#estuaries

[great-and-small]

yo my mom works on erosion on coastlines (she manages ecosystems and replants native plants+adds oyster beds. we both have Opinions about sea walls.) got any propaganda as a wildlife lover i should show her?

Good timing- I just started a class on coastal systems! Therefore I can pretend making memes for your mom counts as studying

[aisphotostuff]

Thornham creek at low tide ..also stunning nature reserve Norfolk Coast. by Adam Swaine Via Flickr: The area features wooden jetties, a historic coal barn, and small boats surrounded by salt marshes.The old jetty at Thornham Harbour, located along the North Norfolk coast, is a rustic, weathered wooden structure situated within a tidal creek

[chasingrainbowsforever]

Manatee and Fish ~ National Geographic

[400millionyears]

Bull shark

Carcharhinus leucas

Family: Carcharhinidae

As a member of the requiem sharks, the bull shark is a robust, aggressive species, found worldwide in warm, shallow waters.

It is famous for its unique ability to thrive in both saltwater and freshwater, because of that, this species comes into close contact with human populations which has earned it a place among the most potentially dangerous sharks to people.

Physical Description and Size

On its dorsal (upper) side the coloration is light to dark gray, while the ventral (underside) is white, providing countershading camouflage. Juveniles have black tips on their fins, which fade as they mature.

The features that make this species distinctive are: the extremely short, broad, and blunt snout (rounded), which is wider than it is long; its small, round eyes and a massive, heavy body, and the absence of an interdorsal ridge. Its teeth are also distinctive: upper jaw teeth are broad, triangular, and heavily serrated, while lower jaw teeth are narrower, more slender, and pointed with fine serrations.

Size and Weight: This species has size variation, North American bull sharks tend to be larger than those in the Caribbean or Costa Rica. ◦ Length: Males typically reach up to 3.6 meters, while females are larger, reaching up to 4.0 meters. ◦ Weight: Maximum recorded weight is around 317 kg.

Distribution and Habitat

The bull shark has a worldwide distribution in tropical and subtropical waters making it one of the most widespread species of requiem sharks. It's primarily a coastal and freshwater shark, inhabiting shallow waters such as bays, estuaries, rivers, and lakes.

Their geographic range covers the Western Atlantic (Massachusetts [USA] to southern Brazil, Argentina, the Gulf of Mexico and the Caribbean), Eastern Atlantic (Morocco to Angola), Indo-Pacific (Kenya, South Africa, India, Vietnam, Australia and from southern Baja California (Mexico), to Ecuador.

They are also well-known for traveling far up rivers and into lakes. The most notable are the Mississippi River, the Amazon River, Lake Nicaragua, the Zambezi, Ganges, Tigris, and Euphrates.

Behavior and Diet

The bull shark is an apex predator known for its aggressive, unpredictable behavior. They are capable of covering great distances (180 km in 24 hours) and move randomly between fresh and brackish water. In rivers, they often go upstream during the day and return downstream at night.

They are considered one of the most aggressive shark species and their aggression has been associated with notably high testosterone levels, though the direct link to aggression remains a subject of study.

Diet: As opportunistic feeders, they have a varied, generalist diet. ◦ Bony fishes (especially catfish), stingrays, and other elasmobranchs (sharks and rays). ◦ Turtles, birds, dolphins, crabs, squid, sea urchins, and even terrestrial mammals (carrion)

Reproduction and Life Cycle

Bull sharks are viviparous, females give birth to 1 to 13 pups per litter (average 5 to 10) after a gestation period of 10 to 11 months. Pups are born large, measuring between 56 and 81 cm and weighing 1.5 to 3.0 kg.

Young sharks may remain in estuaries and river mouths that serve as nursery grounds, offering protection from larger predators.

Males mature at 14 to 15 years of age; females mature later, approximately 18 years of age, and their lifespan is estimated at 30 to 32 years, though this varies by region.

Relationship with Humans

According to attack statistics from the International Shark Attack File (ISAF), which attributes approximately 175 unprovoked attacks to bull sharks, with an estimated 18% fatality rate, this species is considered by many experts to be the most dangerous shark to humans, alongside the great white and tiger sharks.

