viewPager.setOnPageChangeListener(new OnPageChangeListener() {

        @Override
        public void onPageSelected(int arg0) {
            //verifique se usuario esta na posicao 0 e atualize o fragment
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {}

        @Override
        public void onPageScrollStateChanged(int arg0) {}
    });