Are sharks apex predators? Does it matter?

We commonly refer to sharks as apex predators. Are they really? If they are not, does it matter? A few Australian researchers have come up with some answers to both questions.

First, are sharks apex predators? According to their findings, the answer is yes .... and no.

Example of an apex predator!

Here is what they found. "While size can be important in terrestrial ecosys- tems, size is crucial in marine ecosystems — which tend to be dominated by indeterminate organisms that grow continuously throughout their lives (Trebilco et al. 2013). Individual function changes due to onto- genetic diet shifts as organisms grow in size (Karpouzi

& Stergiou 2003, Pinnegar et al. 2003). The conse- quence is that size-structuring within communities, rather than species identity, is an important factor in determining the strength of competitive and predatory interactions (Dickie et al. 1987, Kerr & Dickie 2001). For example, studies have shown high overlap in diet between similar-sized sharks regardless of maturity state and species identity (e.g. Bethea et al. 2004). Therefore, designation of marine species into apex and mesopredator categories should consider the life stage and size of individuals."

I'm not a scientist, but what I'm getting is, size matters!

But so, why should we care? We are not scientists, (well, you may be, but I'm not) so what does a classification matter? 

Here is what they have to say to that. 

Example of a meso predator!

"Our size-based view of the classification of predatory roles raises important questions about what objectives to manage, and how these objectives can be best achieved. Protection of reef communities through marine protected areas (MPAs) or fisheries regulation (or indeed, naturally on those few locations far from human population centres) would ensure the mesopredator sharks on these reefs are sheltered from fishing pressure. However, the same may not be true for apex predators because their broad movement patterns and large home ranges (Meyer et al. 2009) would expose them to a greater diversity of fishing fleets and gears, and thus a greater overall mortality than the smaller-ranging, reef-dwelling mesopredators. Hence, the apex pred- ators of coral reefs may be silently eliminated by offshore pelagic longline fisheries, unbeknownst to those managing reef diversity and function (Cox et al. 2002). Therefore, reef-based MPAs are not adequate to protect these species"

So basically they are saying that we need to do more than establish MPAs to adequately protect apex predators.

Here is a graphic that may be a bit more clear on the subject.
 

This graphic shows, that without MPAs prey species would greatly increase, while both mesopredators and apex predators decrease. With reef scale (small, local) MPAs, the mesopredators thrive, keeping the prey species in balance, but the apex predators still decline.

 

In practical terms, this means that we have to protect apex predators on a much larger scale than the less migratory mesopredators. In order to do that, we need to know both where they are and when they are there. With that knowledge we can push for local and/or seasonal protection for these migratory apex predators. In order to get that data, we need data that shows the migratory behavior of the various species of apex predators. 

You can read the entire paper here.

Cheers,

Martin Graf

CEO

Shark Diver

About Shark Diver. As a global leader in commercial shark diving and conservation initiatives Shark Diver has spent the past decade engaged for sharks around the world. Our blog highlights all aspects of both of these dynamic and shifting worlds. You can reach us directly at staff@sharkdiver.com

Mote Marine Labs Spearheads Gulf Shark Effort

SARASOTA, Fla. – For months the Deepwater Horizon oil spill shut down tourism and commercial fishing along the coast of the Gulf of Mexico. Along with killing 11 people, the disaster cost billions of dollars and the full environmental impact may not yet fully be known. But groundbreaking research happening in Southwest Florida could give us a better idea of the long term effects of the spill on the ecosystem.

Hundreds of millions of gallons of crude oil spewed into the Gulf of Mexico as a result of the Deepwater Horizon disaster.

“Once you have oil, that massive amount of oil spilled into the environment, you already got severe problems,” Dr. Richard Pierce, director of Mote Marine’s Center for Ecotoxicology told WINK.

The spill would eventually become the largest accidental marine oil spill in history. Mote Marine scientists jumped into action last summer to examine the immediate impacts. But the long term effects are the biggest concern. Mote’s Senior Vice President of research, Dr. Michael crosby explains the concept of trophic cascading, a way to refer to major changes in the food chain that could occur as a result of oil contamination.

