You can only catch spheals in the cave behind the city with the apace station, where you get the shell bell.
Chat with our AI personalities
Level 44.
Normally you can catch it in pearl after beating the elite 4 but in diamond the only way is to trade with someone who has a sealeo on their pearl, or migrate it from emerald.
Spheal evolves at level 32 into Sealeo. Sealeo evolves into Walrein at level 44. http://serebii.net/pokedex-dp/363.shtml
Sealeo will evolve to Walrein at level 45.
you can't catch sealeo but you can catch spheal in rt. 30