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6 Selected Fish Species from Congaree National Park

April 22, 2026

The Congaree National Park, located near Columbia, South Carolina, is the largest remaining bottomland forest in Southeastern North America and has the largest trees east of the Mississippi. It’s mostly a swamp and hosts an abundance of aquatic species of wildlife. I follow Friends of the Congaree on my Facebook page, and recently they posted photos of a fish survey they took. They put the fish in aquariums on display. They found over 6 species.

Location of Congaree National Park.

This tank held freshwater shrimp, warmouth sunfish, dollar sunfish, pirate perch, piedmont darter, and mosquitofish. I once caught a freshwater shrimp with a net when I was trying to capture crayfish.

Bluegill, striped sunfish, madtom, and crayfish. The aquarium pictured above this holds a spotted sunfish.

The pirate perch (Aphredodurus sayanus) prefers still, clear, warm water. They get their name because they will eat all the smaller fish in a tank. In the wild they mostly eat insect larva, glass shrimp, worms, and smaller fish. This species has an unusual anatomical feature–its anus is next to its throat. They like to hide from predators under riverbanks formed by tree roots. They grow up to 5.5 inches long.

The warmouth (Lepomis gulasus) is a species of sunfish in the Centrarchidae family. They are a popular game fish that grows between 6-15 inches long. They are good for pan-frying and taste better than largemouth bass. They eat insects, crayfish, and minnows. Every spring they make nests in gravel, and the males defend the nests from cannibalistic females. They can hybridize with green sunfish, bluegills, black crappies, and even largemouth bass.

The dollar sunfish (l. marginatus) is a small species of sunfish that grows to just 4-5 inches long. They feed upon detritus, algae, and insects. Like other species of sunfish, the males defend the nests.

Madtoms (Nocturus sp.) are small catfish that grow to 3-5 inches long. There are 29 species. They have venomous spines. Their diet includes crayfish and fish.

Mosquito fish (Gambusia sp.) are small fish growing to about 2 inches long. They are a beneficial species because they eat mosquito larva, and they’ve been introduced into many areas outside of their natural range in order to control mosquito populations. There are over 40 species.

The redfin pickerel (Esox americanus) is a predatory ambush species that prefers clear shallow water. It’s an active predator that hides in the weeds and rapidly bursts from cover to catch other fish. They grow to between 7-15 inches long.

Redfin pickerel.

Another redfin pickerel. The red fins are more pronounced on some individuals than others.

The fish survey in the Congaree National Park also collected bluegills, spotted sunfish, piedmont darters, and golden shiners. The latter species is not native to the park but was introduced by fishermen as bait.

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There are No Known Cases of Man-eating Hammerhead Sharks

April 15, 2026

I was quite surprised when I learned there are no known cases of man-eating hammerhead sharks. Facebook algorithms inundate my feed with numerous nature-oriented posts, and when I came across this fact, I couldn’t believe it. I consulted Google AI, and the results confirmed this fact. Hammerhead sharks have been responsible for 18 unprovoked attacks against humans but no confirmed fatalities. Great hammerhead sharks (Sphyrna mokarron), the largest hammerhead species, reach lengths of 20 feet and feed upon bull sharks (Carcharhinus leucas) –a species that is a confirmed man-eater. Great hammerheads are a dangerous species but ordinarily do not attack people.

There are 9-11 species of hammerhead sharks. Taxonomists don’t agree on the number.

Great hammerheads are a dangerous species but don’t ordinarily attack people. I don’t respect the intelligence of anyone who would attempt this stupid stunt.

Scalloped hammerheads don’t grow as large as great hammerheads.

Google AI’s list of shark attacks vastly undercounts the incidents, according to other sources I found on the web. Google AI admits it may be in error sometimes.

There are 9-11 species of hammerhead sharks–the uncertain number indicates a dispute among taxonomists. Genetic evidence suggests hammerheads diverged from other sharks about 20 million years ago, but some believe they may have begun diverging as early as the Eocene over 33 million years ago. Hammerhead shark teeth, dating to the Pleistocene, are commonly found.

