationship as mutualism.  The great abundance of eggs from several different species dilutes the losses to predators, and more young of each individual species survives.

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Bluehead chub range map.

Bluehead Chub

Bluehead chub.

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Rainbow shiner (Notropis chrosomus).  Some shiners can get quite colorful.

Many other species of fish associate in the same nests.  Rough shiners (Notropis baileyi), saffron shiners (N. rubicroceus), and greenhead shiners (N. chlorocephalus) spawn in creek chub nests.  Redfin shiners (Lythurus umbratalus) spawn in green sunfish (Lepomis cyonellus) nests.  All of these associations result in increased reproductive success for both species.  Some shiners will use central stoneroller nests, but prefer chub nests and will move their spawning activity to bluehead chub nests, if they become available.

The evolution of fish nest association must be very ancient.  It seems likely the host fish evolved first, and the species of fish using the host’s nest lost their ability to make their own nests when they came into contact with the larger  host species because the host could build bigger nests that offered more protection.  Host species are usually larger and better able to defend the nest than the smaller minnows, but they benefit too from the sudden population explosion of potential food for predators that might otherwise eat their hatchlings.

Reference:

Johnston, Carol

“Nest Associate in Fishes: Evolution of Mutualism”

Behavioral Ecology Sociobiology 35 1994

Swartwout, M.; F. Keating, and E. Frimpas

“A Survey of Macroinvertebrates Colonizing Bluehead Chub Nests in a Virginia Stream”

Journal of Freshwater Ecology 2016

Pleistocene Fish of the Tennessee River System

December 28, 2017

Many Italians like to celebrate Christmas Eve with the feast of the 7 fishes.  I’m not Italian, but I like to eat seafood during the holiday season too, though my immediate family is small, and we enjoy the feast of the 2 fishes.  I wonder what species would’ve composed a feast of fishes for Paleo-Indians when they first entered the Tennessee River Valley.  Fish populations were much higher in the pristine pellucid waters of all southeastern rivers before man began destroying the environment, but the composition of species is poorly known because fish remains that old are rarely preserved.  A new study of fish remains excavated from Bell Cave partially unveils this mystery.  Bell Cave in Colbert County, Alabama overlooks the Tennessee River and floods periodically stranded fish inside the cave from ~13,000 calendar years BP-~30,000 calendar years BP.  Predators carried fish into the cave as well.  Scientists collected vertebrate bones from this cave between 1984-1987, but no one identified the fish remains and published the data until 2016.  This study also catalogued fish remains from other sites near the Tennessee River including Baker Bluff Cave, Beartown Cave, Guy Wilson Cave, Cheekbend Cave, Dust Cave, Little Bear Cave, Appalachian Caverns, and Saltville.

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Map of the Tennessee River.

The authors of this study identified 41 taxa and 38 species that lived in the Tennessee River during the late Wisconsin Ice Age.  The number of species they identified is a subset of the population that actually swam in the river because, by chance, many species just never got trapped in the cave or were too decayed to be identified.  This is especially true for smaller species.  Almost all of the species they identified still live in the Tennessee River system today, but there are 3 exceptions.  Northern pike (Esox lucius) no longer naturally occurs this far south, although man has introduced this species into some bodies of water.  (Muskellunge, a related species, surprisingly still occurs in the Tennessee River.  Fossil evidence suggests they were fairly common here during the Ice Age.)  Northern madtom (Noturus stigmosis), a small species of catfish, also no longer occurs this far south. The harelip suckerfish (Moxostoma lacerum) became extinct during the late 19th century.  This species required very clear water with gravel bottoms, but deforestation and agriculture caused erosion that muddied its spawning grounds.  Pleistocene rives were clear enough for this species.

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Northern pike.

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Northern madtom.

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Harelip sucker.

Rock bass were the most commonly represented fish from the Centrarchidae family catalogued in this study, but curiously they found not a single specimen of sunfish.  Bluegill sunfish are 1 of the most common fish in the Tennessee River today because they thrive in manmade reservoirs, but that kind of environment was rare before man began impounding rivers.  Sunfish probably lived in oxbow lakes that weren’t close enough to caves where their remains could’ve been preserved.

