If you don't already know of the Lambent Chicken Easter Egg. After meeting Prescott and you fight the Lambent or after you get the message from Prescott in the Captain's Chamber if you are Marcus go towards any of the 4 Pipes on the deck and shoot with the Snub Pistol or Hammerburst. Reload and he should say "Hellooo." and do it to all 3 of the pipes. The last one should spawn a Chicken and Marcus should say "What the hell?". Shoot the Chicken until it turns Lambent/Into a huge Golden Chicken and kill it. Now go to the Deck-lift and Marcus should tell the COG Gear to raise the lift. After it's raised go to the right where the barriers are and the ocean should be in front of you. Use cover onto the barriers and you should be able to vault over it. Go up the stairs and you should find a dead COG Gear with some Frag grenades and the Cluckshot next to him.
The Cluckshot ONLY Spawns if you kill the Lambent Chicken.