The odd shape of the hammerhead is known as cephalofoil, and it serves several useful functions. It gives the sharks 360-degree vision, especially helpful when hunting prey. The hammerhead gives the sharks better electro sensory perception–another advantage–and they actually use their heads to pin prey to the ocean floor. This is useful when they prey upon stingrays, a species that normally hides in the sand on the ocean bottom.

While researching information for this blog, I found a wide discrepancy between Google AI and other sources on the total number of shark attack incidents and deaths. I counted the total number of fatal shark attacks on Google AI, and it was 124 since 1580. Wikipedia reports 459 fatalities just between 1958-2016. Wikipedia is likely more accurate in this case. There’s something wrong with Google AI’s information retrieval. Both use the International Shark Attack Files. Curiously, when I asked the question a slightly different way, Google AI mentions several of the more famous shark attack incidents in history, including the sinking of the USS Indianapolis in 1945 when 859 sailors were eaten by sharks (more than the total in history from a previous search result). These numbers don’t include many 3rd world countries where some fatalities may go unreported.

3 species of sharks are responsible for most shark attack fatalities. Great white sharks (Carcharodon carcharias) prey upon marine mammals and occasionally mistake humans for their normal prey. Bull sharks can survive in fresh water and often swim far up rivers. Tiger sharks (Galeocerdo cuvier) are another confirmed man eater, perhaps because they will scavenge just about anything. Oceanic white tips (Carcharhinus longimamus) may be responsible for more fatalities than are known because they attack shipwreck and plane crash survivors who are never found. Bronze whaler sharks (C. brachyurus), so named because they used to congregate around whales killed by whalers, have been known to attack and kill men as well.

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Great White Sharks (Carcharadon carcharias) Almost Went Extinct During the Last Ice Age

August 13, 2025

Scientists attempting to solve a genetic mystery about great white sharks instead discovered a surprising detail about the history of this species. 20 years ago, scientists learned there were big genetic inconsistencies between great white shark mitochondrial DNA, mostly inherited from the female side, and nuclear DNA material inherited from both parents. This could be caused by genetic variation before speciation, hybridization before speciation, different dispersal patterns between sexes, or different environmental selection processes between sexes. Scientists collected genetic data from great white sharks for 13 years and put this data into different models to try and understand why. They assumed this dissonance was most likely caused by females staying in the same geographic area, while males migrated long distances and interbred with other populations. The models they used couldn’t solve the mystery. Even extreme models that assumed females didn’t migrate at all couldn’t explain why mitochondrial DNA was so different. However, the scientists who studied this did learn great white sharks almost became extinct during the last Ice Age.

Great white sharks almost went extinct during the last Ice Age because their shallow water habitat was replaced by dry land. There were no great white sharks in the Atlantic Ocean until about 7000 years ago, though they may have repopulated it during previous interglacials. Loss of shallow coastal habitat is probably the same reason megalodon went extinct 2 million years ago when Ice Ages became more severe.

Seals make up a good part of great white shark diet in some regions.

Frontal view of a great white shark.

10,000 years ago, great white sharks were on the decline and limited to 1 population between South Africa and Australia. Their favored habitat–shallow coastal waters–was nearly eliminated when sea levels fell, as so much of earth’s atmospheric moisture became locked into massive glaciers. Dry land extended into what was formerly and would become shallow coastal waters. This is also likely the reason megalodon became extinct at the beginning of the Pleistocene. 7,000 years ago, great white sharks began to increase in numbers and today there are 3 populations–the coasts of South Africa and Australia, North Atlantic coasts, and North Pacific coasts. Scientists estimate the great white shark population worldwide is only 20,000. They are still vulnerable to extinction.

