Course:CONS200/2023WT1/White sharks in Atlantic Canada: population dynamics and conservation

Introduction

Over the past decades, populations of predators around the globe have declined in significant numbers as a result of a multitude of negative impacts on the biosphere.One of Earth’s most vital ecosystems experiencing these effects is the Atlantic Ocean, the second biggest ocean in the world, covering approximately one-fifth of the Earth's surface. On Canada’s East Coast, the Atlantic Ocean supports many communities by offering provisioning ecosystem services such as food and natural resources, and on a larger scale, the Atlantic supports the biosphere of all life on Earth by regulating global climate, nutrient cycling, and contributing to biodiversity.

As one of the most productive ecosystems in the world, the ecosystem in Atlantic Canada supports a variety of species ranging from small microscopic phytoplankton to some of the largest animals on Earth such as the blue whale. However, many of these species are under detrimental threat as anthropogenic factors such as climate change, pollution, and overfishing have driven many species populations to decline. One of the most prominent predators in the waters of Atlantic Canada impacted by these anthropogenic factors is Carcharodon carcharias, the Great White Shark.

Adult male great white shark.

Populations of the white shark in Canada’s Atlantic Ocean have been closely observed since their decline was first detected in the 1970s and 1980s to be as high as 73% fewer. In more recent years, these population declines appear to have halted as numbers have been more or less stable and even growing in certain regions. Though these trends suggest that populations may now be somewhat stabilized, many studies reaffirm that there is still an apparent need for immediate conservation measures, even under the situation of abundance increase given the white sharks’ inherent sensitivity to exploitation and low productivity. Through an analysis of the threats towards white shark populations, their causes, the actions currently being taken and their potential effectiveness, conclusions about white shark populations’ current prospects can be made as well as solutions for a more optimistic future for Atlantic Canada’s white sharks.

Species information

The great white shark, Carcharodon carcharias, is one of the ocean’s most widespread predators and is distinctive by its dark grey pectoral fins and white dorsal surface with black tips. These sharks are an important and valuable species globally, as they play a significant role as apex predators in a wide range of sub-polar to tropical seas.

Distribution

Global range of the great white shark Carcharodon carcharias as of 2010.

The white shark is sporadically distributed throughout sub-polar to tropical seas in both hemispheres but is most frequently observed and recorded in waters of the western North Atlantic, Mediterranean Sea, southern Africa, southern Australia, New Zealand, and the eastern North Pacific. Due to recently observed declines in species abundance, the species is currently listed in Canada's Species at Risk Act (SARA) as 'endangered' status.

Habitat

The great white shark populations thrive in habitats of temperate and subtropical waters. They are known to migrate to different regions of preferable conditions with the seasons as well as with age. Young shark pups tend to live in near-shore habitats for warmer water conditions as they mature and later migrate to colder, more open ocean habitats. In Canada, the species has been sighted in the range of northern Newfoundland and Labrador to the southern areas of Nova Scotia and New Brunswick, with occasional appearances along the Pacific coast of British Columbia.

Biology

A male great white shark will reach maturity at around 10 years of age. On the other hand, female great whites reach maturity at around 12 to 18 years of age. Their territory are in the coastal and offshore waters from the subarctic to the tropical regions, but could never be found in brackish or fresh waters. They are found in surface waters and down up to 1280 meters with temperatures ranging from 5°C to 27°C which can be considered a wide range for sharks.

Their reproduction is viviparous, which means that the fertile egg will be retained within the body until they are fully developed, then the shark gives birth to a live pup. Females give birth , on average, to 7 live pups and may only produce 45 pups in their lifetime, implying how they are relatively unproductive as a species. As a juvenile, sharks feed on small fishes and other small sharks. As they mature into adults, their diet consists of bigger prey such as turtles, seals, porpoises, and small whales.

Behaviour in Northern Atlantic

Research conducted in 2021 have shown that some tagged sharks spend the summer months in the southern part of Atlantic Canada before migrating back down to the US waters where they spend most of their time. This is significant toward conservation of White shark in Canada because this shows that conservation efforts toward the North Athlantic’s white shark population need to be a combined effort from both the US and Canada. Most sharks in the North Atlantic stay relatively shallow. Majority of shark in Canadian water stay above 50 meter deep. However, it is interesting to note that they take deeper dive in the US water. While most sharks in the US water stay above 100 meter, there are frequent cases of them diving below 200 meters.

