614 



Fishery Bulletin 93(4), 1995 



Table 3 



Two-way table of dominant taxa showing the station and 

 species groups as determined by TWINSPAN. Numbers in 

 parentheses represent the number of stations in each sta- 

 tion group. The numbers within the matrix correspond to 

 the mean density (no./lOOO m 3 ) of that taxon for each sta- 

 tion grouping ( — = taxon not present). Life stages of T. 

 chalcogramma and G. macrocephalus are designated af- 

 ter species name (l=larvae, j=juvenile). The total 

 ichthyoplankton for each station group represents all spe- 

 cies including the rare taxa not included in the TWINSPAN 

 analysis. 



Station group 



Taxon 



1 

 (13) 



2 



(6) 



3 



(22) 



4 

 (19) 



Lumpenus spp. 



G. macrocephalus (1) 



A. hexapterus 



0.02 



1.05 

 0.02 



0.02 



0.08 0.66 



0.09 

 0.38 



0.05 



spawn during spring are poorly sampled as late lar- 

 vae and early juveniles by bongo-net gear in sum- 

 mer (Shima and Bailey, 1994). 



Another study that examined the distribution of 

 late larvae and early juveniles in our study area used 

 neuston sampling gear, which tends to capture signifi- 

 cantly larger specimens than do bongo nets (Doyle et 

 al., 1995). These collections, however, were made mostly 

 before June, and the taxonomic composition of the catch 

 was markedly different from that of the present study 

 in that only 3 of the 15 most abundant larvae (A. 

 hexapterus, T. chalcogramma, and Mallotus villosus) 

 caught in the neuston nets occurred in our samples. 



One motivation for conducting ichthyoplankton 

 surveys is to provide an alternative estimate to trawl 

 surveys for the abundance of commercially exploit- 



able fishes (Heath, 1992). Although there are biases 

 involved with both ichthyoplankton and trawl sur- 

 veys that may result in an incomplete picture of true 

 fish population sizes, it is of interest to compare the 

 results of these two assessment methodologies for 

 the stocks in the western Gulf of Alaska (Kendall 

 and Dunn, 1985). Trawl surveys tend to exclude small 

 and cryptic taxa, particularly those that inhabit 

 untrawlable bottom types. Diel differences in verti- 

 cal distribution and aggregation patterns may also 

 influence trawl survey abundance estimates. Ichthyo- 

 plankton surveys are restricted to sampling only the 

 life stages that are pelagic at the time of the survey, 

 therefore they are strongly dependent on the timing 

 of spawning and the mode of development. Moreover, 

 extrapolation of catches to population abundance 

 requires additional information on basic life history 

 strategies (e.g. hatch size, pelagic/demersal eggs, num- 

 ber of spawning events, oviparity/viviparity), spawn- 

 ing locations, population egg production, and mortal- 

 ity rates. 



Differences in life history patterns may explain 

 some of the disparities observed between the trawl 

 and ichthyoplankton rankings. Two abundant trawl 

 species, Pleuronectes asper and Microstomous 

 pacificus, spawn in late spring and early summer off 

 Alaska (Hirschberger and Smith, 1983; Matarese et 



