The white shark research team has published two papers in the past few days, documenting the ability to recognize individual sharks year after year by the distinctive shapes and markings on their dorsal fins; and then using this information to estimate the total size of the white shark population in this region.
The first study, which was published March 1 in the journal Marine Biology (Anderson et. al., 2011) shows that it is possible to positively identify the same shark year after year - even over time periods as long as 15-22 years!
Figures a and b show the fin of a single shark in 2007 and 2008;
Figure c shows a different shark in 2008 - illustrating how
distinctive the fin edge shape can be.
The second study, published today in the journal Biology Letters (Chapple et. al., 2011), uses fin photographs like those above to calculate the total size of the white shark population that returns to northern California each year - and the estimate was just 219 individuals.
Because this marks the first census of this population, we have no way of knowing whether this number is typical, or if it is unusually low (or even unusually high). What it provides, however, is a baseline that can be used in the years ahead to monitor changes in the adult white shark population - which will be a key step in managing and, if needed, protecting these animals in the wild.
As one might expect, we've had a lot of media interest in the story. You can check out the latest news coverage at the GTOPP website.