Giant Bluefin tuna are the largest tuna species in the oceans and can attain weights over 1500lbs. Photo by Bill Boyce
The cold clear green water got my heart started as I turned to face the oncoming fish. I saw the first one rise out of the green abyss, gliding, silent and purposeful, eyes wide, mouth slightly agape, the dorsal fin suddenly raised, pelvics lowered and the gills flared as the fish inhaled a slowing sinking herring. It turned sharply and the afternoon sun caught its bronze flanks and the water around the fish was momentarily lit in a golden glow. The fins and tail cut the surface and the bubble stream followed the fish down into the green depths. Then another one rose up and another and then several came in a rush to suck down the drifting herring…..one came so close I could see the scale detail on its cheek and it popped its gills the size of trash can lid. Then a blur of bright yellow finlets as the huge fish passes. The average size of these giant bluefin tuna is 800 pounds. Giants… is the correct terminology. These fish are up to 12 feet long with a 7 foot girth and several that swept by me were in the 1,200 pound range. I panned my video camera on them as they swam past me gobbling up the chum that kept them close to the boat.
In the late summer and fall these remnants of a once larger population of bluefin tuna take advantage of large schools of herring spawning in the Gulf of St. Lawrence and around Nova Scotia, Canada. They put on weight prior to undertaking lengthy migrations south to the Gulf of Mexico or swim across the Atlantic to the Mediterranean.
I was on board the “Fin Seeker”, a 50 foot lobster boat from Wedgeport, owned by Eric Jaquard and crewed by sons Joel and Camille who had a permit to take 5,000 pounds of bluefin this season. Eric was very selective about what tunas were taken (only five in six days of fishing) and the rest were all tagged and released for science. Those fish that were harvested were meticulously cleaned and iced down before being shipped by air to waiting markets in Japan.
There are two research efforts currently under way in Nova Scotia, one being conducted by Dr. Barbara Block of the Tuna Research and Conservation Centre, based at the Stanford University’s Hopkins Marine Station, please visit: http://tunaresearch.org/. The GHOF gives this research organization a small grant to assist with this effort which is based at Port Hood in the northern district of Cape Breton.
The other research effort is being conducted by Dr. Molly Lutcavage of the Large Pelagics Research Centre based at the Natural Resources Conservation Dept , University of Massachusetts Amherst, please visit: http://tunalab.org/. Dr. Lutcavage’s team were based in Wedgeport in the southwest. The plan was to visit both operations and conduct interviews with respective scientists and crew. Both teams have spent the last decade in the field tagging and tracking the migrations of the bluefin tuna along the eastern seaboard of North America and across the Atlantic to Europe.
Their results have indicated main feeding areas, spawning areas, trans-Atlantic migrations and have assisted in the sometimes controversial management of this species by ICCAT, the international organization that allocates quotas and attempts to regulate commercial fishing for this valuable nomad of the ocean.
This is not my first brush with giants. In January 2003, I did a shoot with Barbara Block off Cape Lookout, North Carolina while she was tagging medium sized and giant bluefin tuna, for my TV series “Portraits from the Deep”. “Giants” are individual tuna that are over 315 pounds and this species grows to at least 1,500 pounds. The previous year I had visited the tuna traps or “almadraba” in Tarifa and in Barbate on the southern coast of Spain. Here I dived with the captive tunas caught in land based traps and witnessed the harvest of 300 giants in a 2000 year old ritual that began with the Phoenecians and then the Romans.
Guy Harvey is working on a Bluefin Tuna Documentary
Long before the species became desirable food, the bluefin tuna was fished by recreational anglers out of Wedgeport, Nova Scotia from 1935 until 1975 in a famous tournament called the Sharp Cup which attracted international teams from many countries. Of these large, powerful animals Charles F. Holder said “Weight for weight, they have double the fighting power of a tarpon. They are living meteors that strike like whirlwind and play like a storm”. Some say the recreational fishery, catch and release only, should be revived in Nova Scotia.