“If any of those species are negatively impacted over the longer term following the oil spill, it has cascading impacts throughout the entire ecosystem; the entire seascape,” he said.

It’s easy to imagine that all forms of marine life, up and down the food chain, could be impacted in some way by the oil spill. At Mote Marine they are already conducting a study, starting at the very top.

Groundbreaking research is happening right now at Mote Marine involving sharks. Dr. Robert Hueter says when he started looking for other studies on the impacts of oil on sharks, what he found surprised him.

“Incredibly, we discovered there was only one paper in the entire world on oil contaminants. There are lots of other papers on other types of contaminants. But on oil (or hydrocarbons) and sharks — one paper in the whole world. So we’re really dealing with a vacuum of information and we realize this study that we’re doing now is not only going to tell us what’s happened, perhaps, with the Deepwater Horizon incident, but also lay the groundwork for understanding what the effects of oil worldwide could be on these shark populations,” he said. “We are looking at fertility and if the animal’s reproductive systems have been affected by the chemical pollution they may have been exposed to.”

Dr. Robert Hueter is leading a study to see how oil affects the top predators in the gulf, sharks! The team will take four, week-long cruises to the area around the well over a two-year period. They catch the sharks, collect blood and tissue samples, and in some cases tag them for future study.

“It’s a health assessment of the entire gulf. The Gulf of Mexico is a huge place. You don’t just figure these things out in months or even a year two,” Dr. Hueter said. “I’ve heard people say we dodged a bullet… I say we took a bullet. We didn’t dodge a bullet, but we took a bullet and we’re now assessing how bad the wound is and how much blood we’ve lost.”

Funding for Mote’s shark study is coming from a grant by the Florida Institute of Technology. The grant is paid for by money from BP. It even led to the purchase of new equipment to help analyze the data collected in the field. They take their next cruise into the spill zone next month.

Update: Special lecture series Dr. Robert Hueter's talk "Tracking the World's Largest Shark." tonight information here.

Study - Shark Navigation, Amazing

A new study released in the Journal of Animal Ecology this week from the Florida Museum of Natural History reveals that some shark species can pinpoint navigate long distances.

US ecologists analysed data from eight tiger sharks, nine blacktip reef sharks and 15 threshers which had been tagged with trackers and released off Hawaii, Palmyra atoll in the Pacific or southern California before being followed for between seven and 72 hours.

The research team featured some well known names in the shark research field:

1. Yannis P. Papastamatiou
2. Daniel P. Cartamil
3. Christopher G. Lowe
4. Carl G. Meyer
5. Brad M. Wetherbee
6. Kim N. Holland

Summary

1. Animal search patterns reflect sensory perception ranges combined with memory and knowledge of the surrounding environment.

2.  Random walks are used when the locations of resources are unknown, whereas directed walks should be optimal when the location of favourable habitats is known. However, directed walks have been quantified for very few species.

3. We re-analysed tracking data from three shark species to determine whether they were using directed walks, and if so, over which spatial scales. Fractal analysis was used to quantify how movement structure varied with spatial scale and determine whether the sharks were using patches.

4.  Tiger sharks performed directed walks at large spatial scales (at least 6–8 km). Thresher sharks also showed directed movement (at scales of 400–1900 m), and adult threshers were able to orient at greater scales than juveniles, which may suggest that learning improves the ability to perform directed walks. Blacktip reef sharks had small home ranges, high site fidelity and showed no evidence of oriented movements at large scales.

5. There were inter- and intraspecific differences in path structure and patch size, although most individuals showed scale-dependent movements. Furthermore, some individuals of each species performed movements similar to a correlated random walk.

6. Sharks can perform directed walks over large spatial scales, with scales of movements reflecting site fidelity and home range size. Understanding when and where directed walks occur is crucial for developing more accurate population-level dispersal models.

More here.

