Researchers Document Patchy Pigmentation in Deep-Sea Sevengill Shark

A sharpnose sevengill shark retrieved as bycatch from 400 meters off Puerto Rico displayed irregular dark blotches, pale zones, and pigment-free white patches across its body. The individual was not albino or leucistic. Researchers transferred the specimen to the Sharklab ADRIA Research Center for analysis.

General director Andrej A. Gajić said the pigmentation pattern did not match previously described anomalies in elasmobranchs. The team examined liver lipid composition and compared the shark with normal males from Puerto Rico and the Adriatic. The shark’s condition factor was 37 percent lower than expected.

The hepatosomatic index was reduced by more than 60 percent. Total hepatic lipid content measured 16 percent, compared with 56 percent in a normal conspecific. Spectroscopic analysis showed weakened triglyceride signals and signs of lipid degradation. The shark’s stomach was empty. Its liver was smaller than normal. These indicators together point to prolonged energetic depletion.

Sharpnose sevengill sharks normally display brownish-grey dorsal surfaces and paler undersides. This countershading reduces visibility from above and below. The patchy coloration observed in this specimen created gradual transitions rather than a uniform gradient.

Gajić noted that even at depth, light gradients remain relevant for predator avoidance and prey detection. The study did not determine whether the pigmentation anomaly caused the energy deficit or resulted from another factor. The full study received support from The Explorers Club and the Save Our Seas Foundation.