Friday, November 17, 2000

The Río Yanayaquillo

It rained all night. As morning came, the hard rain gave way to a soft gentle rain and like most mornings, we could hear dolphins splashing and "snorting" as they swam around the Mirón Lento.

Right after breakfast (have we mentioned that we eat breakfast at 6:30 AM?) we left on Mango to perform a transect of the Yanayaquillo, a tributary of the Río Samiria. The water was too low to take the Mirón Lento up the river.

We quickly decided to turn off the motor so that we could count dolphins and try to capture them with our cameras. To our amazement, there were two tucuxi and ten botos-including a baby boto. This is the largest group of dolphins we have seen in one spot this trip.

Navigating the narrow tributaries is quite an adventure and sometimes requires the assistance of everyone on the skiff. Avoiding fallen trees with trunks and branches obscured by the murky water requires the skill of a seasoned captain. Captain Antonio is quickly able to figure out which branches are connected and guide the boat safely between them. A couple of times a large thump indicated that the propeller of the boat had hit a submerged branch. These branches are almost impossible to avoid as the calm water gives very little indication that an obstacle is below. Luckily, the propeller wasn't bent and we were able to continue the transect.

Vultures, Dead Fish, and Necropsy

The transect came to an end when a tree completely obstructed the river. Overhead was a paper wasp nest hanging from a tree. Tamara said that she has watched this nest grow over her years of research. She estimates that the nest is now over two meters long.

Early in the transect, there was a large number of turkey vultures along the river. We soon learned why. Dead fish littered the riverbanks. The captain said that perhaps someone had been fishing with poison as is sometimes done in this area.

There are two types of poison made from plants which are common to the forest. Huaca is a poison made from the ground up leaves of the plant. The stronger barbasco is made by grinding its roots into a paste.

Handfuls of the prepared leaves or roots are thrown into the river. The fish are quickly killed and can be scooped up and taken away for immediate eating or salting. This method works well for catching fish as nets can easily become entangled in the many fallen trees and branches in the river.

Unfortunately, though, the current carries the poison downstream and fish outside the immediate area are also killed.

As we reversed our route, the captain pointed out a larger fish that was in the last stages of dying. Enzo scooped it out of the water with an oar. Captain Antonio said that the blood in the eye and the bloated, red-tinged side were not consistent with the use of the poisons. We decided to quickly kill the fish so that it would not suffer and bring it back to the Mirón Lento to dissect it. Tamara and Enzo wanted to look for parasites or other obvious signs of disease.

Once we were back on the Mirón Lento, Tamara preformed a necropsy. Wearing rubber gloves and being careful not to contaminate any of the boat's surfaces, she dissected the fish to try and determine the cause of the swelling.

Tamara began the necropsy by scraping the armor-like scales from the bottom of the fish. A vertical cut was made from the bottom of the mouth to the beginning of the tail. As she examined the internal organs, there was no sign of parasites in the fish. From all accounts, the fish looked healthy, well fed, and had produced a sac of eggs.

However, on the left side of the fish (where the bulging had occurred) the muscle of the fish between the body cavity and the scales had liquefied. There also appeared to be some bleeding into the left eye.

When Letser and Herocio went to get more supplies from the village, they asked if anyone had seen the dead fish and if they knew what the cause might be. A man said that at this time of year the cormorants gather and feed off the fish. The birds have a virus that is transmitted to the water and the fish die.

Tamara and Enzo were unable to determine why this fish was found dying or why the muscle had liquefied. They would have to examine many more fish and conduct a biopsy on the liquefied tissue in a laboratory to learn more.

In the end nobody here anyway knows why the fish are dying. It demonstrates how difficult it is for scientists to find answers and how careful they must be when they make their conclusions. What appears obvious at first may not in the end be the truth.

Caught on Camera

We are now heading up the Rio Samiria to the second ranger station counting dolphins as we go. As we turned into the river there were many dolphins swimming. Tracy took out her digital video camera and FINALLY got great footage of the botos. If you followed us last year, you know how difficult it is to get pictures of the dolphins. It was the right combination of skill and luck. We will post the QuickTime movie when we return but for now here is a frame from that movie.

Today we saw our first caiman. It was between 2.5 and 3 meters long! We hope to see many more as we get further into the reserve. No swimming tonight.

We're Taking the Weekend Off!

Well, not quite. Although we will continue to conduct research and take photos over the weekend, we will not be posting daily highlights or data. Look for more updates on Monday, Nov.20.