A Paleo-Indian trapping fish in the Tennessee River could’ve enjoyed a feast of 7 fishes consisting of sturgeon, northern pike, walleye, sauger, freshwater drum, bullhead catfish, and eel.  These were probably the best tasting fish available to them then.

Reference:

Jacquemin, S.; J. Ebersole, W. Dickinson, G. Ciampaglio

“Late Pleistocene Fishes of the Tennessee River Basin: an Analysis of a Late Pleistocene Freshwater Fish Fauna from Bell Cave (site Acb-2) in Colbert County, Alabama”

Peer J 2016

Floodplain Fish

July 31, 2017

River systems host a hidden world of tiny invertebrates.  Some are microscopic, while others, though visible to the naked eye, remain unseen unless a curious fisherman cuts open the stomach of his catch.  A fish’s stomach might contain small crustaceans including water fleas (Cladocera), seed shrimp (Ostracada), amphipods, copepods and/or isopods.  These minute shrimp-like creatures form the basis of a food chain that supports fish populations.

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Seed shrimp (Ostracods) along with other small crustaceans are an important part of the food chain in aquatic habitats.

In southeastern North America rivers overflow their banks between November and March because cooler temperatures reduce evapotranspiration and dormant riverside vegetation takes in less water.  The flood stage is especially wide in the flat coastal plain region where a sheet of water 2-3 feet deep can cover hundreds of square miles alongside major rivers, though modern dams, ditches, and canals have reduced the former extent of these flooded wetlands.  This flooded land offers more territory for fish to forage and reproduce.  The diet of many fish species changes from the aquatic crustaceans mentioned above to prey that normally lives some distance from the river.  1 study found fish occupying floodplains ate a species of isopod that lives in small pools of water, terrestrial species of crayfish, beetle larva, and caterpillars.  These terrestrial species were not normally found in fish’s stomachs until the flood stage.  Some species of fish even breed over floodplains that become dry land during summer.  The blueback herring (Alosa aetivalis) spawns in flooded hardwood swamps, unlike its relatives the American shad and hickory shad that spawn in the main channel and tributaries of a river.  Blueback herring eggs adhere to twigs on the forest floor.

 

Blueback herring spawn over flooded land.

White bass (Morone chrysops) also spawn on floodplains during high water.  This species is probably the “white fish” mentioned by John Lawson in his book A New Voyage to the Carolinas.  A few years ago, I wrote a blog article identifying the fish Lawson wrote about in his early natural history book.  (See: https://markgelbart.wordpress.com/2014/08/31/identifying-the-species-of-fish-described-by-john-lawson-in-1710-part-2/   )I was able to figure the identity of most of them despite the archaic names and vague descriptions, but his “white fish” stumped me.  Zach Matthews, editor of The Itinerant Angler, suggested to me that Lawson was referring to the white bass.  Lawson’s description that it was found in “freshets” or floodwaters is good evidence he was discussing the white bass.

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White bass also spawn over floodplains.  This is probably the “white fish” John Lawson discussed in his book A New Voyage to the Carolinas.

There have been plenty of genetic studies of the white bass and its cousin the striped bass because the 2 closely related species are hybridized for sports fishermen.  But I can’t find any genetic studies that explore the evolutionary origin of this genus.  It seems likely white bass diverged from the same ancestor as the striped bass, and this common ancestor was probably an anadromous fish, like the latter species. The initial ancestral population of white bass began spawning on floodplains and became landlocked and unable to return to the ocean when something temporarily blocked access to the ocean.   This explains how the 2 species diverged from each other.  White bass evolved the ability to survive entirely in freshwater habitats and were able to colonize aquatic environments much further inland than striped bass.  White bass collect fat reserves and can endure cold winters.  They became well adapted to the colder temperatures of Pleistocene Ice Ages.  Geneticists could probably use a molecular clock to determine when this divergence occurred, and they may be able to tie the timing to some climatic event.

