MSGID: 1:317/3 62735357   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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.   
      
      
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   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.   
      
      
      
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   "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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