Table 1: Resident sharks species of British coastal waters
Resident sharks (Table 1) can be found along the coast throughout the year even though individuals may engage long distance migrations.
Table 2: Seasonal shark species found in British coastal waters
Seasonal sharks (Table 2) occur in British coastal waters for only part of the year due to seasonal migration patterns.
Table 3: Vagrant shark species found in British coastal waters.
Vagrant sharks (Table 3) are rarely found in British coastal waters and are usually single specimens.
3.0 Shark attacks:
3.1 Shark attacks around the world.
Sharks attack between 50-75 people a year Worldwide, with the number of fatalities ranging between 8 and 12 according to the ‘ISAF’ (International Shark Attack File). The ‘ISAF’ has a record of shark species that have been implicated in shark attacks across the world from 1580 to October 2000. The attacks are categorised as those, which have occurred as a result of an ‘air-sea disaster’ (plane crash or sinking of a ship), non air-sea disaster’ and whether or not the attacks were provoked.
Table 4: Global unprovoked, non air-sea disaster shark attacks by species found in British coastal waters.
Table 4 does not include information relating to, unconfirmed, provoked or attacks that have resulted from air-sea disasters. The justification for this is that this paper is trying to examine the effects of global warming has on the shark attacks on recreational water users.
Provoked attacks occur when a person physically interferes with the shark, an example of this would be trying to stroke the fish while it is swimming and therefore divers contribute most to this statistic.
Air-sea disaster attacks have mainly occurred in the tropical waters and by a limited number of species. By adding these attacks, the above statistics would not reflect the number of attacks on recreational water users.
The number of shark attacks in Table 4 is relatively insignificant in comparison to the White (Carcharodon carcharias), Tiger (Galeocerdo cuvier) and Bull shark (Chacharinus Leucas), which have 254 (67), 83 (29) and 68 (17) confirmed, unprovoked, non air-sea disaster, attacks respectively. (The figures in brackets represent fatal attacks). It should be noted that in ‘A Field Guide to the sharks of British Coastal Waters’, Vas (1991) notes the possible presence of ‘Great white’ (Carcharodon carcharias) and ‘Tiger sharks’ (Galeocerdo cuvier) along the British coast but excludes them from his report as there is no evidence to support this. After the publication of Vas (1991) a fisherman along the Cornish coast at Padstow reported seeing a 15-18ft White shark in 1995, but again this is unsubstantiated.
3.2 Shark attacks on recreational water users:
Figure 2: Number of shark attacks on water users ISAF.
Figure 2 shows that from the beginning of the century the number of shark attacks on recreational water users has increased. The number of attacks on divers peaked in the 1960’s. This pattern is again reflected with the number of swimmers attacked also reaching the maximum level in the same decade. Divers and swimmers tend to enter the water at greater depths. This makes these water users more susceptible to attack. The number of ‘Enter, Exit Water users remains consistently low and this can be attributed to the shallow depths entered by this type of water users. These attacks are largely attributed to the three species mentioned in section 3.1. The most significant increase in attacks is that on surfers from the 1950’s onwards. This increase is shown more clearly in Figure 3.
Figure 3. Number of attacks on surfers ISAF.
Figure 3 shows that as surfing has increased in popularity, particularly between the 1980’s and 1990’s, so too have the numbers of attacks on wave riders.
3.3 Types of attack:
Shark attacks, that are unprovoked have been categorised as;
- ‘hit and run’
- ‘bump and bite’
- ‘sneak attacks’
http://mote.org/~rhueter /sharks/shark/.phtml (2002)
Hit and run attacks are considered to be the type of attack that effect recreational water users at the surface, within the surf zone according to George Burgess of the ISAF. The initial attack is usually the only attack and the victim is left alone. This would explain why swimmers and in particular surfers are more susceptible to attack than enter exit water users Figure 2.
Bump and Bite attacks occur after the shark has circled its victim and has inquisitively nudged him/her. Along with sneak attacks the attack comes without warning. These forms of attack are usually attributed to air-sea disasters but are followed by more attacks, which injure or kill the victim.
