The grief being felt by South Koreans over the April 16 sinking of a ferry, in which more than 300 people, most of them high school students, died, continues to have an economic impact. A survey last week of 400 small grocery stores, restaurants and travel agencies by the Korea Federation of Small and Medium Business found that 80% of respondents said business has declined since the tragedy. On average, they reported that sales have dropped 33% over the same time last year. Travel agencies have been hit especially hard, and some are saying they are having difficulty paying staff.