I am told I have beginning cataracts. Is there anything I can do do prevent further development:nutritional supplements?

Yes and no.... Unfortunately there is no known method to completely stop the progression of cataracts. The rate of progression can be slowed by using uv protection, quitting smoking and maintaining a healthy diet. No nutritional supplement has been clinically proven to significantly slow cataract progression to date. Regular eye exams for early detection is the best management of cataracts.
Cataract delay. Cataracts develop at their own pace and the only clearly known risk factor other than heredity, is sunlight exposure. Nutritional supplements are not known to influence the speed of progression. Since surgery is so often highly successful, there is little to fear from progression.
UV protection. It is very important to protect your eyes from sunlight with good quality sunglasses, although the younger you start , the better. Once you have visually significant cataracts, surgery is usually the best option.