Jun 7

Atlantic bluefin tuna (Thunnus thynnus)

Species: Atlantic bluefin tuna (Thunnus thynnus)

Status: Endangered (EN)

Interesting Fact: The Atlantic bluefin tuna can swim at speeds of up to 72 kilometres per hour when pursuing its prey.

More information: The enormous Atlantic bluefin tuna can grow to lengths of 4.6 metres and weigh up to 684 kilograms. This fish species has two types of muscle, one for continuous long-distance swimming and the other for short, fast bursts of speed. This amazing adaptation means that individuals of this species are able to swim across the Atlantic Ocean in just 60 days. Although the Atlantic bluefin tuna is generally found swimming in mixed species schools close to the surface of the water, it is capable of diving to depths of up to 1,000 metres when chasing prey. Another fascinating adaptation of the Thunnus genus is the blood exchange system known as the rete mirable which enables individuals to swim in water that is much to cold for other fish. The Atlantic bluefin tuna is a highly migratory species and has a naturally occurring magnetic mineral located in its head that helps with navigation to and from its spawning grounds.

The severe exploitation of the Atlantic bluefin tuna has led to the drastic decline of every known population, particularly in the North Atlantic Ocean. Despite quotas being in place to ensure sustainable numbers are removed from the population, the limits are frequently not respected and unless the legal levels are suitably enforced, it is predicted that some Atlantic bluefin tuna stocks will collapse. The western Atlantic stock may have already collapsed and is now in grave danger of extinction due to overfishing. In the Mediterranean, tuna ranching poses the greatest threat to this species. Individuals are captured alive and taken to a ranch where they are fattened before being sold. Since 1998, catch limits have been in place and in 2006 the International Commission for the Conservation of Atlantic Tunas (ICCAT) established a 15 year recovery plan for the Atlantic bluefin tuna. The plan includes stricter catch limits and closing certain fisheries at specific times of the year to allow the local stocks to recover.

Find out more about Atlantic tuna conservation: International Commission for the Conservation of Atlantic Tunas (ICCAT).

See images and videos of the Atlantic bluefin tuna on ARKive.

Hannah Mulvany, ARKive Content and Outreach Officer.

May 24

Russian sturgeon (Acipenser gueldenstaedtii)

Species: Russian sturgeon (Acipenser gueldenstaedtii)

Status: Critically Endangered (CR)

Interesting Fact: The Russian sturgeon can reach lengths of nearly two and a half metres.

More information: The Russian sturgeon belongs to an ancient and unique group of fish, relics from the time of the dinosaurs. This prehistoric giant was formerly found in the Black, Azov, and Caspian Seas in Eastern Europe and the Middle East, as well as the deep sections of fast-flowing rivers, such as the Volga, Danube, and Ural Rivers. Populations of this species are now mostly found in the lower reaches of these river systems and along coastlines.

The male Russian sturgeon does not reproduce until it is between 8 and 13 years old and only do so every 2 or 3 years, while the female does not reach sexual maturity until it is 10 to 16 years old and then only reproduces every 4 to 6 years. There are two distinct forms of this fish species, the anadromous type which migrates up rivers from the sea to spawn and the freshwater form which remains in its freshwater habitat to spawn, although this form is now thought to be extinct. For the anadromous type, there are two separate migrations, one in spring when spawning occurs in the lower levels of the river and one in autumn when individuals migrate into freshwater where they spend the winter before spawning upstream the following spring.

Vast areas of the Russian sturgeon’s spawning grounds have been lost due to damming and exploitation. Dam construction is highly detrimental to this and other migratory fish species, as the usual migration routes to its spawning grounds are blocked, meaning that individuals either do not reproduce, or spawn in unsafe areas. Pollution in the Caspian and Black Sea basins is causing hormonal imbalances in this species and subsequently a greater number of hermaphroditic, infertile individuals are found in these areas.

