We are working on a Cooperative Research project that utilizes fishing vessels to sample the pelagic (midwater) and benthic (bottom) habitats off Newport Oregon. We were recently aboard the F/V Timmy Boy and the last post focused on what we collected in the beam trawl that samples the seafloor. Today, I’d like to show you some of the critters we collected from our plankton nets.
To sample the midwater, we use different nets that target certain organisms in varying habitats. We use a fine mesh net (202-um) to sample small and abundant organisms such as copepods and amphipods. This net is deployed while stationary and is hauled vertically from 100-m water depth to the surface.
We use a bongo net (named as such because it resembles a set of bongo drums) that has coarser mesh (335-um) to sample larger, more mobile, and rare organisms such as krill and fish larvae. This net is towed through the water at 2 knots to capture the more mobile critters and it samples the upper 30-100-m. This net is also black so that the organisms can’t see it and thus avoid it.
We also use a neuston net that is towed at the surface and thus only samples the upper 0.3 meters of the ocean. This net targets organisms such as fish and crab larvae that often congregate at the ocean’s surface.
Patterns we observed
The most apparent patterns we observed while sampling from 2 - 150 kilometers from shore were the striking change in the water color and what we collected as we moved from inshore to offshore. Inshore of 10 miles, the water clarity was minimal, the water was a distinct brown color. Here, our nets were clogged with thick mats of phytoplankton (with the domoic acid producing harmful algae Pseudo-nitzschia present in most samples) and jellies were the highest abundance I have ever observed. Lit up from the ship’s lights as we moved along, it looked as if you were looking out onto a starry sky with the white jellies as the stars amid the black ocean surface.
As we moved from inshore to offshore, the ocean changed from a pea-soup green to dark blue to brilliant blue. Eskimos supposedly have many different words for describing ice; I’d imagine mariners have many different words for describing the color of the ocean.
What did we collect?
As with the beam trawl, it was always exciting to see what our nets collected. I’d say the highlight of the midwater collection on the trip is what was appropriately dubbed by the Timmy Boy crew as “The Tinfoil Fish”, which Toby explained was a juvenile king-of-the-salmon fish. Apparently these fish can reach up to 1.8 meters in length, however the little one we caught was only 3 cm in length.
We also collected juvenile Velella velella (by-the-wind sailors) which are a type of jelly. As juveniles they appear as small blue orbs and they do not have the large apparent blue sail that gives them their name and that transports them along the ocean surface by the winds. We also collected a few Porcelain crab larvae that merely appeared as small brown dots until further investigation revealed their tiny claws and long antennae. These larvae will remain pelagic (free-swimming) for weeks until they are transported close to shore where they will metamorphose and settle into their benthic habitat on rocky shores.