Special Importance

As an apex predator, the Great White shark holds many significant roles in the oceanic ecosystem. One of these roles is to maintain a balanced equilibrium in an ecosystem. This means that they control the population of their prey such as seals, sea lions, and other fishes. This helps ensure sustainability and project the health of the food web. Sharks also hold a crucial role in nutrient distribution in the ecosystem. When they consume their prey, they break down bones and other hard parts and release many of the nutrients back into the water. These nutrients are then consumed by other organisms such as zooplankton and phytoplankton, which are food sources for other organisms in the ecosystem.

The decline or removal of an apex predator, such as the white shark, can cause a physiological and behavioral change in prey species such as seals. An example of this is that seals can be found rafting and moving further away from shore into deeper water. Previously, this would put them at threat of shark attack. However, the decline or loss of sharks in many areas have allowed changes to their behavior. While there are hypotheses that these changes can cause a negative in a species fitness, there has been no research to confirm or deny the hypothesis.

The Great White Shark also holds significant value within many economies around the world. Shark hotspots such as Australia attract thousands of people every year that go to see these amazing creatures. These tourist attractions such as shark diving generate a large amount of profit without any extraction of animals.

Species population trends

The vulnerability of great white shark populations to fishing pressure underscores the critical importance of maintaining strict conservation measures, even when confronted with an increase in their abundance. Historical data from the 1970s and 1980s highlights a stark reality: the removal of hundreds of juveniles resulted in significant population decline, exceeding 60%. This historical context underscores the pressing need for conservation efforts to be nearly 100% effective in order to double the population over the course of 30 years.

Analyses of great white shark populations are equally alarming. Abundance has declined significantly, with estimates ranging from 59% to 89% over just the past two decades. This decline is not confined to a single region; rather, it reflects a global concern. Observations and sightings reveal a dramatic drop in shark populations in Eastern Canada and other parts of the world.

Although recent analyses showed improvement in the abundance of the great white shark population which stabilizes the population number and even grows in specific regions, given the white sharks' inherent sensitivity to exploitation and low productivity, fishery bycatch mortality remains a concern to the long-term sustainability of their populations.

Threats

Humans are the greatest threat to the great white shark population. People hunt them as sport fish, commercial bycatch, and internationally trading their body parts such as their fins. Great white sharks are also curious and tend to investigate boats and other floating objects on the surface of the water, which puts them in an even more vulnerable spot. In addition to being directly caught, human activity has caused habitat degradation, pollution, and climate change, both of which harm the great white shark population .

Climate Change

Climate change is also affecting the species of prey fish that great white sharks hunt. The increased temperatures and changing ocean currents lead to changes in the abundance and locations of the prey that great white sharks rely on, forcing them to adapt.

Sightings of white sharks off Canada’s east coast had been rare, up until 2006 . Due to warming waters, white sharks are becoming more common in the north, as they follow their prey populations. The abundance of seals has greatly increased over the past few decades due to successful conservation efforts. With the high abundances of seals staying up north in colder waters, white sharks have been more commonly spotted near Canada. As water temperatures increase, the geographical range of white sharks will be altered, which increases the difficulty to study and observe these species.  

Great White Shark (Carcharodon carcharias) attacking a fish lure

Fishing and Bycatch

Overfishing has also been a prevalent issue, affecting all marine life and their ecosystems . As the fishing industry continues to grow, larger ships have a greater capacity, increasing the potential for bycatch with larger nets and long baited hooks. A study in 2014 said that between 1800 to 2009, 66% of the recorded white sharks in the US had interaction with fishing gear. Out of this 66%, 41% of these sharks were captured with rod and reel, 13% are fishery dependent, 11% are fishery independent, 11% are harpoon, 11% are gill net, 8% are caught in trawl, and 4% are caught in fish traps or weirs. Harpoon were the dominating factor of shark capture prior to 1980, responsible for the most major shark capture. After 1980, most of the captures were from fishery dependent events. The IUCN Red List of Threatened Species has been re-assessing their extinction risk status, with more than one-third of shark and ray species being at risk because of overfishing .

There is a high number of shark bycatch in the southern US longline fleet, with more than 400 capture per year between 1986 and 2000. This appears to be the most significant fishery capture and mortality in the North Atlantic. This means conservation efforts for white shark in the North Atlantic will also depend on the U.S.

Pollution

Organic pollutants, heavy crude oil, and marine debris are some of the most common pollution found in the ocean. Many of these pollution originated from things such as fertilizer or pest control while the other indirectly came from things such as car emission and forest fire. Despite the origin, these pollutants have had many important impacts toward the health of many shark populations. This pollution usually bioaccumulates within the shark, which means that the amount of pollution grows faster than they can excrete it.

