Basking sharks have surprised researchers by leaving the cold waters of the north Atlantic during fall and head down to Bahamas and the Caribbean.

“While commonly sighted in surface waters during summer and autumn months, the disappearance of basking sharks during winter has been a great source of debate ever since an article in 1954 suggested that they hibernate on the ocean floor during this time,” said Gregory Skomal of Massachusetts Marine Fisheries. “Some 50 years later, we have helped to solve the mystery while completely re-defining the known distribution of this species.”

Basking Shark

Basking sharks are notoriously difficult to study for several reasons. They feed exclusively on plankton which means you can’t catch them using traditional rod-and-reel methods and they disappear down to deep waters for extended periods of time. During the part of the year when they do stay close to the surface, they are only found in cool waters teaming with plankton where the underwater visibility is close to zilch.

This situation has led to a lot of speculation about their life style and where they actually spend the winters. Despite being the second largest fish in the world, the basking shark is remarkably elusive and mysterious.

What finally solved the puzzle was the aid of new satellite-based tagging technology and a novel geolocation system which made it possible to track the basking whales as they commenced their annual migration. Data sent out from the tags unveiled that basking sharks migrates to warm tropical waters in fall. Their migrations have been able to go undetected until know since the sharks travel at depths of 200 to 1,000 meters and sometimes remain at those depths for weeks or even months at a time.

Skomal said he and his fellow researchers were absolutely surprised when they first received a signal from the tagged sharks coming from the tropical waters of the western Atlantic, since virtually everyone assumed basking sharks to be cool-water dwellers found in temperate regions only.

This new breakthrough show just how little we still know about even the largest marine animals inhabiting the world’s oceans. The basking shark can reach a length of 10 metres and weigh up to seven metric tons, yet it has managed to spend every summer in the Caribbean without anyone noticing it.

You can find more information in the report published on May 7 in Current Biology.

A recent study on intersex abnormalities in fish living in the Potomac River watershed carried out by researchers from the U.S. Fish and Wildlife Service and the U.S. Geological Survey showed that at least 82 percent of male smallmouth bass and in 23 percent of the largemouth bass had immature female germ cells (oocytes) in their reproductive organs. This number is even larger than anticipated.

This type of intersex indicates that the fish has been exposed to estrogens or chemicals that mimic the activity of natural hormones. The condition is believed to be caused by hormone-like chemicals, so called endocrine disruptors, found in medicines and a variety of consumer products. Earlier, researchers suspected that the contaminants were entering the Potomac from the wastewater treatment plants that discharge into it, but further sampling showed that the problem existed in areas located upstream from sewage plants as well. Officials are now investigating if multiple chemicals, and not just those from sewage plants, may be responsible. A larger study that includes the entire Potomac River and other East Coast rivers will be launched to find out how widespread the problem actually is.

“At the moment we don’t know the ecological implications of this condition and it could potentially affect the reproductive capability of important sport fish species in the watershed,” said Leopoldo Miranda, Supervisor of the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office.

The Potomac River is the fourth largest river along the Atlantic coast of the USA (in terms of area), with a length of approximately 665 km (383 statute miles) and a drainage area of roughly 38,000 km² (14,700 square miles). It flows into the Chesapeake Bay along the mid-Atlantic coast of the U.S. The river is shared by West Virginia, Maryland, Virginia, and District of Columbia, and all of Washington, D.C., the nation’s capital city, lies within the Potomac watershed.

More information is available in the Intersex fact sheet released by the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office.

Fish females subjected to stress produce highly active offspring but the risk of abnormalities also increases, according to new research carried out by Dr Monica Gagliano, a research fellow with the AIMS@JCU joint venture, and Dr Mark McCormick from the ARC Centre of Excellence for Coral Reef Studies at the James Cook University.

The research focused on the Ambon damsel fish (Chromis amboinensis), a common reef species in the Indo-Pacific, and has deepened our understanding of how stress factors affect not only the adult fish themselves but also their offspring. Being more active than normal affects survival and more active offspring will therefore have important implications for fish populations in a changing environment.