In the early years this species was fished sparingly by harpoon, some were caught on line for canning as they were more of a “nuisance fish” damaging gear set for herring and mackerel. In the mid 1970s demand in Japan for the fresh tuna grew exponentially and so fishing effort for bluefin tuna was greatly increased. Industrial scale long lining and purse seining were added to the traps and harpoon fishery so the populations of bluefin tuna declined to the present day levels where some authorities consider the species close to commercial extinction. However, the researchers are of the opinion that if the quota system is properly regulated (as it certainly appears to be in Canada) then this fishery has the potential to be sustainable in spite of the huge worldwide demand for bluefin tuna sushi.
Along with my documentary producer and camera man, George Schellenger, I spent three days with the crew of the “Fin Seeker” as willing anglers using ultra heavy tackle caught, tagged and released some two dozen giants. Pop-up archival tags were deployed on many fish following capture. The hook was removed using a de-hooking device and the tunas swam free. The PATs record the migration of the tunas as well as depth and temperature data along their routes. A special physiological adaptation called a counter current heat exchanger allows metabolic heat to be kept in the body and not lost through the gills thus maintaining the body temperature well above ambient temperatures, allowing faster swimming speeds in areas rich in prey species. Being “warm blooded” these giant tuna, often called “super fish”, can penetrate the cold northern latitudes and dive to great depths in search of fish and squid.
The winter is coming soon and bad weather arrived so I was unable to visit the Tag–a-Giant research team in Cape Breton. They will be back next year and I will complete the documentary shoot with them at that time. Meanwhile, I will be completing the story of the life cycle of the bluefin tuna including interviews with other research efforts to study aspects of the early life history of this long lived super fish.
What a thrill to spend an hour in the water with these magnificent creatures and to capture their brilliant colours and movement for my next work. These are big fish and I will need to prepare a big canvas. The adventure continues….
It is our collective responsibility to conserve the marine environment and maintain the biodiversity of the planet.
—Guy Harvey
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit:www.guyharveysportswear.com
The sale of Guy Harvey Sportswear supports the marine resource in many different ways with its sale of each Guy Harvey product, a contribution is made to the GHOF
During the spring sampling season, three ongoing projects of the Florida Program for Shark Research at UF’s Florida Museum of Natural History, one in collaboration with researchers from Florida State University (FSU), focused on the distribution and movements of adult and subadult sawfishes in the southern portion of its Florida range.
We produced a survey of the waters surrounding U.S. Navy properties in the Key West region in order to determine the current status of sawfishes in those areas for the U.S. Navy/U.S. Army Corps of Engineers. Because of obvious security constraints, we were the first fish biologists to sample in these waters in decades.
Concurrently, in conjunction with Dean Grubbs and fellow FSU scientists and the John Carlson of the National Marine Fisheries Service, we sampled the middle and lower Keys and Tortugas region and Florida Bay, catching and satellite tagging eleven sawfishes. Satellite tags give long time and distance of movement information and we hope our tagging will help us better understand seasonal horizontal (up and down the coast) and vertical (depth) movements of the critters.
We also caught and multiple tagged two large adults in Florida Bay, the tags being traditional “spaghetti,” satellite, and active acoustic models. The last allowed us to manually track the minute to minute movements using a receiver held under the boat. Our first saw was “lost” within the first hour or so as it gave us the slip by scooting over a shallow bank, then boogying before we could detect its signal. Having learned our lesson, on our second capture we got in 38 hours of tracking over three days, including day-night comparisons. The sawfish moved about in deeper channels by day, then moved onto shallow, seagrass beds by night. It chose the same shallow grassy area on successive nights, demonstrating some short-term site fidelity. Next spring we plan to initiate placement of underwater listening stations on the bottom and tag the sawfishes with passive acoustic tags. These tags will leave a unique “bleep” on any receiver as the sawfish swims near, allowing us to track localized movements over longer periods and larger areas. We also will continue to satellite tag these and other sawfishes.