Guy Harvey Tiger Tracks - Just The Facts

The Guy Harvey Tiger shark (Galeocerdo cuvier) tracking program is delivering the goods, and for folks like us who just love to know the "what,why and where" of the animals we are fortunate to encounter each year, this is just good stuff:

An important requirement for the proper management and conservation of any shark species is a robust understanding of its migratory patterns, how it uses its environment, and identification of what is termed its “critical habitat” – areas that are key to successful reproduction and feeding. To understand tiger shark movements and aid in conservation efforts, the GHRI/GHOF in collaboration with the Bermuda Shark Project and with financial support from AFTCO is investigating tiger shark movements in the western North Atlantic in a long-term study. The sharks’ movements are being studied by employing satellite tags that relay information on where the tiger shark is and/or its depth in the ocean.

Kudos to the entire Guy Harvey team and the good folks at the Bermuda Shark Project for helping us all learn more about these magnificent animals.

Study results so far.

Tagged Tiger Sharks - Cayman Islands

(Media-Newswire.com) - Marine biologists who are working with the Department of Environment to study the area's predator species caught and tagged two tiger sharks last week fitting each shark with two types of high-tech electronic tracking devices.

One type is a satellite tag that includes a GPS receiver and transmitter, and signals via satellite the location of the shark. The other type is a small acoustic tag or pinger that transmits a signal that can be detected by a permanent or hand held receiver, so showing that the animal is near.

The acoustic tags ( pingers ) can be used to detect movements on a finer scale, providing a more detailed picture of the behaviour and movement of the tiger sharks while they are in Cayman. They will show which sea areas they actually use, and at what time of day.

The sharks, a ten feet female called Tina and a seven feet younger, immature female Luiza, will help the researchers understand their species' migration patterns, movements and behaviour when they are in Cayman.

"Both of them seem to being doing fine. Tina has reported in several times a day while moving around the island; she seems to be deep during the day, coming into shallower water at night to look for the stingrays and turtles on which these species normally feed," said lead researcher Dr. Mauvis Gore.

"Tiger sharks like many other species are increasingly endangered, as a result of intense overfishing globally. In fact large shark species are becoming so scarce globally that in many countries they are either fully protected, or else their fishing quotas have been reduced to zero," she added.

Only in the last few years have scientists discovered that tiger sharks can make extensive annual migrations between countries or even across oceans. The tracks revealed by the satellite tags results will show whether the tiger sharks that are sometimes observed in the Cayman Islands move around or between the islands, and whether, as suspected, they are here for only part of the year, and then migrate elsewhere.

International efforts to protect dwindling shark populations have come to the fore in the last few years because of the dramatic crash in shark populations that has taken place globally. Unlike bony fish, sharks mature very slowly and reproduce only once every one to two years, producing only a small number of pups. Yet over the last decade or two 70 million sharks per year have been fished and killed, almost entirely for their fins that are in demand as a component of sharks' fin soup.

"Even if we agree to exploit sharks," said Dr. Gore. "We want to do it sustainably, not in this crazy way that will see the resource completely destroyed in another 10 years. As it is, sharks are now far more valuable in the sea, than in the fishing boat. Divers will pay good money to dive in places where they have a chance of seeing such iconic wildlife, and the same sharks can be seen over and over again - whereas once it's dead that's it, and it fetches very little in the market."

"Tiger sharks are one of my favourite animals;" added Guy Harvey, whose Ocean Foundation provided the satellite tags, and who helped the team catch Luiza.

"They are the most handsome of all the sharks, and I just love painting them. It's just unfortunate they have these stripes that give rise to their name, making people think they are much more dangerous than they really are."

Guy, a well-known artist and local resident, has also assisted with tagging of tiger sharks in Bermuda and the Bahamas.

The tiger shark study is part of a project that is being undertaken by a team from Marine Conservation International led by Dr. Gore. The project is funded by UK Overseas Territories Environment Programme ( OTEP ) together with the Cayman Islands Department of Environment, the Save Our Seas Foundation, and the Guy Harvey Ocean Foundation. The team have been working in the Cayman Islands over the past year and a half to assess the species and abundance of species of both sharks and rays as well as whales and dolphins.

