PhD defence on the genetics of tiger shark

The tiger shark—one of the largest shark species—is in decline and is currently classified as “near threatened”. This is mainly due to anthropogenic pressures, e.g., fishing and “beach protection” measures to prevent shark attacks.

So far, there has been a lack of knowledge about the genetics of tiger sharks and their demographic and evolutionary development through the ages and in different areas. To investigate this, PhD Student Alice Manuzzi and her colleagues have analysed historical and contemporary (1820-2018) samples from tiger shark jaws collected from museums, fishery institutes and universities across the world. Furthermore, they have investigated the genetic composition of samples from tiger shark jaws from Eastern Australia between 1910 and 2012.  

Based on the analyses, Alice Manuzzi and her colleagues have created the first standardized global DNA database for tiger sharks making it possible to compare results between genetic studies conducted in different laboratories.

Alice Manuzzi’s research confirms that tiger sharks from the Atlantic and Indo-Pacific basins are very distinct from each other, potentially at the sub-species level. In contrast to previous beliefs, the results also show an extensive genetic structuring within both ocean basins, strongly suggesting isolated population structure at a much smaller geographical scale than previously documented. Furthermore, the analyses of the sharks from Australia indicate the possible disappearance of one local population that was abundant in older samples, but diminished over time, perhaps as a direct or indirect consequence of human exploitation.

In her thesis, Alice Manuzzi concludes that the finding has strong implications for how we should preserve the tiger shark and other highly migratory shark species. She suggests that management should have an increased focus on effects of local scale human impacts, such as bather protection programs, as a significant threat to vulnerable local populations.

The PhD project was conducted in cooperation between DTU and University of Queensland.

About the defence

Alice Manuzzi will defend her PhD thesis "Genomic analysis of DNA from archived shark jaws" on Friday 5 June 2020 at 10.00 CEST. The defence will be held online via Zoom. Please contact Rikke Hansen, rikh@aqua.dtu.dk, no later than 4 June 10:00 CEST for a link to join the defence.

Supervisors

• Principal supervisor: Professor Einar Eg Nielsen, DTU Aqua
• Co-supervisor: Senior Researcher Dorte Bekkevold, DTU Aqua
• Co-supervisor: Associate Professor Jennifer Ovenden, University of Queensland
• Co-supervisor: Professor Mike Bennett, University of Queensland

Examiners

• Senior Researcher Jakob Hemmer-Hansen, DTU Aqua
• Professor Stefano Mariani, Liverpool John Moores University, UK
• Professor Sophie von der Heyden, University of Stellenbosch, South Africa

Chairperson at defence

• Senior Researcher Niels Jepsen, DTU Aqua