Fish use floodplains to migrate to new habitats and maintain genetic vigor between populations.  During flood stages many fish from the Okefenokee Swamp swim through flooded habitat to the Suwannee River.  Warmouth, flier, bowfin, pickerel, bullheads, and lake chubsuckers have all been recorded traveling through 2-3 feet of water to the river.  Floods can also connect breeding fish from oxbow lakes with fish from the main branch of the river.  Shiners, bream, catfish, darters, mosquito fish, and starhead minnows often travel through flood waters between oxbow lakes and rivers.  Eels also use these corridors but they don’t breed in freshwater.  Many fish get trapped in oxbow lakes and sloughs after floodwaters recede.  However, oxbow lakes provide better habitat for fish than rivers, often holding 12 X more fish per acre though species diversity is identical.  The most common fish in Altamaha River oxbow lakes are gizzard shad, spotted sucker fish, and channel catfish.

During Ice Ages rivers in the southeast didn’t flood as much as they do today.  The fish best adapted for braided river patterns were most common.  Cut-off channels within river beds probably held concentrated populations of catfish and killifish.  Anadromous fish such as shad and striped bass spawned in areas that have since been inundated by rising sea levels.  Following the end of the Ice Age, there was a supermeandering phase of rivers when flooding was more extreme than it is today.  This caused a resurgence of floodplain fish species.

Reference:

Clark, J.R.; and J. B. Forado

Wetlands of Bottomland Forests

Proceedings of Bottomland Hardwood Forest Wetlands in Southeastern United States 1980

Native Fish Species Composition of Piedmont Tributary Creeks of the Chattahoochee River

November 7, 2016

The many present day creeks and small rivers that flow through the piedmont region of central Georgia originated between 15,000 years BP-8,000 years BP when water tables rose as a result of melting glaciers far to the north of the state.  Before this, during the Glacial Maximum, the regional landscape was much more arid and only the largest of rivers and creeks still flowed…and those were often low flowing and clogged with sandbars.  Intermittent springs probably occurred in the lowest areas of topography along the present day courses of smaller streams.  Climatic phases with increased precipitation raised the water table enough to cause water flow between springs, and these creeks eventually emptied into the nearest river.  So much atmospheric moisture was released at the end of the last Ice Age that rivers and creeks had a larger flow than they do today.  This occurred between ~10,000 years BP-~5,000 years BP when rivers were classified as “supermeandering.”  Fish found their way from rivers into newly formed creeks during the late Pleistocene/early Holocene, though a few species may had persisted in relic Ice Age springs before water tables rose.  About 40 years ago the noted naturalist, Charles Wharton, electro-fished a small unnamed creek located 1.4 miles south of Sopa Creek, a tributary of the Chattahoochee River, and he determined the “near original” composition of fish species typical of piedmont streams that flow into this river.  These creeks flow through steep terrain often between high bluffs and where protected are still very beautiful natural areas.

Map of Georgia highlighting Cobb County

Cobb County, Georgia.  Charles Wharton electro-fished a small stream here over 40 years ago and determined the original fish species composition of piedmont Chattahoochee feeder creeks.

This is where Sopa Creek flows into the Chattahoochee River.  Sherman ordered his troops to cross over the rocks here during the Civil War.

The fish species Wharton found in his survey included band fin shiner ( Notropis zonistius ), central stoneroller ( Campostoma anomalum ), creek chubsucker ( Erimyzon oblongus ), Alabama hog sucker ( Hypentelium etowanum ), yellow bullhead catfish ( Ictalurus natalis ), bluegill ( Lepomis machrochorus ), and banded sculpin ( Collus carolinae ).  The band fin shiner is a small minnow native to the Chattahoochee River drainage, though it has been introduced to other river systems wherever fishermen dump their bait buckets.  The stoneroller is a widespread species in the Midwest.  It eats algae and may school in the hundreds.  They grow up to 8 inches long.  The creek chubsucker can grow twice as long as the stoneroller, and it eats small crustaceans and insect larva in addition to algae.

