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Background

The blue shark is the most commonly caught species of shark globally, with recent estimates of ~10M individuals caught annually. The species is globally assessed as Near Threatened, but in the North Atlantic the species is inferred as Endangered having sustained population declines of 54% in the last three generations. These numbers are in line with a Mediterrenean assessment that concluded that the species was Critically Endangered there due to population delcines of >90%. The blue shark comes under the management of Regional Fisheries Management Organisations (RFMOs) given their interactions with pelagic tuna and billfish fisheries.

Given that the species is globally distributed in tropical and temperate waters, and likely the most globally distributed species of shark, regional population declines are thought to balance out from healthier stocks. However, recent evidence suggests the blue shark might indeed have some population sub-structuring geographically, which has raised questions about the sustainability of fisheries within threatened stocks (mainly the North and South Atlantic stocks). Our work will build on this recent study, by employing novel genomics from regions not previously covered with the goal of determining this population sub-structuring in detail in order to inform the species management. This should provide RFMOs with the evidence needed to determine regional limits or bans relevant to the species status and ecology.

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Objectives

The objectives are to:

• Conduct a global assessment of blue shark genetic population structuring to identify management units
  
  
• Investigate blue shark genetic structuring in the North Atlantics
  
  
• Provide recommendations for fisheries management by identifying candidate blue shark management units

A recent study found genetic differences between the Northern (Mediterranean and North Atlantic) and Southern hemisphere (southeast Atlantic, Indian Ocean and southwest Pacific) oceanic regions. There is potentially a single population of blue sharks across the entire Southern hemisphere, but further samples are required to establish a global view of genetic connectivity. There is little evidence of migration between the northern and southern hemisphere, and these stocks may operate on different reproductive cycles. It is critical to understand genetic connectivity between oceanic regions, so blue shark stocks can be assessed and managed effectively. Therefore, we will complete a genomic analysis of blue sharks across six new areas, complementing existing literature.

Six new sample areas will be added to this global survey: (1) NW Indian Ocean (Oman), (2) NE Atlantic (UK), (3) NW Atlantic (USA & Canada), (4) SW Atlantic (Argentina & Uruguay), (5) SE Pacific (Ecuador), (6) NW Pacific (Taiwan).

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Project Status

The Shark Foundation is partially funding this project. Sample collection has already been started and progresses. Samples from the collaborators will be sent to and specifically analyzed by the genomics facility of the Diversity Arrays Technology (DArT, Australia) lab.

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Administrative Details

Project Status:   in progress since 2023
Project leader: Gonzalo Araujo, PHD
Funding Funding since 2023: approx. CHF 8,000

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