Burkett 



Chapter 22 



Food Habits and Prey Ecology 



were noted as feeding mainly on anchovy and to a lesser 

 extent on sand lance (table 1). 



Another instance of anchovy in murrelet diet came from 

 mist netting of murrelets in Redwood National Park for 

 radio-telemetry purposes during summer 1989 (Ralph and 

 others 1990). During this work, on July 3, 1989, one murrelet 

 hit the mist net and bounced out (05:30 p.d.t.), leaving a 

 whole northern anchovy at the base of the net. The anchovy 

 weighed 10.0 grams and was 113 mm in length. It seems 

 most likely that this prey item was destined for a murrelet 

 nestling (table 1). 



It is unfortunate that systematic studies of murrelet food 

 habits in this region of California did not occur before and 

 after the great sardine fishery (mid 1930 to mid 1940). The 

 anecdotal information from above mirrors the documented 

 change in prey abundance over time, from sardine to anchovy. 

 The interesting history of sardine and anchovy population 

 fluctuations and their fisheries are briefly summarized below 

 under the prey ecology section of this chapter. The fact that 

 murrelets have persisted in the central California region 

 after a decline in the largest fishery in the Western Hemisphere 

 is probably another indication of the opportunistic feeding 

 behavior of the bird. This flexibility in prey choice has 

 probably helped to sustain the murrelet population in this 

 geographic region in spite of massive loss and deterioration 

 of inland nesting habitat. 



Anecdotal information on nestling diet was obtained 

 from video footage recorded during observation of an active 

 nest site in Big Basin State Park in the Santa Cruz Mountains 

 (Naslund 1993a). Three fish carried to the nestling were 

 identified (table 1). Two of the fish appeared to be either 

 northern anchovy or possibly of the clupeidae. The third fish 

 was judged to be a smelt (osmeridae). 



Rockfish make up an important component of seabird 

 diet in California, and if more intensive studies of murrelet 

 diet were conducted it is possible that these fish would be 

 found to be eaten by murrelets (Ainley and others, this 

 volume). Both Sealy (1975c) and Carter (1984) documented 

 scorpaenids in the murrelet' s diet (table 1). 



Food Habits Summary 



The sand lance is the most common food of the murrelet 

 across its range (table 1). For the fish species, records of 

 sand lance represent 52 percent of the compiled information 

 (11 occurrences per 21 studies/anecdotal observations) on 

 murrelet food habits. The next most commonly recorded 

 species are anchovy and herring at 29 percent, followed by 

 osmerids at 24 percent, and by Cymatogaster at 14 percent. 



Euphausiids as a group represented 24 percent of the 

 compiled information (table 1). They were generally not a 

 dominant component of murrelet diet during the breeding 

 season; however, euphausiids were an important prey source 

 for murrelets in the spring (Sealy 1975c) and during the 

 breeding season in some years (Krasnow and Sanger 1982). 

 Euphausiids were also important during the winter in the 

 Gulf of Alaska (Krasnow and Sanger 1982) and in British 



Columbia (Vermeer 1992). Mysids and gammarids were 

 another component of murrelet diet, especially in winter 

 (Krasnow and Sanger 1982, Munro and Clemens 1931, 

 Sanger 1987b). 



Studies under the OCSEAP program revealed the 

 importance of seasonal and interannual variation in prey 

 abundance (Krasnow and Sanger 1982, Sanger 1983, Sanger 

 1987b). The OCSEAP compilation (Sanger 1983) revealed a 

 broader prey spectrum compared to systematic studies (Carter 

 1984, Sealy 1975c, Vermeer 1992), though this may have 

 been partially because of the larger time period and larger 

 geographic extent of collection (table 1). It may also have 

 been a function of the larger sample size compared to these 

 other studies (table 1). 



Comparison of results from Sealy (1975c), Carter (1984), 

 and Vermeer (1992) reveals the influence of site-specific 

 conditions on prey availability and selection by murrelets 

 (table 1). Differences between adult, nestling, and fledgling 

 diet were also apparent (Carter 1984, Mahon and others 

 1992, Sealy 1975c) (table 1). 



Though much work needs to be done on food habits in 

 different geographic regions and seasons, in general it can 

 be said that murrelets feed on invertebrates such as 

 euphausiids, mysids, decapods and amphipods. and small 

 schooling fishes including sand lance, anchovy, herring, 

 smelt, and seaperch. The fish portion of the diet is most 

 important in the summer and coincides with the nestling and 

 fledgling period (Carter 1984, Carter and Sealy 1990, Sealy 

 1975c). 



Prey Ecology 



Because few systematic studies of murrelet food habits 

 have taken place and the murrelet occupies such a large 

 geographic area with a wide variety offish species potentially 

 available, the rest of this chapter will focus on selected 

 prey species considered most important in murrelet diet at 

 this time. Due to the long-standing commercial value of 

 anchovies, herring, and sardines, there is a large body of 

 information on life history and factors affecting their 

 abundance and distribution. The following overview is not 

 an attempt to compile the rich literature on these or the 

 other known prey species, but instead focuses on interesting 

 aspects of their life history and the interrelationship between 

 prey species, murrelets, humans, and the marine 

 environment. The relationship between other seabirds and 

 these same prey resources, along with the marine 

 environment, will be discussed. Sand lance and euphausiids 

 have been little studied compared to the commercially 

 valuable fish species, but are discussed first because of 

 their position and interaction in the marine food web, and 

 their importance in the murrelet' s diet. 



Euphausiids 



Euphausiids are a group of small crustaceans which 

 make up part of the zooplankton ("krill") found in the 

 marine environment. Euphausiids are more or less transparent 



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



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