Burkett 



Chapter 22 



Food Habits and Prey Ecology 



Table 3 Comparison of May 1978 breeding season diet of Marbled 

 Murrelets between IJiut Bay and Northern Sittaliaak Strait, Alaska" 



2 Data from Krasnow and Sanger (1982) 



b Values are Index of Relative Importance values calculated after Pinkas 

 and others (1971) 



The difference between the two areas in the May diet 

 (table 3) may be due to the small sample sizes or may 

 represent a local difference in prey abundance as discussed 

 above relative to winter diet. The two study areas showed 

 similarity in murrelet diet in June, with fish (primarily capelin) 

 the most important food item. The July samples indicated 

 the importance of sand lance and fish in murrelet diet during 

 that period: three birds collected at Izhut Bay had only sand 

 lance in their stomachs, while four birds collected at Sitkalidak 

 were full of sand lance and other unidentified osteichthyes. 



Sanger (1983) 



Sanger' s compilation of data from throughout the Gulf 

 of Alaska, and across all seasons, provides an overview of 

 the broad spectrum of the murrelet's diet (table I). Data were 

 derived from multiple Outer Continental Shelf Environmental 

 Assessment Program (OCSEAP) studies (including Krasnow 

 and Sanger 1982, Sanger and Jones 1982) and from the 

 National Marine Fisheries Service (n = 129). At least 16 prey 

 species were identified. This broad spectrum of prey species 

 from different trophic levels is a good indication that the 

 murrelet is an opportunistic feeder, though preferences have 

 been documented (Sealy 1975c). Generally, murrelets seem 

 to prefer euphausiids in spring and fish in summer though 

 prey availability and energetic requirements during these 

 seasons are also important factors in prey selection (Carter 

 and Sealy 1990. Cody 1973, Sealy 1975c). 



Additionally, "food-chain pathways that include detritus 

 may result in a more stable food supply than non-detrital 

 food chains. This could be reflected in demersal-benthic 

 feeders like Pelagic Cormorants [Phalacrocorax pelagicus] 

 and Pigeon Guillemots [Cepphus columba] showing stable 

 productivity over the years, compared with midwater and 

 surface feeders. Winter survival of species like Common 

 Murres [Uria aalge] and Marbled Murrelets may be enhanced 

 by their ability to alter their 'normal' diet of pelagic fishes 



to include demersal crustaceans, thus seasonally linking 

 themselves to a detrital-based food chain" (Sanger 1987a). 



Sanger (1987b) 



One last example of the importance of local conditions 

 on murrelet diet from the OCSEAP work in Alaska comes 

 from a summary of work done in Kachemak Bay during the 

 winter of 1978 (Sanger 1987b). Twenty-one murrelets were 

 collected from January to April 1978, and 18 stomachs were 

 used for the analysis. Capelin and osmerids dominated the 

 diet, followed by euphausiids (Thysanoessa sp.), mysids, 

 unidentified gammarid amphipods. and sand lance. Compared 

 to the work of Krasnow and Sanger (1982) in Chiniak Bay, 

 euphausiids were more important, and sand lance were taken. 

 Thus, although the sample sizes are similar, the relative 

 importance of prey species is variable. This disparity is 

 another example of the importance of local and interannual 

 conditions in determining murrelet food habits. 



Carter (1984) 



Carter's intensive study occurred in Barkley Sound, on 

 the southwest coast of Vancouver Island. Field work was 

 conducted from 10 May to 7 September 1979, 18-19 

 December 1979, and 8 June to 13 October 1980. Eighty- 

 seven murrelets were obtained during the study and examined 

 for diet information. Carter (1984) noted that small fish 

 larvae (<31 mm) were apparently digested quickly, and 

 therefore this size class was under-represented in the results. 

 Food samples from both sexes were taken throughout the 

 day in both years and were combined for analysis. Carter 

 also separated the diet of breeding, molting, hatching-year, 

 and winter birds and calculated a relative importance value 

 in the same way of Sealy (1975c), though he referred to this 

 percent value as frequency. 



Breeding adults fed primarily on sand lance and Pacific 

 herring (Clupea harengus), including larval and juvenile 

 fish (table 1). Molting and hatching-year birds also fed 

 primarily on herring and sand lance, and four juvenile northern 

 anchovy (Engraulis mordax) were found in the stomach of 

 one molting bird. Carter (1984) noted that molting murrelets 

 consumed more herring (90 percent) than sand lance (7 

 percent), and the same was true for the hatching-year 

 murrelets, with herring consumption at 81 percent and sand 

 lance at 13 percent. By contrast, the breeding murrelets 

 consumed more sand lance (63 percent) and less herring (36 

 percent) (table 1). 



In contrast to the work of Sealy (1975c), euphausiids 

 were absent in the diet of murrelets in Barkley Sound. Though 

 Carter's (1984) work began approximately one month later 

 than Sealy's (1975c), euphausiids in minor amounts should 

 have occurred at least in May and throughout the summer at 

 least as a minor component of the diet. Additionally, the 

 overall diversity of prey species in the summer diet of 

 murrelets from Barkley Sound was low (4 different prey 

 items) compared to 9 from Sealy's (1975c) study and 10 

 from Krasnow and Sanger (1982). 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



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