Ralph and others 



Chapter 1 



Overview of Ecology and Conservation 



Although murrelets are often encountered as widely 

 dispersed pairs, in some instances they gather into flocks 

 that may contain a significant fraction of the local population 

 (Strachan and others, this volume). Murrelets most often 

 form flocks in the sheltered waters of Washington, British 

 Columbia, and Alaska (Carter and Sealy 1990; Kaiser and 

 others 1991; Piatt and Naslund, this volume; Prestash and 

 others 1992), but they also occasionally aggregate along the 

 open coasts of California (Ralph and Miller, this volume), 

 and Oregon (Strong and others 1994). Information about 

 where murrelets are likely to concentrate at sea is relevant to 

 the prediction of where murrelet populations are likely to be 

 particularly vulnerable to bycatch in gill nets, a local oil 

 spill, other pollution event, or disturbance from good feeding 

 areas by boat traffic (Kuletz 1994). Protection of these areas 

 of aggregation may be important in reducing anthropogenic 

 sources of adult mortality. 



There are relatively few data on the distribution of 

 murrelet aggregations or their frequency. Several authors 

 have noted the correspondence between murrelet 

 distribution and certain physical processes in the ocean. 

 For instance, some observations indicate that along the 

 open coasts, aggregations may be more frequent in the 

 vicinity of river plumes (Strong and others, this volume; 

 Varoujean and Williams, this volume), although old-growth 

 stands may also be most numerous in river valleys, thus 

 confounding the cause of the aggregations. In the bays and 

 sounds of Washington. British Columbia, and Alaska, 

 aggregations of murrelets are common, but little is known 

 about the environmental conditions causing these 

 concentrations. Piatt and Naslund (this volume) suggest 

 that murrelets prefer stratified as opposed to well-mixed 

 waters, but they also report that murrelets often concentrate 

 near the outflows of large rivers and in rip tides. Burger 

 (this volume b) reviewed the available data for British 

 Columbia, and found equivocal evidence linking densities 

 with water temperature. Kaiser and others (1991) found 

 some correlations with temperature which they attributed 

 to the effects of local tidal rips. Also there were instances 

 where murrelets aggregated at some tidal rips and upwelling, 

 but they were scarce or absent at other tidal rips where 

 other species aggregated. 



Murrelets have also been associated with particular marine 

 habitats that are favored by prey, such as sand lance 

 (Ammodytes hexapterus), and surf smelt (Hypomesus 

 pretiosus). Burger (this volume b) suggested that murrelets 

 aggregate in shallow bays of fjords, in estuaries, and off 

 beaches because these locations are where prey such as sand 

 lance might be common. In British Columbia, Carter (1984) 

 found murrelets in waters over sand and gravel bottom, 

 possibly because of the concentration of sand lance. Strong 

 and others (1993) hypothesized that adjustments in local 

 distribution off Oregon was in response to movements of 

 surf smelt. Ainley and others (this volume) suggested that 

 murrelets favor areas of upwelling, high productivity, and 

 concentrations of prey along the more open coasts of 



California, and that local movements here were also hi 

 response to food availability. We need considerably more 

 information before we will be able to predict the types of 

 locations where murrelets are likely to be concentrated. Our 

 success in identifying the factors responsible for aggregations 

 is likely to depend on concerted efforts to investigate the 

 issue of prey distribution, and also on our sensitivity to the 

 underlying spatial and temporal scales of the various 

 mechanisms involved. 



Seasonal Movements 



In some, if not all, areas of their range, Marbled 

 Murrelets exhibit seasonal redistributions of then- populations 

 (Klosiewski and Laing 1994; Kuletz 1994; Piatt and Naslund, 

 this volume; Ralph and Miller, this volume; Strachan and 

 others, this volume; Strong and others 1993). The studies 

 of Burger (this volume b) and Speich and Wahl (this volume) 

 provide important data showing that in winter murrelets 

 move from the outer, exposed coasts of Vancouver Island 

 and the Straits of Juan de Fuca into the sheltered and 

 productive waters of northern and eastern Puget Sound. 

 Although the available data are sketchy, the possibility 

 exists that a large portion of this murrelet population, which 

 hi summer is widely dispersed along remote coasts, is 

 concentrated in winter in an area with heavy ship traffic, 

 including the frequent movement of oil tankers to and from 

 refineries. Less is known about seasonal movements along 

 the outer coasts of Washington, Oregon, and California, 

 but Speich and Wahl (this volume) suggest that birds from 

 the outer coast of Washington move into Grays Harbor 

 channel in whiter. The potential for whiter concentrations 

 of murrelets to encounter industrial and oil pollution in the 

 sheltered waters that they prefer is a conservation issue of 

 considerable concern (Carter and Kuletz, this volume; Fry, 

 this volume). 



Social Influences at Sea 



Association of murrelets hi pairs, probably for foraging, 

 is well documented (Strachan and others, this volume). The 

 possible costs or benefits of interrelationships with other 

 species, such as kleptoparasitism by gulls (Hunt, this volume 

 b) or predation by Peregrine Falcons (Falco peregrinus) is 

 more speculative. However, the possible effects of human- 

 caused increases hi gull populations may be of some concern. 



Estimates of Abundance and 

 Historical Trends 



Summary We estimate, based on information in this 

 volume, that the total North American population of Marbled 

 Murrelets is about 300,000 individuals. Approximately 85 

 percent of this population breeds along the coasts of the 

 Gulf of Alaska and in Prince William Sound. There are few 

 murrelets in the Aleutian Islands and Bering Sea. Murrelet 

 populations in both Alaska and British Columbia have 

 apparently declined substantially over the past 10 to 20 



USD A Forest Service Gen. Tech. Rep. PS W- 152. 1995. 



