Salmon in Santa Cruz County live on the edge. Quite literally: Monterey Bay marks the southern extent of the range for several salmon species in California, where naturally warmer water, smaller creeks that run low or dry in summer and fewer cool places to shelter leave local populations more vulnerable than their counterparts farther north. Recent years have brought cautious optimism about a rebound statewide, with scientists and restoration groups saying salmon here are still “hanging on,” sustained by decades of monitoring and an expanding web of restoration efforts.