Despite the danger, research in Seychelles and elsewhere emphasizes their ecological importance as apex predators. Negative public perception often overshadows their role in maintaining healthy marine ecosystems.

Even so, they are a popular attraction in large public aquariums. The Okinawa Churaumi Aquarium housed a specimen that lived to 30 years old, a testament to how well bull sharks adapt to captivity, unlike many pelagic species.

⚠️Conservation Status

The International Union for Conservation of Nature (IUCN) classifies the bull shark as Vulnerable globally (assessed 24 November 2020).

The primary threat is overfishing, followed by the fin trade, bycatch, the commercial use (utilized for their meat [fresh or smoked], skin [leather], liver [oil], and carcass [fishmeal]), the lost of their habitats and climate change.

Conservation Efforts: Bull sharks are listed under the Convention on Migratory Species (CMS), which encourages range states to cooperate on conservation measures. These efforts have led to the creation of Marine Protected Areas (MPAs) that include estuaries and river mouths, helping protect critical nursery habitats for juvenile bull sharks and reduce bycatch.

🦈Fascinating Facts

Their English name is thought to derive from their stocky, bull-like build, though their habit of bumping prey with their blunt snout before biting may have also contributed to the name.

In 2013, a rare dicephalic (two-headed) bull shark fetus was discovered in the Gulf of Mexico. It was a single shark with two distinct heads, providing a unique glimpse into congenital anomalies in elasmobranchs.

Their aggressive "bump" is not just for attack. Scientists believe that in murky water (where visibility is low), the bump is a form of communication or investigation, allowing the shark to use its sensitive snout to gather information about the potential prey or threat before committing to a bite.

National Geographic - Bull Shark Animal Diversity Web - Carcharhinus leucas Florida Museum - Bull Shark

[yannicpretzlaff]

@santanabellas playing „Estuaries“ by Naama Tsabar at Hamburger Bahnhof / Berlin

[fishfolkart]

Ganges Stingray - is a member of the Stingray family and is native to the Gangetic (Ganges) river system which include the countries of India, Nepal, China, and Bangladesh. It inhabits rivers, also found in shallow bays and estuaries in the Bay of Bengal. It feeds on small fishes, mollusk bivalves, crabs, shrimps, worms and jellyfish.  It is considered a critically endangered species. It can reach a maximum length of 100 cm (3.3 feet). https://www.redbubble.com/shop/ap/171603987

[aquariuminfobureau]

The concept of brackishness causes aquarists some degree of confusion, because the distinction between fresh and saltwater is blurry, because saltwater does not mean the same thing as marine salinities, and because natural brackish waters - being estuarine - are communicated as a subset of river water.

Hydrologically this is correct, but nonetheless estuaries are saltwater, and emphatically not freshwater environments. Freshwater is defined by the mere absence of salinity, so that more than a miniscule of parts per thousand of salt, makes water saltwater. Thusly not all stretches of river are freshwater, and the brackish conditions of estuaries are non-marine saltwater.

To the aquarist, the only difference between managing freshwater and marine aquaria, is understanding how to measure and manage the factor of salinity. Therefore brackish aquaria are most helpfully understood as a variant of saltwater aquaria, not something that is intermediate in its implication. It is merely the case that their salinity is below that of a natural or simulated marine environment.

Zones within estuaries are subject to different salinities, as a result of degrees of tidal influences leaking upstream, along the lowermost river. 'Brackish conditions' is therefore insufficiently descriptive of any one stretch of estuary, or of the tolerance and optima of any estuarine organism, or of the communities that such organisms form.

Typically a brackish aquarium has a pH of 1.01 to 1.02, which is fine for a mangrove swamp biotope. Some organisms are suited to higher salinities than this, or to lower salinities. Typically, but not always, these species are also naturally found in true marine or freshwater environments, their distributions as the river neets the sea, varying according to their physiology.

In fact, true brackish environmental specialists are rare among fishes. Amphibious creatures such as turtles and crabs in and around estuaries, might frequent saltwater, yet rely on freshwater for drinking. Thus the presence of a species in estuarine habitats, might not indicate its physiological tolerance.

[biology-geology-beaches-india]

The Science Research Diaries of S. Sunkavally, page 346.