Answer E
Option(A) The ease with which lake trout can be caught by anglers varies with the time of year and the water temperature.> Incorrect. (Even if true, this doesn't support the statement "why to avoid lake trout's summer haunts and fish instead in a shallow bay or close to the surface off a rocky point")
Option (B) Cold water is denser, and therefore heavier, than relatively warmer water.
Incorrect. (Unrelated)
Option (C) Lake trout are found exclusively in deep temperate lakes.
Incorrect. (The passage is about deep temperate lakes only.)
Option (D) Lake trout do not alter their feeding habits from one part of the year to another.
Incorrect. (Unrelated.)
Option (E)
(E) In deep temperate lakes that have ice residues on the surface, late-winter "turnover" has not yet occurred.
CORRECT !
Turnover takes place during late winters and fall. If turnover has already taken place (it's late winter, summer on the way

), then chances are trouts are now in deapth, where the water is coldest. Then it wouldn't make sense to fish in shallow waters, will it?