We saw two species on that occasion - Pacific and western brook lamprey. River and Pacific lamprey are anadromous (in this case, they spend a couple years in the ocean then return to freshwater to spawn) and parasitic (they grab on to fish and marine mammals with their round many-toothed mouths and feed until they are full). These guys can get big - up to about 30 inches long when they are adults! Western brook lamprey, on the other hand, spend their entire lives in freshwater and are not parasitic. They stay small (reaching only about 6 inches, max) and filter feed on small bits of plants and animals in the water column, and get this - adults don't generally feed on anything at all! Crazy, huh?
So we pulled A LOT of lamprey out of this little creek - but it is difficult to tell the difference between Pacific and western brook lamprey when they are young (larval lamprey are called ammocoetes, see top picture below). We did catch several macropthalmia (bottom picture below), which are Pacific lamprey that are old enough to migrate to the ocean. They are a bit bigger, and are an amazing silver color - their "snout" kind of reminds me of Snoopy's nose because it is big and blunt.
Metamorphosis occurs shortly after and that's when their oral disc and teeth appear so that they can beef up on all the yummy food in the ocean. But check out the mouth of this larval lamprey (below) - it's not formed into a disc yet, and there are very few teeth.
If you'd like to learn more about lamprey in the Pacific northwest, check out the USFWS Pacific Lamprey Conservation Initiative website. If you like these pictures, feel free to use them but please give photo credit to Marci Koski, USFWS. Thanks for reading!