Determining where the most sharks live is challenging due to the sheer scale of the world’s oceans. Sharks are highly migratory, making consistent, basin-wide population counts nearly impossible. Tracking these mobile predators across vast distances and different political boundaries introduces significant methodological hurdles. Global shark populations have also faced a greater than 70% decline since 1970, complicating any historical comparison of total abundance. Therefore, comparing the Pacific and Atlantic must focus on the best available metrics: species richness and the underlying environmental capacity of each basin.
The Primary Answer: Abundance Versus Species Diversity
Generally, the Pacific Ocean supports a greater species diversity of sharks than the Atlantic Ocean. This distinction is based on the number of different shark species present, particularly in the Indo-Pacific region. While the species count is higher in the Pacific, estimating the total number of individual sharks, or overall abundance, is far more complex and varies by location.
Localized abundance can be extremely high in certain Atlantic regions, such as the warmer waters off the Bahamas or Florida. However, the Pacific Ocean’s vastness and variety of habitats create an environment conducive to the evolution and survival of a larger number of distinct species. The Pacific is home to a wider range of shark types, even if isolated Atlantic hotspots host dense aggregations of a few species.
Ecological Drivers of Pacific Shark Populations
The immense size and geological history of the Pacific Ocean contribute significantly to its high shark diversity. Covering nearly one-third of the planet’s surface, the Pacific offers unparalleled geographical space and numerous distinct ecological niches. The basin’s age has also allowed for greater evolutionary time, fostering the development of genetically distinct populations within species, such as great white sharks.
The Pacific contains the deepest trenches, vast expanses of open ocean, and an extensive variety of coastal habitats, including the immense Coral Triangle region. This region, located between Southeast Asia and Melanesia, acts as a global biodiversity hotspot for marine life, including numerous shark species. Deep ocean trenches and countless seamounts provide crucial habitat for both deep-sea and wide-ranging pelagic sharks. This environmental heterogeneity supports a complex food web, sustaining a larger roster of predatory species.
Factors Limiting Atlantic Shark Populations
In contrast to the Pacific, the Atlantic Ocean faces limitations that restrict its shark diversity and have led to pronounced population declines. Historically, the Atlantic has experienced more intensive and localized fishing pressure, particularly in the North Atlantic. This has resulted in significant population crashes for several migratory species like the shortfin mako and oceanic whitetip shark.
The Atlantic’s continental margins are often characterized by wide and shallow continental shelves. These passive margins, such as those off North America and Europe, are highly productive but also easily accessible to industrial fishing fleets. This accessibility has led to a greater spatial overlap between shark hotspots and fishing effort compared to the Pacific, particularly in areas like the Gulf Stream. Mortality from bycatch in fisheries targeting tuna and swordfish has been a major factor in the documented decline of Atlantic pelagic sharks.
Geographic Scope of Shark Studies
Defining the “Pacific” and “Atlantic” for scientific comparison is a significant methodological challenge. Sharks are often highly migratory, with some individuals traveling tens of thousands of kilometers across international boundaries. This movement means a single species can be managed by different Regional Fisheries Management Organizations (RFMOs), such as the International Commission for the Conservation of Atlantic Tunas (ICCAT) and the Western and Central Pacific Fisheries Commission (WCPFC).
Scientists must also decide whether to include marginal seas like the Gulf of Mexico or the Mediterranean Sea in their basin-wide analysis, as these areas often host unique or genetically distinct populations. Genetic studies show that wide-ranging species, including tiger sharks and oceanic whitetip sharks, maintain separate populations in the Atlantic and Indo-Pacific regions. This genetic separation highlights the need for conservation strategies tailored to the unique conditions and pressures within each ocean basin.