Whales - Math Puzzles

Quote from https://en.wikipedia.org/wiki/Whale:

Males typically mate with multiple females every year, but females only mate every two to three years

How is that possible? If there are 100 males and 100 females and let's say 40 of the males mate each year (other 60 are either too old or too young or sick or gay or weird ones that mate with sharks).

Each of the 40 males mates with 2 or more females from among the same pack of 40 females (rest 60 females which again will have some that are old too old, too young etc).

In this scenario, how can we have females that mate only every 2 or 3 years? This can happen if few females mate with most of the males but then they abstain for the next couple of years. 

Is there any other interpretation possible?