While sampling for sawfishes we also caught many sharks and rays. All of these animals also were measured, sexed, sampled (tissue for DNA) and tagged as part of ongoing studies of their biology and movement patterns. We also continued our work in Indian River Lagoon (IRL), where we began tagging young bull sharks with spaghetti and passive acoustic tags in a “new” region for us, the St. Lucie River estuary. This work is being done with our colleague, David Snyder, of Continental Shelf Associates. We also continue to download data from our underwater array of receivers in Mosquito Lagoon, Banana River and the northern IRL, where tagged bull sharks and rays still roam.
During this time period we put 5000 miles in land travel on the Guy Harvey adorned Hell’s Bay and God only knows how many sea miles on our faithful vessel!
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit:www.guyharveysportswear.com
The Guy Harvey Ocean Foundation recently presented a $100,000 donation to the Guy Harvey Research Institute (GHRI) at Nova Southeastern University during a ceremony at the new Guy Harvey Inc. world headquarters in Davie, FL. A significant part of these funds were raised from the sale of Guy Harvey sportswear. You may not know this, but you, the Guy Harvey customer helped provide these funds with your last Guy Harvey clothing purchase. Money is raised for ocean conservation efforts from the sale of every Guy Harvey shirt, Guy Harvey sandal, Guy Harvey hat, Guy Harvey belt, Guy Harvey jacket and all Guy Harvey clothing items. This $100,000 will be used to support the ongoing fishery research projects at the GHRI.
Photo, from left to right: Dr. Mahmood Shivji, Director of the Guy Harvey Research Institute; Guy Harvey; Dr. George Hanbury II, President & COO of NSU; Steve Stock, President of Guy Harvey Inc. and the GHOF; John Santulli, VP Facilities Management, NSU; Dr. Richard Dodge, Dean of NSU’s Oceanographic Center
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit:www.guyharveysportswear.com
It was a beautiful winter day with a light north easterly wind, providing for calm conditions in the protection of West Bay, anticipating the deployment and sinking of the USS Kittiwake here in Grand Cayman. Accompanied by Jessica and Alexander, my kids who are both keen divers, we anchored outside the perimeter marked off by the Department of Environment and the Marine Police. Regular updates on the VHF radio gave us an idea of the history of the ship and the projected sinking schedule. The details of the ship’s construction and service can be found on a number of dedicated websites.
Pumping sea water into the hold began around 10:30 a.m. At approximately 2:25 p.m. she started sinking rapidly, stern going down and listing sharply to port. I bet a number of people were holding their breath as it seemed she would topple over in spite of all the preparations, and then appeared to sink upright as air rushed from the port holes and open hatches.
GHRI and GHOF collaborate with other research organizations to better understand tiger sharks
I am a great supporter of artificial reefs, even in a coral reef environment such as ours. Socio economic studies of artificial reefs in Florida demonstrate hundreds of thousands of dollars generated by individual artificial reefs from diving and sport fishing activity each year. As it took about 8 years for this project to be executed, perhaps we, the diving community, the Cayman Island Tourism Association and the Cayman Island Government should immediately start the search for another suitable ship for an artificial reef to be the successor to the “Kittiwake”. I will put my money where my mouth is and volunteer my Guy Harvey Ocean Foundation (GHOF) to assist in locating and funding the next ship.
Talking of mouths, the tiger shark has a big, wide mouth adapted to ripping large chunks out of dead, decaying marine mammals and has large serrated teeth, with re-curved tips designed like a can opener to feed on turtles. Tiger sharks have been of great interest to me and my research arm, the Guy Harvey Research Institute (GHRI). We have tagged or sponsored the electronic tagging of 41 tiger sharks in the north western Atlantic in the last two years. Each SPOT (Smart Position or Temperature Transmitting) tag deployed to the dorsal fin of the shark costs about $2,500 and then another $500 for the satellite time and monitoring. We have tagged tigers: 28 in Bermuda, 7 in the United States Virgin Islands, 4 in the Bahamas and just recently two in Grand Cayman.
