38 



Fishery Bulletin 91 [1), 1993 



LU 



o 



Figure 4 



Mean densities of all fish larvae, excluding osmerids, in Auke 

 Bay, Alaska during spring and early summer, 1986-89. Error 

 bars are 1SE; where no bars are visible, they are obscured by 

 the point symbol. 



speed was about 1.5 kn. Each tow lasted 7-8 min, and 

 volume filtered was typically around 300 m 3 . Volume 

 filtered per tow was very similar among years. Tows 

 were collected on reciprocal compass courses set at 90" 

 to the wind direction. 



Fish larvae were removed from each replicate and 

 enumerated by species, with the exception of osmerids, 

 agonids, cottids, and cyclopterids, which were identi- 

 fied only to family. Osmerids were not identified to 

 species because larvae of eulachon Thaleichthys 

 paciftcus and capelin Mallotus villosus, the two spe- 

 cies common in the Auke Bay area, are very similar. 

 The other three families (Agonidae, Cottidae, and 

 Cyclopteridae) lack comprehensive identification guides 

 to the species level. Mean densities of each taxon were 

 calculated as the number/m 2 of surface. 



Results 



Total number of larvae collected annually ranged from 

 6087 in 1988 to 18,655 in 1986 (Table 1). Most of the 

 interannual variation was due to differences in catches 



of osmerids. The five most-abundant taxa in all years 

 were osmerids, Pacific sandlance Ammodytes 

 hexapterus, walleye pollock Theragra chalcogramma, 

 flathead sole Hippoglossoides elassodon, and rock sole 

 Pleuronectes bilineatus. We did not include cottids in 

 this summary, as they include at least eight species, 

 none of which was exceptionally abundant; whereas 

 the osmerids were very abundant, and included two 

 species. 



Total abundance of all larvae, excluding osmerids, 

 peaked in March or early April of 1986-88 and in May 

 1989 (Fig. 4). Osmerids were excluded from total abun- 

 dance estimates because in 1986 and 1987 their abun- 

 dance obscured patterns associated with seasonal cycles 

 of other species. In all years, osmerid abundance 

 peaked from late May through June (Fig. 5). Such 

 consistency in time of appearance in Auke Bay was 

 typical of most species. 



Larvae present in late March or early April were 

 well in advance of either the spring phytoplankton 

 bloom or the herbivorous copepod maximum. These 

 early peaks in abundance were due primarily to high 

 numbers of Pacific sandlance and rock sole (Figs. 6, 



