a legislation is passed requiring a riparian zone by the family's waterway. this will reduce the size of their fields by 15%. How much will the family lose per year by having a riparian zone on their farm?

The rate that would change would be the  searching efficiency/attack rate. there are only two other rates in this model: the  growth rate of prey, and the  predator or consumer mortality rate.the  searching efficiency/attack rate is what indicates how effectively can a predator capture its prey whether in the searching process or actual capturing/attacking process. 

Yes yes yes very good