As long lived predators, white sharks bioaccumulate pollutants in their tissue. Some sharks taken from the East coast have been found to have higher levels of PCBs and chlorinated hydrocarbon pesticide than other fishes. While the negative effects of these toxins have not been studied, it is likely that these toxins can negatively impact the reproduction fitness of male sharks, such as compromising gametogenesis or impaired sperm motility. Some research conducted on mammal and other fishes have found that pollutant can also cause neurological disorders, structural damage to organs and gills, and cancer. Some research have shown that organic pollutant can also be pass down to baby shark, showing that some baby great white have a large amount of organochlorine.

Lack of data/information

Another issue with conserving white shark population in Canada is the lack of data. Great white sharks can migrate a long distance and are rarely reported in Canadian water. From 1874 to 2007, only 34 White sharks were reported in Eastern Canada. Due to insufficient data on great white sharks, accurately gauging the recovery potential of the North Atlantic white shark population poses a significant challenge. The scarcity of information hinders scientists from comprehensively understanding the population dynamics, migration patterns, and overall health of these apex predators. As a result, effective conservation strategies and assessments for the potential of recovery for the North Atlantic white shark population remain elusive without a more reliable dataset.

Conservation

Status

White sharks listed under the Species at Risk Act (SARA) as ‘Endangered’ and are illegal to kill, harm, harass, capture, buy, sell, and collect, as of 2011 . The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) has also listed the White Shark. Since 2005, the White Shark has been listed under Appendix-II, which is when a species is at risk of becoming threatened if their trade is not currently monitored. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has also listed the white shark as an endangered species .

Conservation Efforts

The Shark Research Laboratory and DFO are intent on understanding and monitoring White Shark populations to conserve their populations . White Sharks are one of the most highly protected shark species, as they garner a high amount of interest from the public and because of their low population numbers. Since 1993, the DFO has illegalized the act of finning, which is when only the fins are taken. Currently in Canada, there are no laws that reduce White Sharks interactions with fishing gear, including gillnets and deep-water trawls, which can be fatal. White Sharks are sometimes indirectly protected by regulations, such as how hook and line fisheries are not allowed to possess any shark caught, except the dogfish .

The Atlantic Shark Institute examines a great white shark.

There is a lack of information regarding abundance and productivity for white shark populations in Canada, making it difficult to properly evaluate the potential for population recovery . Although, it is assumed that the trends of both the abundance and the North Atlantic population is correlated to one another. History has shown a component of which has declined in recent decades in U.S waters. Thus, the recovery potential in Canadian waters are dependent on the overall recovery in U.S and other North Atlantic waters.

As most captures of White sharks are accidental, the best management approach is the live release of captured individuals to aid with the recovery of White sharks in the Atlantic Ocean. However, there are some management efforts such as implementing regulations and restrictions to keep shark populations in Canada at a healthy level . This includes releasing sharks caught in bycatch, restricting recreational fishing for sharks to be catch and live release, and setting proper commercial shark fishing quotas that will keep populations at healthy levels.

Ever since it was deemed ‘Endangered’ by Species at Risk Act (SARA), the species was protected by the federal Fisheries Management Plan. They implement a strategic framework to steer the conservation and sustainable utilization of marine resouces, facilitate the administration of sustainable fisheries and combing scientific insights and Indigenous traditional knowledge concerning fish species having industry data to regulate optimal harvesting practices.

Having a multitude of angles being put in place to conserve these sharks such as Indigenous individuals, scientific purposes, both ecological and economic factors, this diverse approach leads to a promising start to maintaining a healthy population and supporting sustainable practices, especially within the fishing industry.

Conclusion

White shark populations in the Atlantic have been declining at an alarming rate over the past few decades. Due to their low reproduction rates and vulnerability to exploitation, there is a concern for their population status. They hold significant roles in their ecosystems as apex predators. The decline or removal of white sharks will disrupt the food chain, and overall balance and health of their ecosystems. Bycatch, climate change, pollution, illegal hunting, and overall a lack of information on white shark populations, especially in Canada, are all contributing to status of this species. With the information deficit in Canada for white shark populations, it will be a challenge to provide effective and efficient conservation strategies. Although there are some regulations for shark populations in general and other marine species that are benefiting the conservation of white sharks in Canada, there is an absence of regulations specifically targeting white sharks.