That is caused by birds; when the lemon is green it has an oil in the peel that birds use as a repellent for mites.

A net, or something flashy hung from the branches usually keeps most of them away.

I agree, this is physical damage caused either by birds or possibly by the wind, and the fruits brushing up against thorns or sharp branches. But, most likely bird damage as John has well described.

Patty S.

Definitely birds! The grackles are the culprit here in SE Texas. I haven't found anything that they won't soon get used to and ignore. Some say CD's will keep some birds away but I haven't tried them. I tried draping bird netting over my lemon trees but my trees have thorns and are quite tall. The netting just got tangled in the trees and turned out to be a real mess, especially after the new growth began growing through the netting. Good luck and let us know if you find something that works. It's really frustrating to spend the time and produce fruit that doesn't look as good as it tastes. The good news is that the fruit looks awful on the outside and grows irregular but is usually just fine on the inside. You WILL loose some of your zest where the damage is.

Thanks for posting. I have the same problem with my meyer lemons. And now that I know it was birds I can recall seeing black birds all over my tree early on.