Shark Research - Lateral line scales can make sharks fly

New research published in the Journal of Fish Biology has examined the scale pattern around the lateral line pores of the spiny dogfish shark (Squalus acanthias) and the shortfin mako shark (Isistius oxyrinchus).

The lateral line system is an important sensory organ in fish and is used to detect vibrations and movement in the surrounding water; this sense can be utilised in predator avoidance, schooling and prey detection. The lateral line runs down the side of a fish and comprises a series of sensory neuromasts, connected by tubules. Whilst some neuromasts remain below the dermis, at sections of the lateral line superficial neuromasts will be exposed to the outside environment via pores in the lateral line system.

Surrounding the pores of the lateral line system are the sharks' scales; unlike the scales of teleost fish sharks possess rough, placoid scales which (as well as being biologically similar to our teeth!) contribute to reducing drag whilst swimming and give sharks a rough, sandpaper like texture. The channelling of water over the neuromasts by the surrounding placoid scales will, of course, have an affect on the sensitivity of these sensory organs.

The fast swimming mako shark has a very different lifestyle to the spiny dogfish, which inhabits the ocean floor and has a much more sedentary lifestyle. The study found that the patterning of placoid scales around the neuromast pores in the mako shark may reduce turbulence in the water immediately surrounding the lateral line; this will affect lateral line sensitivity.

The arrangement of placoid scales around the neuromast pores in the spiny dogfish was entirely different, with S. acanthias exhibiting an entirely different divergent pattern to I. oxyrinchus. The placoid scales of I. oxyrinchus were orientated dorsally and ventrally from the pore, whilst those of S. acanthias were orientated exclusively ventrally away from the pore.

Whilst further research is required to fully analyse these differences across shark species, the results here suggest that the different lifestyles of these 2 shark species may be contributing to different sensory requirements in the lateral line and therefore different arrangement of the scales around the sensory organs.

Mckenzie, R. W., Motta, P. J. and Rohr, J. R. (2014), Comparative squamation of the lateral line canal pores in sharks. Journal of Fish Biology, 84: 1300–1311. doi: 10.1111/jfb.12353

Shark news - Megamouth shark caught off the coast of Japan

Following on from Tuesdays exciting news about the sighting of a goblin shark, a rare megamouth shark (Megachasma pelagios) has been caught off the coast of Japan. The specimen - which is only the 58th to have ever been found - was caught off the waters of Shizuoka last month and is currently on display at Marine Science Museum in Shizuoka.

Very little is known about these sharks but they are believed to be a filter feeding species which feeds primarily on krill. A single specimen was tagged and followed for 2 days and exhibited patterns of diel vertical migration (spending the daylight hours at depth and returning to shallower waters at night).

The megamouth shark is currently classified alongside white sharks (Carcharodon carcharias) and mako sharks (Isurus oxyrinchus) in the order Lamniformes (or mackerel sharks).

News source with pictures: http://www.wptv.com/news/local-news/water-cooler/rare-megamouth-shark-caught-in-waters-off-japan

Shark News - Drum lines removed from WA waters

At 2pm yesterday, the Western Australian Government removed the drumlines which had been set to catch target sharks off the coast of WA, Australia. Whilst this news will be warmly welcomed by the majority of the public - who overwhelmingly oppose the shark cull - there is a chance that the drumlines could be back in the water by the end of the year.

The initial policy to place drumlines in the water around Perth had always been a short term policy set to run for 13 and a half weeks the intended deadline for the removal of the drumlines set as 30th April. By negotiating the placement of the drumlines on a short term, "trial" basis, Colin Barnett was able to circumnavigate some of the laws which would otherwise prevent such a policy going ahead - such as the fact that the great white shark (Carcharodon carcharias) is a protect species in Australian waters.

Currently the Environmental Protection Agency (EPA) is assessing an application by the Barnett Government to extend the drumline policy for a further 3 years. The new submission to the EPA requests permission to put drumlines in the water for 4 and a half months of each year for 3 years and is requested to begin on November 15th 2014. Since the new proposal is for a much longer time period than the initial setting of the drum lines, the EPA has decreed that the policy must be subjected to the highest level of assessment.