The Russian sturgeon was once very important commercially, and its caviar was one of the most sought after of any species. Illegal fishing still continues, despite legal catch quotas being in place, with the illegal catch thought to far surpass the legally set limits. The Russian sturgeon is unprotected in many areas throughout its range and the absence of a strict monitoring system makes the control of fishing very difficult. Despite restocking efforts, the creation of artificial spawning grounds, and the introduction of fish lifts to help individuals to get around dams, the population is still in decline and over the last 15 years, global catches have dropped by 98 percent. As a slowly maturing species, it does not have the ability to recover from overexploitation, especially without complete cessation of fishing.

Celebrate World Fish Migration Day and find out more about why we need to protect these species and their habitats.

Find out more about sturgeon conservation.

See images of the Russian sturgeon on ARKive.

Hannah Mulvany, ARKive Content and Outreach Officer

May 17
Scalloped hammerhead

Scalloped hammerhead

Species: Scalloped hammerhead (Sphyrna lewini)

Status: Endangered (EN)

Interesting Fact: The hammer-shaped head of the scalloped hammerhead is thought to be a mechanism to spread out the ampullae of Lorenzini which are sensory organs that detect electric currents, chemicals and temperature changes.

More information: The scalloped hammerhead can be distinguished from other hammerhead shark species by the ‘scalloped’ front edge of its head. This species has a relatively slim body and is counter-shaded, with a brown-grey or bronze upperside and a white underside. This relatively large shark can grow up to lengths of 4.3 metres and can weigh up to 152 kilograms. Fish, cephalopods, lobsters, shrimp, crabs, other sharks and rays make up the diet of this species, and prey items are usually eaten whole. Generally occurring in the warm temperate and tropical waters of the Atlantic, Indian and Pacific Oceans over continental shelves, the scalloped hammerhead is also known to enter closed bays and estuaries and generally swims between depths of 0 and 275 metres.

Occasionally caught as bycatch by longline fisheries, the scalloped hammerhead is also caught commercially. Various products are made from the body parts of sharks, including shark fin soup from the fins and vitamins from the liver, as well as the meat which is sold for human consumption. Certain parts of this shark’s range are protected, including the area around Melpelo in Colombia, and there are plans to extend the legal protection to other areas. There are no other known conservation measures currently in place for this Endangered species.

Find out more about marine conservation at the Save Our Seas Foundation and Project AWARE.

Find out more about shark conservation at Bite Back and the Shark Trust.

See images and videos of the scalloped hammerhead on ARKive.

Hannah Mulvany, ARKive Content and Outreach Officer

May 14

1aOur oceans are critical to our very existence; it’s a simple matter of healthy oceans = healthy people.  Besides providing us with food (today almost one in six people in the world rely on fish as their primary source of protein), oceans provide us with many other important services that our survival depends on.  They maintain our renewable supply of fresh water through the water cycle, regulate our climate, and produce more oxygen than the world’s rainforests. With growing concern over climate change, we are turning more and more towards the oceans for clean, renewable energy.

In addition to being an important source of protein, many marine organisms have been found to provide therapeutic uses in antioxidant, antiviral, anti-inflammatory, anti-fungal, or antibiotic medicines. Additionally, the marine and coastal ecosystems offer endless recreational opportunities such as sea kayaking, sport fishing, surfing, whale watching and scuba diving, activities which not only feed our souls, but also drive economic benefits through employment for local peoples.

2a

Today almost one in six people in the world rely on fish as their primary source of protein.

Although critical to our existence, our oceans are in desperate trouble.  Depleted fishery stocks, habitat destruction, pollution, coastal development, climate change and invasive species, are some of the major issues threatening the healthy existence of our oceans.  In the Pacific Ocean for example, there is an area 1000 kilometres from the US coast which is larger than the entire land mass of South Africa and which is covered in plastic. It contains six times more plastic than plankton, and is growing all the time as more than 10 million tonnes of plastic finds its way into the sea each year.

3a

The marine and coastal ecosystems offer endless recreational opportunities such as sea kayaking, sport fishing, surfing, whale watching and scuba diving.

