This maxim holds true for other varieties of shellfish as well. Not only is low tide the drier, safer method for harvesting mussels, but you get mussels that spend nearly all their time in water, but with an hour or two of open air hang-time each day. Some folks claim that this improves flavor. Either way, they need to be pried off the rocks and that means skinned knuckles, so wear some tight fitting gloves if you have them. Watch your step.
Wet rocks covered with seaweed can be treacherous.
Don't forget the brandy. Good morale and a warm body are important considerations when harvesting mussels or other shellfish. It should be noted at this point that mussels can be purchased at any well stocked fresh fish market, but, due to irregular demand, the quality and price can vary. And there is no adventure or brandy to be found at the fish market. The byssus is a hair like filament that needs to removed before cooking by scraping or pulling from the mussel.