In their laboratory testing, Dr Gagliano and Dr McCormick exposed fertilized Ambon damsel eggs gathered from the wild to various amounts of the stress hormone cortisol. Previous studies have shown that female Ambon damsels release cortisol from their ovaries when subjected to environmental stress. Fish that lived on reefs with few predatory fish around and little competition released less cortisol than those who lived in environments where they had to deal with a lot of competition and predators.

In addition to making the offspring more active, high doses of cortisol also increases the risk of developmental defects.

“If the mother fish is more stressed and she passes on more cortisol, then the offspring will have a faster developmental rhythm and therefore errors will be more likely in their development. One likely result of this is that the offspring are born asymmetrical,” Dr Gagliano said.

“These baby fish can’t make these important hormones until later in life, so their whole initial development is determined by hormones they obtain from their mothers,” Dr McCormick added.

Developmental errors can naturally cause serious problem for fish and lower their chances of survival. In 2008, Dr Gagliano and her colleagues showed that fish born with asymmetrical ear bones have a hard time handling the open ocean stage of their life and that a large percentage of these fishes die before being able to find a reef to settle on. The asymmetry hurts the fish’s hearing ability and makes it difficult for it to pick up reef-related sounds.

In her new research project, Dr Gagliano has been able to show that maternal stress has a large measurable effect on the shape of ear bones. Offspring subjected to a high dose of cortisol are more than twice as likely to have asymmetrical ear bones compared with those that received no dose of cortisol.

You can find more information in the study published in Oecologia.

Can fish get seasick? A German scientist now claims to have at least a partial answer to this timeless question.

According to Dr Reinhold Hilbig, a zoologist from Stutgart, fish exposed to a steep dive will lose their sense of balance.

While studying the effects of weightlessness in water to learn more about how humans are affected in space, Dr Hilbig sent up a mini aquarium with 49 fish in a plane that went into a steep dive. Steep diving is a way of simulating loss of gravity; the kind of loss astronauts are exposed to during space travel.

During the steep dive, eight of the 49 fish started to turn around and around in circles.
“They completely lost their sense of balance, behaving like humans who get seasick,” says Dr. Hilbig. “The fish lost their orientation, they became completely confused and looked as if they were about to vomit. In the wild such a “seasick” fish would become prey for others because they are incapable of fleeing from danger.”

When the aeronautic adventure was over, the eight circle-swimming fish were culled and their brains were examined to investigate the exact cause of their behaviour. Dr Hilbig says the loss of eye contact with water movement and vibrations probably played a large part in their disorientation.

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Here at AC Tropical fish we would very much like to know what a fish looks like when it looks as if it is about to vomit. If you have any pictures, please send them to admin@aquaticcommunity.com and we will post them here on the blog.

New research has revealed that the tapetail, bignose and whalefish are in fact all the same fish.

For decades, three different names have been used for three very different looking underwater creatures: the Tapetail, the Bignose and the Whalefish. A team of seven scientists*, including Smithsonian curator Dr Dave Johnson, has now discovered that these three fishes are in fact part of the same family.

After studying the body structures of the tapetails (Mirapinnidae), bignose fish (Megalomycteridae) and whalefish (Cetomimidae) and taking advantage of modern DNA-analysis, the team realized that the three are actually the larvae, male and female, respectively, of a single fish family – Cetomimidae (also known as Flabby whalefish).

“This is an incredibly significant and exciting finding,” says Johnson. “For decades scientists have wondered why all tapetails were sexually immature, all bignose fishes were males and all whalefishes were females and had no known larval stages. The answer to part of that question was right under our noses all along—the specimens of tapetails and bignose fishes that were used to describe their original families included transitional forms—we just needed to study them more carefully.”