Reference:

Lasa-Judart, R.; S. Corrigan, C. Yang

“A Genomic Test of Sex-Biased Dispersal in White Sharks”

PNAS 122 (32) July 2025

https://www.pnas.org/doi/10.1073/pnas.2507931122

See this article for an explanation about how scientists use the molecular clock to study the history of a species.

https://www.nature.com/scitable/topicpage/the-molecular-clock-and-estimating-species-divergence-41971/

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Sea Horses are Most Abundant in Tampa Bay During October

July 3, 2025

There are many strange creatures inhabiting earth’s oceans. Sea Horses could be considered among the strangest fish to live in the sea. There are about 46 species of sea horses, and they belong to the genus Hippocampus, a Greek word meaning horse. Their heads and bodies superficially resemble those of horses. Genetic evidence suggests they diverged from pipe fishes between 25 million-30 million years ago. During this time period tectonic processes expanded shallow water habitat favorable for sea horses. They prefer shallow ocean where sea grass can grow. These odd fish use camouflage in sea grass beds to avoid predators and to sneak up on prey. They were probably most abundant during Pleistocene Ice Ages when sea levels dropped, creating extensive sea grass habitat. However, fossils of sea horses are known from just the Miocene and Pliocene. Genetic evidence suggests sea horses originated in the Pacific and colonized the Atlantic during 2 separate expansions.

Sea horses are an evolutionary improvement over pipe fish, though the latter are still extant. Both types of fish suck in tiny animals such as brine shrimp, copepods, and newly hatched fish fry, but the vertical position of sea horses helps them suck in prey from a greater distance than pipe fish can. 3 more traits make sea horses seem unusual. They are armored, they have prehensile tails, and the males get pregnant. During mating females transfer their eggs to the male’s pouch. The males then give birth to up to 2500 live young.

The vertical position of a sea horse allows them to suck in food from a greater distance than their cousins, the pipe fish. They have to eat constantly because their digestive systems are inefficient.

Sea horse life cycle.

Scientists who authored a new study about sea horses captured them in Tampa Bay, Florida for a year during 2022/2023. They found dwarf sea horses were most abundant during the month of October. Sea horses are vulnerable due to the loss of sea grass beds caused by dredging and pollution. They are also a frequent bycatch of shrimp trawlers. Some Chinese cooks make a medicinal soup from sea horses, but reportedly they are flavorless.

References:

Brown, P.; P. Bland, and E. Rov

“Seasonal Population and Ongoing Morphometric Analysis of Wild Dwarf Sea Horses Hippocampus zosterae“

Georgia Journal of Science 82 2024

Teske, P.; M. Cherry, and C. Matthee

“The Evolutionary History of sea horses (Syngnathidae: Hippocampus): Molecular Data Suggests a West Pacific Origin and two invasions of the Atlantic”

Molecular Phylogenetic Evolution 30 (2) 2004

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Late Pleistocene Cichlid Radiation

April 17, 2025

There are about 1,760 extant species of cichlid living in the world today, making them 2nd only to the Cyprinidae (carp and minnows) as the vertebrate family with the most species in all the animal kingdom. They are an ancient family. Scientists estimate they first diverged from perch 80-100 million years ago when dinosaurs still roamed the earth. However, the oldest known fossil of a cichlid dates to 48.5 million years ago during the early Eocene. There is also fossil evidence of cichlids living in Italy during the Miocene. Cichlids no longer occur this far north. Cichlids are a rapidly speciating family, and this gives scientists an excellent opportunity to study evolution.

A genetic study determined over 700 species of cichlids in Lake Victoria, Africa speciated during the Late Pleistocene over the past 150,000 years, and incredibly of these over 500 speciated within the past 15,000 years. Closely related species of cichlids, isolated over time, often come into contact with each other and hybridize. Scientists believe these periodic admixtures result in the facilitation of new speciation. These populations may not be isolated by geographic barriers. Instead, they evolved different feeding strategies causing them to occupy different ecological niches. Some specialized in eating other fish, others specialized in eating snails, insects, plankton, or algae. Then, species that overlap in territory, for some reason, begin mating again, thus hybridizing into yet more species. Scientists refer to the speciation of African cichlids as a “super flock.” Cichlid ancestry in Lake Victoria originated in the Nile and Congo River basins, and the hybridization of these 2 groups of cichlids led to even greater diversity. Cichlids are by far the most common fish in African rift valley lakes.

Chart from below referenced genetic study showing the ancestral relationships between different species of cichlids.

Cichlids really thrive in volcanic lakes in both Africa and Central America.

The Nile tilapia is the most commonly farmed fish and today is found in most grocery stores.

