11 October 2009

Fish Collection

It has been a non-stop endeavor working with the Smithsonian group. This morning, however, I'm taking some time off from it. Ever since it arrived, the focus has been on using their other chemical, rotenone (the one that kills the fish rather just anesthetizing them). It hugely more effective. Almost devastatingly effective. In fact, on the first outing when it was used, I questioned whether or not I'd continue helping. I eventually decided that I would, but I'm still not entirely comfortable with its effect.

Deployment on our first station.

Rotenone is a substance that occurs naturally in the roots of several plants (one of which is the commonly eaten jícama plant). It has actually been used for 1000s of years by indigenous tribes as a method of catching fish for food. It's a poison, but according to Wikipedia, it's only weakly absorbed through skin and the GI tract. So it's harmless to mammals. For fish, on the other hand, it's readily taken up through the gills and kills them quite quickly. What is being used here is rotenone in powder form. It gets mixed with water and a splash of dish soap (as an emulsifier) to make a sort of dough or thick batter (one of the researchers does this with his bare hands so it's some indication of how certain he is that it won't harm him). Then it gets double-bagged and is ready to be deployed.

The bags are taken down to a selected reef (usually on SCUBA), opened, and slowly shaken empty in the area. Since corals don't have gills, they are completely unaffected. The fish, however, die quickly. It has sort of a shotgun effect, killing everything with gills, whether a sample is needed or not. This is what made it so troubling for me. I don't like seeing things die for no reason. Fortunately, it quickly dilutes and is rendered inert by sunlight, so it doesn't have long lasting or widespread effects. It also mostly only kills small fishes. Anything larger than about 5 or 6 inches can withstand it long enough to swim to safety. Sadly, though, a large fish doesn't mean a large brain. Some big fish, mostly Yellowtail Snappers but also one large Yellowfin Grouper, were lured back into the toxic cloud by the prospect of an easy meal. They see the dead little fish and come swimming back in to gobble them up. If they do it enough times, they get a lethal dose themselves.

This big Yellowfin Grouper couldn't help but go after the easy meal. Not to waste, we took our genetic sample and then ate him for dinner.

This Coney was done in while attempting to down a Peppermint Bass. We also found 4 or 5 other small fish deeper in its throat. Apparently it entered and re-entered the rotenone cloud several times before it died.

After the cloud settles out enough for us to see, we swim in and scoop up the dead fish lying on the ground. Those that are easily identifiable and which have already been collected, are left behind and, eventually, eaten by scavengers (which is harmless even to fish because the toxin is only effective when absorbed through the gills). The affected area is eventually repopulated from neighboring reefs or from unaffected portions of the same reef (the size of rotenone stations being done here is only about 20 or 30 feet). Again, its a matter of viewing it from an ecosystem-wide level or on an individual level - the impact is minimal on the ecosystem, but the impact on individual fish is dramatic.

Its understandable, though, why rotenone is such an important tool for this project - many species just can't be captured in other ways. As you can see from the pictures of the lab, a great diversity is turned up:

Preliminary sorting by appearance before close examination under a microscope.

Waiting to be positively identified: Peppermint Bass, Fairy Basslet, and something with a yellow tail.

Three Tongue Fish

Blue Chromis, Redspotted Hawkfish, and a Juvenile Rock Beauty

Some sort of Brotula. Almost impossible to positively ID without genetic testing.

A Slender Filefish and two Blackfin Cardinalfish

Two of the new Soapfish (used to be confused with Rypticus subbifrenatus, but is genetically distinct). The spots on these ones cover the belly, but not so on the other.

A load of Brotula. Part of the reason I am troubled by the rotenone method - more specimens are taken than are needed.

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