Hi Shaun,
I posed pretty much the same question to the ODFW (Oregon Dept Fish & Wildlife) fisheries biologist about a couple of lakes I like to fish near Cottage Grove. I asked if there was an online database which would tell me what certain specials used on a continual basis to sustain themselves. The first answer back came from a biologist who copied my question to a warm water species biologist. I asked and received an okay to reference the contact information of these biologists.
It might serve you to contact Gary Galovich (second response below) to see if he can supply you with information. It could take a couple of weeks for him to get back to you as you'll read below.
It would be nice to see a database of forage species. That said there are so many bodies of water, it would be difficult to create. My intention for the information is to use it on album pages of my Website in the "Destinations" section to let folks know what is in the waters we fish. I mention this because if you get information on the bodies of water you use, post it or PM me so I can spread the word...
SECOND ODFW RESPONSE:
Bill –
My apologies for the slow response, but I’ve been out in the field quite a bit.
Like Jeff, I’m not aware of a single source that would provide the detailed information for all Oregon waters that you’re looking for. He has referred you to a good site for info on the Willamette Basin reservoirs. I also sample these and other waters across the state for warmwater fish, but have not done dietary or predator-prey studies on each. However, we can make some assumptions about forage based on the other species available.
For example, at both Cottage Grove and Dorena the list of other fish species includes bluegill, crappie, bullhead catfish, and native fish such as cutthroat trout, largescale sucker, and sculpin. Dorena – but not Cottage Grove – also has yellow perch. We also stock these and many other waters with hatchery rainbow trout, which can be preyed on by the larger predators such as bass. Also, species such as bass will be cannibalistic.
In terms of amphibians, several species of frogs can be present, though in areas with habitats that are or have been disturbed or are heavily used by the public the non-native bullfrog is most common. As for invertebrates, the species list of aquatic insects, zooplankton, etc. can get pretty lengthy, but in terms of larger invertebrates it is primarily the native signal crayfish. However, there are a number of waters where non-native crayfish including red swamp and ringed crayfish have been illegally introduced so even this list is getting more complicated.
In general, the bass and other non-native predators tend to be more opportunistic than the larger trout and aside from the aquatic insects will have a more diverse prey base. Also, the fish communities tend to be more diverse in the waters where they are found.
Gary Galovich
Warmwater Fish Biologist
Oregon Department of Fish and Wildlife