Sharks are a diverse group of cartilaginous fish, encompassing over 500 known species that inhabit every ocean ecosystem on Earth. These animals range from the small, deep-dwelling dwarf lanternshark to the massive, filter-feeding whale shark. A single, precise number for the global shark population does not exist and is currently unattainable. The vastness of marine habitats and the biological nature of these species make any direct census impossible. Understanding global shark numbers relies on complex scientific estimations and trend analyses rather than direct counting.
The Challenge of Global Shark Quantification
Obtaining an exact worldwide count of sharks is hindered by logistical and biological factors inherent to marine life. The ocean is a three-dimensional environment that covers over 70% of the planet’s surface, making comprehensive sampling across all depths and regions an overwhelming task. Many shark species, particularly those that live in the open ocean or bathypelagic zones, are simply inaccessible for regular observation or study.
The migratory nature of many larger species further complicates quantification efforts, as these sharks frequently cross international boundaries and move vertically through the water column. A single population may be subject to different management rules—or a complete lack of rules—in the various regions it traverses. Moreover, the sheer species diversity means many populations are poorly studied, lacking sufficient basic life history data.
Sharks are a relatively low-density, highly mobile group, meaning a typical scientific survey may go long periods without encountering an individual. This makes statistically robust sampling difficult, requiring extensive time and resources to generate reliable population estimates. The lack of species-specific data in historical and current fisheries records also creates significant gaps, often lumping multiple shark species together, which obscures the status of individual populations.
Current Methods for Population Estimation
Since direct counting is not feasible, scientists rely on methodologies to estimate shark abundance and monitor population trends. These methods are broadly categorized into fisheries-dependent data (from commercial fishing operations) and fisheries-independent data (from dedicated research surveys). Both types of data are often integrated into mathematical models to infer population size.
Fisheries-dependent data analyzes commercial catch statistics, landing records, and fishing effort to generate a metric called Catch Per Unit Effort (CPUE). CPUE tracks the number of sharks caught for a standardized amount of fishing effort, such as per 1,000 hooks or per day at sea, which acts as a proxy for relative abundance. However, this method is often compromised because fishing vessels frequently fail to report shark catches by species, and a significant portion of the global catch is illegal, unreported, or discarded as bycatch.
Dedicated research surveys provide more controlled, fisheries-independent data, such as through the use of Baited Remote Underwater Video Systems (BRUVS). BRUVS consist of a camera unit and a bait arm deployed on the seafloor, which records the number of sharks that visit the area. Scientists use the MaxN metric, which is the maximum number of individuals of a species seen in a single frame, to determine a relative abundance index without harming the animals. Stereo-BRUVS, which use two cameras, can also be used to accurately measure the size of the recorded sharks.
Another important fisheries-independent technique is tagging and recapture programs, where sharks are fitted with conventional or electronic tags. Tracking these tagged individuals provides data on movement patterns, habitat use, and survival rates, which are then used in complex demographic models. These sophisticated stock assessment models integrate all available data on birth rates, mortality rates, and age structure to produce an estimated total population size and predict how the population will respond to fishing pressure.
State of Global Shark Populations
While a total global count is elusive, the scientific consensus is that shark populations are in significant decline. A major study published in the journal Nature estimated that the global abundance of oceanic sharks and rays has declined by 71% over the past 50 years, primarily due to overfishing. This decline is not uniform across all species but indicates a widespread crisis, especially among larger, slow-reproducing species.
Current assessments by the International Union for Conservation of Nature (IUCN) confirm this trend, revealing that more than one-third (37.5%) of all chondrichthyans—the group that includes sharks, rays, and chimaeras—are now threatened with extinction. Overfishing is identified as the universal threat affecting all species categorized as threatened. This includes targeted fishing and the high rates of incidental catch, or bycatch, in other fisheries.
Many formerly abundant species are now facing severe risk, with the iconic Oceanic Whitetip Shark classified as Critically Endangered and the Shortfin Mako Shark listed as Endangered. These documented population collapses in certain regions point toward a state of functional extinction, where a species is no longer numerous enough to play its historical ecological role. The high proportion of species listed as “Data Deficient” also suggests that the true number of threatened shark populations may be even higher than current assessments indicate.