3.4 Why sharks attack humans:
Shark attacks generally occur in near shore waters. There are several reasons that sharks attack humans.
http://mote.org/~rhueter /sharks/shark/.phtml (2002)
- Mistaken identity
- .
- Easy prey.
- Inquisitive testing.
- Territorial invasion.
3.4.1 Mistaken identity
.
Swimmers and Surfers are believed to resemble shark prey from below the surface, in particular sea mammals. The surf zone reduces visibility as wave action stirs up the water and sediment. Figure 3 supports mistaken identity as the number of shark attacks on surfers increases as the length of surfboards was reduced. The reduction in surfboard length makes surfers resemble seals and sea lions. In the 1970’s San Francisco became a focus for shark attacks. It is believed that legislation protecting sea lion colonies was the cause of the increased attacks (Steel 1989). 75% of great white attacks are non-fatal, this would suggest that the mistaken identity theory is valid. This theory has been attributed to sharks disliking the taste of human flesh or wetsuit material, neoprene. Larger sharks such as the Great white and Tiger sharks usual prey, aquatic mammals have a higher fat content than humans and therefore sharks may leave human attack victims as they wish to conserve energy.
3.4.2 Easy Prey.
The Mako shark can reach speeds of up to 50 Km/hr (). Because humans natural habitat is not water, their movement and sensory ability is not particularly well adapted to the sea, making them particularly susceptible to shark attacks. Great white attacks around the world are usually hit and run and human prey is rarely eaten. However the Mediterranean Great Whites that have been caught and had an autopsy performed on them have contained the highest proportion of fully ingested human corpses compared to the rest of the world. (Jaws in the Med) This is likely to be the result of increased pollution killing their natural prey. An example comes from the Tuna fishermen of Favigiana who have seen their Tuna catch numbers reduced over the decades as a result of pollution and over fishing. Mediterranean Great whites have been noted by the fishermen attacking tuna as they swim in to the nets. (Jaws in the Med).
3.4.3 Inquisitive testing.
Sharks are believed to test objects by biting them. Therefore the theory of sharks taking a single bite ‘hit and run’ could simply be as a result of the inquisitive nature of sharks.
(http://mote.org/~rhueter /sharks/shark/.phtml 2002).
3.4.4 Territorial Invasion
Many terrestrial animals show behavioural patterns that include defending territory. It is believed that shark attacks could be the result of human invasion of territory (Steel 1989) particularly during mating when competition between sharks is at its greatest.
3.5 Shark Attacks in Europe.
Figure 5: ISAF 1907-2000 Map of Europe's confirmed, unprovoked shark attacks.
Figure 5 shows the distribution of shark attacks across Europe. It is believed that the North African coast is a breeding ground for Great White sharks. Small Great white jaws have been found around the Mediterranean and therefore provides evidence to support the theory. Remnants of shark teeth found in attack victims around the Mediterranean show that the majority of attacks are by Porbeagle sharks, a species found in British coastal waters. There is no conclusive evidence to support this as the Porbeagle sharks could simply be scavenging the remains of attacks. The key shows that there have been between one or two shark attacks in the British coastal waters. There has been one attack and this occurred in on the 1st June 1971. A Diver was attacked but not injured by a Porbeagle shark whilst diving at Beesands, South Devon (Steel 1989). Porbeagles and Thresher sharks are believed to swim up the English Channel hunting shoals of mackerel. As the number of mackerel are falling due to over fishing this may bring the sharks closer to the coast as they forage for food (Steel 1989).
4.0 Climate change.
To provide a balanced argument on the effects of global warming the earths past climate must be observed to ascertain whether climatic changes have been influenced by anthropogenic activity or it is simply part of a natural cycle.
4.1 Sources of evidence for past variations in climate.
4.1.1 Ice cores.
Vertical cores are drilled into ice sheets. As the composition of ice is hydrogen and oxygen, isotopes are examined to give information about past temperatures. It is usual to find a higher concentration of oxygen 16 isotopes in cooler periods when there was more snow accumulation. The composition of air bubbles within the cores can also be analysed to find the gas concentrations in the atmosphere.
