Night Trawlers and Crawlers — SE 1501 Blog from Team Trawl!

By PIFSC EOD guest blogger Laura Lilly, guest scientist acoustician aboard SE1501, under Chief Scientist Phoebe Woodworth-Jefcoats.

One important aspect of our SE1501 cruise was the nighttime shallow-water (20-150 meter) trawls that we conducted to determine the composition of the mesopelagic layer (small fishes, squids, crustaceans, jellies and other creatures) across the Transition Zone Chlorophyll Front and the North Pacific Subtropical Gyre. During the cruise, our trawl team sorted through eight net tows, and highlighted some of the more unusual organisms they found.

Don Kobayashi – Spiny eel (Notacanthid leptocephalus)

My favorite trawl catch organism on this project is the very large leptocephalus we caught on the first trawl of this project. Leptocephalus is the general name for the larval stages of eels and a few other normal-looking fish such as tarpon, ladyfish, and bonefish. They are usually entirely clear but large and leaf-shaped. The odd thing about this leptocephalus was its size. It was so long (well over a meter) that it would not fit in any of our catch processing trays! It was clear, like most leptocephalus I have seen, but it also had a row of uniformly spaced black pigment spots extending down the length of its body. At first glance I thought this was the larval form of an unknown giant sea-serpent-like eel! After looking through the identification books that colleague Bruce Mundy from PIFSC had compiled I saw that there was another taxa of fish that is known to have large leptocephalus larvae. These are called notacanthid fishes, or spiny eels. The ID was also confirmed with a quick email to Bruce back at IRC. The notacanthids are not true eels, but deep-sea fishes with a long tapered body. Amazingly, the larval forms can get much larger (~2m) than the adult size (~20cm-1.2m), meaning that when the larvae settle down to the adult habitat they somehow shrink considerably. The other reason I like this larval form is that it is about the closest thing to a shore fish larvae that we caught on this entire project. I’m interested in connectivity in shore fishes via their pelagic egg and larval stages, but we have not been catching many of those species due to our distance from land. The adults of this spiny eel do not live close to shore, but they do live near or on the sea floor, so their larvae are still quite a ways away from where they normally would live as adults. On a side note, it was a great pleasure working as Trawl Team Lead on this research project and I thank all the members of the night-shift who contributed to the effort. I also have a handful of ideas to make our Cobb trawl cod-ends cookie cutter shark-proof.

This is the notacanthid leptocephalus we caught.spinyeel2

This is what an adult notacanthid looks like.

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Melanie Abecassis – “Bob the Blob” Squid (Cranchia scabra)
On our second night of trawling we caught an interesting – and new to us – squid, shaped like a blob. He was still alive and kicking, I mean inking, out of shear indignation at our intrusion in his life. Quickly named Bob the Blob, he was placed in a big tub of sea water, in the hope that he would remain alive for a few days, while we tried to identify him to species level. A Google search for “blob squid” yielded no satisfying result. After learning from trawl lead Don K. that he might be from the “cranchiidae” family, another Google search yielded amazing pictures (try it) of specimens from that family of translucent squids. None resembled Bob very closely though.  After a couple of days, Bob unfortunately died. A picture of Bob was sent to PIFSC director Mike Seki, who is also a cephalopod expert, and Dick Young, retired squid expert professor from UHM. Based on the picture, the best guess is that Bob is a Cranchia scabra. Most importantly, in the words of Kristen G., UH grad student, the main thing to know is that “Bob was a good squid. He inked a lot.”

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Jesse Abdul – Cookie cutter shark (Isistius brasiliensis)

I visited the Honolulu fish auction for the first time earlier this year and saw firsthand the damage that the parasitic cookie cutter shark (Isistius brasiliensis) can do to large fish; many fish had deep circular cuts in their bodies caused by this parasitic animal. I was surprised by the amount of damage this small shark could inflict on fishes that were many times bigger than it.

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During our SE1501 cruise, we caught multiple cookie cutter sharks in the mid-water trawls. It was exciting to see a live specimen, although the excitement was short-lived because on three occasions sharks bit a perfectly round hole through the trawl cod-end (the bag at the end of our trawl net that collects the organisms), causing the majority of our trawl catch to be lost. Despite that problem, we did catch and preserve five cookie cutter sharks, which can be studied further after the cruise. The catches were particularly exciting for me because I work in data applications development at NOAA, so I don’t usually participate in field work. I feel fortunate to have had several sightings of this relatively rare species.

The mouth of a cookie cutter shark (Photo courtesy of Jesse Abdul)ccshark2

The perforated cod-end of our Cobb trawl, caused by a cookie cutter shark.

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Erin Kawamoto – Ocean sunfish (Mola mola and Ranzania laevis)

During our trawls on SE1501, we caught juveniles of two species of sunfish, Mola mola and Ranzania laevis. They were so cute! These fish have odd body proportions, which made me think that they were slow swimmers, but they are actually very speedy! Molas are the heaviest of all bony fish and can weigh up to 5,000 pounds. They can be seen basking in the sun near the surface of the ocean, and can even breach out of the water in an attempt to rid themselves of parasites. That would be amazing to see in person!

Juvenile ocean sunfish, Mola mola

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Juvenile slender mola, Ranzania laevis

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Phoebe Woodworth-Jefcoats – Phronima

Phronima are small (roughly one inch long) marine amphipods, but they look pretty fierce. Check out the pincers! Their transparency gives them some protection in the ocean because predators can’t see them, and prey can’t see them coming. On top of that, Phronima often hijack other organisms called salps for protection. Phronima crawl inside these barrel-like animals, eat their guts, and then use the body as protection for their own eggs.

A Phromina captured during one of the nighttime Sette trawls (Photo courtesy of Jesse Abdul)

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PIFSC Science Operations technician Eric Mooney and UH graduate student Kristen Gloeker also contributed to nighttime trawl collection and processing on SE1501. IMG_2306

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