The GHRI and GHOF collaborated with a number of research organizations in each of these island territories, which is why the project has been so successful. Tiger sharks, we are now discovering, make seasonal migrations spending much of the warm summer months cruising in the open ocean, often in very deep water, looking for migrating turtles and feeding opportunistically on dead floating animals such as dolphin, whales, fish and sea birds. In the winter, they move into the reef environment around oceanic islands in the Caribbean and Bahamas and will come into very shallow water targeting rays, fish and lobsters.
The Overseas Territories Environmental Programme, with assistance from the DoE, has sponsored a shark population analysis study in the Cayman Islands. Being particularly interested in tiger sharks here, the GHOF sponsored SPOTs when the team caught and tagged two tigers in early December 2010. Both were caught at night in North Sound and successfully released bearing an internal sonic tag and external SPOT attached to the dorsal fin. Each time the animal swims at the surface, the tag sends a signal to a satellite giving its position very accurately. The team was also able to tag Caribbean reef sharks, black tip sharks and nurse sharks—all caught at night in North Sound.
Divers and photographers have been safely interacting with tiger sharks for decades and have watched in horror as their numbers and those of other pelagic migratory sharks have been annihilated for the last three decades in the shark fin trade that threatens to clear all sharks from the planet.
If you are lucky enough to see one of the tiger sharks we have tagged, please send me or the DoE a photo of the animal. If you happen to catch one while out fishing, then please release the animal alive (as you should release all sharks alive) responsibly. In time, all shark species around Cayman will receive the protection they surely need under the new Conservation Law.
Fish responsibly, dive safely.
— Guy Harvey
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit:www.guyharveysportswear.com
The stripy and pug-nosed tiger shark gets little coverage or respect in the world of media shark stories compared to the idolizing attention showered on species such white sharks and whale sharks. And when they do receive the occasional mention, tiger sharks bear the brunt of disparaging descriptors such as “garbage cans of the sea” just because a few individuals of the many thousands killed around the world have been found with indigestible, man-made objects such as a beer bottle, tin cans, chicken wire in their stomachs. Tiger sharks do indeed have broad diets and are opportunistic feeders, but the reality is they consume almost entirely their normal prey of fishes, turtles, marine mammals, and even large invertebrates. The discovery of man-made objects in their diet is rare, and it does a magnificent apex predator injustice to assume tiger sharks make a habit of wandering around near human population centers focused on scooping up our garbage that ends up in the sea. On the contrary, ongoing research being conducted at the Guy Harvey Research Institute and Guy Harvey Ocean Foundation (GHRI/GHOF) on tiger shark migrations is shedding new light on how remarkable and environmentally flexible these amazing sharks are.
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.
What have we found so far?
Sharks that we outfitted with satellite tags in Bermudian waters are providing exceptional information about their long-term migratory behavior. We have been fortunate to be able to follow these tiger sharks for a record length of time (12-17 months and counting), and are discovering fascinating information about their seasonal movements. The migratory tracks of two sharks are shown as examples. Please visit the GHRI web site: http://www.nova.edu/ocean/ghri/tshark.html to see long-term tracks for other tiger sharks.
In brief, the sharks left Bermuda in the fall of 2009 as the waters cooled and made notably direct pathways to the Bahamas or Caribbean, where they spent 6-8 months in close association with island habitats. Then starting in the spring of 2010, the tiger sharks reversed course showing highly directed migrations northwards, moving beyond and often east of Bermuda and staying well out in the open ocean. In two instances, the batteries on the tags have lasted over 17 months and have revealed a consistent migratory pathway back to the Bahamas starting in the fall of 2010. What is also amazing is that after their pelagic sojourn these sharks have returned to locations in the Bahamas really close to where they were hanging out a year ago! Who gave them a GPS?