From this evidence scientists can deduce temperatures (from O2 isotopes) and CO2 levels up to 160,000 years ago. (Aherns 2000).
4.1.2 Sediment cores.
CLIMAP a multi university research project (Climate: Long range Investigation Mapping and Prediction.) sampled deep ocean sediments and allowed the study of the climate over the last million years. Calcium carbonate organism shells were analysed as certain organisms only live within a certain temperature range. This allowed scientists to calculate the temperature. The ratio of oxygen 18 and 16 isotopes within the calcium carbonate also correlates to temperature. A higher ratio of 18 to 16 suggests a colder temperature and a higher ratio of 16 to 18 would suggest a warmer temperature. (Aherns 2000).
4.1.3 Dendrochronology.
The study of tree rings can determine the state of the climate. The thickness of the grow ring will determine at what stage the climate was in.
4.1.4 Other ways of determining past climate.
- Lake sediment
- Historic records (particularly from Victorian times onward, 1880 +)
- Ancient coal beds
- Sand dunes
- Fossils and Pollen
- Oxygen isotopes ratios in corals
(Aherns 2000)
4.2 Analysis of climate change evidence.
The study of this evidence has shown how the earth’s temperature has altered in the past. It has also shown a relationship with the amount of CO2 in the atmosphere and temperature. The more CO2 in the atmosphere is related to warmer temperatures. This correlation can be seen in figure 6.
4.3 Evidence for present climate change.
- Global annual temperature has been rising since the last ice age (10,000years ago) evidence has come from ice and sediment cores.
- Rate at which temperature has been rising is greater than any previously observed rates since the last ice age.
- CO2 concentrations in the atmosphere have risen from 280ppm to 360ppm over the last 150 years.
- Other green house gases have risen dramatically enhancing the warming effect.
The increase in green house gases has been attributed to Anthropogenic activity since the industrial revolution.
- Burning of fossil fuels for transport and energy generation
- Agriculture
- Deforestation (for raw materials and grazing land). Trees absorb C02 and albedo is altered
-
Mean annual temperature has risen between 0.3°C and 0.6°C over 150 years.
-
In the last 40 years (most reliable data) 0.2-0.3°C rise.
- 7/10 warmest years in twentieth century occurred in 1990s.
- Mountain glaciers are receding as a result of increased temperature.
- Artic ice pack has lost 40% of its thickness.
- Global sea level has risen 10-20cm over past 100 years. This has been attributed to melting land, sea ice and thermal expansion of warming seawater.
- Loss of the Odden feature. A tongue of ice that acts as natural pump to drive ocean currents in the North Atlantic. It started to falter in 1972 and disappeared in 1994. It is believed this may weaken the Gulf Stream.
4.4 Predicted oceanic changes as a result of global warming.
Global warming may cause the following Oceanic changes:
- Circulation and ocean transport
- Salinity and stratification
- Sea surface temperature
- Sea level
- Sea ice cover
- Population dynamics of mammals, birds and fish
- Marine ecosystems
- Pollution levels
(Bunyard,2001)
4.5 Impacts on Fish.
Global warming and its impacts on the worlds oceans have the potential to effect marine fish because most fish, including sharks, are cold blooded (Vas 1990) and do not have the ability to regulate body temperature. (Wood 1997)
Fish are susceptible to changes in temperature as follows,
- metabolism (O2 consumption)
- cardiac output
- ventilation
- excretory processes
For example a 10 °c rise equals a 2-3-fold increase in reaction rates within fish. Higher temperatures result in less O2 available in the water. The gills of fish can account for up to and over 60% of total surface that is exposed in water. If there is less O2 in the water more water has to pass over the gills, which can be susceptible to pollutants. The effects pollutants have on fish is partially reduced through the increase in excretion. The most common marine pollutants are metals such as copper (Cu), cadmium (Cd) and aluminium (Al), detergents (organic compounds) and pesticides. The reduction of O2 is the most significant factor effecting fish because it effects all of the above changes in fish physiology. Temperature alone does not constitute a threat to fish as a 2°c reduces oxygen solubility by 4.5%. A reduction in O2 along with other environmental stressors such as pollution can lead to disastrous consequences (Wood 1997).
