Editor’s Note: Marine biologist William Gilly is on an expedition to study Humboldt squid on the University-National Oceanographic Laboratory System research vessel New Horizon in the Gulf of California. He and other scientists are learning about the giant squid, their biology and ecology on this National Science Foundation-funded expedition. This is his third blog post about the trip.
GULF OF CALIFORNIA—Days 4-5 Punta San Carlos to San Francisquito and into the Salsipuedes canal to Bahia San Rafael: Day 4 was the first real day of experiments for our group. Seas were calm and warm as we made our way along 300-meter depth contour carrying out a zigzag transect for Oregon State University’s Kelly Benoit-Bird’s acoustic survey of squid in this area well north of Santa Rosalia. Instead of engaging in nautical or oceanographic activities that one would expect on an expedition like this, our group has sequestered itself in a small wet-lab equipped with a bench and a sink and an alcove to tuck away our experimental setup. With a computer, amplifiers, oscilloscope, high-speed video camera and many cables running every which way, the whole arrangement has a well lived-in look about it and reminds me of the lab at home. That’s good, because it will be home for the next three weeks.
What do we really want to do and why? Let’s start with why and that will lead us to what. We learned from tagging Humboldt squid and sperm whales in the same general area at the same time (near Santa Rosalia and Isla Tortuga in 2004) that sperm whales tend to hunt squid at depths associated with the upper Oxygen Minimum Zone (OMZ) both day and night. This makes sense in the daytime, because that is where the squid spend most of their time. But what about at night, when the tagging data clearly show that squid tend to migrate to near-surface waters like the small mesopelagic creatures on which they feed? Well, that’s not the whole story—squid are rarely near the surface all night, at least in the warm waters of the Gulf, and spend 25 percent or more of nighttime hours at OMZ depths. We’re not sure why they do this. They could be hunting at depth, because some of their prey organisms remain in the OMZ all night. Or they could be recovering in the cool, deep water from strenuous activity in warm surface waters. Nonetheless, the squid spend some time at depth at night, and whales apparently prefer to hunt them there. Why? Maybe the squid are easier to catch, because they are slowed down by the cold, hypoxic conditions in the OMZ. Whales of course could care less about either problem, and the increased probability of catching a sluggish squid may outweigh the reduced probability of encountering a squid at depth. I think the whales are telling us this—animals never lie.
Our experiments are therefore designed to see how a squid’s peak athletic performances—escape responses and strong jetting—are impacted by conditions in the OMZ. A simple and biologically relevant comparison would be between warm, oxygenated surface water versus cold, hypoxic deep water. We can also hold the squid at a constant cold temperature and see what the specific effects of low oxygen are. This may all sound straightforward, but it is challenging task away from the blackboard. Although I have made many similar studies on the escape responses in the smaller, California market squid, Loligo opalescens, that work only serves as a rough guide. It is becoming rapidly clear that a small Humboldt squid (Dosidicus gigas) is not a simply a beefed-up Loligo in regard to what they consider a threatening stimulus. Loligo bolts at the flash of a strobe light, whereas Dosidicus seems to care less. A brief, mild electric shock (one that you might not even feel) will send Loligo flying typically in less than a second, but Dosidicus seems more resistant and often requires several shocks in quick succession to stimulate a strong jet. We have discovered an extremely sensitive spot on the "neck" of Dosidicus that produces fast, powerful jets that appear to involve the giant axon system, but more on that later. So for the time being we are figuring out how to stimulate the squid in a reproducible way—we have a lot to learn about this new species.
And during all of this we continue to push on in the ship. Dawn on Day 5 brings us to San Francisquito and the entrance to the Salsipuedes canal, the place to "get out while you can." This name reflects the strong tidal currents that run between the peninsula and Isla San Lorenzo and make navigation difficult for sailing vessels. These fast currents pass through the deep channel and result in intense tidal upwelling—you can see boils on the surface of the sea as if it were a running river, which it really is for several hours every day as the tides change. Upwelling of this sort is not driven by wind (like coastal upwelling), and this means these waters are productive year-round. You can see this in the greenish color of the water due to the rich phytoplankton and to the intense, thick scattering layers of plankton throughout the water column on Kelly’s sonar.
One of the most amazing things about this spot is that it is literally a doorway into a new oceanographic environment compared to that in the Guaymas Basin. Because of the intense tidal upwelling, the deep basins in the channels between the midriff islands (as they are called) are well mixed to great depth, and there is no OMZ. An OMZ needs high surface productivity and a deep, stable water column, which the Guaymas Basin has, but the Salsipuedes canal does not. And as if to make sure that these two environments stay even more separated, there is an underwater ridge, or sill, that runs east from San Francisquito all the way across the Gulf. This sill is less than 300 meters deep over most of its course and less than 200 meters at spots. On the south side you have the deep Guaymas Basin and its OMZ. On the north side you have the deep Salsipuedes Basin with no OMZ. There may be other places where these two different mesopelagic environments exist so close to one another, but I am not aware of them. This place is beautifully perfect.
The air over the channel is pocketed with dense foggy spots due to the cold, upwelled water meeting the hot air. It is somewhat unreal. And there is much life—diving birds and marine mammals are all over. As we proceed along the coast we enter the broad bay of San Rafael. Dave, the New Horizon‘s captain, points out the best camping spots on the long sandy beach in a low spot on the dunes. He has come here often kayaking and fishing, and I can sense the magnetic pull this place has for him. We cruise along examining the beach through binoculars and suddenly enter a fog bank that obscures all view. But we move on, searching through the world deep beneath us with sonar. We are looking for squid.
An hour or so later we emerge into blazing sunshine south of Punta las Animas, the place of the soul. Along the distant shoreline we see a dozen steel vessels at anchor—the squid fleet at rest.
Image of dolphin and bird feeding frenzy courtesy of Capt. D. Murline; image of Liz and squid-behavior experiment courtesy of K. Benoit-Bird; image of Gilly and squid jetting experimental chamber courtesy of K. Benoit-Bird; image of voyage map courtesy of W. Gilly; image of fog bank courtesy of Capt. D. Murline
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