This current state of affairs is largely as a result of the dilemma known as “The Tragedy of the Commons”, in which multiple individuals acting independently in their own self-interest can ultimately destroy a shared limited resource, even when it is clear that it is not in anyone’s long term interest for this to happen.

Plastic debris littered along the beachfront

Our oceans are in desperate trouble. Depleted fishery stocks, habitat destruction, pollution, coastal development, climate change and invasive species, are some of the major issues threatening the healthy existence of our oceans.

Overfishing, together with global climate change and habitat destruction, are considered as the three major risks facing our oceans. When looking at this, obviously the first thing that we have to do is to control our own levels of exploitation. That means fishing within the biological limits of a fish population and assuring that the gear that we use does not destroy habitats. Today, many stocks are just hanging on to survival because of regulations that were inadequately or not properly enforced in the past. We need to abide to these regulations and support good science that guides the future regulatory parameters around fishery off-take.

5a

Fishing is taking place across food chains and thereby breaking down the efficiency of the oceans.

Globally, as human populations continue to grow, along with the popularity of seafood, fish stocks are coming under increasing pressure and can no longer keep up with pressure of current commercial fishing operations. A recently published report on the state of the world’s fisheries by the United Nations Food and Agricultural Organisation (FAO), estimated that approximately 80% of the world’s fisheries were fished at (52%) or beyond (28%) their maximum sustainable limits.

A small-pelagic fishing trawler at dawn and surrounded by seagul

Overfishing, together with global climate change and habitat destruction, are considered as the three major risks facing our oceans.

Increased levels of fishing do not only result in the overexploitation of our marine resources, but also results in the destruction of marine habitats. More than 50% of the world’s total marine catch (81 million tons) is harvested using towed fishing gear. Studies have shown that fishing can damage the seabed by, for example, breaking deep-water coral reefs and other fragile habitats.

7

The United Nations Food and Agricultural Organisation (FAO), estimated that approximately 80% of the world’s fisheries were fished at (52%) or beyond (28%) their maximum sustainable limits.

Habitat destruction is not only about the physical loss that may come from the destruction of a reef or the damming of a river, but also from pollution, diverted stream flows, and even the introduction of invasive species. Through habitat destruction, biodiversity is negatively impacted which ultimately is the cornerstone of a productive ecosystem that in turn drives the fishery resource upon which we depend. We know that 85 % of all commercially valuable fish are dependent upon wetlands and estuaries during some part of their lifecycle. Two-thirds of our estuaries and bays are already severely degraded through torrents of chemical and other poisonous runoffs and irresponsible development and agricultural practises.

8

Pollution is negatively impacting on the biodiversity of our oceans.

Protecting our oceans and coast is more than stopping pollution and regulating fishing. It also means controlling our activities onshore and controlling unregulated coastal development. With all of these poisonous pollutants running into the oceans, “dead zones” have been created where only some of the smallest marine organisms can survive. These areas are created in significant part by synthetic nitrogen fertilizers flowing into the sea and nourishing massive algal blooms which then decay and cause oxygen- depletion, killing everything except the hardiest in its vicinity.

9

We know that 85 % of all commercially valuable fish are dependent upon wetlands and estuaries during some part of their lifecycle.

Although these kinds of reports on the state of our marine resources may be disheartening, it is important for us to realize that there are solutions, and that if we all work together, we can turn things around. Marine Protected Areas are globally recognised as an essential tool for marine conservation and for helping restore the health of our oceans. They allow for the protection of habitats and provide areas where fish species can grow and breed without disturbance. As habitats are able to re-establish back to their natural state, they help in preventing damage from severe storms, reducing the impacts of pollutants while also aiding in reducing the impacts of climate change.

Blouberg Strand and Table Mountain

Protecting our oceans and coast is also about controlling unregulated coastal development.

Where fishing is concerned, it is important that all stakeholders abide by set fishing regulations and laws- we need to build a culture of voluntary compliance and self-regulation. Fisheries need to start implementing what is known as an Ecosystem Approach to fisheries (EAF), which seeks to protect and enhance the health of our marine ecosystems as a whole, to ensure the long-term survival of marine life and the communities that depend on it.