These migratory patterns makes one wonder what the sharks are doing so far out in the Atlantic Ocean after spending approximately half a year acting like reef sharks tightly associated with island habitats in the Bahamas and Caribbean. Something must be seasonally attracting these sharks into the deep open-ocean far offshore. We’re guessing it is not indigestible man-made garbage. Are they out in nearly the middle of the north Atlantic for 2-4 months for mating? For feeding on migratory prey such as turtles? It’s still an open question. Notably, however, these tiger sharks are displaying a remarkable ability to drastically switch their habitats comfortably, using shallow, coral reef environments for part of the year and completely open-ocean, deep environments for the other part with rapid travel in-between. Few other shark species show this flexibility in the habitats they can use.
Based on these initial but novel findings, we are continuing this study in additional places to get a more detailed picture of tiger shark movements in different parts of the world. Our hats are off to these stripy, majestic fishes for their astonishing migratory abilities!
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com
This New Guy Harvey Florida license plate will help fund The Guy Harvey Ocean Foundation
On Wednesday morning I attended several presentations at the ASA meeting including one by Nick Wiley the executive director of the Florida Fish and Wildlife Conservation Commission. That afternoon I drove up to Nova Southeastern University, home of the Guy Harvey Research Institute, to attend the Guy Harvey Ocean Foundation (GHOF) board meeting. A major part of that meeting was to review the various Gulf of Mexico research proposals. Guy Harvey teamed up with AFTCO and our partners to raise $500,000 from the sale of two unique Guy Harvey T-shirt designs. The charge of the GHOF board is to insure that this money is spent in a way that will provide the most benefit to marine life in the Gulf. On Wednesday night I attended the annual GHOF fund raising dinner, where among other things the new Guy Harvey car license plate was announced. Our plan is that sales of this new plate will generate some $1 million to support the work of GHOF.
On Thursday morning after giving my government affairs report to the ASA board of directors, I drove up the coast, visiting a few AFTCO & Guy Harvey customers along the way. I attended the opening of the Hubbs-Sea World Research Institute (HSWRI) east coast research station in Melbourne Beach, which now provides an east coast facility to add to the longtime HSWRI marine research center in San Diego, CA. At Melbourne Beach we will be developing a hatchery operation for red fish, snook, seatrout and red snapper along with providing a base for marine stranding operations, turtle research along with various other Indian River Lagoon and east cost ocean issues. SeaWorld, as it has from its very beginning, continues to quietly, unselfishly and without fanfare or control, support the good work of the HSWRI.
Bill Shedd, Don Kent and Milt Shedd at California hatchery in 1999. HSWRI plans a similar project for Melbourne Beach, Florida
On Friday after breakfast with Don Kent president of HSWRI, I attended the HSWRI board meeting with Florida board members at SeaWorld in Orlando with a video conference connection to fellow board members in San Diego. As Chairman of the Board of HSWRI, I usually run the board meetings from San Diego, so it was interesting to be at the other end of the line. For 47 years the HSWRI has been doing important work to benefit the ocean realm. That is just the way Dad intended it to be.
Friday evening I drove back down from Orlando to Ft. Lauderdale to attend the Ft. Lauderdale Boat Show on Saturday. The Guy Harvey team had set up a booth with a beautiful display of all Guy Harvey products including the Guy Harvey shirts and other Guy Harvey clothing we produce. Much can be learned spending a day in the jammed packed Guy Harvey show booth talking to reps, customers and consumers about the Guy Harvey sportswear brand. Taking care of some business at the show was a great way to end the week.
— Bill
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit:www.guyharveysportswear.com
It’s official, Guy Harvey is a Facebook phenom. He might not have achieved Ashton Kutcher’s e-society geek status with millions of Twitter followers but on October 11, at 10:53 EST, his fanbase on the Facebook rocket ship blasted past the 200,000 mark. Guy’s popularity began 20 years ago with his fabulous marine art and then slowly blossomed with his ubiquitous t-shirts seen at every fishing dock, tournament, and beach bar bungalow. But he never would have imagined that in less than two years hundreds of thousands would be following him online.
