ALL ABOUT THE ENVIRONMENT – June 2010

ALL ABOUT THE ENVIRONMENT

By Dr. Todd Stong

 

tod-strongcolor2010(Ed. Note: This marks Dr. Stong’s debut column. He has served as a volunteer engineer with Lakeside local governments for the past eight years in regards to water supply, waste water treatment, streets, malecons and the general area of infrastructure planning. At Lakeside he advises on lake shore improvements. Welcome, Dr. Stong!)

 

Lake Chapala Fishing Industry

 

Currently the most plentiful fish in the lake are tilapia, carp, catfish and charal. Since no water has flowed out of the lake in over 30 years it is becoming saltier and thus the variety of fish today has changed with time. With the measure of pH to define if water is more acid, lower than 7, or more basic, higher than 7, note that the lake is at about 8.7. In that the pH scale increases by 10 as you go from 7 to 8 and by 100 as you go from 7 to 9, the 8.7 pH means the lake water is about 80 times more alkaline than normal.

Native fishing is surely a mystery to most readers of this English language publication. So let us try to define an initial view which may at some point assist the fishermen in better planning their industry which has been on the decline for over 20 years. Readers with better knowledge may then step forward with better numbers to be emailed to the author.

Analysis: Fishermen unions/cooperatives – 66; Fishermen – 3000 but only 1000 are believed to each day fish seriously; Wives, children and others dependents of fishermen – 24,000; Days of fishing/year – 250. Based on visits with fishermen the following estimates are presented that suggest an average of a 75kg catch/day/fisherman. This may amount to 2-3 kg of charal, 20 carp and 80 tilapia for each fisherman which he is in turn able to sell wholesale for about 220 pesos/day (6-8 pesos/kg for tilapia and carp, 50 pesos/kg for catfish and 10p/kg for charal). Retail price is often up to three times the wholesale.

The current unwarranted claim by a university out of New York that there is excessive mercury in the carp is now reducing almost over night the income of fishing families by a third. In reality the proper reporting of these student’s very small sample, 6 carp, should have been stated as having a median value of 0.4 ppm (parts per million) which might then be compared to the 1.0 ppm limit of the USA-EPA. A plan has now been prepared to test 250 carp to be taken from 25 locations about the lake to offer a statistically valid assessment of mercury levels with a 95% level of confidence. It is anticipated that funding for this effort will soon be provided by the 9 municipios about the lake.

Given 350,000 people about the lake the catch of 124,000 fish a day, perhaps 620,000 fish a week, suggests an average of 2 fish a week per person. In reality it is assumed the fishermen families eat 3-5 times the average per person. Over all it seems about 10% of the natives are in the fishing industry, perhaps down from 30% half a century earlier.

Aquaculture, raising fish along the lakeshore or in pens inside the lake, may offer a better future for this industry. The consumption of grain to produce a kilo of beef or pork is 4-8 times that required to produce a kilo of fish. An existing commercial facility at Jamay which produces over 150 tons of tilapia per year is an excellent example of modern technology and efficiency.

Ojo Del Lago
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