Shifting Blacktip Shark Migration Patterns

Story by: Ellie Stevens

Visual by: Noah Weinberg

Date: 4/12/21

Every year, blacktip sharks migrate to southern Florida from North Carolina in pursuit of warmer water. Similar to many other organisms, the sharks possess an optimal temperature range for proper function. Deviation from this range can threaten their reproduction capabilities, and ultimately, the species’ survival. Thus, blacktip sharks adapt to the changing seasons by making the southbound trek to a region with this ideal temperature. In sexually segregated schools, the male sharks swim south during the coldest months of the year to warmer water until the spring, when the journey back northward to mate with females.

blacktip shark on vistory article

The East Coast’s warming waters have caused increasing numbers of blacktips to remain in the North during migration season, however. This year, only about one-third of the usual number of sharks migrated to Florida. Although seasonal variability is mainly responsible for the drastic decrease in the number of migrating blacktip sharks this year (resulting in a striking 5.4-degree increase in ocean temperature), the change represents the impact of global warming’s increase in water temperature to deter migration.

The increased concentrations of greenhouse gases in the atmosphere, primarily from fossil fuel consumption, force the ocean to absorb vast amounts of heat energy, creating a long-term rise in ocean temperature. The average global sea temperature has increased by approximately 0.13°C per decade over the past century. Yet, the northeastern states’ waters have warmed faster than over 99% of the world’s oceans. Since 1960, the ocean stretch from North Carolina to the Gulf of Maine has warmed by 3.6°F. As water temperatures continue to rise, blacktip sharks will accordingly shift northward.

These changes in migration could possess devastating ecological and economic consequences. Blacktip sharks play an integral role in maintaining ecosystems in the southern part of the United States. Through predation, they prevent the overpopulation of other species, which holds cascading effects. For example, overpopulation of herbivores can lead to the overgrazing of kelp, depleting species like lobsters and crabs that take cover beneath this plant. Additionally, other fish species, such as dogfish and cod, follow the blacktip sharks northward with changing temperatures. As a result, southern commercial fisheries must travel north to catch fish once available in their own waters. The resources of large-scale fisheries would allow them to crush their smaller counterparts, already plagued with overfishing, regulation, and industry consolidation. Among other expenses required for this northern shift, the migration of sea life is on track to cause long-lasting economic consequences and ecosystemic destruction.

Sources :

"More Sharks Ditching Annual Migration to Florida as Ocean Warms"
Ocean Warming
"Feeling the Heat: How Fish Are Migrating from Warming Waters"
Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida