FISHERY BULLETIN: VOL. 80. NO. 4 



(Microsetella, Temora, and .Ba/anits nauplii) and 

 M. scorpius larvae (Balanus nauplii and Cosci- 

 nodiscus) in the Damariscotta River estuary dur- 

 ing winter and spring 1979 were the same as 

 reported from 1973. 



Copepods which were relatively abundant dur- 

 ing winter and spring months in the Damaris- 

 cotta River estuary were Eurytemora herdmani, 

 Oithona similis, and Pseudocalanus minutus 

 (Lee 1974). Of these species only Pseudocalanus 

 was an important prey of cottid larvae (one spe- 

 cies, Triglops). Oithona, a relatively small cyclo- 

 poid, was abundant in early spring but was not 

 eaten by cottid larvae. However, two somewhat 

 larger species were eaten: Temora longicornis, 

 whose abundance in winter was variable and 

 lower than in summer and fall, and Pseudo- 

 calanus. Ivlev (1961) noted that when food is 

 plentiful, fish will take the largest available prey 

 present. But this does not explain why larvae 

 preferentially ate Temora and not the same-sized 

 but probably more abundant Eurytemora or why 

 they apparently "preferred" the smaller species 

 of pelagic, harpacticoid copepod, Microsetella 

 norvegica, over the larger, abundant winter spe- 

 cies Parathalestris croni. It is perhaps signifi- 

 cant that four of the five major prey of Myoxo- 

 cephalus and Triglops larvae, Balanus nauplii, 

 Temora, Pseudocalanus, and Microsetella were 

 also found to be important natural prey of fish 

 larvae in widely different regions (Lebour 1918, 

 1919; Sherman and Honey 1971; Arthur 1976; 

 Last 1978a, b). Food selection by fish larvae is 

 controlled by factors such as prey size (the most 

 investigated variable), morphology, catchability 

 (as determined by swimming speeds, escape re- 

 sponses, etc.), and availability (temporal and 

 spatial distribution). None of these factors are 

 well understood. 



Most studies of the feeding ecology of fish lar- 

 vae have focused on prey size, but color (Arthur 

 1976) and body transparency may also be impor- 

 tant cues for "selection" of various copepod prey 



by fish larvae. All of the harpacticoid copepods 

 ingested by cottid larvae were brightly colored: 

 Tisbe spp., red and white stripes; Zaus sp., blue- 

 green; Harpacticus sp., brown; and Microsetella, 

 red. Furthermore, except for Microsetella, all 

 are epibenthic forms whose abundance in the 

 water column would not be expected to be high 

 (Noodt 1971). Among the calanoid copepods, dif- 

 ferences in body transparency and resulting visi- 

 bility to predators may explain why Temora 

 (which has a dense, thick carapace) was ingested 

 by cottid larvae rather than the more abundant 

 but nearly transparent Oithona. 



Balanus nauplii, which at times during late 

 winter and early spring can be the most abun- 

 dant zooplankter in the Damariscotta River estu- 

 ary (Lee 1974), were the most ubiquitous prey of 

 cottid larvae and appeared to be ingested in 

 direct relation to their abundance in the plank- 

 ton, i.e., in density-dependent fashion. Compari- 

 son of frequencies of occurrence of the six naupli- 

 ar stages of Balanus ingested by Myoxocephalus 

 and Triglops murrayi larvae in early and late 

 March showed that, with one exception, larvae of 

 all four species caught in early March were feed- 

 ing solely on naupliar stages 1-3 (Table 14). Later 

 in the month when Balanus nauplii became the 

 dominant zooplankter in most ichthyoplankton 

 samples, larvae of all four species (i.e., larvae of 

 varying size and, presumably, prey-catching 

 ability and "preference") were feeding on all six 

 naupliar stages. Percent frequency of occurrence 

 of each stage was remarkably similar among the 

 four cottid species, suggesting that these values 

 might actually reflect relative abundance of 

 each stage in the plankton assuming that each 

 stage is equally susceptible to capture and inges- 

 tion. The apparent reliance of cottid larvae on 

 Balanus nauplii may be explained by the ten- 

 dency, observed among adult fishes, to ingest 

 more intermediate-sized rather than larger prey 

 when both are present in abundance (Ivlev 1961; 

 Hyatt 1980). Among larval cottid prey, naupliar 



Table 14.— Percent frequency of occurrence (%FO) of six naupliar stages of Balanusspp. (Crisp 

 1962) in the guts of four species of cottids on (1) 5-6 March and (2) 19-20 March 1973. 



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