Like everything else related to nature, air and water temperature largely determine when certain species make their first appearance. Back in the early 80's we used to see some of the first squid appear in the Peconic's and eastern LI Sound in late April with the big explosion fueling the fabulous early season Fluke fishing we used to enjoy starting in early May. It was so good at that time that the Prime Time out of Orient used to run targeted "Squid Fishing" trips at night!
Now, it seems to take until early May before we see any reasonable sized schools of squid that last through most of June. However, the size of the run is much smaller than in the past. This is probably one of the big reasons our early season Fluke action is just a shadow of what it once was. Regardless, if you know your stuff and work hard at it you can still come up with some decent Fluke for dinner in the bay.