appendix b final 2008 biological surveys of los angeles and long ...

4.0 Ichthyoplankton
studies (Horn and Hagner 1982) showed that higher densities of ichthyoplankton were collected
then than during daytime collections.
Additional samples were collected for a special methods comparison study, described in Section
4.2.4, below. These samples were collected using more recent and widely employed gear and
methods developed by the California Cooperative Fisheries Investigations (CalCOFI) for their
coastal ichthyoplankton studies.
4.2.2 Laboratory Sample Processing
In the laboratory, eggs and fish larvae were
removed from each sample, and identified to the
lowest practicable taxon and counted. During the
start of sample sorting, if the sorter estimated that
there were more than 500 fish eggs in the sample,
eggs were not removed during the initial sample
sorting for larval fish. After the removal of the fish
larvae, 10 percent of the sample was removed
from the sample using an aliquot transfer pipette
(Hensen Stempel pipette) and the eggs in this
aliquot (subsample) were counted. When aliquot
sampling was required, an estimate of the number
of eggs in the entire sample was determined by
multiplying the number in the subsample by the fraction that was sorted. For example, if 10% of
the sample was sorted for eggs, the number of eggs of each taxon in the subsample was
multiplied by 10 to estimate the total number in the entire sample. All laboratory data was
recorded on sequenced datasheets and then entered into a computer database and reviewed
for completeness prior to data analysis.
Myomere counts and pigmentation patterns were used to identify larval fishes to the lowest
taxonomic classification possible. Generally, individuals that could not be identified to the
species level were identified to either the genus or family level. For example, many species of
the family Gobiidae have the same pigment pattern during early life stages (Moser et al. 1996),
making accurate identifications to the species level questionable. Accordingly, early larvae of
the arrow goby (Clevelandia ios), cheekspot goby (Ilypnus gilberti), and shadow goby (Quietula
y-cauda) were combined into an unidentified goby category referred to as “CIQ gobies”.
The identification of fish eggs is even more difficult than the identification of larvae. Egg
identification is generally based on a number of characters including egg size and shape,
number and size of oil globules, presence and type of ornamentation on the chorion (outer egg
membrane), and characteristics of the developing embryo, if present (Ahlstrom and Moser 1980,
E. Sandknop, CalCOFI pers. comm.). In many instances, some of these measurements can
overlap between taxa, making positive identification problematic; in those cases the individual
egg was recorded as belonging to a ‘slash’ category (one of two or more fish families). Many of
the eggs were left in the category “undeveloped egg” because there was no embryo inside the
egg, possibly due to the short period of time between release from the female and capture in the
net. Eggs with a visible embryo that could not be identified were recorded as unidentified fish
egg.
4.2.3 Data Analysis
The ichthyoplankton catch was standardized to number of eggs or fish larvae per 100 m 3 using
information from the calibrated flowmeter mounted in the net mouth during sample collection.
4–2 2008 Biological Surveys of Los Angeles and Long Beach Harbors
April 2010