Let me preface this by saying I am not a criminal attorney so if you're really concerned about this, I'd suggest contacting one. Their may be provisions or cases that allow one who is conducting an activity such as fishing to carry an appropriate knife.
The Gerber folding knife should be fine. I often carry one when fishing and doing other outdoor activities; however, I wouldn't carry the dive knife around on your belt (I leave a fillet and boning knife in my tackle box).
It appears that you can have any folding knife, but the fixed blade diving knife can be no longer than 1.5 inches long. Refer to MGL Ch. 26 sec. 10(b)
I've copied and pasted the relevant section below (emphasis added by me):
(b) Whoever, except as provided by law, carries on his person, or carries on his person or under his control in a vehicle, any stiletto, dagger or a device or case which enables a knife with a locking blade to be drawn at a locked position
, any ballistic knife, or any knife with a detachable blade capable of being propelled by any mechanism, dirk knife, any knife having a double-edged blade, or a switch knife, or any knife having an automatic spring release device by which the blade is released from the handle, having a blade of over one and one-half inches
, or a slung shot, blowgun, blackjack, metallic knuckles or knuckles of any substance which could be put to the same use with the same or similar effect as metallic knuckles, nunchaku, zoobow, also known as klackers or kung fu sticks, or any similar weapon consisting of two sticks of wood, plastic or metal connected at one end by a length of rope, chain, wire or leather, a shuriken or any similar pointed starlike object intended to injure a person when thrown, or any armband, made with leather which has metallic spikes, points or studs or any similar device made from any other substance or a cestus or similar material weighted with metal or other substance and worn on the hand, or a manrikigusari or similar length of chain having weighted ends; or whoever, when arrested upon a warrant for an alleged crime, or when arrested while committing a breach or disturbance of the public peace, is armed with or has on his person, or has on his person or under his control in a vehicle, a billy or other dangerous weapon other than those herein mentioned and those mentioned in paragraph (a), shall be punished by imprisonment for not less than two and one-half years nor more than five years in the state prison, or for not less than six months nor more than two and one-half years in a jail or house of correction, except that, if the court finds that the defendant has not been previously convicted of a felony, he may be punished by a fine of not more than fifty dollars or by imprisonment for not more than two and one-half years in a jail or house of correction.