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Alabama hog sucker.

The yellow bullhead catfish is omnivorous and can grow up to 6 pounds, though it normally reaches a weight of about 2 pounds.  Bluegills also grow large enough to make a good meal.  Early settlers placed fish traps in the nearest streams and caught supper, while they were busy clearing and cultivating their land.  Bluegills and catfish living in clear moving streams with rocky  bottoms probably taste better than those taken from muddy ponds.

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Yellow bullhead catfish.

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Bluegill sunfish or bream.

The banded sculpin is a freshwater relative of a large family of saltwater species.  Banded sculpins are nocturnal ambush predators that live under stones.  They compete with crayfish for the same type of habitat.

Banded Sculpin - Cottus

Banded sculpin.

The origin of the name Sopa Creek has a disputed origin.  This stream flows for 11.6 miles through Marietta until it empties into the Chattahoochee River.  Today, the headwaters emerge from a spring under a manmade culvert, but I’m sure the original landscape was picturesque.  Now, it is surrounded by suburban sprawl.  Some say this creek gets its name from the foam caused by water rushing through rocks.  The foam resembles soap spuds, and supposedly an early mapmaker misspelled soap.  Others claim the creek is named after an old Cherokee Indian (Old Sopa) who lived nearby.  He reportedly refused to be removed when is compatriots were force marched to Oklahoma on the Trail of Tears.

Reference:

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1978

 

Pleistocene Bluefish (Pomatomus saltatrix)

October 4, 2016

The bluefish, a powerful fast-swimming predator, is popular with many saltwater anglers because it fights hard when hooked.  They inhabit tropical and semi-tropical waters year round, but a segment of the American population migrates as far north as Nova Scotia when water temperatures exceed 64 degrees F during summer.  They prey on small fish, such as silversides, menhaden, sand eels, and their own young; as well as squid and sea worms.  The blues prefer shallow coastal waters and especially like to congregate the down current side of shoals between narrow gaps of land. Here, they wait in underwater holes for  small fish swept over submerged sandbars by strong currents. Populations of bluefish have historically and mysteriously fluctuated, and like most other marine species of fish are in danger of being overfished.

There is little fossil evidence of bluefish dating to the Pleistocene.  In the ocean fish remains usually won’t survive the ravages of time.  But a few middens do hold evidence of bluefish.  The Old Oak midden in Florida–a mound consisting of shellfish and vertebrate bones made by generations of the Weeden Island Culture–contained bluefish bones.  This culture existed from 1200-200 years ago. However, bluefish didn’t suddenly pop into existence then.  Without paleontological evidence it’s still possible to learn something interesting about a species’ past by studying their DNA. One genetic study determined western Atlantic bluefish populations off the coast of America have been reproductively isolated from eastern Atlantic and Mediterranean populations for 480,000 years.  And there are 2 populations of bluefish living in the Mediterranean Sea that have been reproductively isolated from each other for over 100,000 years.  The isolation of these 2 Mediterranean populations is associated with barriers that formed during Ice Ages.  These underwater geographic barriers still remain.

The divergence of the western and eastern bluefish populations occurred during Marine Isotope Stage 13a–a warm peak with a cold split.  Deep waters of the mid-Atlantic are the present day barrier that keeps these 2 populations reproductively isolated from each other.  Blues prefer shallow water and are unlikely to traverse deeper waters where baitfish may be scarce over large areas.  The last time a population of bluefish traversed the mid-Atlantic could have been a summer migration that may have gone off course chasing a massive school of menhaden.  It seems likely this occurred during a stadial when the distance between the continents was smaller.  Perhaps a normal summer migration swam into unseasonably cool water that occurred because the Gulf Stream suddenly shut down, and they headed east because they became disoriented.  Bluefish probably originated long before the Pleistocene, before continents were as widely spaced as they are today.

