Custodial Parent Tax Rights

My ex husband and I have 2 daughters who are now 17 and 14.  I am the custodial parent and have the them 89% of the time. He lives 1.5 hours away and only sees them Friday afternoon to Sunday morning every other weekend. Does he have any right to claim them on his taxes or does that right belong to me?

 

Thank you,

Danielle Kent