"We are very pleased with the preliminary results of this work," stated Gina Ebanks-Petrie, Director of the DoE, "it is our duty to manage our marine environment in the best interests of the people of the islands; it makes sense to find ways of managing our resources so they benefit us in the long-term, not destroy them; and we also have international obligations to protect these threatened species."

Sharks, because of media "hype" and their "Jaws" image, often cause public concern. But shark attacks on man are in fact very rare, typically causing only 4 - 6 fatalities throughout the whole world per year.

The resident project officer Mr. Oliver Dubock explained that people's fear of sharks was greatly exaggerated. "Of course they can be dangerous," he said, "but no more than fierce dogs. You need to know how to behave and how to handle them. Just as an example, in Florida on average over 70 people per year die from boating accidents, but less than one every two years as a result of shark attack."

Tim Austin, Deputy-Director at the DoE, added "We plan to keep people informed about the behaviour of Tina and Luiza. We hope to be able to keep the press updated with maps of their migrations. Of course it is essential that they are not harmed. All past experience has shown that killing local tiger sharks does not get rid of them; others simply come in from elsewhere. We urge fishermen and divers to join this important conservation effort and help look after these two beautiful animals."

Sharm el Sheikh Shark Attacks, Farm Animals Dumped Causing Trigger Effect?

As an international team of shark experts land in Sharm el Shiekh to review a simply unprecedented series of shark attacks, resulting in one shark related death last week, some in the region are already blaming local dive operations for illegal shark feeding.

This is a dynamic map of the region, you can zoom in and move around the area for a better view:



What is not being discussed are the numerous eyewitness reports of dead farm animals floating in local waters prior to the attacks. The animals were first sighted in the Tiran Strait off Tiran Island (top right of image) with reports of a commercial vessel dumping dead animals at sea.

At least two eye witness reports say that dead sheep washed onshore during the preceding week not far from where the first attacks took place. What is absolutely sure, looking at the facts through a commercial shark diving lens, is that something caused a normally curious and manageable shark population to suddenly "turn on".

A floating train of large dead farm animals with sharks feasting on these remains in the days prior to encounters with swimmers, might be the trigger.

We decided to explore the "theory" that dead animals dumped at sea off Tiran Island could in fact end up close to shore off Sharm el Shiekh. We asked John Amos from Sky Truth to review satellite data from the region to see if wind and current could move dead animals, floating on the surface, in the right direction. The answer was yes, theoretically animals dumped in the Trian Strait might end up in the most populated regions off the coastline off Shark el Shiekh.

The first step in proving the dead farm animal theory is done. The next step would be to track back the offending vessel by reviewing cargo manifests of all vessels in the region during the preceding two weeks to see if any were:

1. In the Tiran Straits

2. Had a cargo of sheep and perhaps cows

The notion that commercial diving operations could radically alter sharks normal cautionary behaviour towards swimmers and divers with some basic chumming has been put forward by those with little to no experience with sharks. In short, this kind of shark behavior has never happened during past chumming efforts by local dive operations, so why would it now?

The animals who encountered surface swimmers in and around Sharm el Shiekh were in full predation mode, the unfortunate loss of an arm and leg to a 70 year old German swimmer is testament to animals that were recently accustomed to large volume surface feedings.

These were not frenzied animals as has been suggested by the main stream media, rather, these were conditioned animals.

We're leaning towards the theory that multiple sheep and perhaps a cow carcass, bloated by the sun, and floating in a current and wind driven southbound train, was followed and consumed by a number of Oceanic Whitetips (Carcharhinus longimanus), and Makos (Isurus oxyrinchus) which is absolutely normal for these species. This carcass train eventually found it's way closer to heavily populated areas off Sharm el Shiekh with the now conditioned sharks in tow. When these sharks, in full predation mode, encountered swimmers, normal cautionary behavior sets towards unknown objects in the water had been turned off.