The Rio Grande cichlid is the only species of cichlid native to the U.S. Cichlids can’t endure harsh winters.

The Lake Chala tilapia colonized a volcanic lake and until recently when 2 other species were introduced was the only species of fish in that lake. Unlike most other cichlids, it lives in deep water.

Angel fish are popular aquarium cichlids.

1600 species of cichlids live in Africa, 120 species live in Central and South America, 9 species live in Asia from Israel to India, and the balance live in Madagascar. They can’t survive in regions with harsh winters. Scientists aren’t sure how cichlids colonized the Americas. Some thought they evolved before Gondwanaland broke up when South America and Africa were part of the same supercontinent, but it seems more likely cichlids arrived in America when rafts of vegetation with freshwater lenses drifted to America following storms. This occurred when the distance between the 2 continents was less than it is today. This is also how scientists believe some species of monkeys, rodents, and lizards made it to America.

The Rio Grande cichlid (Herichthys cyanogattatus) is the only cichlid native to the United States. It is an omnivorous species reaching lengths of 13 inches. It lives in the Rio Grande and its tributaries in south Texas. It’s an invasive species introduced to Florida and Louisiana. The Nile tilapia (Orechromis niloticus) is the most commonly farmed tilapia in the world. Egyptians farmed them as early as 3000 years ago, but the rest of the world didn’t begin farming them until the 1970s. Tilapia is 2nd only to crappie as the best freshwater fish I have ever tasted. They feed upon algae in the wild and are fed plant food in captivity, explaining why they have such a clean taste. The Lake Chala tilapia (O. hunteri) was the only species of fish that lived in this volcanic lake until 2 other species of cichlid were introduced by man. Volcanic lava flows must have isolated the ancestral population of this species. Unlike most cichlids, it is a deep water fish living at depths of 66-148 feet. Angel fish (Pterophyllum sp.) and several other species of cichlids are popular aquarium fish. Angelfish are native to the Amazon basin and feed upon small fish, insects, and other arthropods.

Reference:

Meier, J.; D. Marques, S. Mwaika, C. Wagner, G. Escoffier, and O. Seehousen

“Ancient Hybridization Fuels Rapid Cichlid Fish Adaptive Radiation”

Nature Communication Feb 2017

https://www.nature.com/articles/ncomms14363

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Primeval Shad Runs

April 3, 2025

It’s hard to imagine how abundant river fish used to be during their spawning runs, especially the anadromous species such as herring and sturgeon. Captain John Smith, founder of Jamestown, Virginia, recounted how shad were so thick, he could catch them using a frying pan. Other early settlers waded into rivers and used shovels to toss shad onto riverbanks. During the 1700’s Andrew Barnaby reported that a group of men caught 600 sturgeon and 5,000 shad on a small stretch of the Potomoc River in just a day. During 1830 1 net caught 4000 shad and 310,000 herring, and another caught 450 striped bass averaging 60 pounds each on the same river. The total shad catch on the Potomoc River during 1837 was estimated to be 22.5 million totaling 110 million pounds. Today, adult American shad average 5 pounds, but they formerly averaged 7 pounds.

Shad was an important food source for wildlife long before humans colonized North America. They spawned on every river connected to the Atlantic Ocean. They are an anadromous fish living in the ocean but swimming up to fall line rocky shoals where they spawn. Eagles, ospreys, dolphins, bears, striped bass, and cod all gorged on schools of shad. They were a crucial food for Indians during early spring when their stores of corn, beans, and acorns ran low. Indians referred to the shad as an inside-out porcupine because they are so bony, but that didn’t stop them from enjoying this timely abundance of protein. Early European settlers caught barrels of shad and salted them to keep year-round in their root cellars. They also didn’t mind the bones and savored the sweet flesh. They were one of George Washington’s favorite fish, and a shad run saved American troops at Valley Forge from starvation.

