Estuary Animals: What Lives in an Estuary? A Guide From Panama

Estuary animals · Gulf of Montijo, Panama

Twice a day, the Pacific walks up the river. Everything here lives by that clock.

Meet 23 animals of a real tropical estuary, from snook and black clams to baby hammerheads and roseate spoonbills: who they are, what they eat and why they chose brackish water.

Low tide, 6:30 in the morning. The channel has shrunk to a ribbon of brown water, and the mud on both banks is moving. Thousands of small crabs are out, picking at the mud between the mangrove roots.

A tiger heron stands on a root, so still it looks carved. Then the water turns. Within minutes the river is running backwards, salt water from the Pacific pushing in, and the crabs vanish into their holes. Something bigger is coming in with the tide.

That is an estuary. And the cast of characters that lives by its clock is bigger, stranger and hungrier than most people imagine.

Estuary Animals: What Lives in an Estuary?

Estuaries are home to fish, crabs, shrimp, clams, sharks, rays, wading birds, crocodiles, monkeys and dolphins, and many of them live here only for part of their lives. An estuary works like a crossroads: some animals are born here and leave, some arrive from the open sea to feed or give birth, and a few never leave at all.

The list below is not a generic one. These are the animals that share the Gulf of Montijo with us, grouped by family, with the job each one does to keep the estuary running.

How Do Animals Survive in Brackish Water?

Animals that live in estuaries have to cope with water that turns saltier or fresher several times a day. They solve it in three ways:

Estuary Fish: What Fish Live in an Estuary?

Corvinas, snappers, snook, grouper, jacks and pompano are the fish you are most likely to meet in a Pacific estuary like the Gulf of Montijo. Most of them are brackish water fish only while they are young: the mangrove roots hide them from bigger predators, and the channels are full of shrimp and small fish to eat. If you want to know how to catch them, read our Puerto Mutis fishing guide. Here we care about how they live.

Croakers

Cynoscion stolzmanni

Yellow Corvina, the Queen of the Gulf

Corvinas belong to the croaker family. The yellow corvina lives in lagoons, estuaries and coastal waters down to 30 meters, hunting mostly small fish and shrimp, and it can grow past a meter and 9 kilos. With red snapper, it is the fish we catch most often in the gulf.

Estuary job: eats shrimp and small fish, and is one of the main catches that feed the families of the gulf.

Croaker family

Croaker Corvina, the Grunter

Its Spanish name, corvina roncona, comes from “roncar”, to snore. Croakers make their sound with muscles that drum against the swim bladder, and in most species only the males sing, to call the females at spawning time.

Estuary job: its song is data: scientists listen to croaker choruses with underwater microphones to find out when and where they spawn.

Snappers

Lutjanus peru

Pacific Red Snapper

Young red snapper travel in schools through estuaries and river mouths. As adults they turn solitary and move out to rocky caves at sea, and around Coiba they gather in large groups to spawn. In El Nino years they become harder to find.

Estuary job: a teenager that grows up in the estuary and then stocks the reefs offshore.

Lutjanus novemfasciatus

Cubera Snapper, the Giant With Fangs

The biggest snapper of the Pacific starts small: juveniles grow up among mangrove roots and in river mouths. Adults move to rocky reefs as deep as 60 meters and can top 35 kilos, with canine teeth to match.

Estuary job: proof that a healthy mangrove makes the big fish of Cebaco and Coiba.

Snook, Grouper, Jack and Pompano

Centropomus

Snook, the Ambush Hunter

Six species of snook live on the Pacific coast of the Americas, all in bays, estuaries and the lower part of rivers. A black line runs along their sides. They wait under the roots and strike whatever the current carries past, and in the species studied, snook start life as males and turn female as they grow.

Estuary job: hunts the small fish and shrimp that hide between the roots. Young snook even mix with schools of mojarras and catch whatever the mojarras stir up from the bottom.

Grouper family

Grouper, the Fish That Changes Sex

Groupers do the opposite of snook: they are born female and the biggest ones become male. Take the large fish out and the population runs short of males. That is why every grouper we catch goes back into the water.

Estuary job: helps keep the populations of smaller fish in balance.

Caranx caninus

Pacific Crevalle Jack

Jacks travel in schools and are not afraid of fresh water: the young grow up in estuaries and adults sometimes swim up rivers. It can live 15 years, and until 2007 scientists thought it was the same fish as the jack of the Atlantic.

Estuary job: keeps schools of anchovies and other small fish in check. Anchovies are its favorite prey.

Trachinotus kennedyi

Pompano

A flat, silvery fish that is common in Pacific estuaries and can grow past 70 centimeters. Look for a black spot at the base of its side fin. Young pompano grow up in estuaries eating small bottom animals, and adults eat mostly mollusks.

Estuary job: turns shellfish and small bottom animals into food for bigger predators.

Crabs, Shrimp and Clams: The Mud Crew

Nobody photographs them, but without these five the estuary would stop working. They live in, on or under the mud, and their whole lives are timed by the tide. Look closely at a red mangrove root at low tide, too: barnacles and small oysters cling to it, a tiny reef on stilts that the sea feeds twice a day.

