CHAPTER 13 



Table 13-9. — Summary of dead finfish observed on oxygen-depletion investigation cruises in 1976 



Vessel 



1976 date 



Station 



Species* 



Number 



Weight, kg 



Ocean pout (Macrozoarces americanus) 

 Fawn cusk-eel (Lepophidium cervinum) 

 Little skate (Raja erinacea) 

 Lined seahorse (Hippocampus erectus) 

 Silver hake (Merluccius bitinearis) 



12 

 1 

 1 

 1 

 1 



4.6 

 <0.1 



0.2 

 <0.1 



0.1 



* Stations locations are shown in figure 13-1. 



Tabi.k 13-11). — Species of finfish reported in 1976 mortality observations' 



Common name 



Species 



Reports of finfish mortality 



Scientific name 



Beach 



Smooth dogfish 



Little skate 



Silver hake 



Red hake 



Fawn cusk-eel 



Striped cusk-eel 



Ocean pout 



Lined seahorse 



Black sea bass 



Bluefish 



Spot 



Tautog 



Cunner 



Northern stargazer 



Searobin 



Summer flounder 



Windowpane 



Winter flounder 



Weakfish 



Striped bass 



Muslelus cams 

 Raja erinacea 

 Merluccius bilinearis 

 Urophycis chuss 

 Lepophidium cervinum 

 Rissola marginata 

 Macrozoarces americanus 

 Hippocampus erectus 

 Centropristis striata 

 Pomatomus saltatrix 

 Leioslomus xanthurus 

 Tautoga onitis 

 Tautogolabrus adspersus 

 Astroscopus guttatus 

 Prionolus sp. 

 Paralichthys denlalus 

 Scophthalmus aquosus 

 Pseudopleuronectes american us 

 Cynoscion regalis 

 Morone saxatilis 



X 

 X 



X 

 X 



X 

 X 



X 

 X 



X 

 X 

 X 

 X 



X 

 X 



After Steimie 1976. 

 Northeast Fisheries Center. 



a Stressed condition, because the rate of oxygen con- 

 sumption does not keep pace with the increased metabohc 

 cost of pumping water across the gills. 



Davis et al. (1963) found that the sustained swimming 

 performance capability of coho salmon (Oncorhynchus 

 kisutch) and chinook salmon (O. tsawytshcha) is increas- 

 ingly impaired as D.O. levels decrease. Possibly fish so 

 impaired may have difficulty avoiding predators or catch- 

 ing prey, or both. 



As D.O. level decreases, the metabolic cost of respi- 

 ration exceeds the fish's ability to maintain respiratory 

 processes and death ensues. The oxygen level at which 

 this occurs varies with temperature. Voyer and Hennekey 

 (1972) found that adult mummichogs (Fundulus hetero- 

 clitus), a species "more resistant to acute low dissolved 

 oxygen levels than other marine fishes," are able to with- 



stand 1.5 ml 0,/l (20° C, approx. 317oo). The (6-hour) 

 mortality rate at 0.8 ml/0,/l was 10 percent, and 100 per- 

 cent at 0.3 ml Oo/l. About 50 percent of the test animals 

 died in 6 hours when tested at 0,6 ml 0,/l (20° C). 



Shepard (1955) found that brook trout (Salvelinus fon- 

 tinalis) could withstand lower oxygen levels if gradually 

 acclimated to them. When brook trout were acclimated 

 to air saturation, the 50 percent lethal level (5,000 min- 

 utes) was 1.3 ml OVl, whereas the lowest concentration 

 to which young brook trout could be acclimated without 

 significant mortality was estimated to be 0.7 ml 07I. It 

 would seem to follow that if the oxygen level of their 

 environment began to drop slowly, fish could acclimate 

 to reduced oxygen levels for a period of time. 



In addition to acclimation, a few species are capable of 

 varying degrees of anaerobic metabolism (Hochachka and 



309 