If you wish to find out more, the article “Deep-sea mystery solved: astonishing larval transformations and extreme sexual dimorphism unite three fish families” has been published in the journal Biology Letters by the Royal Society, London.

http://publishing.royalsociety.org/

http://journals.royalsociety.org/content/g06648352k5m1562/

* The seven scientists behind the discovery are:

G.David Johnson, Division of Fishes, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA

John R. Paxton, Ichthyology, Australian Museum, Sydney, New South Wales 2010, Australia

Tracey T. Sutton, Virginia Institute of Marine Science, Gloucester Point, VA 23062, USA

Takashi P. Satoh, Marine Bioscience, Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan

Tetsuya Sado, Zoology, Natural History Museum and Institute, Chuo-ku, Chiba 266-8682, Japan

Mutsumi Nishida, Marine Bioscience, Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan

Masaki Miya, Zoology, Natural History Museum and Institute, Chuo-ku, Chiba 266-8682, Japan

The Suffolk Police has decided to call off their investigation into the mysterious disappearance of 27 koi and seven goldfish, since the culprit turned out to be a hungry heron.

When the expensive fish disappeared from their home in Carlton Colville, UK, the police suspected human thieves and promptly issued a witness appeal which asked if locals had seen “anything suspicious” or if they had been offered similar fish. The appeal was however recalled soon, as the police found out the true identity of the perpetrator.

A further statement issued by police explained: “This incident is now being attributed to a large heron.”
“We take all incidents very seriously and we were worried that someone might have made off with fish worth thousands of pounds”, a police spokesman explains. “Thankfully, on this occasion an arrest wasn’t necessary.”

A research group[1] studying the hunting ability of the great white shark has found evidence indicating that this notorious predator actually has a fairly weak bite. In several movies – including the legendary Spielberg film “Jaws” – the great white shark has been portrayed as a hunter blessed with an exceptionally strong bite, but the allegedly fierce jaw power of Carcharodon carcharias is now being questioned.

According to research leader Dr Daniel Huber of the University of Tampa in Florida, sharks actually have very weak jaws for their size and can bite through their prey mainly thanks to their extremely sharp teeth – and because they can grow to be so large.

Photo by Terry Goss, copyright 2006

“Pound for pound, sharks don’t bite all that hard,” says Dr Huber. Compared to mammals, sharks have amazingly weak bites for their size. Lions and tigers are for instance equipped with much more jaw strength than sharks when you account for body size. According to Huber, mammals have evolved much more efficient jaw muscles.

During the study, Dr Huber and his team studied 10 different shark species. The bites of small sharks were fairly easy to measure, while large sharks had to be knocked out and subjected to mild electricity in order to stimulate their jaw muscles.

As mentioned above, sharks don’t really need strong jaws since they can grow so large and are fitted with extraordinarily sharp teeth. In addition to this, they also benefit from having very wide jaws. When they tear an animal apart, they frequently use a sawing motion.

Dr Huber hopes that their study will lead to the development of protective swim wear and other types of shark-proofing gear.

If you wish to read more, you can find the study “Is Extreme Bite Performance Associated with Extreme Morphologies in Sharks?” in the journal Physiological and Biochemical Zoology.

http://www.journals.uchicago.edu/doi/abs/10.1086/588177?prevSearch=(shark)+AND+[journal%3A+pbz]

In addition to the recently proposed areas in the Pacific Ocean, (See this and this) president Bush now says he wants to find even more regions of the Pacific Ocean to protect.

This Friday, Bush made public that he has asked the secretaries of the Interior, Commerce and Defense to identify additional areas of the Pacific Ocean that could be eligible for conservation. He also revealed that the Monterey Bay National Marine Sanctuary will be expanded by 585 square nautical miles and come to include the Davidson Seamount. Davidson Seamount is a 42 km long underwater mountain located roughly 120 km southwest of Monterey, California. The seamount rises 2400 meters off the ocean floor, but its highest point is still more than a kilometre below the surface.

The proposed Coral Sea marine park is now one step closer to becoming a reality – it has gained support from Coral Sea fishermen. According to Bundaberg fisherman Seth Parker, all of the 16 Coral Sea license holders support the proposal and are willing to let the Commonwealth buy back their permits. “They would buy the whole lot out for 25 to 30 million [dollars] and we would leave this pristine area,” Parker says to ABC News.