Shad belong to the herring family known by the scientific name of Clupeiformes. The most popular and largest species in North America is the American shad (Alosa sapidissimus). Sapidissimus is Latin for delicious. The hickory shad (A. mediocris) is edible but not as tasty. The blueback herring (A. austrelis) and the alewife (A. psuedoharengus) are considered good eating. Menhadden (Brevoorta tyrannus), gizzard shad (Dorosomo capedianum), and the bay anchovy (Anchos mitchelli) are also members of the herring family that live in the Atlantic Ocean.

Shad were an important food source for settlers who lived in rivers in eastern North America. Many kept barrels of salted cod in their root cellars.

Photos of American shad and hickory shad. They are a bony but tasty fish. Early colonists liked shad, but they are less popular today because most people don’t know how to prepare them.

I watched a youtube video recently of a man who fried shad and didn’t care for the texture. He thought they were too soft and mushy. Frying is the wrong way to cook shad or herring. The best way to prepare herring is to cut them up with onions and marinate them in vinegar and wine. The acidity dissolves the bones, and they can be eaten as an appetizer or on a kaiser roll with butter. They are juicy and delicious.

Reference:

Cummins, J.

“A Compilation of Historical Populations on the Natural History and Abundance of American Shad and other Herring in the Potomoc River”

Always Draft 2012

https://academic.oup.com/gbe/article/17/1/evae276/7934935

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Freshwater Drum (Aplodinatus grunniens) Remains Found in Indian Middens

October 24, 2024

I went to my brother-in-law’s wedding 2 weeks ago. The ceremony was held at a winery with a beautiful view of Nickajack Lake and the surrounding mountains located in southern Tennessee. Benny Hull caught the world record freshwater drum in this lake during 1972. This specimen weighed 54 pounds, far larger than any other freshwater drum ever caught. Josh Cole caught the largest freshwater drum when using bow fishing equipment, and it was about 31 pounds.

I can’t find a photo on the web of the world record freshwater drum caught by Benny Hull, but this is the world record specimen caught using bowfishing equipment by Josh Cole. The record caught by Hull using rod and reel was almost twice as big.

Adult freshwater drum average 5-15 pounds.

The freshwater drum belongs to the Scianidae family. Most of the species in this family live in shallow salt water. Atlantic croaker (Micropogonias undulatus) and red drum (Sciaenops ocellatus) are better known species in this family. Like their saltwater cousins, freshwater drum make a drumming noise when fishermen land them. Freshwater drums dwell near the bottom where they feed upon mussels, snails, crayfish, small fish, and aquatic insects. The shellfish diet suggests freshwater drums have a good flavor, but many fishermen consider them trash fish and throw them away. An article written on the meateater.com website stated 95% of people who try freshwater drum like the flavor, so it is another fish species with an unfounded poor reputation. Adult drums average 5-15 pounds, showing just how unusually large the world record specimens were. This species spawns in shallow water during early-midsummer. They inhabit large rivers and lakes.

Freshwater drum remains are often found in ancient Indian middens, and without modern food prejudices Indians probably preferred them over other species. Preservation bias, however, might explain why their remains are prevalent in Indian trash refuse. The ear bones (known as otoliths) of drums consist of calcium carbonate and are more resistant to decay, making them more likely to be preserved. Indians caught freshwater drum using hook and line, nets, fish traps, and night fishing techniques when they used torches to attract fish that were then speared.

Ear bones of drums yield valuable scientific information about age and size of the fish. They also provide data about past climate. Some people call them lucky stones and collect them.

Indians used torches at night to attract freshwater drum to the surface where they could be speared. They also used hook and line, nets, and fish traps.

A scientist who published a study in 1960 looked at hundreds of otoliths from 5 sites including Lee Mill Cave, Minnesota; Nader Rock Shelter, Illinois; The Clear Lake Site, Illinois; Dustin Green Point Site, Michigan; and Etowah Indian Mounds, Georgia. All the sites are located near rivers. The otoliths date from 985 AD-1530 AD. He used otoliths to estimate the age and size of the fish. Oddly enough, freshwater drum from ancient times were smaller on average than modern drum–a finding that seems counterintuitive because the pristine environment should have produced larger fish. Huge sturgeons were abundant then, and of course trees in virgin forests grew to prodigious size. I hypothesize that because there was less fishing pressure from fewer people perhaps population sizes were larger, and there was more competition for resources, just like underfished lakes and ponds today produce smaller fish. Another study used isotopic values of drum otoliths to estimate past average temperatures, and the results were interesting. During the medieval warm period about 1000 years ago average temperatures were 4-11 degrees F warmer than modern day temperatures–additional evidence the current rate of warming is not unprecedented as alarmists claim. Average annual temperatures equaled modern-day averages after the medieval warm period ended, but between 1400 AD-1500 AD there was an increase in seasonality with winter temperatures averaging 14 degrees F cooler, while summer temperatures averaged .7 degrees warmer than those of today.

