Before searching for any First Wyverians whosits, consider returning to the Rotten Vale on an expedition. You've been there a few times and have done plenty of searching (two "look for Zorah Magdaros clues" expeditions thus far), but previously you were either on business, or you didn't have access to the entire area, making this the first real opportunity to deal with the usual field researchers. Granted, you could have helped out the Endemic Life Researcher already, but the other two either required you to - or are easier to - deal with now. Their tasks are listed below.
Research Help: Goldenfish Capture
Descend to the depths of the Forgotten Vale (AREA ) to find the Piscine Researcher again. What sort of fish would dwell in this horrid place is... well, a matter of his next challenge, actually. Apparently Goldenfish pollute their scales by swimming in these fetid waters, but nonetheless you'll need to catch one to impress the Piscine Researcher. This starts the delivery request Research Help: Goldenfish Capture, and again he claims such fish aren't present at the current fishing spot.
You will need to head to the depths of the Rotten Vale to find the Goldenfish (or hunt for one in the Coral Highlands, but what fun is that?), so travel to the Central Camp and head north, then west to AREA 10. From there head south through a hole to reach some caves (AREA 15) where you'll find a pool of water just southwest of the hole you crawled through wherein Goldenfish dwell. They're skittish, so be careful approaching the pool and don't bob your bait. If you're extra careful, you may be able to capture one with the Capture Net. However you manage it, nab yourself one, then return to to Piscine Researcher, who of course refers you to the Resource Center in Astera.
Research Help : Scavantula Capture
Head over to the northern part of AREA 1 and you'll find the Endemic Life Researcher, who has yet another task for you. She wants you to capture five Scavantula specimens so she can "watch them eat dead monster flesh". Seems like she's been spending too much time in this wretched place. This starts the critical bounty Research Help: Scavantula Capture.
You can find a number of these purple arachnids scuttling about along the ground in AREA 4, which just so happens to be the Radobaan's lair. Fortunately the monster is docile if you don't provoke it, so it shouldn't be too much of a bother. The Hornetaurs nearby are another matter, however. Also be wary of the fact that the Scavantulas are skittish, so don't waste too much time before capturing them. If they flee, simply move away to a different area for a while and return and repeat the process until you have five of the spiders. Report back to the Endemic Life Researcher, who will then, of course, tell you to return to the Resource Center in Astera.
Make your way down to AREA 14 (the Odogaron's lair) where you may find the Lynian Researcher - possibly along with a Grimalkyne, which will flee at your approach. Talk to the Lynian Researcher and he'll identify these Grimalkynes as the Plunderer tribe before encouraging you to make contact. Make your way back east to AREA 10, then head south into the cramped caverns (AREA 15) where you found the Goldenfish pond.
You'll find the Grimalkyne you're looking for in a chamber to the northwest, but unfortunately it'll run off again when it sees you. Follow your Palico's advice and move away from where it fled (consider climbing up a ledge to the south) and press [X]/[A] to crouch. When your Palico says the Plunderer came back, go after it again, only to have it run away. This time your Palico will suggest you leave some Raw Meat behind, leave a piece in the middle of the chamber (select Raw Meat with your Item Bar and press [Square]/[X]), then scuttle back south onto the ledge and crouch again, then wait until the Grimalkyne and its friends arrive to feast. Run up to them and this time they'll stay and chat, ultimately overcoming their disgust at your appearance. After all, how bad can somebody be if they drop hunks of raw meat around?
One of the Plunderer Grimalkynes will now join you, and they'll give you the Plunderblade Palico tool. Tell the Lynian Researcher and he'll merrily rush off to end the food crisis here - don't bother worrying about how he plans to manage this. Next time you talk to your Palico it'll share the news that the Plunderers taught it how to talk to Girros. Good stuff.