SHF = 10 D 

 V 



where D = depth of haul = cosine of the average angle 

 of stray of the towing cable multiplied by 

 cable length (m) 



V = total volume of water (m ) strained 



during the haul 



V = R * a ' p 



where R = total number of revolutions of the current 

 meter during the haul 



a = area (m ) of the mouth of the net 



p = length of column of water (m) needed to 

 produce one revolution of the current 

 meter. 



Tow depth, volume of water strained, and standard haul factor are 

 listed in Table 1 for each tow taken during 1951. Detailed 

 descriptions of factors involved in calculating these values are 

 presented in Ahlstrom (1948), Kramer et al. (1972), and Smith and 

 Richardson (1977) . 



IDENTIFICATION 



Identification of ichthyoplankton species beyond those 

 separated during the sorting process was carried out by a 

 separate group of specialists. Ontogenetic stages of fishes are 

 inherently difficult to identify and this is further complicated 

 by the large number and diversity of species which contribute to 

 the ichthyoplankton of the California Current region. Most 

 identifications were accomplished by establishing ontogenetic 

 series on the basis of morphology, meristics, and pigmentation 

 and then identifying these series by relating them to known 

 metamorphic, juvenile, or adult stages with overlapping features 

 (Powles and Markle, 1984) . A total of about 118 taxa were 

 identified in 1951, with 63 taken to species, 26 to genus, 25 to 

 family, and 4 to order (after present corrections 132, 67, 29, 

 31, 5, respectively). Some of the developmental series 

 recognized at the time could not be assigned scientific names, 

 particularly in the Bathylagidae, Myctophidae, and 

 Pleuronectiformes. These were given descriptive names, which 

 later were changed to scientific names as they became known. 

 Knowledge of the ontogenetic stages and of the taxonomy of the 

 regional ichthyofauna have increased markedly over the years so 

 that we now identify twice the number of taxa known in 1951. 



The task of producing a reliable and equitable 

 ichthyoplankton data base required extensive procedures to 

 verify, correct, and edit the original identifications. The 



