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

Shark research: Spiny dogfish like their salt!

New research published in Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology has found that the North Pacific spiny dogfish (Squalus suckleyi) have difficulty adjusting to low salinity levels in the water.

The North Pacific spiny dogfish is known to tolerate a narrow range of salinities; whilst this species has been found in salinities of less than 25‰ in the wild, this low salinity cannot be tolerated for long. This is in contrast to certain other elasmobranch species such as the blue shark (Prionace glauca) which has been known to infiltrate river systems for extended periods of time.

Elasmobranch species moving between salt water and fresh water can experience changes in the concentration of Na^+, Cl^- and urea in their plasma, the pH of their blood and the volume of body water as they attempt to readjust to their new environment.

In this study, the researchers exposed S. suckleyi to dilute saltwater at a salinity of 21‰, in order to assess the time taken to acclimatise and the physiological effects this hyposmotic solution had.

They found that the concentration of plasma Na⁺, Cl^- and urea dropped, and the body weight of the experimental animals increased - most likely owing to an influx of water. Whilst S. suckleyi was able to begin to balance the Na⁺ and Cl^- concentrations, possibly by active transport, steady states in the concentration of plasma urea was not achieved and it is hypothesised that this is the key limiting factor for the survival of the North Pacific spiny dogfish in low saline environments.

Whilst it appears as though this species can tolerate an environment of 21‰ for a short period of time, the ability to regulate key body processed in a lowered salt environment would appear to restrict the long term survival of this species in water of this salinity.

Samuel C. Guffey, Greg G. Goss, Time course of the acute response of the North Pacific spiny dogfish shark (Squalus suckleyi) to low salinity. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. Volume 171, May 2014, Pages 9-15.

Shark Research: Public perceptions of shark conservation

New research has conducted a survey on aquarium goers to assess the views of the public on sharks and their conservation.

The survey, published in the journal Marine Policy, posed a series of questions related to shark conservation to the visitors of the National Marine Aquarium in Plymouth. The questions focused on assessing the respondents general knowledge of sharks as well as their knowledge of shark fisheries. Whilst nearly all survey participants displayed a good general knowledge of sharks, there was a large degree of uncertainty when questioned about shark fisheries with 21% of respondents incorrectly believing that sharks were not fished in European waters and 19% answering (incorrectly) that shark meat was not consumed in the UK.

The participants were also interviewed regarding their perception of sharks. Approximately two thirds of the survey group had a positive image of sharks and individuals who had encountered sharks in the wild displayed a more positive attitude towards sharks.

Public perception of sharks could be an important factor influencing shark conservation. When people hold high views of wild animals, they have a tendency to participate in activities to promote the protection of those animals and to avoid products and practices which could be detrimental to the survival of that species in the wild. Public opinion can be a strong driving force for policy making and bolstering protection for certain animals; a well informed and motivated public may hold the ability to drive change in terms of shark conservation.

Sharks are under threat globally owing to the pressure exerted on many species from shark finning and fishing bycatch and the study states that around half of sharks in European waters are at risk of becoming endangered or threatened with extinction. Low fecundity, slow growth rates and length of time taken to reach maturity mean that most shark species do not rebound easily once their numbers have been depleted. Finding more ways to drive public perception of sharks and to motivate individuals to become involved with shark conservation could be a real driving force for preventing the decline of these vulnerable species.  

Shark Research: Population composition of blue sharks in the Central Atlantic

A group of researchers has examined population structure, size, abundance and migration patterns of blue sharks (Prinace glauca) in the Azores Archipelago in the Central North Atlantic.

Unlike many other shark species, blue sharks are relatively productive and may attain high abundances locally. This is reflected in the fisheries catch composition which the researchers monitored in the local area where blue sharks constituted 81.5% of the total catch in terms of number of individuals caught.  

Blue shark composition varies with sea surface temperature (SST), time of year and lunar cycle. The highest catch rate of blue sharks in the Central North Atlantic occurred during the winter months whilst the summer months yielded the lowest catch rate. This is congruent with evidence that female blue sharks migrate in the warmer months and appear off the coasts of Ireland and SW England. The highest catch abundance of blue sharks also coincided with the coolest SSTs, with the highest catch rate occurring in waters of 17.5°C and the lowest at the higher SST of 23°C. Evidence of several life stages of the blue shark in the Central North Atlantic indicates that this is an important ecological area for blue shark populations from both sides of the North Atlantic, as well as being a nursery area for blue sharks.

Owing to the over exploitation of many shark species by the fisheries industry, in depth knowledge of population structure and composition of shark species is an important tool in assessing vulnerability of each species. The blue shark is the most frequently caught pelagic shark species by the fisheries industry, with an estimated 86,000 tonnes fished per year; in recent years the swordfish fisheries have begun to target blue sharks owing to a reduction in the swordfish catch in the region.

Vandeperre, F., Aires-da-Silva, A., Santos, M., Ferreira, R., Bolten, A. B., Serrao Santos, R. and Afonso, P. (2014) Demography and ecology of blue shark (Prionace glauca) in the central North Atlantic. Fisheries Research. 153, 89-102

Shark research - insights into trophic position of sharks

Scientists at Shanghai Ocean University have used stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) to assess trophic postions of 5 shark species.

Previous work on the trophic levels of sharks has primarily used stomach content analysis to assess where sharks sit in the food web. Assessing trophic position by examining stable isotope ratios is a less invasive method than stomach content analysis.

Sharks are apex predators and play a pivotel role in marine ecosystems. Detailed understand of where apex predators sit in the food web, in relation to each other, gives us a better understanding of the top down effect they may have on an ecosystem.

The five species included in this study were the blue shark (Prionace glauca), bigeye thresher (Alopias superciliosus), silky shark (Carcharhinus falciformis), scalloped hammerhead (Sphyrna lewini) and oceanic whitetip (Carcharhinus longimanus). These five species are all caught by the Chinese longline fleet in the mid-east Pacific.

Stable isotope analysis (SIA) can be used to assess a number of mechanisms in the food chain. By examining δ¹⁵N isotopes in organisms, researchers can make an estimate of the position that organisms inhabits in the food web. δ¹⁵N isotopes move through the food chain as organisms consume each other. Therefore organisms residing in a higher position in the food web will have higher δ¹⁵N values than those further down.

The researchers also examined δ¹³C isotopes; these isotopes originate from the primary producer and remain relatively unchanged as they make their way through the food web; they can be used to give an indication of the source of primary production supporting the entire food web.

From these analyses, the team discovered that A. superciliosus occupies the highest trophic position in the food web; possibly owing to the fact that this species consumes more cephalopods than the others - cephalopods have higher δ¹⁵N and δ¹³C values than fish prey. The team also discovered that A. superciliosus had the largest variation of δ¹⁵N - possibly owing to its highly migratory lifestyle.

C. longimanus occupied the lowest trophic position in the food web.

Li, Yunkai , Gong, Yi , Chen, Xinjun , Dai, Xiaojie and Zhu, Jiangfeng. Trophic ecology of sharks in the mid-east Pacific ocean inferred from stable isotopes. Journal of Ocean University of China 13(2):278-282

Shark research - Sharks get their speed from spring loaded spines

New research has discovered that the vertebral columns of sharks behaves like a spring, providing power when swimming.

Sharks differ from most other fish in that their skeleton is made of cartilage instead of bone. By examining whole body curvature of the spiny dogfish (Squalus acanthias), and strain placed on the vertebrae of sharks during swimming, a team of researchers have discovered that the entire vertebral column bends during locomotion. This indicates that the spine is behaving like a spring and providing power to the sharks when swimming.

The morphology of the spine of cartilaginous fish appears to allow for spring loading. The vertebral column of S. acanthias displayed an open, intracentral canal, covered by a velum layer which effectively strengthens the vertebral column and could facilitate elastic recoil of the entire spine. This recoil in the cartilaginous vertebral column of sharks assists undulatory swimming by providing springback power to the motion of the tail. A shark requires 6% of its metabolic power to flex the tail and load the spring, but this investment is a relatively inexpensive cost for the recoil power generated.  

The results indicate that the bodies of sharks have been positively selected for speed, which is in keeping with the lifestyle of many large, metabolic sharks.

This method of swimming differs from bony fishes, whose spines consist of hardened vertebrae and flexible joints, and may provide a clue for one reason why sharks diverged from the ancestral state of having a bony skeleton.