Marine Protected Area signage overlooking an estuary mouth

Marine Protected Areas are globally recognised as an essential tool for marine conservation and for helping restore the health of our oceans.

It is also important that we promote a sustainable seafood trade. By simply asking questions about our seafood and making more informed choices about the fish that we trade, buy and eat, we could make a huge impact in influencing positive change in the seafood chain of custody.  But this requires urgent and concerted effort from all parties involved- from the fishing industry all the way to the consumer.

12

It is important that all stakeholders abide by set fishing regulations and laws.

Our oceans are a common heritage, and we all have the responsibility and the ability to help conserve and protect them- if not for our sake, then for the sake of future generations- our children.

13

Support the South African Seafood Initiative (SASSI) and only eat and buy the healthiest and most well managed fish populations.

More tips on what you can do to help save the oceans:

1. Support South Africa’s Marine Protected Areas
2. Eat sustainable seafood: Support the South African Seafood Initiative (SASSI) and only eat and buy the healthiest and most well managed fish populations. For further information visit: www.wwf.org.za/sassi
3. Don’t dispose of trash or toilet waste in the ocean.
4. When enjoying recreational fishing, obey regulations and try to enjoy only catch-and-release fishing and use care when releasing fish back into the ocean. Take photos, not fish
5. Keep beaches clean. Plastics and other debris harm sea life and pollute the ocean. Clean up after yourself. Get involved! Participate in beach cleanups if you live in a coastal area.
6. Don’t purchase items that exploit marine resources unnecessarily such as shell and coral jewellery and sharks teeth.
7. Spread the word: Tell people what’s going on with the world’s oceans and what they can do to make a difference.

14

Peter Chadwick
http://www.peterchadwick.co.za

Apr 23

It’s a well-known fact that Britain is a nation of animal lovers and is particularly obsessed with its wildlife. However, there is one group which often gets overlooked – our piscatorial friends the freshwater fish. Currently there are 54 species of freshwater fish swimming around the United Kingdom, including species like the mullet and flounder which, despite just visiting the estuarine parts of rivers, can be found surprisingly far up from the sea! Non-native species such as the wels catfish, which resembles a giant tadpole, and the topmouth gudgeon are also present in the UK. Despite the UK not suffering from the presence of non-native species as much as other countries such as Spain, the tiny topmouth gudgeon does still cause big problems by outcompeting native fish and spreading disease.

The topmouth gudgeon has been described as Europe’s most invasive fish species

In recent years, the number of native European eels has declined by around 95%. However, 2013 was recorded as one of the best elver runs in recent years, with millions making their way up the Severn. Whilst many may think that floods are not good for fish, flooding helps the European eels get into ponds and lakes where they can grow before returning to the Sargasso Sea with the next floods.

European eel image

The European eel is very long-lived, potentially reaching an impressive 85 years old

There are many other native freshwater fish species which are less well known to the general public and even wildlife enthusiasts (I bet most birders in the UK have never heard of a spined loach or allis shad, for example). One such species is the Arctic charr, a cousin of the trout, which lives in deep glacial lakes mostly in the Lake District and Scottish Lochs. The Arctic charr can also be found in Iceland where it reaches much larger sizes of up to 20lb and, unlike the British populations, goes out to sea like a salmon.

Male and female Arctic charr

So next time you’re walking by your local canal or river, take a look and see what you can spot -  you’ll be surprised by the wealth of fish life beneath the waterline in British waterways.

Video showing 28 species filmed by me: http://www.youtube.com/watch?v=mjAIUKfYtHA

Jack Perks Photography – Underwater & Wildlife Photographer

Website – http://www.jackperksphotography.com and http://www.btwlfishproject.com/
Twitter – @JackPerksPhoto

About

RSS feedArkive.org is the place for films, photos and facts about endangered species. Subscribe to our blog today to keep up to date!

Email updates

Sign up to receive a regular email digest of Arkive blog posts.
Preferred frequency:

Arkive twitter