Reference:

Patterson, W.

“North American Continental Seasonality During the Last Millenium: High Resolution Analysis of Sagittal Otoliths”

Palaeogeography, Palaeoclimatology, Palaeoecology 138 April 1997

Witt A.

“Length and Width of Ancient Freshwater Drum, Aplodinatus grunniens, Calculated from Otoliths Found in Indian Middens”

Copeia September 26, 1960

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The Sand Tiger Shark (Carcharias taurus)–a Palaeocene Age Survivor

June 1, 2022

The sand tiger shark is the oldest still extant species of shark, having existed for at least 65 million years. Some sources claim it first evolved during the Cretaceous Age and lived with the dinosaurs 72 million years ago, but according to the scientific literature I can find, the oldest fossils of this species were found in the Cannonball Formation located in the Dakotas, a region that was formerly undersea, and species from fossil sites here date to the Palaeocene–the era immediately following the extinction of the dinosaurs. This is still impressive longevity for a species. By comparison modern man (Homo sapiens) has existed for about 200,000 years. The sand tiger shark should not be confused with the similarly named tiger shark (Galeocerde cuvier). Although sand tiger sharks occasionally bite people, they are not maneaters. Tiger sharks definitely are maneaters. The scientific name for sand tiger shark may also cause confusion. Carcharias taurus means bull shark in Latin, but the commonly named bull shark (Carcharhinus leucas) is also a different species.

Sand tiger shark, the oldest still extant shark species.
The sand tiger shark should not be confused with this species–the tiger shark. The former is not a maneater, but the latter is.

Sand tiger sharks can reach lengths of just over 10 feet long, and they feed upon fish, squid, and shrimp. They are known for preying on stingrays and smaller, slower sharks near the sea bottom at night. They rest during the day. They are the only species of shark to gulp air. This helps them retain buoyancy, so they don’t have to constantly swim like other kinds of sharks. The shark pups are born alive, the survivors of cannibalistic embryos attacking and eating each other while still inside their mother. Sand tiger sharks range in shallow coastal waters along the Atlantic coasts of North America and Europe. They also occur off the coasts of China, Japan, Australia, and South Africa. Scientists believe they were overfished to extinction in the Mediterranean Sea where they used to live.

Fossil sand tiger shark teeth.
Fossils from the Cannonball Formation. The majority of fossils from this site are sand tiger shark teeth. Image from the below reference.

Paleontologists found fossils of 22 species in the Cannonball Formation. This region was under ocean water until the end of the Palaeocene 55 million years ago. Sand tiger shark teeth are the most common fossil specimens found in this formation. Sand tiger sharks may be the oldest still extant species of shark, but the still extant Hexanus genus is even older. The Hexanus genus includes the gill sharks. Some species of extinct gill sharks lived 190 million years ago during the Jurassic.

Reference:

Cvancara, A.M.; and Hogansan, J.W.

“Vertebrates of the Cannonball Formation (Palaeocene) in North and South Dakota”

Journal of Vertebrate Paleontology 13 (1-23) 1993

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Unique Fish of the Yucatan Peninsula

July 23, 2021

Underground rivers flow through the limestone bedrock underneath the Yucatan peninsula of Mexico. When a river enters a cavern it flows in a circular pattern, eroding the walls into a circular shape. The roofs of these caverns eventually collapse, creating a small bucket-shaped lake known locally as a cenote. There are almost 20,000 cenotes on the Yucatan peninsula, and they host many unique fish species found nowhere else on earth. A recent survey of 4 cenotes captured 1,350 fish including 11 species from 5 families. The cenotes studied were small and deep–less than 2 acres wide but over 30 feet deep.

