MEMORANDUM

Tetra Tech, Inc.

400 Red Brook Blvd., Suite 200

Owings Mills, MD 21117

phone	410-356-8993

fax	410-356-9005

DATE:	February 18, 2008

TO:	Paul Shriner and Jan Matuszko, EPA

FROM:		Blaine Snyder, Henry Latimer, Ann Roseberry Lincoln, Kelly
Meadows and Shari Goodwin

SUBJECT:	SEAMAP and Other Data Applicability to Other Coastal Settings

Introduction

In 2005, Tetra Tech prepared a memorandum for EPA entitled “A Summary
of Ichthyoplankton Presence and Abundance in the Gulf of Mexico, as Part
of an Assessment of the Potential for Entrainment by Offshore Oil and
Gas Facilities” (DCN 9-5200; FDMS ID EPA-HQ-OW-2004-0002-1956[1]). In
that memo (included in the rulemaking record for the Phase III rule),
the Southeast Area Monitoring and Assessment Program (SEAMAP) (Hanisko
2004) database was used to characterize ichthyoplankton (fish eggs and
larvae) presence, composition, and density within the Gulf. Recently,
EPA expressed interest in understanding how well the SEAMAP data/results
translate to a coastal setting (as opposed to open water) or if similar
data exists for other coastal locations. Of particular interest to EPA
is the relationship of ichthyoplankton density to water depth and how
the SEAMAP conclusions translate to other coastal areas (particularly
the California coast).

Review of Data

The 2005 memo presented a plot of average ichthyoplankton densities
against depth at 10 meter intervals (copied here as Figure 6). General
trends were similar between egg and larval fish densities. The densities
of both declined rapidly from 0 to 60 meters in depth. As depth
increased past 60 meters, the decline in ichthyoplankton and egg
densities was less pronounced. 

We also prepared a map of SEAMAP sampling locations (copied here as
Appendix A) that color-coded sampling site location symbols to reflect
ichthyoplankton density ranges (darker shades represented higher
densities). The site density information, combined with bathymetry
contour delineations, mirrored the results of ichthyoplankton density
graphs, i.e., that density generally increased as depth decreases.

 

Applicability of SEAMAP and Other Data

EPA is interested in knowing how well the SEAMAP conclusions (e.g.,
relationship of ichthyoplankton density to water depth) translate to
other coastal areas (particularly the California coast). Intuitively, it
would not be prudent to simply assume the SEAMAP data/results could be
applied to (or represent trends in) other coastal areas. For example,
when comparing the Gulf of Mexico to the California coast, there are
notable differences in fish assemblages (species composition), water
temperatures, currents, tides, and coastal zone morphology. It would be
advisable to collect ichthyoplankton data from other coastal areas of
interest and perform the same analysis that we applied to the SEAMAP
data. Fortunately, Tetra Tech able to find a few literature sources that
documented applicable research in other coastal areas (California,
Oregon, and Washington). We also obtained ichthyoplankton density data
for the Gulf of Maine. In addition, a study conducted in Great Britain
further corroborates the statement that ichthyoplankton densities
increase with decreasing depth. 

Auth et al. (2007) examined diel variation in the vertical distribution
of ichthyoplankton from a point location off the Oregon Coast. Their
sampling consisted of continuous oblique ichthyoplankton tows from a
depth of 350 meters to the water’s surface. Their research documented
that the vast majority (96%) of fish larvae were present in the upper
100 meters of the water column. The authors stated that, “One
implication from these findings is that sampling in the upper 100 meters
of the water column should be sufficient to characterize pelagic summer
ichthyoplankton abundances and distributions of the majority of fish
taxa along the northeastern Pacific coast.”

This particular paper (Auth et al. 2007) included a figure that
summarized diel differences and in the proportion of total abundances
for the dominant larval taxa (A = slender sole; B = scorpionfishes and
rockfishes; C = northern lampfish; and D = lanternfish), copied here as
Figure 2. This figure also summarized their abundances at depth
intervals, and reflects the text conclusion that ichthyoplankton
abundance is greatest at depths less than 100 meters (and perhaps
further, abundances are greatest at depths less than 50 meters during
night and early morning hours).

