II

Introduction

The Amazon River basin has a large number of fish and other aquatic lifeforms. The immense diversity of species in the Amazon River basin can be demonstrated by observing the number of frogs in the basin. For example, at a single site in Amazon rainforest in Santa Cecilia, 81 species of frogs have been recorded. For comparison, there is approximately the same number of frog species in the entire United States (Rainforest Ecosystems, Animal Diversity, 2002). Furthermore, every year, about 35 species of fish are discovered and named in the Amazon basin. Many new species have even been discovered unintentionally as a side effect of studies on known species. This diversity of the fish population of the Amazon River basin is due to three factors:

1) The size of the Amazon River basin, which enables many species of fish to flourish.

2) The location of the Amazon River basin near the equator, which is favorable to fish growth. Because the basin absorbs so much energy from the sun, there is a large aquatic flora population able to maintain a large fish population. In addition, the position of the rainforest near the equator also means that the amount of energy absorbed from the sun is fairly constant throughout the year. Thus, there is little seasonal variation, that is the temperature and day length are fairly stable throughout the year.

3) The low extinction rates of the Amazon Basin rainforest. Additionally, since the extinction rate is lower than the rate at which new species are introduced to the basin, the net number of species is increasing.

Miscellaneous

Fish from the Amazon are a popular export to Asian countries, especially Japan. They are also a key element in the diet of people living along the Amazon River. Because of the high protein content of their diet, inhabitants along the river are much less likely to be malnourished than rural people in regions without fisheries.

As the Amazon River rises, fish move through river channels into the floodplains. Some fish, such as the tambaqui, are specially adapted to the flooded forest environment. A keen sense of smell leads the tambaqui to fruit which has fallen from the tree tops to the water. The tambaqui are genetically adapted, with powerful jaws and teeth that enable them to consume fruit. Not only do they gain and store fat to last them through the dry season, but in the process they propagate the tree species by providing a dispersing mechanism for the seeds.

Over the past 15 years, naturalist Michael Goulding has noticed a steady decline in the size of many of the fish. This, together with increasing agriculture, raises concern about over-fishing and habitat depletion, especially in the lower Amazon where extensive agricultural production already exists and continues to expand (Hauser, 2002).

Affects on fish populations by water management

The reproductive success for both native and non-native river fish populations is related to the water flow of the previous year. Therefore, water flow manipulations can be a powerful tool for managing fish populations. Such manipulation can be accomplished using dams, flow diversions, and river channelization. Conversely, the implementation of artificial flow control means can have an adverse effect on fish populations.

Damned rivers can be divided into four main segments:

1) The upstream segment, which is largely unaffected by the dam.

2) The segment immediately behind the dam.

3) The segment immediately downstream of the dam; this segment of the river is most affected by the dam. In this section, native fish populations are the most severely affected, to the point that they may be dominated by non-native species.

4) The segment downstream of the dam. With increasing distance from the dam, and with the influx of other rivers and streams, the effect of the dam in this segment is decreasingly severe. Correspondingly, native fish populations are more successful with increasing distance from the dam (Brown et al, 2002).

B. Fish Monitoring

VHF Telemetry

VHF transmitters in the frequency range 173-174MHz with 1mW output are used to monitor the position of tagged animals. The transmitters can be detected from up to 6000m away, depending on the amount of intervening vegetation and the orientation of the transmitter. Receiving stations are commonly placed in the canopy level of the rainforest.

Researches have used VHF telemetry systems to monitor botos[1]. Over one four year period, one group of researchers was able to study the movement of the animals in yearly bases as well as their reproductive cycles and social behaviors, among other activities.

Although this is a very effective method for monitoring the location of aquatic life, this is a very labor intensive and expensive method. In addition, because of the high density of the rainforest, signals are often blocked, reducing their effective range. This means that animals will often move out of range of the receiving stations. Another problem the use of VHF telemetry this is that the receiving stations often become nests for bees and other insects (Martin et al.).

Robotic Boat

This method was initially developed as a less costly alternative to VHF telemetry. The entire tracking system can be contained in a 10' kayak hull, including subsystems that allow the boat to autonomously follow a tagged, swimming animal. GPS also is used to navigate and monitor the position of the boat. Acoustic transducers are used to locate aquatic life. The entire system has an endurance of 24hrs, meaning it operates on a one-day cycle. Because the kayak is only 10ft long, 27in wide, and 34lbs, the system is very easy to maintain. Moreover, the kayak-like shape also makes the device durable. Because this is currently an experimental system, no data is available yet (Goudey et al).

C. Parasites

Parasites are effective potential indicators of environmental quality due to the variety of ways in which they respond to anthropogenic pollution. Thus parasites provide valuable information about the chemical state of their environment through their presence / absence and ability to concentrate environmental toxins within their tissues.

Specifically, parasites are useful in two different ways. First of all, they are "effect indicators,” that is they can reveal the effects of various pollutants on the abundance and distribution of fish. However, because there is a wide variety of factors which affect the population of parasites, parasites do not allow any conclusions to be drawn concerning the concentration of specific toxins in the environment.

One example of the use of parasites as an effect indicator is the Monogenean Trematode, which lives on the gills of fish. Because this parasite is in direct contact with both the surrounding environment and the host fish, it is a particularly good indicator species. In addition, its short lifespan means that it immediately reacts to environmental changes. Other effect indicator species include the Dreissena and Salmo gairdneri, which are hosted by zebra mussels and rainbow trout, respectively. These species are good indicators of the quality of water treatment in sewage plants. Dactyloyrus and Paradiplozoon are also effective indicators of the concentration of effluent resulting from pulp and paper mills.

Second, parasites can be used as "accumulation indicators"[2]. By looking at the concentration of environmental toxins within the parasites, we can monitor the environment. This method takes advantage of the fact that parasites usually have higher concentrations of metals in their bodies than their host has in its tissues. For example, the lead burden in the parasites is about 1000 times that of the host's muscle. This is because metal concentrations in parasites are likely to respond rapidly to changes in environmental changes.

For example, the presence of acanthocephalans had a significant impact on lead accumulation in the intestinal wall. The fish infected with acanthocephalans only half of uninfected chub's lead concentration. Acanthocephalans is a group of intestinal worms commonly found in fish. Adult worms live inside the intestine of the final host and absorb their nutrients across their tegument[3]. There are three major species: 1) Pomphorhyndchus laevis, 2) Acanthocephalus lucii, and 3) Paratenuisentis ambiguous. Among these, P. Laevis most rapidly reacts to changes in the environment. The mean concentrations of lead and cadmium in P. Laevis are respectively 2700, 400 times higher than in the muscle of the host and 11000, 27000 times higher than in water. Acanthocephalans can accumulate toxic metals from the aquatic environment to concentrations even surpassing those in Dreissena polymorpha[4] (Sures, 2001).

Next: Sedimentology -->

[3] Acanthocephalans do not have mouth nor intestine

[4] Dreissena polymorpha is a kind of mussel. It is one of the best established accumulation indicators in fresh and brackish waters in Eruope and USA.