Given a very strong public and scientific objection to the drumline policy, the hope is that the EPA will not allow the Barnett Government to continue with this policy long term.

You can read more about the assessment here 

Shark travel - whale sharks in the Philippines

For many people, the whale shark (Rhincodon typus) is top of their list to see. Whilst I have had the opportunity to encounter many types of shark on my global wanderings including white sharks, bull sharks, blacktips and grey nurse sharks, it feels as though I almost left the poor whale shark until last!

Capable of attaining lengths of up to 12m, the whale shark is the largest living fish in our oceans. However they are no threat to humans (unless you don't mind out for that powerful tail!) as their diet primarily consists of plankton which they filter out of the water.

Whale sharks are found all over the world in tropical and warm temperate seas, however there are some spots where sightings are quite common. I visited one of those such spots recently: Donsol in the Philippines.
Legazpi airport is the closest dropping off point for Donsol. I flew there from Manilla with Cebu Pacific Air (about 1 hour). Once you are at Legazpi airport a 1 hour drive through hilly, forested terrain will bring you to Donsol. I was pleasantly surprised at the lack of impact by tourism on Donsol - despite having a major tourist draw in the form of the whale shark, the town still feels very local and I didn't encounter too many other tourists there during my stay.

Donsol has plenty of local delicacies available at the market!

The peak time to see whale sharks here is over the Easter period, but the season runs from December to May. I had booked into a hotel in town - Giddy's Place (http://www.giddysplace.com/) and they were able to arrange my trip out with the whale sharks. Once you arrive at Donsol Bay you are assigned a Butanding Interaction Officer (BIO), a guide and a spotter and out you go on your boat for a maximum of 3 hours to try and find some sharks!

The spotters risk it all to get up high and spot whale sharks!

Known locally as butanding, the whale sharks are often found near the surface as they feed on plankton blooms. On our first day out we were incredibly unlucky - no sharks at all - only a pod of dolphins which put on a real show leaping clear out of the water! However on our return for day 2, we had a total of 5 whale sharks show up. The boat does not stop as it positions itself close to the shark - a quick leap from the moving boat and you are in the water with the largest fish in the world. And for anyone who might be worried that the clumsy monkeys in the water are capable of harassing these gentle giants, please rest assured that you will swim with everything you have just to try and keep up with the shark for 30 seconds. A few, slow flicks of their giant tail and the whale sharks had accelerated way past our group.

On one encounter, as the shark began to dive, I was lucky enough that it passed a few meters below me. I simply lay perfectly still in the water as the behemoth cruised past underneath me seemingly not bothered by my presence.  

Whale sharks are currently only legally protected in 10 countries - one of which is the Philippines. There is no doubt that the Philippine government has realised the tourist value of the whale sharks and this has led to them protecting the shark. I am happy to report that the standards of the guides and spotters on the whale shark trip were very high. All participants had to watch a video informing them of correct ethical conduct around the sharks - no touching, no riding, only 6 people maximum around a shark and only for a maximum time of 10 minutes. Once on board the boat and out at sea the crew enforced the rules and made sure that the sharks were not harassed. With such pressure on sharks from the trade for fins (a whale shark fin can fetch up to USD$10,000), tourism is the best chance we have now to encourage governments to really make the effort to protect their sharks from poaching.

To see a video of my time in Donsol, click the link below!

Shark research - evolution of the vertebrate jaw

A recent article published in Nature has found new evidence that the origins of the vertebrate jaw may lie with bony fish, as oppose to cartilaginous fish as previously thought.

By examining a 325 million year old, Palaeozoic shark-like fossil (Ozarcus mapesae), the researchers found many similarities to the visceral branchial arch arrangement of osteichthyans (bony fish). This has thrown into question the existing idea that cartilaginous fish are responsible for the origin of the vertebrate jaw.

All vertebrate embryos develop pharyngeal arches - in fish these develop into the gill (or branchial) arches and in humans they ultimately become part of the larynx and trachea.

