Those are Day Signals or Day Shapes used for communcation (just like Navigation Lights at night). The fishing vessels are displaying correct Day Shapes
There are five types of day shapes: Circle, Diamond, Cone Apex Pointed Up, Cone Apex Pointed Down, and a Cylinder. All day shapes are black in color. See the USCG Navigational Rules.
1) At Anchor - Single round ball
2) Aground - Three round balls in a vertical line.
3) Making way with sails up and motor on - Inverted cone ( only required for sailboats, 12 meters or larger ).
4) Dredging or making way with an obstruction on one side - Two green lights or two diamonds in a vertical line to indicate the side safe to pass. ( Diamonds are a sailors best friend - Thus, safe to pass. ) Two red lights or two circles in a vertical line to indicate the side which has the obstruction.
5) Vessel not under command - Two round balls in a straight line.
6) Vessel restrained by draft - A cylinder.
7) Vessel restricted in her maneuverability - Three shapes in a straight line. The top and the bottom are a ball and the middle is a diamond.
8) Vessel engaged in fishing - Two cones in a vertical line with their apexes pointed at the center.