A Boaters Question - Does any boater familiar with hydrographical charts know what squiggly black lines mean?

Question

Around certain small land sections or islands, some are surrounded with a black squiggly line, running all around the edge of the small island....trying to find out what that means.

Answer 1

that means like small little earth tremors

Answer 2

Here you go - link to Chart 1 - a reference book for all the charts squiggly lines and more.

http://nauticalcharts.noaa.gov/mcd/chart...