(NBBJ) - Sales of higher-end wines are making North Coast winegrapes a hot item, but availability of workers to pick them has fallen sharply, driving wages higher, according to a large vineyard owner in the region.

The average number of unskilled workers employed locally during the peak season of vineyard activity — generally, harvest — has fallen by about 50 percent in the past five years, while average wages for such jobs in that time have risen by almost the same proportion, said Eric Pooler, vice president for winery relations for Napa-based Silverado Investment Management Co., at North Bay Business Journal’s Wine Industry Conference in Santa Rosa on April 28.

This comes, he said, as several national, statewide and local forces are pulling on the North Coast winegrape workforce: tighter U.S. border security and immigration enforcement, ever-higher cost of living, competitive pay in other crops and industries, and new state labor rules that increase employer costs.