Jaws hold crucial knowledge on the fate of sharks
Date:
May 4, 2022
Source:
Technical University of Denmark
Summary:
A significant change in the genetics of tiger sharks reveals a
vulnerability to direct exploitation and shark control programs.
FULL STORY ==========================================================================
Jaws was the only word needed to give the iconic 1970's thriller about a
great white with a preference for humans its eerie title. Though a strong
and important player at the top of the foodchain, sharks face a range of enemies: overfishing, habitat loss, pollution and climate change and human
fear resulting in the use of shark control programs in some locations.
==========================================================================
The fear and fascination for sharks have made people collect shark jaws
for decades. These collections of shark jaws from museums, national
fishery institutes and personal collections, including modern samples
from fishery institutes represent a great opportunity for scientists.
Using genomic data retrieved from historical tiger shark jaws, an
international group of scientists including Professor Einar Eg from the Technical University of Denmark has found evidence of the disappearance
of a local southeastern Australian population of tiger sharks. A
disappearance associated with a documented local decline in abundance
of tiger sharks, likely caused by the ongoing shark control program.
The international study Retrospective genomics highlights changes in
genetic composition of tiger sharks (Galeocerdo cuvier) and potential
loss of a south- eastern Australia population has just been published
in the journal Scientific Reports "Our study shows that tiger sharks
can have local and genetically isolated populations at a restricted geographical scale -- such as the south Eastern Australian coast --
and that these local populations are vulnerable to direct exploitation
and shark control programs," says Einar Eg.
Top predator controls the ecosystem balance The study shows that there
are still tiger sharks in the area. However, these individuals belong to
an, apparently, more widespread population found across the east/north
coast of Australia.
========================================================================== "When we, through genetic analysis, better understand the distribution
and migration of shark populations and their responses to human
activities over historical time, we are better able to design proper
management plans and actions at the appropriate geographical scale. Not
only for the benefit of sharks, but for marine ecosystems as a whole,"
says Einar Eg and explains: "Sharks are top predators. They control the abundance of other species below them, and sick fish, in the food chain, ensuring species diversity. I.e. they are important for maintaining
ecosystem balance. They are generally long lived and slow reproducers,
so a healthy shark fauna signals a healthy ocean and ecosystem."
Genetic diversity is the fuel that drives future evolution Before the new study, it was believed that tiger sharks did not display local population structure. Thus, genetic differences among tiger shark populations were
only found at a basin wide scale, such as between tiger sharks in the
Pacific and Atlantic oceans. Accordingly, tiger sharks were expected to
display low vulnerability towards local depletion. Therefore management
of the species at a large geographical scale was in focus.
"From our samples alone, it appears that the historical local population
has been extirpated or significantly reduced. This means that management
of the species also has to focus on regional processes and exploitation patterns in order to protect local populations and biodiversity of the
species as a whole," says Einar Eg and points to the crucial aspects of
genetic research: "Genetic diversity within a species, is the fuel that
drives future evolution and adaptation to the environment, e.g. climate
change. Without historical genetic/genomic data, there is no way of
assessing the loss of genetic diversity within a species."
==========================================================================
Fear and facts -- are sharks moving North? With regards to the shark
control programs having an impact on shark numbers, the obvious question
arises "How afraid should one actually be to go swimming in Australia or
South Africa?" "In 2021, there were 73 cases of unprovoked shark bites worldwide, with a total of 11 fatalities. Most attacks were related
to surfing and board sports. In Australia, there were three fatalities
and 1 in SA. So, the chance of being attacked and killed by a shark is
almost non-existing. One should definitely be more afraid of driving in
your car writing txt messages," says Einar Eg.
As climate change causes sea temperatures to rise, some researchers
say that we may be looking into a future with large sharks entering Danish/European waters.
However, Einar Eg stresses that though changed temperature conditions
could allow for more large sharks occurring in Danish/European waters,
many other factors determine the distribution of a species.
"The Mediterranean, for instance, is very suitable for large sharks,
but we do not see large assemblages of white, tiger, mako sharks
there. If they come, it is highly unlikely that this would result in
any bather-shark conflicts. As an example, there were no reported shark
bites in Europe for 2021," says Einar Eg.
A future for sharks On a global scale, the tiger shark is near
threatened. According to Professor Einar Eg that covers a significant
species depletion in some areas, while they're doing ok in other regions
of the world: "We need to shift tiger shark management conceptually
from an exclusive species view to also include the local population
aspect. I.e. saving global populations has to go through protection and
proper management of local populations," says Einar Eg.
"Now, by having our temporal genetic data, we can study the genetic
impact of anthropogenic pressure on marine species, enabling us to
improve management in order to secure biodiversity." How can genetic
research continue and help improve shark control and hunting in favour
of sharks? "Genetic research can help to elucidate the proper biological
units (genetic populations), which should be the target for fisheries management, conservation and biodiversity protection," says Einar Eg and concludes: "Studies like ours can illustrate the likely consequences
of local over- exploitation in relation to shark control and make us
realize what we can lose by not paying attention to the distribution of
genetic variation within a species." The tiger shark project is part
of a larger project umbrella GENOJAWS where the scientists have studied retrospective genetics/genomics of 4 big sharks: sand tiger shark,
mako shark and white shark in addition to the tiger shark.
========================================================================== Story Source: Materials provided
by Technical_University_of_Denmark. Original written by Anne
Trap-Lind. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Alice Manuzzi, Belen Jime'nez-Mena, Romina Henriques, Bonnie
J. Holmes,
Julian Pepperell, Janette Edson, Mike B. Bennett, Charlie Huveneers,
Jennifer R. Ovenden, Einar E. Nielsen. Retrospective genomics
highlights changes in genetic composition of tiger sharks
(Galeocerdo cuvier) and potential loss of a south-eastern
Australia population. Scientific Reports, 2022; 12 (1) DOI:
10.1038/s41598-022-10529-w ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/05/220504110438.htm
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