We’ve been targeting both Copper and Quillback rockfish as we fish our sites before and after the herring spawn. They seem to be the most ubiquitous species at our sites, but we’ve also found greenlings, sole, lingcod, herring and a host of other rockfish species. Here’s a beautiful Quillback specimen (see right). I slowly overcame my ruefulness (definition: feeling of pity or compassion) towards these beauties of the sea (hardly “rock garbage” as some people refer to them) as I bonked them over their heads in the name of science.
When we took a look at the stomach contents from the fish at the sites where herring had spawned, we found that many of them were in fact indulging in the roe! In fact, some of their stomachs were completely full of roe, algae and herring. This is pretty cool, and you can check out some examples of this here. Here’s one fish that feasted on some roe-on-algae (top right). Here’s another specimen that devoured a female herring full of roe (bottom right). We only found fish bones and vertebrae of the herring, but a lot of the roe remains, so it appears that the roe breaks down more slowly that the fish. We had no idea that the rockfish would be eating the roe, but it appears that they do! In fact, these fish, which normally feed on invertebrates and other small fish seem to be preferring herring roe when its available.
With each rockfish that we catch, we take tissue samples from the muscle, liver, gonads and heart, which will be used in isotopic analysis. This will show how organisms may switch their prey sources during herring spawn season. Herring, and herring roe, will likely have a more marine isotopic signature than other common sources of prey.
Marine isotopic signatures come from marine food sources (plankton) that they feed on in offshore waters before coming ashore to spawn. These distinct herring and herring roe signatures will become integrated in the tissue samples and we hope to pick up on these marine signatures once we analyze the tissues in the lab.