Page 51 of the 2010-2011 California Ocean Sport Fishing Regulations (28.65.d) states, "No person shall take finfish from any boat or other floating device in ocean waters without having a landing net in possession or available for immediate use to assist in landing undersize fish of species having minimum size limits; the opening of any such landing net shall be not less than eighteen inches in diameter."
Link to regulations:
http://www.dfg.ca.gov/marine/pdfs/oceanfish2010.pdf
This is why so many guys carry a net even though they rarely use it. Some store it inside the kayak just to comply.
