Researchers are trying to figure out how many fish in the ocean have been caught and then returned to the water. Researchers can tell by finding certain markings on the fish and watch 15 fish get returned to the water on Saturday. On Sunday, they monitor the waters and find out that 21 out of 300 fish were returned to the water. Using this ratio, what is the best estimate for the total number of fish caught on Saturday, rounded to the nearest whole number?