White sharks observed at the surface were identified by unique markings.

Earlier this year, reports of the results of study which estimated the number of white sharks off central California made headlines. Researchers formulated the estimate after surveying known and unknown white shark specimens, which were observed at the surface. Individual sharks were identified based on each shark’s unique markings.

Dr. Michael Domeier of Marine CSI has recently posted commentary on the methodology used in the above mentioned study. Domeier cites that the study assumed that the sampled white shark population was a closed population. Domeier goes on to say that the long term monitoring of white sharks at Isla de Guadalupe has shown that adult white sharks leave and join the population, which violates the assumption of a closed population.

Additionally, Domeier states that the assumption that individual sharks have an equally probability of being observed has been invalidated by previous research.

Domeier concludes that since estimate was based on “faulty assumptions” the estimate is invalid. He also states that the actual number of white sharks in the respective region is “likely dramatically higher” than the estimate reported in the published study.

Dr. Domeier’s full discussion of this study can be found at the Marine CSI website.