“It’s an amazing phenomenon,” Guy said, “especially seeing all the young people who are attracted to my artwork, apparel, and conservation efforts.”
In fact, the Guy Harvey popularity surge toward high-school and college kids is due in part to the explosion in social media and his message of ocean conservation which resonates so strongly with today’s youth. Ten years ago the Guy Harvey demographic was mostly grizzled fishing dudes with sun-faded Guy Harvey t-shirts stained in mahi-mahi blood and guts. Today, that paradigm has shifted dramatically. Sure the hard-core fishermen are still solid fans but women and kids are identifying with Guy Harvey more and more as is evident with the meteoric growth on Facebook.
“We have a tremendous amount of pride in the quality of our products,” Guy said, “but it’s our message of conserving our oceans for future generations that is our core mission. I believe that’s one of the biggest reasons for our growing support.”
The Guy Harvey Ocean Foundation and the Guy Harvey Research Institute have spent millions of dollars on scientific research to help protect endangered marine species. Perhaps Facebook, Twitter, and other social media networking will help to perpetuate the vital conservation efforts of Dr. Guy Harvey.
By Fred D. Garth
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com
The Guy Harvey Ultimate Shark Challenge is shown here as seen on the NBC Nightly News with Kerry Sanders. This effort supported by the Guy Harvey Ocean Foundation encourages the release of all sharks and involves a satellite tagging component to help determine shark movements.
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com
We were honored to be featured on CNN recently for our Save Our Gulf fund raising effort. Guy Harvey and AFTCO Bluewater are dedicated to keeping our oceans and waterways clean and safe for marine wildlife. CNN picked up on the fact that our cause marketing efforts are authentic and part of the DNA of who we are. The following copy is text from CNN’s blog.
Every year, companies spend billions of dollars on good causes. But in this challenging economy, corporate giving is taking on a new level of importance.
“Cause Marketing” is a term coined in the 1980s. But today, it’s becoming a popular method for companies to get through tough times, and build their brands.
We are accustomed to big companies like Pepsi and Nike getting behind global causes, but smaller businesses can get in on the action as well.
I profiled a small company, Guy Harvey Inc., that reports record revenues in 2008/2009, at the height of the recession, and management credits Cause Marketing with the success.
A pioneer in this field, Harvey says the cause started as an authentic desire to save the world’s oceans, and became a business strategy much later on.
“Sometimes you need to have money to do the good,” says Harvey, “and I feel good to be in this position now, to have the influence to really make a difference.”
Carol Cone, an expert on marketing and the author of “Breakthrough Nonprofit Branding” says companies spent more than $9 billion in 2001 on charitable causes. The challenge, she says, his ensuring they meet their business objectives at the same time.
According to Cone, recent surveys show six out of 10 consumers say they are more loyal to a company that backs a cause. Social media is an important factor in the success of cause marketing. Cone says, “By word of mouth and social media, consumers can find out what a company truly stands for. Consumers want to be in control, they want to feel empowered to be good, so this really resonates.”
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com
For the longest time after the 1975 blockbuster “JAWS” gave us a spine-tingling ride, there was an often used saying that “the only good shark is a dead shark”. This man- against-beast thriller and its many progeny shark horror flicks still pervade the public’s psyche, anointing all sharks as human-eaters and keeping many beach-goers out of the ocean.
The public and media’s morbid fascination with sharks as killing “machines” continues today. There is a steady stream of media coverage when fishers catch and drag back a large shark for photo-ops. In some minds, catching and killing a large shark is almost heroic and fashionable, and a testament to man’s superiority in the “battle” against the beast.
Meanwhile, the enormous toll taken on shark numbers worldwide due to indiscriminate fisheries continues unabated. All this shark killing causes some to wring their hands in anguish about longer-term ecological impacts. Others say “what’s the big deal if sharks are killed?”
