For over a decade, basking shark numbers around the Isle of Man told a grim story. Sightings plummeted from 885 in 2009 to a single individual, prompting researchers to halt their tagging program in 2022. The leading theory blamed electromagnetic fields from underwater electricity cables for repelling the migrating sharks. That theory now looks wrong. This summer has delivered more than 100 sightings so far, with the island's south-west corner — particularly around Bradda Head and Port Erin Bay — emerging as a hotspot. The fisheries department credits a strong bloom of copepods, the microscopic crustaceans that are the basking shark's primary food source. The sharks migrate north through Manx waters from May to August, following zooplankton that they filter-feed near the surface. No food, no fish — it really is that simple. The supplementary data from Basking Shark Scotland underscores the point: these animals spend 90% of their time underwater and only surface when plankton concentrations justify the energy cost of open-mouth feeding. Their presence at the surface is a proxy for food abundance, not population size. Tagged sharks have shown site fidelity to Hebridean waters year after year, returning to the same feeding grounds when conditions allow. The cable theory was never firmly established — it was the best available explanation for a collapse that coincided with new subsea infrastructure. But the 2026 rebound happened without cable removal, strongly suggesting that interannual variation in plankton productivity is the dominant driver. Warmer seas remain a background concern, but this season's copepod bloom demonstrates that the food web can still deliver. Migration routes for these ten-tonne filter feeders are genuinely vast. Tagged individuals have been tracked from the Isle of Man to Morocco and Newfoundland. The research program that placed those tags involved steering inflatable ribs alongside sharks capable of smashing the hull — hair-raising work that yielded irreplaceable movement data before funding dried up with the population crash. The rebound raises a harder question than the decline did. If plankton variability can swing sightings from 885 to 1 to 100+ across 17 years, what does that say about the stability of the food web these sharks depend on? Climate-driven shifts in copepod distribution and abundance are well-documented in the North Atlantic. A good year does not make a trend. For the Isle of Man's fisheries department and the citizen-science network of coastal spotters, this summer is a reprieve. But the underlying system — vast migratory megafauna dependent on microscopic crustaceans dependent on ocean temperature and nutrient cycles — remains as fragile as it looks.