M.E. Porter, Candido Diaz Jr., Joshua J. Sturm, Sindre Grotmol, A.P. Summers, John H. Long Jr., Built for speed: strain in the cartilaginous vertebral columns of sharks, Zoology, Volume 117, Issue 1, February 2014, Pages 19-27, ISSN 0944-2006, http://dx.doi.org/10.1016/j.zool.2013.10.007

Shark research - Evidence that human immunoglobin originated in sharks

Researchers at China Agricultural University in Beijing have traced the evolutionary pathway of modern immunoglobin back to sharks.

Immunoglobin D (IgD) is present in all jawed vertebrates, but its existence in acipenseriformes has previously not been proven. The acipenseriformes are fishes with a cartilaginous endoskeleton which are evolutionarily placed between elasmobranchs and teleost fish. The discovery of the IgD encoding gene in the Siberian Sturgeon (Acipenser baerii) bridges the gap in immunoglobin evolution between elasmobranchs and teleosts.  

A gene encoding immunoglobin W (IgW) has been identified in sharks, whilst the IgD encoding gene has been proved to be present in teleost fish. As IgW has previously been believed to be a homolog of IgD, this would indicate that the IgD found in teleost fish and mammals - including humans - can be traced back to the early evolution of sharks. However, without evidence of similar IgD genes in the intermediate phase between elasmobranchs and teleost fish, the evolutionary pathway could not be assured.

The researchers used polymerase chain reaction (PCR) and high throughput sequencing to identify the IgD gene in the acipenseriform fish A. baerii. The researchers found for the first time that the IgD encoding gene was expressed in the Siberian Sturgeon and furthermore that the gene shared features with that of teleost fish.

Immunoglobins (or antibodies) are key components of the vertebrate immune system and being able to trace the lineage of our own immune system back to sharks provides evidence that sharks have been an important evolutionary template for our own species as well as all fish and mammals which express this antibody.

Lin Zhu, Zhenxin Yan, Mengyang Feng, Dezhi Peng, Ying Guo, Xiaoxiang Hu, Liming Ren, Yi Sun. (2014) Identification of sturgeon IgD bridges the evolutionary gap between elasmobranchs and teleosts.  Developmental & Comparative Immunology. 42(2):138 

Shark Research - Small spotted catsharks are smarter than first thought

Researchers at Cranfield University have found that small spotted catsharks (Scyliorhinus canicula) exhibit cognitive ability with rapid learning skills. The experiment, led by Dr. Joel Cranfield, set out to assess the capacity for cognitive ability in sharks.

Cognitive ability is important for animals inhabiting changing environments such as the oceans - it facilitates memory and learning which improves the ability of an animal to catch prey or search for mates. Whilst marine mammals have been shows to possess cognitive ability, less is known about the capacity of sharks for learning and memory.

To assess the cognitive ability of the small spotted catshark, the researchers focused on the electroreception sense of the shark. Electroreception is an important sensory tool for sharks and rays; it allows them to detect natural electric fields such as those which might be given off by prey items. An assessment of the ability of sharks and rays to distinguish between electric stimuli given off by prey and that of an artificial object - such as undersea electric cables - will be valuable when assessing the impact these artificial electric stimuli may have on marine fauna.

The researchers split the sharks into 4 groups - those which would undergo positive reinforcement and would receive a food reward upon showing interest in an electrical stimulus and those which would not. After each group had participated in the experiment, the groups were switched so that the ones who previously received positive reinforcement no longer would and vice versa.

The researchers found that sharks conditioned to receive a food reward upon investigation of the electric stimulus were far more likely to return and bite the probe than those which had not received any reward, demonstrating rapid learning ability of this species. However when examining the ability of the sharks to retain this information as memory, the researchers found that the sharks possessed a memory of 12 hours to 3 weeks. The small spotted catfish inhabits mainly coastal waters which are highly variable and a memory of longer than 3 weeks may not be a survival requirement of this species. Therefore investigation into other, preferably pelagic shark species, may yield different results and potentially a longer memory time.

Kimber, J., Sims, D, Belamy, P. and Gill, A. (2014) Elasmobranch cognitive ability: using electroreceptive foraging behaviour to demonstrate learning, habituation and memory in a benthic shark. Animal Cognition. 17(1): 55-65

Shark Research – Brazil looks for a better way to keep beaches shark safe

Whilst shark attacks are relatively rare, when there is a sharp increase in the number of attacks it will often provoke public outcry. Between 1992 and 2011 there was an abnormally high number of shark attacks in Recife, Brazil – around 55; the increase in attacks was owing to the development of a new port area in the region.

