To collar the animals with a GPS so they can track them. 
This allows them to:
- Find the animals more easily so they can observe and evaluate what the animals are eating. 
- Obtain samples from the food source and evaluate it for nutritional content. So they can determine if the environmental factors correlate with nutritional content. Eventually showing a causal effect and validating the research.

Also:
- The act of netting the animals also allowed them to substantiate and quantify the claim that Chugach range sheep were in fact "skinnier than anything we've ever seen," because they would have evaluated the animals more accurately at that time.