It will depend on just how the actual appropriation reads. If funding for the "whale food" is an actual line item in the budget, then that is all it can be spent on without re-authorization. If it is just folded into the budget it can be moved around.

I recall one year when the Leg had a line item for each hatchery because the agency was believed to get money for A and spend it on B. So, so one year, the budget to the hatcheries was rather fixed.

Need to dig a bit deeper on the number surplussed. If they were surplussing fish, then they either had "enough" to meet goals; that they didn't suggests they were going for the 8.7(9.5)M. Or, they surplussed males as they carry few eggs, which means fecundity was way below planning numbers (smaller fish?).