Whilst the Government was eager to take preventative measures against future attacks, they valued the aquatic ecosystems and understood that gill nets and longlines are non-discriminatory measures which kill species other than sharks. The Shark Monitoring Program of Recife (SMP) was set up to find a technique which could reduce shark attacks whilst causing minimal disturbance to the surrounding ecosystem.

Two researchers from Universidade Federal Rural de Pernambuco (UFRPE) looked at ways this could be achieved. They first used baiting techniques to attract sharks and then relocated problem sharks away from the hazardous area. These techniques showed a 97% reduction in the amount of attacks around the site, and reduction in the mortality rates of sharks and bycatch when compared with gillnets.

During the survey the researchers aimed to reduce the mortality rate of the sharks, as well as to reduce the mortality rate of people using the water in this region. The SMP techniques involved catching sharks using circle hooks – as oppose to the traditional J style hooks – as this lowered mortality rates in the sharks. During the relocation process steps were taken to reduce the stress caused to the sharks – such as covering their eyes with a cloth. Finally the capture and relocation of the sharks afforded the researchers the opportunity to tag the sharks. The tags proved that relocation was a suitable technique in this area, as the sharks did not return to the region after being transported.

The reduction in shark mortality rates was most prevalent in tiger sharks – in South Africa 40% of tiger sharks (Galeocerdo cuvier) are released alive, whereas using the techniques employed by SMP, 82% of tiger sharks were released alive. For the remaining shark species (including bull sharks, blacktip sharks, silky sharks etc) mortality averaged about 30% - which is still a fairly high number when we consider that many of these species are considered Near Threatened in the IUCN Red List of Threatened Species.

The notion of relocating sharks as oppose to culling them is something which this study proved can work – at least in this location. However, whilst it is refreshing to see a government attempting to protect their wildlife whilst keeping sharks away from the public, the fact remains that this study still uses hook based fishing gear to attract the sharks. If steps could be taken to reduce the mortality rate of captured sharks even further, then relocation could be a real, ecologically sound solution to removing sharks from certain areas – after all relocation techniques have been used to remove venomous snakes from properties for years and are a very successful strategy in this regard. 

Hazin, F. H. V. and Afonso, A. S. (2013), A green strategy for shark attack mitigation off Recife, Brazil. Animal Conservation. doi: 10.1111/acv.12096

Shark research: attitudes of divers towards encounters with grey nurse sharks

A recent paper published in Aquatic Conservation: Marine & Freshwater Ecosystems has examined the attitude of scuba divers towards the practice of diving with grey nurse sharks (Carcharias taurus). The research, led by Kirin Apps, interviewed divers who had dived with grey nurse sharks at Julian Rocks and Fish Rock in NSW. Using interview techniques, the researchers sought to learn more about the behaviour of scuba divers at these sites.

The main motivations for wanting to approach grey nurse sharks were to get a better view of the shark and to interact with the shark. However, divers were also concerned that their behaviours might scare the sharks or disrupt the natural behaviour of the sharks. A large proportion of the respondents were concerned that environmentalists would disapprove if they were to approach the sharks and most interestingly there was a great deal of concern regarding the opinion of other divers with some respondents thinking the dive community would approve of their approaching a grey nurse shark and others believing this behaviour would draw disapproval from their fellow divers.

Diver interaction with delicate marine structures such as corals, and marine species such as sharks can unintentionally have a negative effect on the conservation of the marine ecosystem. Furthermore, for many people diving with sharks is a unique experience and the desire to “make the most” of the experience can sometimes lead to behaviours which may not be wholly beneficial to the animal such as touching or disturbing the animal.

However, scuba divers do tend to show respect for the underwater environment and to be in favour of conserving the oceans and recent research has suggested that shark dive tourism overall can contribute to the conservation of many shark species as it is a very effective way of making a shark worth more alive than dead. In a world where the price of shark fin has increased the rate of poaching, making live sharks valuable to governments via shark dive tourism could be a realistic way to ensure that many shark species receive government protection. In an ideal world, all forms of shark tourism would be conducted in a responsible manner which attracted divers to the activity whilst ensuring minimum disturbance to the species involved.  