The results?

An unprecedented series of attacks on swimmers and an ensuing media frenzy.

The facts about this case need to be known as it's impacts are already being felt worldwide. Our industry will have to remain vigilant against theories put forward by non-industry members who see sharks though a 1970's era lens of frenzied or rouge animals. .

Hopefully the shark attack specialists who are now in Sharm el Shiekh will find the answers.

Extensive coverage from RTSea Productions.

Update: Dead sheep story confirmed, September 26, 2010.

Winter migration and diving behaviour of porbeagle shark, Lamna nasus, in the Northeast Atlantic

"Winter migration and diving behaviour of porbeagle shark, Lamna nasus, in the Northeast Atlantic."

Abstract:

The porbeagle is one of the top marine predators in the North Atlantic. However, little is known about its biology, abundance, or spatial ecology there. Results are presented on the migration and behaviour of three porbeagles tagged with archival pop-up tags off Ireland between September 2008 and January 2009. One shark migrated >2400 km to the northwest of Morocco, residing around the Bay of Biscay for approximately 30 days. The other two remained more localized in off-shelf regions around the Celtic Sea/Bay of Biscay and off western Ireland. The sharks occupied a broad vertical depth range (0–700 m) and a relatively limited temperature range (∼9–17°C), with notable variations in diving behaviour between individual sharks. There were distinct day–night differences in depth distribution, each shark being positioned higher in the water column by night than by day. Night-time depth distribution also appeared to be driven by the lunar cycle during broad-scale migration through oceanic waters. Our results show that porbeagles occupy and traverse regions of high fishing activity where they are potentially vulnerable to population depletion. Such large-scale movement outside the ICES Area underlines the need for international coordination in their assessment and management.

Link to study.

Shark Diver New Zealand Announces New Great White Shark Location – “Open For Conservation”

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SharkDiverNZ.com -- Press Release Distribution 2/15/2010
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Shark Diver New Zealand is currently on hold while parent company Shark Diver makes necessary changes to websites and working partnerships in the region. Please stand by.

The revelation that one of the operations on site has a second commercial vessel that engages in commercial shark finning was a non starter for us. We'll keep you updated as new, conservation minded operations start here.

Shark Research Isla Guadalupe - Complex Emotional Data

Science is not always pretty. Field science even less so. The headlong rush to extract data from big charismatic mega fauna like the white shark has lead us to a real debate within the shark community over invasive tagging methods.

SPOT tagging is a questionable method of tagging whites that involves catching them with baited hooks and attaching a "drilled on" dorsal tech package. The argument is these packages last longer and deliver more data to researchers which is then used to protect the species.

We have been supporters of this method until recently.

Unfortunately when reviewing videos of SPOT tagging, one comes to the conclusion that these efforts are in dire need of set protocols that do less invasive harm to magnificent breeding aged animals. The loss of just one of these animals through invasive research would be a major blow to the entire western pacific population.

At no point should anyone on this team be lacking for any contingency, seconds count, and the lack of basics, like support tires for this animal, multiple and conflicting directive voices, and a fresh sea water tube that is 10% effective is appalling to watch:



More from the Dorsal Fin Blog.

The changing impact of whale shark tourist expenditure

An updated paper on the shifting financial impact of whale shark tourism in Australia's Ningaloo region is a must read for those within the shark diving industry.

Abstract

In this paper, we examine the expenditure of whale shark tour participants at Ningaloo Marine Park, Western Australia; the location of the world's first whale shark tourism industry, established in 1989. We demonstrate that in 2006, participants' expenditure in the region was $894 per trip, total expenditure was $6.0 million (all figures are in Australian dollars), and between $2.4 and $4.6 million would have been lost to the region if whale shark tourism did not exist. Our measure of participants' expenditure is substantially lower than the calculation of $2370 per participant from a previous study of whale shark tourists using data collected in 1995. We argue that this is consistent with a change in the types of wildlife tourists that participate in an activity as the industry reaches the point of consolidation. Our results also suggest that using old data to forecast wildlife tourists' expenditure needs to take into account the industry's stage of development. Copyright © 2009 John Wiley & Sons, Ltd.

