Worldwide Shark Decline

My name is Scott Seamone.  I have grown up in Halifax, Nova Scotia my entire life. Since I was a child the marine waters surrounding this city have fascinated me. The ocean has provided me with some of the most thrilling, yet relaxing experiences of my life. My mother teases me that the blue veins running through my body are filled with seawater, not blood. The ocean is my passion, and because of this, I decided to study Marine Biology in university. I wanted to learn more about the world that has strongly influenced my lifestyle.

Fig 1. Growing up in Halifax, Nova Scotia, I was privileged to have the Atlantic Ocean as my backyard. Location: Halifax, Nova Scotia

At the end of this semester I will graduate with a BSc in Marine Biology. My studies at Dalhousie University have been a true revelation of the ignorance and greed of the human race. Recently, it has been estimated that close to 7 billion people live on Earth, while approximately 40% live within an hour driving distance to the ocean. At first, I was shocked when I learned how many people live so close to the sea. However, the more I think about it, the more I understand. The ocean is a reservoir for opportunity, escape, freedom, survival, and beauty. The list of words used to describe the marine world is limitless. Unfortunately, it appears that humans believe our oceans resources are also limitless.

Humans have demonstrated our ability to exploit and exhaust marine resources. Whaling and cod fisheries are prime examples where unsustainable practices have pushed species close to extinction. Sadly, we do not learn from these mistakes; rather we move on to new and plentiful species. Sharks, considered one of oldest extant vertebrate species on the planet, are another type of wildlife that humans are driving to extinction. Many shark populations are decreasing at an alarming rate due to unsustainable fishing practices, and additional stressors such as pollution and habitat degradation. Numerous species of sharks are listed on the International Union for Conservation of Nature World Conservation Red List as threatened, vulnerable, or endangered of becoming extinct in the wild. These declines are largely attributable to the demand for an Asian delicacy – shark fin soup. The delicacy is mostly supported by the practice of ‘shark finning’, which by definition means cutting off the fins of the shark, and disposing the carcass at sea. Often times, the sharks are alive when their fins are removed, dubbing this practice as extremely controversial around the world.

Sharks are not only targeted for their fins, but are also caught as bycatch in most fishery types including longlines, trawls, and gillnets. Bycatch is defined as the incidental catch of a non-target species and is a major contributor to declining shark populations. Historically, sharks were considered a non-valuable fish and were usually tossed back into the water. However, due to the high demand for their fins, bycaught sharks are now mostly landed. Nevertheless, the sharks that are discarded at sea often cannot withstand the coinciding stress and most often die upon release. This makes sense, as these animals are often jam-packed in large nets, pulled from great depths, and left on the decks of fishing vessels for an extended period of time before they are put back into the water.

Fig 2. It was an unreal opportunity to see the oceanic blacktip shark up close in person. It is almost impossible to believe how something so powerful can be so sensitive and vulnerable to human disturbance. Location: Aliwal Shoal, South Africa

The natural ability for a given species to recover from human disturbances is estimated by a population parameter known as their rebound potential (r-value). This variable is derived from a combination of the major life history traits (i.e. rates of maturity, fecundity and growth) of an organism. A species with a high rebound potential is more likely to recover than a species with a low rebound potential. Sharks generally have an extremely low r-value due to late sexual maturity, low fecundity and slow growth rate. For this reason, if we continue to exploit sharks beyond their intrinsic ability to recover, we will drive these animals to extinction.

It is estimated that sharks first swam in marine waters approximately 425 – 455 million years ago. From early fossil records to the species we see today, sharks inherently have been equipped with predatory behaviors that have shaped marine food webs. As the top predator of most marine communities, large sharks exert top-down control of their respective food webs. They depress populations of mesopredators (medium-sized predators) through direct predation, and by inducing antipredator avoidance behaviors. It has been suggested that this top-down control of predators helps to maintain ecosystem health by relieving stress on resource species (i.e. shellfish, forage fish, plankton). Resource species are the prey of mesopredators, and are the foundation of marine food webs. By removing large sharks from marine ecosystems, mesopredators are subsequently released from predation and devoting time and energy to antipredator behavior. As a result, the population of these medium-sized predators explodes. Consequently, the intensity of predation on resource species will increase and populations may drastically decline, negatively changing the structure and dynamics of marine ecosystems.

There are several options for you to help without causing havoc to your daily routine. You can support sustainable fisheries that minimize bycatch. There are iPhone applications (Oceanwise and Seafood Watch) that inform consumers on bycatch-friendly seafood. Ask your seafood server (restaurants, grocery stores, markets) about sustainable seafood products. If they are unaware, chances are the awkwardness of being unable to answer will encourage him/her to find out more information for future reference. I challenge you to investigate these issues on your own. The facts are out there and are easily accessible.

Fig 3. I made eye contact with this prehistoric looking animal – the sevengill cowshark. Not once did I feel threatened during this experience. In fact, it was by far the greatest moment of my life. Location: False Bay, South Africa

Approximately 2.8 billion people live within 100 km of the ocean. If each individual puts forward a small effort, this will amplify into a large group impact towards sustaining our marine waters. We must conserve the world’s shark populations so our children can enjoy a healthy ocean, and experience sharks in more ways than simply viewing their fossils behind the glass at the local museum.

Help make a difference:


Barnett, A., et al. “An overview on the role of Hexanchiformes in marine ecosystems: biology, ecology and conservation status of a primitive order of modern sharks.”  Journal of Fish Biology 80.5 (2012): 966-990.

Carrier, Jeffrey C., John A. Musick, and Michael R. Heithaus. Sharks and Their   Relatives. Biodiversity, Adaptive Physiology, and Conservation. Boca Raton  (Fla.): CRC, 2010. Print.

Ferretti, Francesco, et al. “Long-term change in a meso-predator community in response   to prolonged and heterogeneous human impact.” Scientific Reports 3 (2013).


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2 Responses to Worldwide Shark Decline

  1. Joan.Richard says:

    We need more education like this about where our food comes from. Only when we practice ethical consumption will the market change.

  2. Michael Schlech says:

    Great article. Sustainability is a hot topic these days yet it seems to go unnoticed by the majority of the population. With more blogs like this we may be able to change things.

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