CHAPTER 13 



centrations. This is further supported by the fact that no 

 dead finfish were collected in any of the trawls in this 

 general area. 



Several studies support this avoidance behavior. Shel- 

 ford and Alee (1913) noted results ranging from no re- 

 action to a decided response when testing several fresh- 

 water' species in an oxygen gradient. Jones (1952) found 

 that the three-spine stickleback (Gasterosteiis acideatus), 

 minnow (Phoxinus phoxiniis), and brown trout fry (Salmo 

 trutta) reacted to low oxygen only after respiratory distress 

 developed. Whitmore et al. (1960), contrary to Jones' 

 finding, found strong and pronounced avoidance reactions 

 by chinook salmon (Oncorhynchus tshawytscha) , coho 

 salmon (Oncorhynchus kisiitch). largemouth bass (Mi- 

 cropterus sahnoides), and the bluegill (Lepomis macro- 

 chirus). All avoided some depressed level of oxygen. The 

 two Pacific salmon species and the largemouth bass 

 avoided 3.2 ml 0,/l. The coho salmon showed some avoid- 

 ance to 4.2 ml OJl. All species avoided 2.1 and 1.1 m\OJ 

 1. Further, the observations of Whitmore et al. (1960) 

 strongly suggest that the fish are capable of very rapid 

 detection of changes in D.O., even before respiratory 

 distress is apparent. 



Therefore, when we consider that fish, which are highly 

 mobile, are able to detect and survive (at least for short 

 periods of time) decreasing oxygen levels, it is probable 

 that they could successfully avoid hazardous conditions, 

 barring entrapment. 



Avoidance behavior is further supported by the move- 

 ment of summer flounder and bluefish and the unusual 

 catches made by anglers throughout most of summer 1976. 

 Early in that season, summer flounder seemed to show 

 up where they usually did in past years and in about their 

 expected numbers. Off northern New Jersey, this normal 

 pattern ended suddenly beginning late in June, coinciding 

 with the formation of anoxic water along the seatloor. Our 

 information indicates that summer flounder were concen- 

 trated along the leading edge of the anoxic water. At 

 various times and points along the coast, the location of 

 the anoxic water pushed great numbers of summer floun- 

 der, including many large specimens that usually inhabit 

 deeper waters, into the surf zone and into inlets and bays 

 where D.O. levels could sustain aquatic life. This resulted 

 in masses of a very desirable species of fish within easy 

 reach of anglers. Consequently, anglers fishing from shore 

 as well as from boats made large catches. Such was the 

 case in Sandy Hook Bay during mid-July and off Long 

 Beach Island and Atlantic City in mid- and late July. 



Surveys have shown that anglers can account for as 

 much as half the total number of summer flounder re- 

 moved from the sea during normal years (Hamer and Lux 

 1962; Murawski 1970). Because the annual combined har- 

 vest (commercial and recreational) has approached the 

 maximum sustainable yield in recent years (Chang and 



Pacheco 1976), an increase in the recreational catch while 

 maintaining the commercial catch, during July and August 

 1976 along New Jersey, may significantly affect future 

 stocks. 



Tagging returns, fishing reports, and catch rates of rec- 

 reational fishermen indicate that most bluefish between 

 1.4 and 5.4 kg may have been blocked from migrating 

 northward past New Jersey during summer 1976. Thus, 

 bluefish were diverted from their normal patterns of 

 spending the summer feeding and spawning along the 

 coast from northern New Jersey to southern New England 

 and feeding along northern New England. Upon encoun- 

 tering the low D.O. water these migrants apparently re- 

 versed their direction and headed south. During most of 

 July, August, and September they milled about off the 

 coast of southern New Jersey and the northern Delmarva 

 Peninsula (Delaware, Maryland, and Virginia). Fisher- 

 men in the coastal States from New York to Maine re- 

 ported catching few fish of this size. 



A study of the 1976 catch records of New Jersey charter 

 boat anglers shows that from early May to about mid-June 

 bluefish were more or less evenly distributed along the 

 New Jersey coast. But starting in the last week of June, 

 catches fell off along the northern part of the State where 

 the anoxic water first appeared and they tended to be 

 greater along the central and southern parts of the coast 

 where normal conditions still prevailed. This, and the fact 

 that the first return from the June 8 tagging was off Cape 

 Henlopen on June 25, indicates that the bluefish may have 

 detected and avoided the anoxic water at least a week 

 before the earliest reported fish mortality. During early 

 and mid-July, the bluefish were caught almost entirely 

 outside the oxygen-depleted water. Catches made over 

 the anoxic water, especially in the Barnegat Ridge area, 

 were from schools concentrated above the thermocline or 

 in small isolated pockets where the bluefish apparently 

 found tolerable D.O. This could explain the occurrence 

 of large quantities of surf clams (Spisula soUdissima) in 

 the stomachs of bluefish caught off Barnegat Light during 

 the first week or so in August, as observed during the RV 

 Atlantic Twin cruise and reported by various captains. 

 Throughout the rest of the summer, mpst of the bluefish 

 were caught outside, above, or along the edge of the an- 

 oxic water mass. As stated above, specimens caught inside 

 the anoxic region were likely living high in the water col- 

 umn and apparenly had not fed for some time. As ex- 

 pected under anoxic conditions, catch rates were often 

 very light. No bluefish were caught in the area having 

 either hazardous hydrogen sulfide concentrations or very 

 low D.O. 



The inshore contingent of bluefish, that is, those be- 

 tween 0.5 and 1.4 kg and migrating close along the ocean 

 shore, seemed not to have been affected. Throughout 

 most of the summer the anoxic water remained at least 



311 



