Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 



233 



Gulf of Alaska 



169° W 167° 



165° 



163° 161° 159° 157° 155° 153° 



151° 149° 



147° 



53° 



145° 



Figure 1 



Near surface currents and some geographic and bathygraphic features of the western Gulf of Alaska. Currents based on Reed and 

 Schumacher (1986). 



with a mouth opening of 0.3 m x 0.5 m and with a 

 0.505-mm mesh net. Ship speed was 2 knots. Stan- 

 dard MARMAP (Marine Resources Monitoring As- 

 sessment and Prediction) oblique tows (Smith and 

 Richardson, 1977) were conducted to sample subsur- 

 face ichthyoplankton with 60-cm bongo samplers fit- 

 ted with 0.505-mm mesh nets. In shelf waters, tows 

 were made to a depth close to the bottom, usually 

 around 5 m above, and in deep water to a maximum 

 depth of approximately 200 m. Calibrated flowmeters 

 in the mouths of the samplers were used to deter- 

 mine the volume of water filtered by each net. 



Counts offish eggs and larvae were converted to den- 

 sities per 1,000 m 3 for neuston collections, as follows: 



(n)( 1,000 )/[(h)(w )(/)], 



where n = number of organisms in sample; 



h = effective fishing height of net opening 

 (0.15 m); 



w = width of net opening (0.5 m); 

 / = length of tow in meters (calculated from 

 flowmeter). 



In order to determine the importance of the 

 neustonic layer relative to that of the entire water 

 column, we compared the paired catches of neuston 

 and bongo tows from the same stations following the 

 approach derived by Hobbs and Botsford ( 1992). This 

 approach accounts for the differences in surface area 

 sampled between the neuston tows and the bongo 

 tows. The method solves for the density of larvae per 

 unit area in the ith sample (A.) and the portion of 

 total water column larvae in the neuston ( 9) simul- 

 taneously in an iterative fashion. We first calculated 

 the surface area (in m 2 ) sampled by the neuston (A m ) 

 and bongo (A..) net as: 



Kt = 



hxwxl 



