In the wake of controversy surrounding the shark cull in Western Australia, it is a pleasant change to hear some positive attention being given to the great white shark known as Lydia who has been tracked crossing the Atlantic Ocean. Recent studies have started to elucidate the movements of these enigmatic creatures and more is being learnt about the patterns of their different life stages.
The hype surrounding the first shark to cross the mid-Atlantic ridge has been greatly misconstrued in some reports – it’s still a long way off the Irish and British coasts and has since veered westward away from the UK. But this shark is the first that we know of to cross the mid-way point of the Atlantic from the US and Lydia came within 1,000 miles of the Irish and Cornish coasts.
Every summer people are convinced great white shark dorsal fins akin to the Jaws movie are seen in coastal waters off the south coast of England. These reports tend to coincide with the migratory patterns of the Basking shark around the Cornish water or sightings of smaller cousins of the great white, the porbeagle and the shortfin mako.
While we do not associate them with our waters, there is no reason why the seas that surround the UK and Irish coastlines are not suitable for great white sharks in terms of temperature. Lydia has actually spent the last few months in the cold waters off the coast of Nova Scotia.
Great whites have a wide range from both temperate and tropical regions around the world. They are principally a predator of the central part of the sea, inhabiting both coastal and oceanic waters. Their movements seem to be principally linked to the diet in which they feed, travelling in sync with their appetites.
Depending on the size of a shark, the diet varies. Most sharks under 5m tend to feed off teleost fish. Larger sharks feed off seals, smaller species of shark, cephalopods such as squid and even whale carcasses. As predators at the top of the food chain, great whites play an important role in maintaining the balance of marine ecosystems. Having been persecuted for a number of years, it’s important we learn more about these elusive creatures.
Lydia has been tagged and tracked as part of the OCEARCH project, which is seeking to better understand great white shark movement. Representatives described Lydia as around 20 years old and sexually mature for only a short period of time. She is around 14 feet in length which puts her in the category of “sub adult”.
Unconfirmed reports regarding the female being pregnant have resulted in some excited news reporting, but when Lydia was tagged in March 2013 she was reported as not being in a state of gravida. Due to there being no scientific foundation for this report it is hard to believe. Due to the longevity of a shark’s reproductive pattern (estimated at 11 months gestation) it should not be wholly dismissed.
Should Lydia be pregnant then there is evidence to suggest that female sharks of a certain age and maturity can reproduce with males from populations across the ocean. Many shark experts have debated about transoceanic movements of Great White sharks taking place and most likely the females return to their original location to give birth. If this is the case then Lydia has already travelled across the mid-Atlantic ridge on her unknown voyage to the Eastern Seaboard of the United States.
Another reason people may think why Lydia has taken this strange course is that the handling of her during the tagging process caused an adverse effect on her behaviour and migratory pattern. OCEARCH said that Lydia was only on the platform for 15 minutes, during which researchers extracted blood for analysis and performed an ultrasound examination, in addition to attaching the tags.
So the questions remain: surely the ultrasound would have revealed if she was pregnant? And, where has she been tracked since her tagging that could have shown evidence of reproductive activity?
One year on from her tagging, what is potentially a major breakthrough in the understanding of migratory habits of the great white shark is nearing. Could this be a common occurrence with this species that we are only just learning more about, or can this just be put down to another case of human intervention gone wrong and a confused Lydia does not know where she is going or what she is doing? On the bright side, it puts great white sharks in the press for a positive reason and that can only be a good thing.