
The most exiting of these samples are the stomach contents – the fish puke preserved in ethanol and stored in a freezer. Aside from being fun to look at (and they are!), a look at a fish’s last meal can tell us a lot. Because I’m interested in the factors that contribute to production variability in nearshore fish populations, changes in a species’ diet is very important. I’m currently quantifying the extent and magnitude of predation by adult rockfish (and cabbies and lings) on juvenile rockfish YOY (young-of-the-year). By looking at predation patterns over time, then analyzing this data in the context of annual growth information (that I’ll be getting from otoliths – more about that in another post), I’ll be able to determine the influence that variation in YOY has on adult rockfish production.
My undergraduate work was done at Valparaiso University – thousands of miles from the nearest ocean. Not surprisingly, Valpo did not offer a Marine Invert Zoology course, so I did not come into this endeavor with much invertebrate identification knowledge at all. It’s been a learning process that I took on with a wonderful undergraduate volunteer from UCSC’s ecology program. I’ve learned that on long days – past the time in the afternoon when I want to stare at a computer, staring instead into a dissecting scope at partially-digested marine organisms makes for a very productive end to the day. Take a look below for a sampling of the prey items I’ve found.
A full red octopus (Octopus rubescens) is hard to mistake for anything else, though when only a tentacle or beak is present it can be tough to tell an octopus from a squid, both Cephalopods.

Crabs were found in many rockfish and cabezon stomachs. Below is a cryptic kelp crab (Pugettia richii), commonly found in Monterey Bay.

In the next photo you can clearly pick out two critters of the order Decapoda. The top shrimp is a Caridean (Infraoder: Caridea) and the bottom is a pistol shrimp (also a Caridean but of Family: Alpheidae). Another very common Crustacean that we find are gammarid amphipods (Family: Gammaridae). Note: to the left of the shrimp, you see part of a brittle star (Class: Ophiuroidea) which is not a Crustacean at all, but an Echinoderm! This all came from the stomach of a black-and-yellow rockfish (Sebastes chrysomelas).
stomach.

Sometimes you empty a vial and it looks really nice and un-intimidating like this. The larger fish pictured here is a Sebastes YOY!

Other times you empty a vial and have piles of mostly-digested mush, an assortment of claws (none of which seem to go together), white clumps that could be fish flesh, and arthropod bits.

Wonder how we got adult rockfish – the unhappy, spiny mothers that they are – to give up their hard-fought for meals? Most of the fish sampled were caught on hook-and-line, then went through a quick stomach-flushing procedure that scientists like to call gastric lavage. For fish that size that I work with, an 100-mL syringe filled with seawater and a sieve works nicely.

It’s a sea mouse (Genus: Aphroditidae)! A large gopher rockfish (Sebastes carnatus) yielded this polychaete worm – a creature I didn’t even know existed.