462 



Fishery Bulletin 93(3), 1995 



■c 

 e 



c 



<u 



0. 



Empty 



1/4 Full 



1/2 Full 



3/4 Full 



Full 



Distended 



Stomach fullness 



Figure 4 



Relative-frequency histogram of staghorn sculpin, Leptocottus armatus, 

 stomach fullness. All sculpin (n=482) from Grays Harbor, Washington, 

 April-August 1989. 



Table 2 



Summer diet composition of staghorn sculpin, Leptocottus 

 armatus, from Grays Harbor, Washington, all data com- 

 bined, April-August 1989. Values are percent composition 

 by number (%NC), weight (%GC), frequency of occurrence 

 (%FO), and percent of total Index of Relative Importance 

 (%IRI) by prey categories. Bold values indicate the five most 

 important prey categories as measured by % total IRI. The 

 total cumulative percentage of the diet comprised by those 

 five categories appears in the bottom line of the table. 



Prey category 



%NC %GC %FO %IRI 



Nereis brandti 9 30 30 30 



Neotrypaea californiensis 9 27 30 27 



Crangon spp. 12 7 27 13 



Cancer magister 9 7 22 9 



Upogebia pugettensis 3 17 11 6 



Eogammarus confervicola 13 <1 12 4 



Misc./unid. Crustacea 9 2 12 3 



Fish 4 6 12 3 



Bivalve siphon tips 10 <1 10 2 



Misc./unid. amphipods 6 <1 7 1 



Allochestes spp. 5 <1 5 <1 



Corophium salmonis 6 <1 5 <1 



Misc./unid. polychaetes 2 <1 5 <1 



Algae 3 <1 8 <1 



Total cumulative percentage 



of diet within top 5 categories 85% IRI 



0+ and 1+ sculpin). Whole bodies of crab in- 

 stars, J1-J4 (mean CW: 6-21 mm), were 

 found in sculpin stomachs (Fig. 8). 



Habitat comparison 



Sculpin diets from two intertidal sites 

 dominated by eelgrass and epibenthic shell 

 (Fig. 1; E and S) were compared. At each 

 site two trawls per trip were made at high 

 tide after sculpin had moved from the ad- 

 jacent subtidal channels up onto the flats 

 to feed. Mean number of individual prey 

 items per predator (about 3) was the same 

 at both sites, but the percentage of empty 

 guts was significantly lower among sculpin 

 caught over the eelgrass compared with 

 the percentage of empty guts among 

 sculpin caught over shell habitat (2% vs. 

 11%; approximation of Fisher Exact Test, 

 Z=1.98,P=0.024, Zar, 1984). Mean length 

 of sculpin captured at the eelgrass and 

 shell sites were 104 ±24 mm (1 SD) and 

 123 ±27 mm TL, respectively. The most 

 pronounced difference in sculpin diets be- 

 tween sites was that juvenile C. magister composed 

 77% IRI over shell habitat but only 5% over eelgrass 

 (Fig. 9) Frequency of occurrence of crab in sculpin 

 stomachs was 3.6 times greater over shell habitat 

 than over eelgrass habitat (69% FO vs. 19% FO). In 

 addition to C. magister, the other top diet categories 

 at shell habitat were ranked as N. californiensis (7% 

 IRI), U. pugettensis (6% IRI), N. brandti (5% IRI), 

 and unidentified amphipods (2% IRI). In contrast, 

 primary prey at the eelgrass habitat were N. 

 californiensis (27% IRI), N. brandti (25% IRI), and 

 Crangon spp. (24% IRI). Cancer magister and bivalve 

 siphons represented 5% and 4% IRI respectively (Fig. 

 9). There was not significant dietary overlap in 

 sculpin diets between the two habitats (S /o =0.2). 



Staghorn sculpin and 0+ crab densities 



Relative density at intertidal and subtidal 

 channels To assess the availability of crab as prey 

 for sculpin predators, relative density was calculated 

 for both sculpin and 0+ crab to contrast intertidal 

 and subtidal eelgrass and shell habitats. At either 

 site, relative crab densities were initially higher on 

 the intertidal compared with adjacent subtidal chan- 

 nels during peak crab settlement in June. Intertidal 

 densities in shell habitat at South Channel were 

 about 9,500/ha in early June and declined to 6,000/ 

 ha later in the month. However, in the adjacent 

 subtidal channel crab densities were less than 100/ 



