. Commercial fisheries review. Fisheries; Fish trade. O râ en iâ UJ 1- 90 17. I i i â â I I â â â â I â â â I â , , â I 1915 20 25 30 35 40 YEAR 45 50 55 60 65 Fig. 2 - The commercial catch of Lake Erie fish has averaged 50 million pounds since 1915. Before 1954, fishermen landed most of the catch. Now Canadian fishermen reap the harvest and landings are at an all-time low. from overlying surface waters. Oxygen lost in bottom waters cannot be replenished ade- quately until stratification breaks down and a mixing with oxygen-charged surface waters occurs. Increased organic production
. Commercial fisheries review. Fisheries; Fish trade. O râ en iâ UJ 1- 90 17. I i i â â I I â â â â I â â â I â , , â I 1915 20 25 30 35 40 YEAR 45 50 55 60 65 Fig. 2 - The commercial catch of Lake Erie fish has averaged 50 million pounds since 1915. Before 1954, fishermen landed most of the catch. Now Canadian fishermen reap the harvest and landings are at an all-time low. from overlying surface waters. Oxygen lost in bottom waters cannot be replenished ade- quately until stratification breaks down and a mixing with oxygen-charged surface waters occurs. Increased organic production and introduc- tion of reduced, oxygen-demanding organic and inorganic materials have resulted in de- terioration of oxygen levels in many areas of Lake Erie. Bottom Organisms Degradation of the oxygen regime has al- tered dramatically the populations of bottom organisms essential as food to certain valu- able fish. Since 1953, this phenomenon has reduced mayfly larvae (Hexagenia) from 400 to 10 individuals per square meter and, in places, entirely eliminated them. It has "in- creased the numbers and distribution of sludge worms (oligochaetes) many-fold, re- duced caddisfly larvae almost to the vanish- ing point, favored large increases in the populations of low oxygen tolerant forms of midges, reduced the non-tolerant forms, caused an increase in some species of finger- nail clams, and generally reduced the num- bers of all pollution-sensitive bottom organ- ; The original community of organisms was an essential part of the food chain important to desirable fish. Changes in this community have adversely affected these fish and, in turn, the economics of the fishing industry. The narrow stratum in the bottom of Lake Erie, with its low dissolved oxygen content, "is so polluted that the future status of the entire lake as a useful producer of fishery products is ; Thermal Effluents Nuclear power plants on Lake Erie are proliferating.
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Keywords: ., book, bookcentury1900, booksubjectfisheries, booksubjectfishtrade
