During your hunt, you can select the larger species more efficiently. As a result, the random factor of your prey's size decreases. The skill also increases the SE you acquire when hunting. If your skill is at least half of your level, you should expect +5% SE average.
The skill gives +5% from each creature that you hunt that has a level smaller than (expert hunt / 2) so in order to get 5% on all creatures you hunt, your skill level must actually be above half your level, since you can hunt creatures that are 2 levels above your level. If you are level 60, you will need an expert hunt of 31 to gain +5% on all creatures you hunt.
Learning level: 56
Max level: no limit