Ucides occidentalis · The symbol of Montijo

Mangrove Crab, the Pride of Montijo

It goes by a different name in almost every country on the Pacific coast. In Montijo it matters so much that the people of the district proudly call themselves cangrejeros, the crab people, and the crab is the symbol of Montijo. It digs deep burrows among the mangrove roots and feeds mostly on fallen leaves. In the breeding season the crabs leave their burrows in great numbers, and some countries close the harvest during those days so there are crabs next year.

Estuary job: turns fallen mangrove leaves into food, and its burrows let air and water into the mud.

Uca

Fiddler Crabs, the Wavers

At low tide the mud is covered in fiddler crabs. Males wave one giant claw to impress females and warn rivals, while all of them sift the mud for tiny bits of food, cleaning it as they go. When the tide comes back, they plug their burrows and wait.

Estuary job: their burrows bring oxygen into the mud. In a Florida experiment, young mangroves with fiddler crabs grew 27% taller than mangroves without them.

Penaeid shrimp

White Shrimp, the Commuters

Shrimp spawn out at sea, and their tiny larvae ride the tide into the estuary. They grow up among the roots and head back to sea as adults. Shrimp, along with snapper, corvina and snook, is one of the catches that feeds the gulf’s artisanal fishermen.

Estuary job: food for almost every fish in this guide. Young shrimp need the mangrove roots to hide while they grow.

Anadara tuberculosa

Black Clam, the Water Filter

The black clam lives buried in the mud between red mangrove roots and filters the water it breathes. The women of Isla Leones collect it by hand at low and mid tide, and they respect a minimum size and closed seasons that grew out of their own monitoring with the University of Panama.

Estuary job: filters the water, and because it stores what the water carries, scientists use it as a living pollution monitor.

Spiny lobster

Spiny Lobster, the Night Shift

Lobsters hide in rocky cracks by day and come out at night to feed. Las Aventureras of Isla Leones fish them with nets, often at night or before dawn depending on the tide, and stop during the closed season so there are lobsters next year.

Estuary job: cleans the rocky bottom at night, eating mollusks, small crustaceans and dead matter.

Do Sharks Swim in Estuaries?

Yes. Many sharks and rays use estuaries, mostly as nurseries, because the murky, shallow water keeps their young away from bigger predators. The Gulf of Montijo is one of the best examples in the Pacific: it is a recognized birthing area for hammerhead sharks. The full story is in the ocean’s nursery.

Sphyrna lewini

Scalloped Hammerhead Pups

Female hammerheads from Coiba and Cebaco come to give birth south of Isla Leones, and the pups stay in the gulf until they are strong enough for open water. Scientists from STRI consider it the largest hammerhead birthing area on Panama’s Pacific coast. The species is critically endangered.

Estuary job: proof that the gulf is a nursery: 99% of the hammerheads recorded in local landings were newborns or in their first year.

Stingrays

Stingrays, the Buried Neighbors

Stingrays rest half buried in the sand and mud of shallow flats, with only their eyes showing. They dig for clams, crabs and worms. If you ever wade in an estuary, shuffle your feet: the ray feels you coming and swims away.

Estuary job: an ecosystem engineer. Digging for food turns over and oxygenates the bottom, and its pits become shelter for other animals.

Estuary Birds: Who Fishes From Above

Every low tide opens a buffet of exposed mud, and the birds know the schedule better than anyone. The gulf has resident birds that never leave and winter visitors that fly in from North America. It also shelters a rarity: the yellow-billed cotinga, a near-threatened white bird found only in the Pacific lowlands and mangroves of Costa Rica and Panama. For Isla Perdomo, the island where the gulf’s seabirds sleep, read our guide to the Gulf of Montijo wetlands.

Tigrisoma mexicanum

Bare-Throated Tiger Heron

The patient one. It can stand frozen on a root for long minutes, its striped neck blending into the shadows, and then spear a fish or a crab in a fraction of a second. It lives in the gulf all year.

Estuary job: controls the fish and crabs at the water’s edge.

Platalea ajaja

Roseate Spoonbill

It feeds by feel, not by sight: it sweeps its flat, spoon-shaped bill from side to side in shallow water and snaps it shut on whatever it touches. Its pink color comes from pigments in the small crustaceans it eats.

Estuary job: a living gauge. In Florida, scientists use spoonbill nesting to measure the health of the Everglades.

Numenius hudsonicus

Whimbrel and the Winter Visitors

Whimbrels nest in the far north of the Americas and spend the northern winter on tropical mudflats. Their long, curved bill is made for pulling crabs out of burrows. Willets and other shorebirds arrive in the same season, and the gulf is one of their important stops in Panama.

Estuary job: connects the gulf with the far north. Tracked whimbrels have flown 5,000 km without a single stop.

Pelecanus occidentalis · Fregata magnificens

Pelicans and Frigatebirds

Brown pelicans dive headfirst for fish. Magnificent frigatebirds cannot land on the water because their feathers are not waterproof, so they often chase other birds until they drop their catch. At sunset both head for Isla Perdomo to sleep.