Paper Here.

Hawaii Shark Diving - Shark Diving Bill "Thrown Out"

This mornings text message from Hawaii:

"FYI, The bill (banning commercial shark diving in Oahu) was thrown out and deferred to state."

Proving that Hawaii City Council members are not the same as those in Maui, Council members decided, after receiving an unprecedented amount of interest in the form of letters, emails, Op-Eds, and phone calls about commercial shark diving on Oahu to kill the issue before them and "punt it" back up to the state level and Rep Gene Wards office.

To refresh your memory the ongoing saga over the fate of commercial shark diving looks like this, dates are approximate:

1. March-2009 Rogue commercial shark diving operation decides to open cage diving operations Hawaii Kai neighbourhood and kicks off a political brush fire.

2. April-2009 Incorrectly sensing a political gain, Rep Gene Ward uses this regional back lash to propose legislation to prohibit all shark diving in Hawaii.

3. April-2009 Several dubious and linked anti-shark diving websites spring up with loose ties to Cyber Diver Network, and Rep Gene Wards office.

4. May-2009 Long term U of H shark study by Carl Meyer et al shows sharks that are being interacted with 3 miles off shore are not habituating to vessels and following them back into shore as was charged by Rep Wards "Shark Taskforce." Wards office decides to ignore and discredit the study as bogus science, stirring up further controversy.

4. August-2009 Meetings are held with the commercial operators and Rep Gene Ward, pressure in the form of pro-shark diving business owners call Wards office, the theme of "it's the economy stupid" resonates.

5. August-2009 Maui City Council members watching Rep Gene Wards grandstanding, decide to ban shark diving. Shark diving that does not exists on Maui at this time. As one person states "they might as well ban time travel as well."

6. September-2009 Maui's bill passes.

7. September-2009 Rep Gene Ward, sensing a hard political fight over the commercial shark diving issue, punts local issue of banning cage diving on Oahu down to Oahu City Council members.

8. September-2009 Oahu City Council members propose bill, receive sharp backlash from community, they quickly realize this is a "no win" bill on many levels.

9. October-2009 Oahu City Council members throw bill out and refer the entire issue of commercial shark diving and the fate of 40,000 seasonal shark diving tourists back to the state.

10. October-2009 Saga continues.

Group Launches National Shark Tagging Effort

All we can say is - "Ach Aye, Kudos Lads!"

The Scottish Sea Angling Conservation Network (SSACN) recently announced the launch of the Scottish Shark Tagging Programme (SSTP) which will provide a central location for gathering the data necessary to fight for the protection of the shark, skate and ray species found within Scottish coastal waters.

Over the past few years, the stocks of many species of shark in Scottish waters have become severely depleted and the SSACN has long campaigned for Scottish governments to provide real leadership outside the commercial sector and work with them to develop programmes aimed at regenerating the stocks of interest to recreational sea anglers.

So far there has been a high degree of reluctance to act, though now the EC has recently adopted a Community Plan Of Action for sharks which places the emphasis on the member states to gather data for a deeper understanding of sharks and their role in ecosystems and fisheries, there may be additional pressure to do so.

“The SSTP programme will help fill many of the serious gaps which remain in our understanding of shark biology” said Ian Burrett, SSACN's Project Director, “Tagging is one of the few non-destructive assessments of sharks available and will help provide some of the much needed data for species migrations, growth rates, stock populations, make-up and fluctuations.”

The SSTP will initially combine the current Common Skate and Tope data gathering efforts of SSACN and other groups, and then extend them to include additional species such as Bull Huss, Spurdog and Rays. The resultant data will be made available via an interactive website to allow immediate feedback regarding previous captures, distances travelled etc.

SSACN will be running a series of special tagging events each year to promote the tagging programme and to raise the awareness of the need for shark protection.