Complex sentence: Smaller walleye's major forage, yellow perch, are small in number in Brule, which limits the size of the Walleye population, although once they grow large enough they can forage on Brule's much larger cisco population.
Split into simpler sentences: Smaller walleye's major forage, yellow perch, are small in number in Brule. This limits the size of the walleye population, although once they grow large enough they can forage on Brule's much larger cisco population.