Estuary job: the brown pelican is a comeback story. Nearly wiped out by the pesticide DDT, it recovered once the poison was banned.

Reptiles and Mammals of the Mangrove Estuary

The biggest animals of the estuary live on its edges: in the trees, on the mud banks and at the river mouths where fresh and salt water meet.

Crocodylus acutus

American Crocodile

The only crocodile in the gulf, and well suited to it: salt glands on its tongue let it live in brackish and salt water. It basks on the mud at low tide with its mouth open to cool down. Admire it from the boat and never feed it; Coiba’s most famous crocodile shows why, in the story of Tito.

Estuary job: the dominant predator of the channels, and a water gauge: its nesting success follows rainfall, water level and salinity.

Iguana iguana

Green Iguana

Adult green iguanas are vegetarians that spend the day high in the trees along the channels, soaking up the sun. When something scares them, they drop from the branch straight into the water and swim away with their tails.

Estuary job: spreads seeds away from the parent tree and helps some of them sprout faster.

Alouatta palliata

Mantled Howler Monkey

You will hear them long before you see them: the call of a howler monkey can carry for kilometers across the forest. They eat leaves and spend much of the day resting to digest them, so mornings are the best time to catch them moving.

Estuary job: plants the forest. Dung beetles bury the seeds in its droppings and save them from rodents.

Tursiops truncatus

Bottlenose Dolphin

A family of more than 80 bottlenose dolphins lives in the gulf all year. They hunt at river mouths and channel entrances when the tide turns, because that is when the fish move. More about them in our 99 dolphin facts.

Estuary job: a sentinel species. Long-lived and at the top of the food chain, its health reflects the health of the gulf.

The Estuary Food Web

The estuary food web starts with a falling leaf and ends with a dolphin. Every animal in this guide has a place in the chain:

Why Are Estuaries Important?

Estuaries are important because they are the nurseries of the sea, they feed coastal towns and they protect the shore. In the Gulf of Montijo, about 800 artisanal fishermen live off snapper, corvina, snook and shrimp that start their lives in its mangroves. The forest also filters the water and softens waves and floods, which we explain in why mangroves are important.

When an estuary is damaged, the loss shows up far away: fewer fish on the reefs, fewer shrimp at the market and fewer birds on the next winter’s mudflats.

Where to See Estuary Animals in Panama

The easiest way to meet the animals in this guide is to go out with the tide, quietly, with someone who knows the channels. These are our three ways to do it in the Gulf of Montijo, all leaving from El Bongo:

Kayak · $45 per personThe Bird AwakeningA sunrise paddle up the San Pedro River with a local guide and a support boat behind the group. Herons, howlers, iguanas, crabs and the odd crocodile.See the kayak tour →Private boat · $450Isla Leones With Las AventurerasMangrove channels, black clam digging with the women of the island and an optional seafood lunch. You can also plant a mangrove for free.See the Isla Leones tour →Private boat · $450Fishing the EstuaryCorvina, snapper and snook in the channels of the gulf, with dolphins often riding along. We release most of the catch and every grouper.See the fishing tour →Plan your dayA Full Day in the GulfMangroves in the morning, an island beach in the afternoon and the tide calling the shots: this is how a day in the gulf goes.Read a day in the gulf →

Bring reef-safe sunscreen, a long-sleeved shirt and a reusable bottle, and leave the single-use plastic at home. Here is our full list of what to wear and bring on a boat tour.

$45 / personGulf of Montijo · Kayak · Any tideMeet Them at SunrisePaddle quietly up the San Pedro River while the estuary wakes up. Local guide, support boat, water and sodas included. Leaves from El Bongo, 5 minutes from Puerto Mutis.See the kayak tour →

Frequently Asked Questions

What animals live in an estuary?

Estuaries are home to fish such as corvina, snapper, snook and jacks; crabs, shrimp, clams and lobsters; young sharks and stingrays; wading birds like herons, spoonbills and whimbrels; and larger animals like crocodiles, iguanas, howler monkeys and dolphins. In Panama, the Gulf of Montijo estuary has all of them.

What fish live in an estuary?

In a Pacific estuary like the Gulf of Montijo the most common fish are yellow corvina, croaker corvina, red snapper, cubera snapper, snook, grouper, Pacific crevalle jack and pompano. Many of them spend only their early years in brackish water and move out to sea as adults.

Do sharks swim in estuaries?

Yes. Many sharks use estuaries as nurseries. In Panama, female scalloped hammerheads give birth in the Gulf of Montijo, south of Isla Leones, and the pups stay in the estuary until they are big enough for the open ocean.

What is the difference between an estuary and a mangrove?

An estuary is a body of water where a river meets the sea and fresh and salt water mix. A mangrove is a type of tree, and a forest of those trees, that grows along the edges of many tropical estuaries. The Gulf of Montijo is an estuary lined with about 23,000 hectares of mangroves.

Where can you see estuary animals in Panama?

The Gulf of Montijo in Veraguas, the largest Ramsar wetland in Panama, is one of the best places. Kayak tours, boat tours to Isla Leones and inshore fishing trips leave from El Bongo, 5 minutes from Puerto Mutis.