Grey nurse sharks are listed as Vulnerable in the IUCN Red List of threatened species.  A better understanding of the behaviour of divers towards C. taurus will help researchers and policy makers be more aware of the potential threat towards this species from tourism and implement this knowledge accordingly in their efforts to conserve this species.   

Shark research: Older than we first thought: it takes more than “counting the rings” to age a great white.

Despite the overwhelming fame and notoriety of the great white shark (Carcharodon carcharias) in the media, the reality is that there exists relatively little scientific data on this species. A group of researchers, led by Li Ling Hamady at Woods Hole Oceanographic Institution, used radiocarbon analysis to confirm the age of 8 white sharks and found that white sharks in the northwest Atlantic Ocean (NWA) were likely to live up to 70 years.  

The previous method of aging great white sharks – as with most fishes - was to count the number of mineralised layers laid down in specific tissue such as vertebrae; with this method it is assumed that the layers are laid down on an annual basis. However this method can be vulnerable to misinterpretation and collaboration of results gained in this manner by using radiocarbon dating has gained popularity.

The study, which was published in the journal PLOS ONE, increase exponentially the estimated longevity of C. carcharias in NWA. These results not only have implications for a need to reassess the methods by which sharks are aged, but an increased expected longevity in white sharks raises grave conservation issues. Like most sharks, white sharks are slow to reach maturity and have small litters. If NWA white sharks exhibit even greater longevity than we first thought, this could mean that their expected age to reach sexual maturity could also be longer than originally estimated and this would make white sharks even more vulnerable to fishing pressure and population decline. The white shark is listed as Vulnerable in the IUCN Red List of Threatened Species; many countries protect white sharks but a poor media image has left white sharks vulnerable to persecution – such as the recent decision of the Western Australian Government to bait for large sharks.

Obtaining a greater knowledge of the growth rates and longevity of white sharks will be beneficial for ensuring the protection of this species.  

Hamady LL, Natanson LJ, Skomal GB, Thorrold SR (2014) Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks. PLoS ONE 9(1):

e84006. doi:10.1371/journal.pone.0084006

Shark Research: Magnets could be used to successfully repel bull sharks

A group of researchers led by Craig O'Connell at the University of Massachusetts Dartmouth, have discovered that C8 barium-ferrite (BaFe12O19) permanent magnets might be the key to repelling bull sharks (Carcharhinus leucas) from shark nets.

The research - to be published in the journal Ocean & Coastal Management - measured the responses of C. leucas to bait and barriers where permanent magnets were present. They discovered that bull sharks were less likely to approach bait or to enter areas when magnets were present. These results suggest that if magnets were used along shark nets they might deter C. leucas from approaching the nets.  

Shark nets are used extensively in three regions of the world: Queensland and New South Wales in Australia, and Kwa-Zulu Natal in South Africa. The use of these shark nets is somewhat controversial; whilst they have been put in place to protect beach-goers from large sharks who may stray close to shore and pose a risk to anyone in the water, the shark nets also result in the mortality of thousands of sharks per year. Furthermore, as the nets are non-discriminatory, other marine life such as dolphins and juvenile whales can also fall victim to shark netting. Finding a guaranteed way to repel sharks away from the nets would not only ensure that sharks are protected from the nets but could even lead to the removal of the nets altogether if the sharks could be kept away from the shore.   

The finding that permanent magnets can be used to deter select elasmobranchs is consistent with what we know about the biology of certain sharks; sharks have specialist sensory organs called Ampullae of Lorenzini which they use to detect bioelectric fields and are hypothesised to be capable of detecting the magnetic field of the Earth.

The researchers plan to publish similar papers focusing on the great white (Carcharodon carcharias), giant hammerhead (Sphyrna mokkaran) and the tiger shark (Galeocerdo cuvier). The inclusion of multiple shark species in this long-term study is important as there is a possibility that highly visual sharks such as C. carcharias may not be as sensitive to magnetic fields as C. leucas. 

With the recent decision of the Western Australian Government to implement a cull of all large sharks in response to a spate of fatal attacks in WA, further research into methods to repel sharks and the potential practical applications could not come at a better time.