Five years after the largest oil spill in US history spewed millions of gallons of crude into the Gulf of Mexico, many Louisiana oystermen are fearful that a once-bountiful population of the mollusks may never recover.

"My kids are losing hope," said Wilbert Collins, 77, a retired third-generation oysterman in southeastern Louisiana with four sons who followed him into the industry. The family business has endured a 60 percent drop in yields in the past five years.

The explosion and collapse of the Deepwater Horizon oil rig on April 20, 2010, left 11 workers dead and huge stretches of the Gulf fouled with petroleum that gushed from the site for 87 days.