There are plenty of threads on this, so do a search. I find the best overall approach to be reflective mylar "flash tape" streamers (can be hoisted on a line) and hanging CDs also work. Any type of closely spaced spikes (or tie-wraps with ends sticking up) also work, and so does heavy monofiliment fishing line stretched taught about 2-3" above the spreaders.
Just how might one go about deterring birds from their boat. A very good question. Exploring ones options....
Bird control strategies
There are many bird control strategies: visual (streamers, balloons, lights, fake hawks); physical (nets), and acoustical deterrents (electronic sound devices, pyrotechnic pistols). Experts agree a combination of methods is required.
Wine growers use "Bird Bangers". Propane powered cannons. Just think of the fun. Light one of these bad babies up and all the birds in the marina would take flight. Think of the public service you would be doing for all of the boat owners, and as a bonus they are prompted by
Blasting the Banger might create a stir among the residents who prefer the quiet pease and tranquility of a life by the water shore. That would likely eliminate another great deterrent. The 12 gauge shotgun. How do I know they work, cause every time I went goose hunting the buggers would take off and fly high, there was no chance to bring home the "Fatted Goose" for Christmas dinner. But I am fairly sure If you did hit a couple of those pesky birds and left their bodies about on the docks the relatives would stay away... Unless they remember the movie "The Birds" and come back in mass. Then all bets are off and it is everyone for themselves.
Electronic Bird Control Now we are talking. Control through modern science.
Bird Gard units are designed to effectively and permanently remove birds from your environment. A built-in microprocessor in the electronic bird control units continually randomizes the order the sounds play and the relative pitch of each bird sound to give the impression many birds are in distress in the protected area. This random technology prevents birds from becoming habituated and keeps birds out of your grapes all the way through harvest.
This is like using the Ride of the Valkyries in the helicopter approach to the beach in Apocalypse Now. Physops for birds.
These are just a couple of ideas that a limited few have tried but might work, based on thoughts from my caffeinated creative brain this morning.
Looking at the way that bird has a grip on the light, sure hope it is made of steel and glass. Plastic would be toast. And sitting there it looks well above any 12" spike... I'd be worried he would take the light fixture when it flew off.