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Map of the Georgia bight.  The shaded area was above sea level from ~80,000BP-~7,000 BP.  Bluefish prefer shallow coastal water, so their range must have been shifted off the continental shelf during Ice Ages.

Bluefish range map.  DNA studies suggest American and eastern bluefish populations have been isolated from each other for 480,000 years.

Bluefish

John Lawson said bluefish taste like salmon.  I’ve never caught one, nor have I ever seen one in the grocery store.

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School of bluefish.

During glacial periods when much of the continental shelf was above sea level, bluefish must have inhabited bays and river mouths.  There were steep drop-offs adjacent to the continental shelf with deeper water than bluefish prefer.  The Gulf Stream shut down during stadials (the coldest periods of Ice Ages), and there would have been no bluefish migration north because the water temperatures were too cold.  Bluefish range was restricted to tropical/semi-tropical waters during stadials.  The northern bluefish migrations resumed during interstadials when the Gulf Stream periodically restarted and began carrying tropically heated water farther north again.

References:

Hersey, John

Blues

Vintage Books 1987

Miralles, Laura; et. al.

“Paleoclimate Shaped Bluefish Structure in the Northern Hemisphere”

Fisheries 2014

Why did the Giant Great White Shark (Carchocles megalodon) Become Extinct?

April 29, 2016

The giant great white shark (Carchocles megalodon) existed as a species from ~23 million years BP until ~2.6 million years BP, and the evidence suggests this 60 foot monster preyed on whales.  It was 1 of the many marine species to become extinct during the late Pliocene.  Scientists believed megalodon was a warm water species and couldn’t survive cooling ocean waters that resulted from the emergence of the landbridge between North and South America.  However, a brand new study determined climate change could not have been the cause of megalodon’s extinction.

The authors of this study mapped out all of the sites where megalodon fossil teeth have been collected along with all fossil shark collection sites where megalodon remains were absent.  They estimated the range of the species over geologic time. Megalodon, though it originated in tropical waters, later expanded its range to waters that are thought to have been quite cold.  During glacial maximums megalodon’s potential habitat range shrank by a mere 2%, while it expanded by 8% during warmer interglacials.  Most of the area where megalodon lived was not “negatively impacted by climate change.”

Populations of C. megalodon over time. From Pimiento et al., 2016.

Map of megalodon fossil collection sites, dated over geological time periods.  From the below referenced paper.

If climate change didn’t snuff out megalodon, what was the cause of its extinction?  The researchers who published this study suggest 2 possible causes: a reduction in whale species diversity, and competition with other predators.  They note a decline in whale species diversity during the end of the Miocene is correlated with an apparent decrease in megalodon’s range distribution.  This seems a plausible explanation.  Many of megalodon’s favorite prey species went extinct, depriving the giant shark of food that it could efficiently feast upon.  I’m not convinced competition with other predators was a factor in megalodon’s extinction.  An extinct predatory species of sperm whale (Livyatan  melvillei) likely fed upon the same prey species as megalodon.  The ancestors of the modern day great white sharks (Carcharodon hubbeli) and killer whales (Orca sp.), also may have shared the same prey items.  However, megalodon co-existed with these species for millions of years, so I have a hard time accepting this explanation.

Size comparison between megalodon, a killer whale, and a human. A pod of killer whales could’ve rubbed out a single megalodon.  Perhaps this was a factor in their extinction.

skeletal reconstruction Livyatan melvillei by Christopher252

An extinct species of predatory sperm whale–Livyatan melvillei–probably competed with megalodon for the same prey.  

The extinction of megalodon may have  shaped the evolution of baleen whales.  Whales no longer had to be agile fast swimmers to escape megalodon, but instead could grow to a great size that enabled them to store food as blubber.  The stored fat helped baleen whales swim long distances to warmer waters for breeding and calving.  Killer whales, their lone remaining non-human predator, are less common in warmer waters, and whale calves have a greater chance of survival there.

Reference:

Pimiento, Catalina; et. al.

