Burger 



Chapter 29 



Marine Distribution, Abundance, Habitats in British Columbia 



Distance from shore (km) 



Figure 5 Densities of Marbled Murrelets in and near southern Barkley Sound between 1 May and 31 July in 1 980, 1 992, and 

 1 993. The main graph shows densities from grid surveys in Trevor Channel and strip transects near Cape Beale in 1 980 (Carter 

 1984). The inset shows densities from grid surveys in Trevor Channel in 1992-1993 (Burger 1994). 



different, and the presence of islands and reefs adds further 

 complications (see also Sealy 1975c, Sealy and Carter 1984). 



Temporal Patterns 



Using repeated grid surveys in Trevor Channel, Barkley 

 Sound, Carter and Sealy (1990) showed that local densities 

 of Marbled Murrelets declined, but clumping increased 

 through the day. Consistent high densities in some quadrats 

 and direct flights by murrelets into these areas at dawn 

 indicated that the birds were returning to predictable feeding 

 sites. Nitinat Lake, a large semi-saline lake adjacent to 

 important forest and marine habitats appears to be used as a 

 staging area for murrelets which leave the forests at dawn 

 and later move to the ocean (Burger 1994). 



Effects of Temperature and Salinity 



In fjords and channels in Desolation Sound, Kaiser and 

 others (1991) found no correlation between murrelet density 

 and sea surface temperature, and a weak positive correlation 

 with salinity (r 2 = 0.256, n = 20, P < 0.05). Between 6 June 

 and 8 August 1990, the murrelets were often concentrated in 

 areas with strong currents, and densities were negatively but 

 weakly correlated with sea temperature (r 2 = 0. 185, n = 15, P 

 < 0.05). Warm water was associated with algal blooms, 

 creating surface turbidity, which might have affected prey 

 densities and the birds' hunting efficiency. The murrelet' s 

 primary prey, sand lance, was usually found in clear water. 

 These fish are likely to move to deeper water or become 

 dormant in their burrows in unusually warm water (Field 



1988). Murrelet densities declined rapidly in late July as the 

 surface water heated up to near 20 C. Large-scale effects of 

 warm water influxes are described below. 



Tidal Patterns and Presence of Rips 



The relationship between tides and feeding patterns of 

 Marbled Murrelets in British Columbia is not consistent. 

 Repeated surveys in Barkley Sound (Carter 1984, Carter 

 and Sealy 1990) and Desolation Sound (Kaiser and others 

 1991) reported no significant changes in murrelet densities 

 with tidal state or tidal flow rate. Aggregations of murrelets 

 at sites with strong tidal flow were reported from Edye 

 Passage and north of Stevens Island, both on the northern 

 mainland (Fuhr, pers. comm.), Hiekish Narrows (central 

 mainland), and Desolation Sound (Kaiser and others 1 99 1 ), 

 Sechelt Rapids in Jervis Inlet (Vermeer 1989), and Yuculta 

 Rapids between Sonora Island and the mainland (Prestash, 

 pers. comm.). Marbled Murrelets were sparse or absent, 

 however, at strong tidal rips at Malibu Rapids (Jervis 

 Inlet), and Active Pass (Gulf Islands) where many gulls 

 and other birds were feeding (Vermeer 1989, Vermeer and 

 others 1987). 



Abundance Related to Feeding and 

 Nesting Habitats 



Effects of Prey Availability 



There have been no detailed comparisons of murrelet 

 distribution relative to independent measures of prey 



302 



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



