8 



Technical Paper 28: Bureau of Sport Fisheries and Wildlife 



weather and station F-l because of an outflow 

 of ice from Delaware Bay. All stations were 

 occupied on the ensuing six cruises . During 

 cruise D-66-14, stations F -7 and E-8 were 

 initially occupied in sequence with other 

 stations on the respective transects but since 

 the plankton samples were subsequently lost in 

 rough weather, we reoccupied these stations 

 later in the cruise. 



LABORATORY PROCEDURES 



The workload of identification was 

 divided by assigning to each project biologist 

 certain families of fish appearing in the 

 collections. Technicians were assigned the 

 task of removing fish eggs and larvae from the 

 Gulf V samples . Each sample was processed 

 entirely by one technician. Sorting was done 

 by placing individual 2 -milliliter (0.12-in .) 

 aliquots of plankton in a petri dish and examining 

 each for fish eggs and larvae under a micro- 

 scope at a magnification of 7 to 10 X. The 

 larvae from each sample were provisionally 

 separated into groups based on physical 

 similarities. These groups consisted of species 

 from one or more families . 



To estimate the thoroughness of re- 

 moval of ichthyoplankton from the samples, 

 routine quality control was maintained whereby 

 aliquots amounting to about 6 percent of the total 

 were taken at random as sorting proceeded and 

 reexamined by a second technician. A com- 

 parison of the number of fish eggs and larvae 

 found during each examination of the test 

 aliquots provided a measure of the quality of the 

 sorting and a means of evaluating and improving 

 the technician's work. In the few instances 

 where more than 10 percent of the ichthyoplankton 

 had been overlooked, the sample was re-sorted. 

 This checking technique was developed gradually 

 during the course of sample processing and was 

 used fully during sorting of five of the eight 

 cruises . From these cruises we found that 98 

 to 100 percent of the eggs and 91 to 97 percent 

 of the larvae were removed during the first 

 sorting of samples when grouped by cruise. 



Besides checking random aliquots during 

 sorting, an additional aliquot from the whole 



sample was checked immediately after the 

 sorting of each sample was finished. Samples 

 from the cruises sorted before this system was 

 implemented were examined during volume 

 measurement, and re-sorted if sufficient numbers 

 of fish eggs or larvae were found to justify it . 



The volume of plankton taken in our 

 standardized tows was measured to estimate 

 the standing stock of plankton of sizes large 

 enough to be retained in the Gulf V net. The dis- 

 placement method was used as had been done in 

 two previous studies of Atlantic coast waters of 

 the United States (Bigelow and Sears, 1939; 

 Deevey, 1960). Methods for improving dis- 

 placement measurements of plankton have been 

 developed and some were employed in this 

 study (Ealey, 1954; Frolander , 1954; Tranter , 

 1960; Yentsch and Hebard, 1957). Because 

 plankton volumes decrease significantly with time 

 during the first few months after preservation 

 (Ahlstrom and Thrailkill, 1963), measurement of 

 the samples was delayed for at least 6 months 

 after collection. After the fish eggs and larvae 

 and seston items displacing more than 3 milli- 

 liters were removed, the remaining volume of 

 plankton and preservative was measured in a 

 graduate and poured into a filtering funnel con- 

 taining a disc of nylon mesh with 0.5 -mm. 

 (0.02-in.) apertures. The preservative was 

 removed by vacuum filtration and the volume of 

 the filtrate was determined. The difference 

 between the volume of plankton and preservative 

 and of the filtrate was recorded as the plankton 

 volume. The measurements are listed, as 

 milliliters of plankton per tow, in Appendix 

 table II and are shown graphically in Appendix 

 figures Fl to F8 . 



REFERENCES 



Ahlstrom, Elbert H., and J. R. Thrailkill. 

 1963 . Plankton volume loss with time of 



preservation. Reports California Coopera- 

 tive Oceanic Fisheries Investigations, 

 Vol. 9, pp. 57-73. 



Bailey, Reeve M., Ernest A. Lachner, C. C. 

 Lindsey, C. Richard Robins, Phil M. Roedel, 

 W. B. Scott, and Loren P . Woods. 



1960. A list of common and scientific names 