The most common species found in this study were mosquito fish from the Poeciliid family. Cichilids were also common, most notably a beautiful fish, the yellow jacket cichlid. This fish is a popular game fish, reportedly with a good flavor. The yellow jacket cichlid has an interesting habit–it feigns death and preys on smaller fish that attempt to scavenge it. Colorful tetras, popular aquarium fish, live in cenotes, and they are preyed upon by the pale catfish, the top predatory fish in the studied cenotes. Scientists found blind swamp eels in these surveyed cenotes. Blind swamp eels are found throughout underground cave systems in the region and have no need for sight. Although some cenotes are connected to the ocean through underground passages, scientists found little marine influence on them. Instead, zooplankton and insect abundance along with phosphorus concentrations have a greater influence on fish populations.

View from inside a cenote. There are almost 20,000 of these geological features on the Yucatan Peninsula and they host fish species found nowhere else in the world. Photo from Thrillist.com.
Yellow Jacket Cichlid. A beautiful fish that is popular for catching and eating.
Blind swamp eel.
Pale catfish.

The Yucatan Peninsula was also home to an unique mammalian fauna during the late Pleistocene. Cenotes inundated by sea level rise preserved the remains of many species, including a species of giant ground sloth and a species of peccary found nowhere else. 4 complete human skeletons dating to the late Pleistocene were discovered in a cenote that is now below sea level. (See: yucatan peninsula | Search Results | GeorgiaBeforePeople (wordpress.com) )

Reference:

Camargen-Guerra, T; L.K. Escalera Vazquera, L. Zambrano

“Fish Community Structure Dynamics in Cenotes of the Biosphere Reserve of Sian Kaan, Yucatan Peninsula”

Revista Mexicana de Biodiversidae

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Pleistocene Whitefish (Coregonus clupeaformis)

April 17, 2021

Fish have an amazing ability to replenish and increase their populations. Lake whitefish, a species related to salmon and trout, can lay between 8,000-130,000 eggs. During Ice Ages 90% of their present day range was covered by glaciers, making it uninhabitable for them. Yet, in less than 12,000 years they recolonized this enormous territory. The reproductive ability of this species outpaced the population of predatory fish and birds that fed upon them. Scientists used a study of genetics to determine modern day whitefish descend from 2 different refugial populations that clung to survival during the Last Glacial Maximum. 1 population survived in Beringia–the area of Alaska and the Yukon that remained free of glacial ice. They may have survived in lakes now located near Nahanni National Park. The other population occurred in the Missouri/Mississippi River Drainage just south of the Laurentide Ice Sheet. Following the retreat of the Ice Sheet, lake whitefish populations exploded in the newly formed Great Lakes and managed to swim their way into lakes all over Canada. Whitefish are a cold water species and probably didn’t ever live far from Ice Age glaciers.

Map of present day range of lake whitfish. Most of this range was under glacial ice during Ice ages.
Lake whitfish.

Lake whitefish average 4 lbs. as adults, though the record for a rod and reel catch is 15.5 lbs. They spawn during fall, winter, and spring. Their diet consists of snails, clams, and insects. There are 2 ecotypes of whitefish that do not interbreed: the normal population that inhabits the bottom region of lakes and the dwarf population that swims in the upper layer of open water. Commercial fishermen net whitefish, and they are a popular food fish in cities and towns along the Great Lakes, but I can’t remember if I ever had the opportunity to try them when I lived in Ohio as a boy.

Reference:

Foote, C.; J. Clayton, C. Lyndsay, and R. Bodaly

“Evolution of Lake Whitefish (Coregonus clupeaformis) in North America during the Pleistocene: Evidence for a Nahanni Glacial Refuge in the northern Cordilleran Region”

Canadian Journal of Fisheries and Aquatic Services 49(4) April 2011

McDermid, J., J. Riest, R. Bodaly

“Phylogeography and Post Glacial Dispersal of Whitefish ( C. clupeaformis complex) in Northwest North America”

Advances in Limnology 60 Jan 2007

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