W 80 



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TIME imin. 



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Figure 6. Predator avoidance by mayfly nymphs, indicated by their distri- 

 bution in the corners of a chamber depending on whether a fish predator was 

 present (upper line) or absent (lower line) (Charnov et al . 1976). The 

 corners in these experiments are analagous to refuge provided by vegetation 

 within shallow wetland zones. 



conclude that the present high coastal wetland losses in Louisiana will eventually 

 translate into a reduction in commercial and recreational fish yields. The natural 

 potential fish yields are decreasing, not increasing. This decline is not yet apparent in 

 the fisheries statistics of landings for at least two reasons. First, the annual variations 

 in landings are large in relation to the wetland loss rates. For example, the commercial 

 shrimp and blue crab fishing efforts have, at times, been steady from one year to the 

 next. The landings one year might be twice that of the next year, however. In 

 comparison the land loss rates, hence wetland loss rates, are about 1% annually over the 

 last 25 years (Wicker 1980). Secondly, fishing effort in Louisiana has increased 

 dramatically in the last 25 years. Double-rigged shrimp trawling was introduced in the 

 mid-1950's and not completely adopted by all the fleet for several more years. Larger 

 vessels with more horsepower have been added every year, and some industries, like the 

 menhaden industry, have added more fishing vessels (and spotter planes) almost 

 continuously throughout the I960's and I970's. The hidden, cumulative effect of land loss 

 on Louisiana's fisheries is distributed over a long period amongst many fisherman. With 

 the combination of increased fuel costs, inflation, and a now nearly full fishing industry, 

 the effects of land loss rates will be felt dramatically in the coming years; this will be 

 especially true as the loss rates continue to accelerate beyond 1% annually. Doi et al. 

 (1973) documented an example of the effects of coastal habitat losses on fisheries in the 

 Seto inland sea in Japan. As the area of intertidal land was lost to land reclamation, the 

 shrimp catches declined proportionately and sharply. 



If we assume that a 1% decline in the potential fishery yield is equivalent to the 1% 

 per year wetland loss, then the cumulative loss in dockside dollar value over the next 20 

 years is equal to twice the present value ($190 million dollars in 1978) of the entire 

 commercial landings, or $380 million. At least 50% of this value is a result of the high 



118 



