A new study finds low genetic diversity and signs of inbreeding in the smooth hammerhead (Sphyrna zygaena), particularly in the Atlantic.
Of 87 sampled animals, 73 remained in the dataset after quality filtering. The samples date from before 2015. The analysis distinguishes an Atlantic group and a southwestern Indian Ocean group with limited genetic exchange.
What the small numbers mean
The estimated effective population sizes are about 179 and 64, respectively. These are not counts of the remaining sharks.
This measure describes genetic processes within a population. It corresponds to the size of an idealised reference population experiencing the same genetic drift. It cannot directly tell us how many sharks are actually alive.
Conclusions from a limited dataset
The study covers only around two percent of the genome; just 14 animals from the southwestern Indian Ocean were included. Evidence for local adaptation remains weak. The researchers recommend separate management units and maintaining genetic connections. Modelled areas of exchange are not observed migration routes.
The previously featured vertebral analysis of habitat shifts offers a different perspective on the same species: it examines chemical traces of diet and habitat during growth. This ecological perspective complements the genetic questions without measuring the same variables.
