The Urgent Struggle for Survival: Atlantic Shortfin Mako Sharks and Genetic Diversity
The ocean’s fastest shark, the shortfin mako, is facing an existential crisis due to relentless overfishing. Despite global efforts to conserve this apex predator—and despite it being classified as Endangered on the IUCN Red List—the future of shortfin makos in the Atlantic is uncertain. Recent genetic research, however, offers a glimmer of hope, revealing that Atlantic populations still maintain relatively high genetic diversity. This genetic richness is crucial for the species’ resilience, particularly in the face of a changing climate.
The Dire State of Shortfin Makos
Shortfin mako sharks are renowned for their remarkable speed, capable of reaching up to 70 km/hr. However, their speed cannot rival the intensity of overfishing that threatens their existence. The global demand for mako meat and their highly valuable fins has led to significant population declines. These factors have placed makos on both the IUCN’s Endangered list and Appendix II of the Convention on Trade in Endangered Species of Wild Fauna and Flora (CITES).
Atlantic populations are particularly vulnerable. Managed as two separate stocks—the Northern and Southern Atlantic—the fishery-based assessments paint a grim picture. Northern Atlantic mako populations are currently deemed overfished, facing severe depletion due to excessive commercial fishing.
Groundbreaking Genetic Research
A team of researchers, led by Dr. Andrea Bernard and Professor Mahmood Shivji from the Save Our Seas Foundation Shark Research Center and the Guy Harvey Institute at Nova Southeastern University, have made significant strides in understanding the genetic health of Atlantic shortfin makos. Their study, published in the journal Environmental Applications, provides unprecedented insights by sequencing entire genomes of mitochondria DNA and conducting high-resolution scans of nuclear genomes from nearly the entire distribution of the species in the Atlantic.
The findings reveal that, despite decades of fishing pressure, Atlantic mako populations retain relatively high genetic diversity. “Genetic diversity in a population is essential for survival,” explains Professor Shivji. “It allows species to adapt to environmental changes and recover from threats like overfishing and climate change.”
This is encouraging news, as it suggests there is potential for the species to adapt if overfishing is curtailed. In contrast, many shark species, like the critically endangered great hammerhead shark, exhibit low genetic diversity, making them more vulnerable to extinction.
Mako Shark Movement and Genetic Insights
The researchers also explored the movement patterns of makos, predicting that these nomadic sharks would mix their genes freely across the Atlantic Ocean. Their genetic analysis confirms this hypothesis, showing that male makos are widely distributed and spread their genes throughout the Atlantic. Female makos, although capable of similar journeys, seem toreturn to key sites within their respective hemispheres to pup.
The study uncovered a degree of genetic structure in mitochondrial DNA, indicating that northern and southern hemisphere populations have distinct maternal lineages. This finding supports the need to manage mako populations in the Atlantic as two separate stocks: the Northern Atlantic and Southern Atlantic shortfin mako sharks.
The Path Forward
While the discovery of genetic diversity provides a reason for optimism, the urgency to protect shortfin makos remains paramount. The species faces not only overfishing but also other threats including habitat loss, deep-sea mining, pollution, and climate change. Conservation efforts need to be multifaceted and comprehensive.
The management of two distinct Atlantic populations is now scientifically supported, and continued research into their movement and genetic health will be crucial. This information can guide policy decisions aimed at ensuring the conservation of mako sharks and their critical role in marine ecosystems.
“If we can prevent further degradation of genetic diversity and mitigate further overfishing, we have a better chance of ensuring the shortfin mako’s survival,” indicates Professor Shivji.
Protecting the ocean’s fastest shark isn’t just about preserving a single species; it’s about maintaining the balance and biodiversity of our oceans. As we face increasing environmental challenges, the resilience of species like the shortfin mako is vital.
Reference: “Connections Across Open Water: A Bi-Organelle, Genomics-Scale Assessment of Atlantic-Wide Population Dynamics in a Pelagic, Endangered Apex Predator Shark (Isurus oxyrinchus)” by Andrea M. Bernard, Marissa R. Mehlrose, Kimberly A. Finnegan, Bradley M. Wetherbee and Mahmood S. Shivji, 22 January 2025, Evolutionary Applications.
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