“Geographical Distribution Patterns of Carchocles megalodon over time Reveal Clues about Extinction Mechanisms”

Journal of Biogeography March 2016

Pleistocene Paddlefish (Polyodon spathula)

March 8, 2016

A large population of 7 foot long, 150 pound paddlefishes lived in the primeval waters of the Mississippi River Drainage System  from well before the Pleistocene until the 19th century when humans began overexploiting this species.  An even larger population of smaller individuals also swam these waters for eons.  Millions upon millions of paddlefishes existed for tens of thousands of generations, yet, as far as I can determine from the scientific literature, not a single fossil specimen of Pleistocene Age has ever been found.  The paddlefish is a primitive species with a body structure supported by cartilage rather than bone.  There is nothing on their body that is hard and durable, therefore, evidence of their past existence is very unlikely to survive the ravages of time.  Sharks are also primitive fishes supported by cartilage, but at least they have hard teeth that do resist decomposition.  There isn’t even much evidence of paddlefish in the archaeological record, though Indians certainly utilized this species.  The remains of a paddlefish were excavated from a Native-American midden located in Wisconsin.

Scientists do know the paddlefish is an ancient species, possibly originating before the dinosaurs.  William Bemis, a paleontologist, described a Cretaceous Age fossil of a paddlefish found in Montana as “remarkably like (the 2) living species of polyodon.”  The only other extant species of paddlefish in the world occurs in Chinese rivers, and its scientific name is Polyodon gladius.  The 2 living species probably diverged during the Miocene between 25 million-5 million years BP, when climatic changes led to an environmental barrier that divided the American population from the Asian gene pool.  Genetic evidence suggests the American paddlefish has been uniform for a long time.  They travel great distances throughout the Mississippi River Drainage System and interbreed freely and do not live in isolated populations.  One tagged specimen caught in Moon Lake, Mississippi was captured later 870 miles away in Illinois.

American Paddlefish (Polyodon spathula).

The American paddlefish filter-feeding. No Pleistocene aged specimens of this species have ever been found because they are made of cartilage.  The adults have no teeth.

Paddlefish range map.  Paddlefish are now extinct on the periphery of their northeastern range and their populations are in decline elsewhere.

Paddlefish live in large rivers, braided channels, and oxbow lakes.  All of these habitats existed during the Pleistocene.  Braided channels more commonly formed during cold arid phases of Ice Ages.  The lower water table resulted in channels cut off and choked with sandbars.  Warmer wetter climate phases caused an increase in the formation of oxbow lakes as overflowing waters meandered more.  Paddlefish thrived in both habitats wherever there was an abundance of zooplankton.  Paddlefish use their unusual paddle-like structures to locate the tiny crustaceans and insects upon which they filter feed.  Their diet of mini-crustaceans probably explains why their flesh reportedly tastes like lobster.  They are still referred to as “poor man’s lobster,” even though this endangered fish is now rarer in fish markets than actual lobster.

Moon Lake, Mississippi still supports a commercial fishery for paddlefish.  They were so abundant during the early 20th century here that 100 could be caught in a single purse-seine haul.  The catch is much reduced today.

Moon Lake, Mississippi, an oxbow adjacent to the Mississippi River, still has a viable population of endangered paddlefish.

Oxbow lake formation fascinates me.  An oxbow lake is the remains of a meander that gets cut off from the main flow of the river, following a period of high water when the river surges over land to connect the shortest distance between 2 points.  These natural formations provided the only lake habitats over much of the south until man began building reservoirs.  Eventually, sediment builds in oxbow lakes until they evolve into marshes and then dry land.  Old oxbows that dry out are known as meander scars.

References:

Hoover, Jeffrey; et. al.

“Age and Reproductive Condition of an Unusually Large Bighead Carp from the Lower Mississippi River Basin”

Southeastern Naturalist 14 (4) 2015

Theler, James

“Animal Remains from Native American Archaeological Sites in Western Wisconsin”

Transactions of the Wisconsin Academy of Science, Art, and Letters 2010