Cartilaginous fish (sharks, skates, rays and chimeras) are often described as "primitive fish", and are thought not to have changed much since their original evolution. Bony fish (or Osteichthyes) are considered to be the derived state and to have a more "modern" physiology. However, this new shark-like skeleton suggests that far from being unchanged since their evolutionary origin - around 420 million years ago - sharks may have undergone several evolutionary adaptations along the way and that our own mammalian jaw may have a closer evolutionary history with that of bony fish rather than cartilaginous fish.

Pradel, A., Maisey, J. G., Tafforeau, P., Mapes, R. H. and Mallatt, J. (2014) A Palaeozoic shark with osteichthyan-like branchial arches. Nature (16th April 2014)

Shark facts - Wobbegongs!

There was previously thought to be just over 350 species of sharks, but genetic analysis has now put that number at over 400! Of course, when many people think of a shark, they perhaps imagine big, pelagic sharks such as the great white (Carcharodon carcharias). However sharks come in a wide range of shapes and sizes from the eel-like frilled shark (Chlamydoselachus anguineus) to the gentle, filter feeding basking shark (Cetorhinus maximus). One of the aims of this blog is to pass on a bit of information about some of these weird and wonderful sharks. 

Perhaps one of the hardest group of sharks to spot in the wild are the wobbegongs. Wobbegongs - or carpet sharks - belong to the family Orectolobidae. 

Wobbegongs can be very tricky to spot as they are very well camouflaged against the sea floor!

Wobbegongs are bottom dwelling sharks and spend a lot of time motionless on the sea floor. They are found in the Western Pacific - mostly in the waters around SE Asia and Australia and occupy tropical to temperate waters. They are primarily ambush predators and feed on bottom dwelling invertebrates such as cephalopods, crabs, lobsters and even bony fish.

Whilst they don't feed on humans and are generally quite placid animals, wobbegongs have been known to bite when provoked. Owing to the fact that they can occupy quite shallow water they can get stepped on quite easily and have been known to inflict minor injuries as a response. Divers are usually able to get very close to wobbegongs owing to the relaxed nature of the shark.

Of the 12 recognised species, 3 of them have been classified as Near Threatened in the IUCN Red List - the spotted wobbegong, ornate wobbegong and banded wobbegong. The remaining species are classified as Data Deficient. 

A close up of a wobbegong near Stradbroke Island, Brisbane

Wobbegongs can be found in many places around the Australian Coast. The little fella above was snapped on a trip I took with Manta Lodge and Scuba Centre from Stradbroke Island, Queensland.

Shark research - Port Jackson sharks show learning and memory capabilities

New research has found that Port Jackson sharks (Heterodontus portusjacksoni) are capable of conditioned learning and some memory retention.

The researchers exposed Port Jackson Sharks to two different stimuli - air bubbles and an underwater LED. Each stimulus was activated prior to the release of a food reward and the response of the shark post-stimulus was recorded.

Sharks which were exposed to the air-bubble stimulus showed a reduction in the time taken to react to the stimulus, in anticipation of a food reward. Response behaviours included biting or vigorous respiratory pumping such as would be observed when searching for buried prey in the wild.

The group which was exposed to the LED stimulus showed no modified behaviour towards the stimulus suggesting no anticipation of reward. This could be owing to the fact that, as nocturnal predators, Port Jackson sharks do not rely on vision for prey detection and capture and therefore the LED stimulus was unable to elicit a response.  

Owing to the fact that there was a period of 24 hours between trials, the Port Jackson sharks were able to retain memories of the association between the stimulus and reward for at least 24 hours and one of the sharks even remembered the association for 40 days.  

Port Jackson sharks are an excellent model species for this study as they are reef associated and have been shown to return to the same point on the reef up to 24 hours later after being displaced. This suggests that they must have some capacity for spatial memory.

This study demonstrates, for the first time, the learning capabilities of a benthic elasmobranch. Of all shark species, benthic sharks are the group with the smallest brains; previous studies on teleost fish have demonstrated a link between brain size and cognitive ability and therefore the researchers surmise that our understanding of cognitive ability in sharks in greatly lacking.  

Guttridge, T. and Brown, C. (2014) Learning and memory in the Port Jackson shark, Heterodontus
portusjacksoni. Animal Cognition (17): 415-425