4.6 Changes in fish distribution as a result of Global warming.
Over the next century there may be a predicted temperature rise of between 1°c and 4°c as a result of increased green house gases. The predicted temperature rise could result in marine fish distribution changing significantly. Each fish species adapts to changes in temperature differently but it is believed that there will, generally be a northward migration in response to temperature changes (Wood 1997). The unusual temperature rise along the North American west coast in 1958 resulted in several fish species reaching their highest recorded northward migration. A 1°c rise in average sea temperature lead to the Atlantic Mackerel shifting its pole ward migration by 110km. (Wood 1997). If fish species were to alter their migration further northward it can be assumed that the predatory fish that feed on these species would follow.
5.0 Evidence of marine species distribution changes.
Along the south coast of Britain two marine species have been found that typically inhabit the warmer waters of the Mediterranean. A 20lbs, 13ft sunfish was captured along the Dorset coast and a short-snouted seahorse was also found along the south coast. The appearance of these two species has been anecdotally attributed to climate changes by Neil Garrick-Maidment of the ‘National Marine Aquarium’, Plymouth ( 2002).
6.0 The effects of temperature rise on sharks.
In cold water sharks have a slower metabolism. This results in them not having to eat as much to sustain chemical reactions (Steel 1989). As the temperature rises sharks will become more active hunters, possibly resulting in more attacks on humans by native sharks.
7.0 Other factors that could lead to more shark attacks in British coastal waters.
The protective legislation introduced in the 1970’s in San Francisco has been attributed to the increase in shark attacks in the area. It is now illegal for fishermen in Britain to shoot Grey seals, as they are a protected species. There is now the opportunity for larger sharks that feed on seals to find a food source around Britain as seal numbers are expected to increase ( 2002). This could in turn lead to more shark attacks, particularly on surfers as a result of mistaken identity.
8.0 Conclusion.
There has been only one shark attack in the UK and of the 21 species that can be found in British coastal waters only four have been attributed to thirty five unprovoked attacks, five of which where fatal, around the world. This is a very small number considering that there are between 50 and 75 attacks worldwide every year. The majority of these attacks are assigned to species of which there is no evidence to suggest they visit or inhabit British coastal waters.
The green house effect has been exaggerated as a result of anthropogenic activity. The consequences of this will probably affect the world’s climate. The prediction of a rise between 1°c and 4 °c over the next one hundred years will have a profound effect on the distribution of fish. As sea temperatures rise fish species will migrate northwards to overcome, increased environmental stress. While temperature alone is not the only factor that will lead to migration, when coupled with other stressors such as pollution there may be a more significant impact. The rise in sea temperature could result in native species becoming more active and species that do not inhabit British coastal waters finding more suitable environments in this area.
The most significant factor that is likely to increase the number of attacks is the increasing population of seals. This is a staple food source for larger shark species that attack humans on a more regular basis.
It is evident that if the number of shark species where to increase within British Coastal Waters the most susceptible group of recreational water users would be ‘surfers’.
References.
-Aherns,D 2000 Meteorology Today, An introduction to weather, climate and the environment. Brookes/Cole. USA
-Attack 2002 locality. www.mote.org/~rhueters/sharks/sharks.phtml
-British Broadcasting Corporation. 1996. Jaws in the Med.
-Bunyard, P Putting life into climate: The shortcomings of the current IPCC predictions on climate change. Talk at Plymouth University 16/11/01
-ISFA.2000.International Shark Attack File.www.flmnh.ufl/edu/fisk
-Steel,R.1989.Sharks of the World.Blanford an imprint of Cassel PLC. Hong Kong.
-Wood,C,M.McDonald,D,G.1997. Global Warming: Implications for
freshwater and marine fish. Cambridge University Press.UK.
-www.bbc.co.uk
-www.php.aaas.org/meetings/mpe_01.php?thistrack=dgc#7054
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-Vas,P. 1991 A Field Guide To British Coastal Waters. FSC Publications, Central Services. Shrewsbury.
