Older methods from the early 20th century were less efficient.  They would "cut" the kelp by dragging long wire ropes or chains between two tug boats.  Then they would pick up the kelp with grappling hooks or gather it on accesible beaches.  There was a good amount being lost and it would end up on shores because they were not easy to get to in order to reclaim.  Today's methods are much better with the help of the Department of Fish and Game.  To comply with state laws, the harvesters are trained to minimize the loss of kelp while harvesting.  It can be cut 3 to 4 times a year.
People using specialized boats harvest the giant kelps.  It’s like mowing a grass lawn.  The kelp harvesting boats are allowed to chop off 4 feet below the water surface.  They are supposed to remove all that’s taken because it may end up washed along the shores and be an eyesore.  The majority of the kelp washed up is due to storms or grazers, such as Strongylocentrotus purpuratus.  Over one hundred tons are taken per year of the coast of California alone and ninety-seven percent of that is off the Southern California coast.  Algin is obtained from the seaweed.  This algin is used in everyday products like toothpaste, ice cream, chocolate milk, cosmetics, pharmaceuticals and beer.  It is all regulated by the Department of Fish and Game.  There are still pros. and cons. over this subject.  The pros. would be allowing light to penetrate further into the waters and the con would be removing safe places for the juvenile fish to take cover from predators.