Who’s right? Should we care if many of the oceans large sharks are exterminated? Is there really enough of an impact on the marine environment to worry about?
New studies show that sharks also influence the behavior of their prey. Photo credit: B. Watts
It seems intuitively reasonable that sharks, as top-level predators, play an important role in maintaining stability in the ocean’s food chain. Most people objectively or “in their gut” understand that life on earth is a series of complex interactions, with connections through food webs. Simply put, species at the top of the food chain eat species in the middle of the food chain which in turn eat species on the bottom of the food chain. And therefore, changes in the abundance of one community segment will affect the other segments. In fact, recent studies have indeed documented that overfishing of large sharks (the apex predators) has resulted in numerical increases in populations of their normal prey such as smaller sharks and rays (known as mid-level predators or mesopredators) in a phenomenon called “predator release”. In turn, the mesopredators are overeating their own smaller prey such as bay scallops and bony fishes even lower on the food chain. Scientists call such effects that ripple down the food chain “trophic cascades”.
Still, will it really matter all that much if we overfish sharks? Won’t some other large predatory species, such as billfish and barracuda, take over for sharks at the top of the food chain and keep the food webs functioning normally?
If only the interconnections of life were that simple…….
New studies in Shark Bay, Australia by Dr. Mike Heithaus and his team at Florida International University are showing that in addition to playing important roles in the food web by direct predation (or lethal) effects, including keeping prey population sizes in check, sharks also play a large role in maintaining the normal functioning of marine ecosystems by— get this— influencing the behavior of their prey!
How does this prey behavior to ecosystem function connection work?
Let’s take the seagrass ecosystem as an example. Recreational fishers and patrons of the marine outdoors know that seagrass beds are critically important nursery areas for juveniles and sometimes even adults of all types of fishes and invertebrates. The health of seagrass ecosystems is woven into an intricate balance with larger animals such as sea-cows, sea turtles and birds that obtain their sustenance in seagrass beds, either by directly grazing on the seagrass or eating smaller creatures living on the seagrass or in the surrounding sediment. These large animals (mesopredators) are in turn, prey for tiger sharks.
Let’s connect the ecosystem dots: Dr. Heithaus and colleagues have documented that sea-cows, sea turtles and birds avoid hanging out in seagrass beds when tiger sharks are seasonally present in Shark Bay, and jump right back in to devour their favorite foods after the sharks leave in winter. Makes survival sense doesn’t it? What this shows is that the presence of tiger sharks causes the mesopredators to change their habitat-use behavior to avoid the risk of being eaten. And this risk-avoidance behavior keeps the seagrass beds and their inhabitants from being over-consumed.
The take home message is that sharks keep the marine ecosystem in balance not just by directly eating their prey — the role that gets the most attention, but also indirectly by altering the behavior of their prey. The importance of this indirect ecosystem role of sharks is just beginning to be recognized.
We at the Guy Harvey Research Institute, Guy Harvey Ocean Foundation and AFTCO hope that you will keep in mind the delicate balance required to keep our oceans healthy. Please enjoy our marine environment with respect for all of its remarkable life forms. If you catch a shark, enjoy its magnificence, keep its important ecosystem role in mind – and let it swim away.
For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com
I would like to welcome you to the Guy Harvey Sportswear web site. Here we will feature my blog where I will report on expeditions, adventures, and various marine conservation efforts. We will also include various guest bloggers, videos and photos that I believe you will find interesting, whether you are a serious fishing or diving enthusiast, or simply someone who cares about the marine resource, loves living the coastal lifestyle, or just wants to learn more about Guy Harvey sportswear.
I would like to welcome you to the Guy Harvey Sportswear web site. Here we will feature my blog where I will report on expeditions, adventures, and various marine conservation efforts. We will also include various guest bloggers, videos and photos that I believe you will find interesting, whether you are a serious fishing or diving enthusiast, or simply someone who cares about the marine resource, loves living the coastal lifestyle, or just wants to learn more about Guy Harvey sportswear.
