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Night Light

night-light

One night, early in the trip, a guest shown his flashlight into the water alongside Westward to see what animals it might attract. Almost immediately a tiny cloud of, what we assumed were copepods formed in the pool of light. We watched, entranced, as the cloud increased in density. Within a few minutes we began seeing small fish darting into the edges of the cloud, and then, larger dark shapes began circling in from the surrounding darkness.

Excited by the possibilities revealed in the light of that single flashlight, the following night I rigged a work light to shine over the side. The brighter light and broader beam had excellent results, with an even larger cloud of small animals swirling in the light. There had been mobula rays jumping as we entered the bahia that afternoon, and we were hoping that they might be interested in the buffet our light had set out for them alongside Westward. Within a few minutes a pair of rays began coming into view. There were excited shouts from the enraptured audience as the rays swooped, rolled and danced in and out of the light. Their mouths open to scoop in the tiny animals, they remained with us until our bunks called us in, and we turned out the light.

Now we had a new nightly activity, and I made improvements to the original lighting rig. We thought that it would be interesting to rig the light every night, and to compare what animals were drawn to it in each bay we visited.

We used our microscope to determine that the copepods that seemed to be ubiquitous each night were in fact larval crabs. They appeared in such huge numbers in each bay that there must be a very large population of crabs in the region. Carlos used his GoPro camera to capture some underwater images of the teeming populations of prey and predators, and we decided that in addition to a better light, we also need a better microscope and a better way to record the images that we are seeing.

This is starting to get complicated as well as potentially expensive!

As the trip progressed we were visited by a larger group of mobulas and then a large school of mackerel that surrounded the boat. The splashes caused by their surface feeding lunges sounded like a hard rain was falling around us.

I am impressed by the amount of life we’ve seen attracted to our light and my curiosity is aroused by many new questions that I would like to have answered; when will the larval crabs complete this cycle and drop to the sea floor to take up their custodial duties? What, if anything, will replace them as forage for the many species of fish we saw feeding on them? Will the larger predator fish species vary as the winter season progresses? Will we see new, and perhaps larger fish coming to feed in the light? Will the feeding frenzy the light invokes slow during the full moon?

Since there are no books (at least of which I am aware of) that provide answers to these questions, we will work on finding the answers ourselves. And that quest will be great fun!