Dive Into Your Imagination

Pete Davison is our most recent SEAPLEX Scientist to update us on the research he did in the North Pacific Gyre!  Pete is currently getting his PhD in biological oceanography, and spent the cruise studying weather a special group of fishes called myctophids ingests the plastic in the gyre. 

What is a myctophid, and why do you study them?
A myctophid is a member of the lanternfish family—the most common vertebrate on earth (by weight) and they are very important ecologically because they are important prey for larger animals such as squids, birds, bigger fish, and whales.   Also, most of them vertically migrate, which is important for my thesis topic.  There are 2-10 grams of mesopelagic (or “midwater”) fish for every square meter of ocean surface, and it adds up to more than a billion tons of fish worldwide!  I am studying the ecological impact of vertical migration on the global carbon cycle.  To do this, I need to measure the population density of these fish and what percentage of them vertically migrate.

What is vertical migration?
Vertical migration is the 24-hour cycle of moving between shallow water at night and deeper water during the day.  The reason for this is that there are a lot of visual predators like tuna and birds near the surface, and yet because of the closer proximity to sunlight, so is most of the food.  Vertical migration is an evolutionary strategy for taking advantage of a rich food source while minimizing the risk of being eaten oneself.

What can studying the plastic inside myctophids reveal?
Finding out whether or not these fish eat plastic is important because it would document a path by which plastic (and the chemicals in/on the plastic) enters the food chain.  If myctophids are ingesting plastic, then it is very possible that the chemicals accumulate and become concentrated in predatory animals that we either care more about, such as whales, or that we eat such as tuna.

What did you expect to find? What did you find that you didn’t expect?
Expecting results is kind of cheating.  A result is equally important scientifically, even if it is negative.  We try to be objective about this, so that our expectations don’t influence our results.  That said, I know that a researcher in Antarctica attributes plastic in fur seal stomachs to the myctophids that the seals ate.  They predicted that 1/500 myctophids had plastic in their stomach. The Algalita Foundation reported that 50% of myctophids had plastic in their stomach, but that was in a blog, and has not been published.  Two different researchers have placed plastic bits in the end of the net to see if myctophids “net feed” during the capture process.  Some of them did, but you have to understand that a fish in the end of a net is dying, and gasping for breath.  The plastic could have worked its way into the fish simply because all the teeth point backwards in the mouth of a fish.   We have only dissected a few dozen fish in the month we have been home, and we haven’t found any plastic yet.

What are you working on and finding now that you are back on dry land?
What will you be working on in the future?
In terms of the SEAPLEX cruise, we all have 6-months or more of lab work before we get results so I am still identifying, weighing, and dissecting fishes that we caught in the nets to determine whether or not they are eating plastic.  I am also working on 3 other cruises right now that relate more closely to my dissertation.  Since I am entering my last (hopefully) year of grad school, I am a busy bee.  After I graduate, I hope to continue research on mesopelagic fish.

What was your favorite part of the expedition?
I love sorting through the catches from the net.  This cruise was very interesting because we went to a remote area that is poorly studied.  We caught all kinds of animals that I was unfamiliar with.  It adds a sense of excitement, discovery, and novelty to the drudgery of science.  So, I have to say that finding the oddball fish in my net was the most interesting part of the cruise for me.  The weather was nice, too!

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