I wonder if they are comparing men of the same age, or looking at general population fertility, which would understandably be declining in a population whose age pyramid is shifting upward.
This is definitely a big deal but I am at a loss to explain it. Seems like nobody knows why this is happening. I've heard the tight underwear hypothesis before, and it's conceivable that that's a contributor, but I would find it hard to believe that'd cause an almost 1/3 decline in fertility over a mere 16 years.