If you want to see how fish behave underwater when you go fishing, just take your handline and gear as for a handline fishing trip, plus take your dive mask and snorkel. Get to the place, prepare the bait and when you drop the line in the water, put the mask on and hang over the side with your head in the water. You will see how fish react to the bait you give them and eventually know if you doing something wrong, plus you will be able to retract the bait in case unwanted fish try to take it. It is relly interesting to see it and sometimes you can see if there are other fish around, I often spotted squids while fishing and in that case I lower a squid jig.You can also see if the area is good and if the fish population is not enough move somewhere else.