Table 13-6. 



NO A A PROFESSIONAL PAPER 11 

 -Lobster catch per unit effort for New Jersey inshore pot fishery from Shark River and Point Pleasant area, 1975 and 1976 



drop in landings from over double the year before for the 

 first 6 months of the year to only 85 percent for the next 

 3 months is very significant, especially since it coincides 

 so well with the appearance of the anoxic conditions off 

 the coast. 



EFFECTS ON FINFISH 



The "fishkill" phrase often used to describe the anoxic 

 water mass off the New Jersey coast in 1976 is misleading, 

 because finfish populations did not have massive mortal- 

 ities. The first indications of a fishkill were based on re- 

 ports of dead fish caught in trawls of commercial fishermen 

 (Steimle 1976). Diver observations on offshore wrecks 

 (fig. 13-3)further substantiated these finfish death reports. 

 Our first surveys in early July did find a few dead fish in 

 areas reported to have extensive mortalities. But further 

 intensive trawling throughout summer and autumn did not 

 produce significant numbers of dead fish. In fact, of the 

 196 trawl hauls made (52 in waters of s;1.40 mlOVl) only 

 16 dead fish were found (table 13-9). Of these 16 fish, 12 

 ocean pout (Macrozoarces americanns) were caught at one 

 station. Therefore, based on observations, we must con- 

 clude that a significant and sustained kill of adult fish did 

 not take place, although scattered finfish mortalities con- 

 tinued throughout the summer (Steimle 1976). Table 

 13-10 is a compilation (after Steimle 1976) of all fish spe- 

 cies reported to have been killed by anoxia. 



Tolerance to Reduced Oxygen Levels 



Reduction in the D.O. level significantly affects phys- 

 iological, biochemical, developmental, and behavioral 



processes in fish. These effects may range from increasing 

 the respiration rate to switching to anaerobic metabolism 

 or to death. 



Each fish species has a critical oxygen level below which 

 the fish depends on increased respiration rates (thus 

 pumping greater volumes of water across the gills) to 

 maintain its oxygen supply. Fry (1947) called this condi- 

 tion "respiration dependence." Baldwin (1923) found that 

 Atlantic mackerel (Scomber scombrus), butterfish (Pe- 

 prilus triacanthus) and scup (Stenotomus chrysops) were 

 not as resistant to low D.O. as dogfish, skate, tautog 

 (Tautoga onitis), black sea bass {Centrophstis striata), or 

 winter flounder (Pseudopleuronectes americanns). Hall 

 (1929) found that the oyster toadfish (Opsanns tan) was 

 more resistant to low D.O. levels than northern puffer 

 (Sphoeroides maculatus) and northern puffer was more 

 resistant than scup. Shelford and Allee (1913) suggested 

 there is a relation between habitat preference and the 

 oxygen levels necessary to sustain life. Hall felt that oxy- 

 gen consumption is related to the level of activity and that 

 a low activity level may have an adaptive value in areas 

 prone to low D.O. levels. 



Saunders (1963) found that when the ambient D.O. 

 level was reduced from 7.0 to 2.1 ml/1, the rate of oxygen 

 consumption for Atlantic cod (Gadus morhna) decreased 

 only slightly, whereas the respiration rate increased 

 (markedly at oxygen levels below about 3.5 ml/1). Voyer 

 and Morrison (1971) found that winter flounder become 

 respiration dependent between 2.1 and 3.1 mlO,/l. Davis 

 (1975) believed that the "average member of a species in 

 a fish community (marine) starts to exhibit symptoms of 

 oxygen distress" when the oxygen level is about 4.7 mlO,/ 

 1. When fish become respiration dependent, they are in 



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