I'm going to say a different opinion about this.
I would most definitly jump in if I felt the spot was big enough, that my method of casting was the same as theirs and I would ask
"you guys mind If I jump in here"
I have fished many places where if you want to catch fish unfortunately sometimes there's a crowd. Most notably being the Wasque Rip on the Vineyard. When the bass and blues come in there your going to catch 5 times more fish in a half mile strech. I also fished the jetties at menemsha which are way better for albies and bonito than the beach. I made my first trip to Pulaski (salmon river) this past year and if you can't fish with others you may as well not go. The question is do you know how to fish in the crowd? Thoughts to remember.
1. constantly look left and right (more so one way if the rip is moving the other way" this way you can see if the guy 3 down from you hooked up and if you may need to stop and let him follow his fish.
2. Follow the damn fish. If you hook up and the fish runs 200 ft to the right walk with the damn thing. I remember being like 10 years old and some idiot guy was fighting a fish from about 250 to my left and no one could fish because of it. Now that I'm older I would yell at him.
3. Cast straight. Not brain surgery. Don't cast so that your line will cross someones elses. If lines cross pull it in fix it drop the line say something funny or a smile is fine. If it keeps happening then think about mentioning the casting techinque their using.
4. When you do get a fish in. Bring it up the dune if it may take some time to un hook so you don't alter others fishing.
5. If someone is landing a fish or changing a plug don't take his spot or let some shumck take it If your there you may mention "sorry my buddy was fishing right there" hes coming right back
If your with other good fisherman fishing in a crowd isn't that big a deal and if you with a large group it can be real fun. Especially during a blitz and one guy can't hook up or gets all the smalls.
