Posted by: Doc Bruce | September 2, 2011

Tarpon Week: A study in ocean currents

Coconuts ready to be set adrift.

The very last week of the summer at Sanibel Sea School’s summer camp was Tarpon Week; what better way to celebrate a summer of fun and learning than to pay homage to the silver king?

We made beads that represented otoliths, which are the ear bones in fishes that can be used by biologists to determine the fish’s age. We canoed through the backwaters of mangrove forests in Tarpon Bay where tarpon thrive as young fish. We studied how adult tarpon spawn and how the larvae of these mighty giants are to a large degree at the mercy of the currents.

In conjunction with our exploration of larval dispersal, we asked a really interesting question: just where might the currents take tarpon eggs and larvae if they are spawned off the shores of Sanibel? To tackle this question of current movements, we decided to use coconuts to try to track water movements around Sanibel Island. We chose coconuts because they are a natural part of the flotsam of the Gulf of Mexico and we would like to avoid adding plastics to the ocean — and besides, who wouldn’t love to find a message on a coconut?

So, we gathered up 30 coconuts and painted them crazy colors like pink and orange – decidedly non-ocean-like colors. We wanted our coconuts to catch the attention of folks on distant shores to come and have a look – wouldn’t you be intrigued if you saw a pink-and-orange coconut in the shallows off the beach? We painted numbers on each one and affixed laminated tags asking the finder to call or email Sanibel Sea School when they found our wayward coconut.

Kyle Hasenfus paints up a coconut.

On Thursday at 11:15, we anchored our boat just offshore of the Sundial Resort, a favorite hunting ground for tarpon fishermen, and set our coconuts adrift. As we watched and hypothesized the end results of our currents study, the coconuts all seemed to be headed towards Captiva. We eventually weighed anchor and traveled further up island, where we enjoyed a picnic lunch and seined for near-shore fishes, always in search of those elusive tarpon larvae. We then got back in the boat and sampled the plankton with a plankton net – a fine meshed net designed to capture creatures greater than 0.3 mm in size.

Once our plankton observation was done, we headed back to our deployment point to check up on our coconut current drogues. But, we could not find a single coconut on the Gulf of Mexico – it was as though a giant wand had erased our happy little coconuts from the earth. Oh well, we will just have to wait and see if anyone finds our little friends and gives us a call.

The first message arrived at Sanibel Sea School on Friday evening! Someone had found one of our coconuts – in Naples! Our initial prediction of Captiva landings based on the observations of the drifting coconuts didn’t pan out.

Over the weekend, eighteen more were reported from kind people who found coconuts all over the beaches of Naples and even on Keewaydin Island, south of Naples. We plotted the coconut locations on a map that is posted on this website, and were amazed by the distance our little coconuts traveled.

As the coconut reports continue to trickle in, we will update our map. Maybe those last few coconuts have been whisked into the Gulf Stream and are currently en-route to Newfoundland!

Our coconut current study yielded a lot of things. One of them was that what we do here on Sanibel can have a direct impact on our neighbors on Naples – it’s funny, I never thought of Naples as the town next door, but in our ocean world it seems to be.
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