LAROCHE: TROPHIC PATTERNS AMONG LARVAE OF SCULPINS (COTTIDAE) 



categories. Percent by volume or weight is, in 

 most cases, more useful than %Nor %FO in mea- 

 suring diet overlap. However, for predators like 

 larval Myoxocephalus and T. murrayi whose 

 prey are similar in size (Fig. 1), calculation of the 

 Schoener index using %N and %FO produces a 

 relatively unbiased estimate of diet overlap 

 (Wallace 1981). 



Settled volumes of the ichthyoplankton sam- 

 ples were measured by displacement method in 

 either a 100 or 250 ml graduated cylinder after 

 large jellyfish and macrophytic algae or other 

 large plant debris were removed. 



RESULTS 



Feeding Incidence 



The percentage of cottid larvae with empty 

 guts ranged from to 13 depending on the spe- 

 cies, with T. murrayi having the lowest overall 

 incidence of empty guts and H. americanus the 

 highest (Table 1). Only M. aenaeus and M. scor- 

 pius had equal or higher percentages of empty 

 guts in January and February than in March. In 

 addition to this high incidence of feeding, many 

 larvae examined had begun to feed before yolk 

 absorption was complete (Table 1). A remnant of 

 yolk (often sizeable) was found attached to or 

 closely associated with the liver in feeding larvae 

 over a wide size range: 5.3-9.5 mm SL in M. 

 aenaeus; 7.2-11.5 mm SL in M. octodecemspino- 

 sus; 7.5-10.4 mm SL in M. scorpius; 8.5-12.0 mm 

 SL in T. murrayi; and 12.0-15.9 mm SL in H. 

 americanus. 



Among the three species of Myoxocephalus lar- 

 vae with three-fourths of the abdominal cavity 

 filled with yolk (N = 33), about 80% had food in 

 their guts. The number of food items found in 

 these larvae ranged from 1 to 4 in M. aenaeus, 

 2 to 12 in M. octodecemspinosus, and 1 to 21 in M. 

 scorpius. No yolk-sac larvae of T. murrayi were 



Fiih Larvae 

 Decapod Zoeae 



Temora 



Pseudocalanus 



Tisbe 



Turbellana 



Balanus 



Harpacticus 



Coscinodiscus 



Microsetella 



Prey Width (micront) 



-I 1 1 1 1 1 1 // 1- 



Hemitnpterus americanus 



Triglops murrayi 



Myoxocephalus scorpius 



H 1- 



— I 1 1 1 1 U — I— 



160 240 320 400 480 560 640 720 800 880 1260 

 Body Width (microns) 



Figure 1.— Range in maximum body width (microns) of the 

 major prey ingested by larvae of five species of cottids in the 

 Damariscotta River estuary, Maine. 



collected. Of the seven H. americanus larvae 

 with prominent yolk sacs, only two had empty 

 guts. Each of the other larvae contained one food 

 item. 



Diet Composition 



Gut contents were examined of 147 M. aenaeus, 

 5.3-9.5 mm SL; 106 M. octodecemspinosus, 7.2- 

 12.4 mm SL; 87 M. scorpius, 7.5-13.4 mm SL; 58 

 T. murrayi, 8.5-18.1 mm SL; and 24 H. ameri- 

 canus, 12.0-16.2 mm SL (Tables 2-10). Percent 

 number of Coscinodiscus sp. was calculated only 



Table 1.— Incidence of Myoxocephalus, Triglops, and Hemitripterus larvae with 

 empty guts, and those with both food and a remnant of yolk present. (A/ = number of 

 larvae examined.) 



January-February 



March 



829 



