Salmon return to the ocean to feed and frolic. Fry (in salmon form) meets salmon Leela. They grow up with each other, and decide that they should mate with each other when they return. After confusion Fry fish overcomes his instincts to return to his own home-streamand, and goes to Leela fish's side of the lake. They mate and die.
On the Galapagos Islands, Zoidberg is a Blue-Footed Booby, and Professor Farnsworth is depicted as a near-extinct Pinta Island tortoise, lonely and desperately trying to find the only mate of his sub-species on the island. The birds (Fry, Leela, Hermes and Amy) convince the old tortoise to make the long trip across the island to meet his only possible mate (Mom). Bender-iguana accompanies them. Amy is eaten by a Sal-snake, but once the remaining 5 arrive, the Professor-turtle mistakes a rock for Mom, and begins to mate with it. Mom-turtle walks up, enraged at what she see's, pushes the rock over a ledge and off the island. They mate, Mom lays 3 eggs, and they go off separately to die. Once hatched, the 3 new Pinta Island Tortoises (Walt, Larry & Igner) and are immediately crushed by a rock, making the species extinct.
Beachmaster (Bender) is the dominant male of a group of Elephant Seals. Leela and Amy (among others) are females in Beachmaster's harem, and Fry, Professor Farnsworth, Kif, Hermes and Randy are the beta-males, who have no chance to mate while in direct competition with Beachmaster. Scruffy the Walrus apparently hangs out with the beta-male elephant seals. Professor-seal tells the other beta-males that he once was able to mate with a female by sneaking past Beachmaster while he was mating with the Professor's mother, and finding a mate. Kif-seal decides to try this, so after Beachmaster rolls over onto all the children and tlls the women to repopulate with him, Kif brings Amy-seal a delicious treat from the ocean floor. As she's explaining that Beachmaster will kill Kif-seal and agreeing to his request to mate, Beachmaster notices the beta talking to a female and angrily saunters over. Kif-seal bravely challenges Beachmaster, but is crushed in the fight, which Beachmaster carries on long past when Kif-seal is dead and into the night. The next year new children have been born, and Bender-Beachmaster proclaims that it is a new litter spawned by him, despite the fact that they look almost exactly like Fry, Hermes, Randy and the Professor.