This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Editor's Note: William Gilly, a professor of cell and developmental biology and marine and organismal biology at Stanford University, is traveling with a group of students on board the Don José in the Sea of Cortez. They will monitor and track Humboldt squid and sperm whales in their watery habitats. This is the group's third blog post.
SEA OF CORTEZ—And the race is on! Three—no, four—fishing lines snake down into the deep, with more folks using hand lines. Feeding about 20 or 30 feet of fishing line into the water (just to the point where the glow-in-the-dark lure is no longer visible from the surface), scientists, students and crew alike jig for all they are worth, moving the line up and down in the water column—a foot or so up, a foot or so down. Jigging. Curious, the swarm of small Humboldt squid come over for a look and a cursory nibble.
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After four squidless and squid-poor days, squid a-plenty is most welcome. Our crew was getting anxious; we had seen the sperm whales, which commonly eat squid, so we knew we were getting close. We had also seen myctophids, which often turn up in squid stomachs, but the link on the food chain between the three had been missing. We have finally caught up to our elusive prey.
Pull! Pull! The spools on the reels spin furiously until a snagged squid breaks the surface. The chromatophores expand and contract, causing the skin to change from white to red and back again while the squid issues a strong burst of water from its siphon as it comes over the side. Students hurry to and fro, sorting squid for respiratory experiments, removing the stomach and liver for content analysis, and then setting aside the edible portions for a cooking project. Each must be weighed, the circumference and length of the mantle measured, the sex recorded. Near midnight, we pull out a prize from deeper water: a 74-centimeter-long squid, the length of the tube or mantle! This raises a question: Why are the majority of the squid so small (only 16-29 centimeters) when usually they are all giants like our 74-centimeter sample? After examining the guts, students conclude that the miniature squid were sexually mature and unlikely to grow bigger. Could size have to do with the conditions in the water? Hopefully our oxygen, salinity and temperature measurements with the CTD will yield some answers about the mystery of the small squid size.
Other analysis will have to wait until we can get our hands dirty in the lab and utilize high-powered microscopes for stomach-contents data, using a more stable base (nothing gets you seasick like looking through a microscope in a swell; we thought it best not to examine the contents of our own stomachs). However, we are able to expose the contents of two squid stomachs to find fish bones, small squid beaks and even a crustacean, supporting a more complex food chain in the Sea of Cortez.
Image of 74-cm mature Humboldt squid courtesy of Susan Shillinglaw; image of female sperm whale and calf in Farallon Basin courtesy of Susan Shillinglaw; image of 26-cm mature Humboldt squid (not typical of Sea of Cortez) courtesy of Susan Shillinglaw.
