Burkett 



Chapter 22 



Food Habits and Prey Ecology 



Five murrelets collected in winter had eaten scorpaenid 

 rockfish and squid (Loligo opalescens), as well as large 

 juvenile herring and sand lance (table 1). Scorpaenids and 

 Loligo were also found in the murrelet diet at Langara Island 

 by Sealy (1975c) during the breeding season (table ]). 



Carter (1984) also made observations at sea of adults 

 holding fish for nestlings; Ammodytes, Clupea, and Engraulis 

 were documented as nestling food (table 1). 



The importance of herring in the diet of the murrelet in 

 Carter's (1984) study correlates with the local abundance 

 and availability of juvenile herring. He suggested that 

 murrelets fed opportunistically on available prey and noted 

 that juvenile herring were abundant only in localized areas 

 near spawning grounds (Hourston in Carter 1984). This 

 conclusion is further strengthened by the work of Vermeer 

 (1992) discussed below. 



Vermeer (1992) 



Winter food habits of murrelets from Quatsino Sound, 

 British Columbia, were studied for the period from October 

 1981 through March 1982 (Vermeer 1992). Quatsino Sound 

 is located approximately 270 kilometers northwesterly of 

 Barkley Sound where Carter's (1984) work was conducted. 



Twenty -five murrelets were collected, and all birds (100 

 percent) contained food. Most fish were digested, but Pacific 

 herring were identified in 15 of the 25 murrelets. All 

 invertebrates eaten consisted of euphausiids, of which T. 

 spinifera and E. pacifica were the main species. The fish 

 portion of the diet constituted 71.2 percent of the wet weight 

 of the prey items, and the invertebrate portion was 28.7 percent; 

 thus, the murrelets ate mostly fish, primarily herring, during 

 the non-breeding season in Quatsino Sound (table 1). Sand 

 lance were not consumed, and the diversity of prey items (at 

 least 3) was low compared to that found in the winter diet 

 work by Krasnow and Sanger (1982) and Sanger (1987b). 



Vermeer (1992) did point out that the study location 

 has one of the largest herring spawn areas along the west 

 coast of Vancouver Island and that herring spawn constitutes 

 a major food source for piscivorous as well as nonpiscivorous 

 birds, such as diving ducks. The massive presence of herring 

 in March for spawning and the predictable nature of this 

 occurrence has resulted in annual utilization of this resource 

 by many seabirds and other animals (Vermeer 1992). 

 Therefore, it seems apparent that the high use of herring in 

 Vermeer's (1992) study is another example of the 

 opportunistic foraging behavior of the murrelet and another 

 demonstration of the importance of local differences in 

 availability of prey as noted by Krasnow and Sanger (1982). 

 Of further interest, four male murrelets collected in Departure 

 Bay on the southeast coast of Vancouver Island during 

 February and March (in 1928 and 1929) did not contain any 

 identifiable herring in their stomachs even though the study 

 area was also known as a major spawn location for herring 

 during March (Munro and Clemens 1931). Results and 

 implications of the Munro and Clemens (1931) collection 

 effort are described in more detail below. 



Freshwater Feeding 



The studies described previously were conducted to 

 assess murrelet food habits in the marine environment. To 

 assess the importance of freshwater lakes in the feeding 

 ecology of murrelets, Carter and Sealy (1986) summarized 

 records of year-round use of coastal lakes for the period 

 1909 to 1984 from Alaska to California. No records were 

 found for California. Three of the 67 records included small 

 collections of murrelets at lakes in British Columbia during 

 late April and early May. Five stomachs of adults were 

 examined, and three were found to contain yearling Kokanee 

 salmon (Onchorhynchus nerka kennerlyi), while the fourth 

 contained two fingerling sockeye salmon (O. nerka). The 

 examiner of the fifth murrelet, R.M. Stewart, noted, "The 

 stomach was full of small fish which looked like salmon fry" 

 [Onchorhyncm or Salmo sp.] (Brooks 1928) (table 1). Carter 

 and Sealy 's (1986) work contains numerous anecdotal 

 sightings of murrelets feeding at inland lakes and references 

 which document many of the lakes as large nurseries for 

 juvenile salmon. The discussion includes evidence for 

 nocturnal feeding by murrelets and winter-time use of inland 

 lakes. The relative lack of inland lakes near known nesting 

 sites south of British Columbia, along with a lack of census 

 effort for murrelets at inland lakes, could lead to an 

 underestimate of the importance of lakes and freshwater fish 

 species as a food source for the murrelet. The effect of the 

 reduction of salmonid stocks on the use of lakes by murrelets 

 is unknown. This aspect of the murrelet' s life history needs 

 further investigation throughout its range. 



Isotopic Analysis of Diet 



Stable carbon and nitrogen isotopic analyses were 

 performed on tissues of Marbled Murrelets collected from 

 July to December 1979 (Carter 1984), in Barkley Sound 

 (n = 18), and in June 1985 on Johnston Lake, British Columbia 

 (n = 3) (Hobson 1990). Most murrelets showed stable carbon 

 isotopic values (pectoral muscle) between -15.5 and -17.5, 

 and males and females were the same. These values compare 

 favorably to the value of - 1 7 .9 for a sample of five Ammodytes 

 sp. taken from coastal British Columbia for comparison. 

 However, three individuals, an adult male from Barkley 

 Sound and two adult males from Johnston Lake, differed 

 significantly from the group. On the basis of a model, Hobson 

 concluded that the three individuals had short-term freshwater- 

 derived protein inputs to their diets ranging from 50 to 100 

 percent. Hobson (1990) suggested that while some murrelets 

 may feed exclusively on freshwater prey for a short but 

 important period of several weeks, freshwater protein did 

 not appear to be a significant long-term dietary component. 

 However, he concluded that he was unable to ascertain the 

 relative importance of freshwater feeding in different murrelet 

 populations without additional analysis. He suggested that 

 tissues from murrelets found dead or collected for other 

 studies be analyzed by isotopes of stable carbon. 



Analysis by isotopes of stable nitrogen cannot be used 

 for separating dietary differences between freshwater and 



230 



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



