Shrimp Farming and the Environment - Library

Natural factorsShrimp diseaseThe outbreak of disease is the most prominent nature-based risk factor in shrimp aquaculture,sometimes wiping out entire crops. The more spectacular examples of this were found in Taiwan,Republic of China, in 1988, and in China in 1993. In the former country, disease led to investor flightfrom shrimp farming, and many operations were either closed down or converted to other uses.Disease occurrences can be roughly divided into the ones that are environmental and opportunistic inorigin, and that mainly occur in poorly managed farms; and the outbreaks that seem to spread to almostall farms regardless of management. The first category is the easiest for the individual farmer toaddress, but outbreaks require concerted efforts, as described in Chapter 4.The risk of disease outbreaks is related to the capacity of the individual farmer to manage the farm,which can obviously be improved as knowledge of shrimp farming improves. There is also a collectiverisk that arises as soon as one farmer mismanages a farm or introduces disease via seed or feed. Oncethe disease has been established in a region, it can affect relatively well-managed farms just as thoseless well managed. Managing this collective responsibility in an industry that is immature, as it is inmost shrimp farming countries, requires good insight by regulators, as well as farmer associations withsufficient knowledge to limit the risk of disease introduction. One of the main challenges at this time isto prevent shrimp disease spreading to new frontiers for the industry, such as Africa, from the maingrowing regions. In the medium term, there is also a risk of new African diseases spreading the otherway. However, few of the farming countries are taking precautions to limit these risks.WeatherAdverse weather and other climatic conditions can be a risk factor and should be considered in thedesign of the project. For example, seasonal floods may wipe out production unless the construction ofthe ponds takes that risk into account. Low winter temperature, or high summer temperature, can alsostress shrimp. This is a particular problem where farmers attempt two shrimp crops per year, therebysubjecting the beginning of the first crop and the end of the second crop to suboptimal conditions andincreasing the risk of disease. While extreme weather conditions may occasionally affect production, toa large extent the design, construction, and operation of the farm can be adjusted to weather conditionsobserved over the recent past. By taking these conditions into account, the financial risk of the projectcan be assessed and, in some cases, significantly reduced. For example, in China some shrimp farmershave two crops of shrimp that bracket the hottest summer weeks, when production is suspended andponds are fallow.53