42 Frank J. Schwartz 



the latter causing ice flow development on the shoals of the river 

 and in the power plant intake canal. As a result, fish kills were common 

 each of the two years at several river stations. Highest water temperatures 

 were 30.5-32.0 C in July 1977. Oxygen levels associated near the 

 ice flows or high water temperatures were always high, yet were critical 

 for some species such as striped mullet, Mugil cephalus, grey trout, 

 Cynoscion regalis, and menhaden (Brevoortia tryannus). Salinities varied 

 by season, station, and after rainfall and runoff, thereby enchancing 

 or preventing greater range utilization of the river system than usual, 

 i.e., channel catfish Ictalurus punctatus, a species of the upper river 

 was often found as far down river as Buoy 18 (Fig 1). 



DISCUSSION 



Although sciaenids (croaker, spot, and southern kingfish) have 

 been reported eating Donax or other clam siphons (Modde and Ross 

 1983, Currin 1984, McMichael 1986, McMichael and Ross 1988, Irlandi 

 1993, Currin et al. 1994), my study adds 11 species to the list of 

 siphon tip nipping fishes. No attempt was made herein to note the 

 rate of siphon tip regeneration or length of siphon extension (Zwartz 

 et al. 1994). The most severe cold-winter-spring waters ever recorded 

 (1976 and 1977) may have caused increased siphon nipping (Table 

 4), and surface inhabiting invertebrates to vacate the area or influenced 

 their survival, even death. Clams on the other hand could simply withdraw 

 their siphons during the most severe water temperature extremes and 

 remain in the area. Thus, loss of other winter foods may have made 

 clams the only available food for bottom feeding fishes such as croakers, 

 spot, southern kingfish, etc. 



Infrequent literature reports of siphon tips as stomach contents 

 of fishes should be viewed cautiously in light of pre-, during- and 

 post-capture factors. Prevailing environmental events should be factored 

 into the observations rather than simply assuming the presence of a 

 food item was preferred and expected, rather than unexpected (Bonsdorff 

 et al. 1995). Also efforts to interpret the effects of a fish's behavior, 

 such as siphon tip nipping, should consider whether a station was 

 sampled once or repeatedly to determine the long-term effects of fish 

 behavior (aversive or non-aversive; Kvitek 1991) and sampling effects 

 on the local clam population. 



