Here are some fun cultural resources about Sushi and the expression "おつかれさまでした":
I. Sushi
Kids Web Japan: How to Make Sushi
Nipponia Magazine Special Feature - Sushi! Sushi! Sushi!
Nipponia Magazine Special Feature - Eat It Raw: How to Prepare Sushi and Sashimi
JNTO: Sushi in Japan Guide
Begin Japanology: Sushi
II. おつかれさま
Global Manager article (it explains how おつかれさま is used in context)