Completely agree with Hbird11. When herring die due to thermocline, it's oxygen related. When they die up top, it's usually differential in water temps versus temps they're kept alive in. You said the herring were in coolers and probably insulated meaning colder water. Throw a fish which is temperamental to begin with from cooler water into 80 - 82 degree water, it goes into shock. Without knowing, I'd bet Gerry didn't have his herring in an aerated cooler as opposed to maybe a floating bucket or just warm lake water if he didn't experience the same problem.