It can only be years. The last counted noun was 'years' - one and a half million years. Therefore 30 must be 30 years.

The text is quite vague but I assume it's 30 years.

It's unclear- a misprint. They omitted a time reference, most probably mean to print 30 years. However at the rate they are being murdered it will be way less than 30 years. Very sad actually. They are the most amazing animals. When you look into their eyes it is like looking into the windows of the soul.

I think there is a mistake in the text, and that the omitted word is "years."