Applicable research was also presented in Doyle (1992). This paper
discusses the analysis of ichthyoplankton data collected off of the
Washington, Oregon, and northern California coasts during the 1980s. Ten
sampling cruises were completed over a period of seven years, and 125
sampling stations were visited during each cruise. Sampling consisted of
oblique tows to a 200-meter depth (or 5 meters from the bottom in water
shallower than 200 meters) at each station. This research documented
that most taxa of fish larvae occurred close to the coast (over the
shelf and slope) and were absent or scarce in the deepest part of the
oceanic zone. The author stated that, “This is true of the pelagic
Engraulis mordax and the demersal hexagrammids, cottids, Ronquilus
jordani, Cryptacanthodes aleutensis, and Ammodytes hexapterus. Adult
populations of these species are essentially coastal. Some, such as
Hexagrammos decagrammus, H. lagocephalus, Hemilepidotus spinosus, and
Scorpaenichthys marmoratus, are most abundant close to shore, where they
spawn from the intertidal zone to a maximum depth of 100 meters.”

This paper (Doyle 1992) included a figure that summarized patterns of
distribution for dominant larval fish taxa as grid squares on a coastal
map (copied here as figures 7 and 8). The larval density figures reflect
the text conclusion that most taxa of fish larvae (and highest
densities) occur close to the Washington, Oregon, and northern
California coasts (over the shelf and slope).





Runge and Jones collected ichthyoplankton from May 2005 through June
2007 at five sampling locations in the Gulf of Maine. Sampling consisted
of continuous oblique tows to a depth of five meters above the bottom.
Samples were sorted in the laboratory and fish larvae were identified to
the species level. Tetra Tech combined the species data to obtain total
larval densities for each sample, and averaged the samples by maximum
depth, grouped into 15-meter increments. Table 1 shows the number of
samples obtained at each depth for each station. Figure A graphs the
average densities versus the maximum tow depth (again grouped into
15-meter increments), demonstrating that ichthyoplankton densities
generally increase as depth decreases. 

Additionally, we summed the depth-averaged densities to obtain a total
average density for each station, and displayed the results on a map of
the Gulf of Maine. Figure B shows the results: the greatest densities
occur closest to the coast.

Table 1. Number of ichthyoplankton samples collected at each station in
specified depth ranges.

Lowest Tow Depth	Stations

	CT1	CT3	WB2	WB3	WB4

 0 to <= 15 m





	15 to <= 30 m

	1



30 to <= 45 m

17	5



45 to <= 60 m	10	2	15



60 to <= 75 m	12

1	2

	75 to <= 90 m





	90 to <= 105 m



15

	105 to <= 120 m





	120 to <= 135 m



1

	135 to <= 150 m



	1





Figure A. Average ichthyoplankton density by tow depth. Runge and Jones
data result from oblique tows from the ocean surface to approximately
five meters from the bottom. Categories represent the lowest tow depths,
grouped into 15-meter increments.

Figure B. Average ichthyoplankton density at five sampling stations in
the Gulf of Maine. Average total bottom to surface ichthyoplankton
densities presented in number of larvae per cubic meter.

Similar patterns hold in other areas of the world, as well. Fortier and
Harris (1989) studied vertical ontogenetic fish larvae migrations at a
station off Plymouth, UK, on the north coast of the Western English
Channel. Constant-volume samples were collected with a large-volume pump
system at discrete five-meter depth intervals from 55 m to the surface.
Their Figure 6 (copied below) shows the vertical distribution of fish
larvae by species, size class, and time of day. The authors note that
“The vertical distribution of fish larvae varied little over the diel
cycle but changed considerably during ontogeny.” Specifically, the
post yolk-sac larvae of all the species moved progressively deeper in
the water column with growth. These findings suggest that larval
densities do not decrease significantly between the surface and 55 m
depth.

Conclusions

The findings of the SEAMAP analysis for the Gulf of Mexico are generally
supported by the cited papers from the Pacific and British coasts and
the data from the Gulf of Maine, i.e., that ichthyoplankton densities
increase as depth and distance from shore decrease, and that abundance
is greatest at depths less than 100 meters. 

Literature Cited

Auth, T.D., R.D. Brodeur, and K.M. Fisher. 2007. Diel variation in
vertical distribution of an offshore ichthyoplankton community off the
Oregon coast. Fisheries Bulletin 105:313-326.

Doyle, M.J. 1992. Neustinic ichthyoplankton in the northern region of
the California current ecosystem. CalCOFI Report, Vol. 33: 141-161.

Fortier, Louis and Roger P. Harris. 1989. Optimal foraging and
density-dependent competition in marine fish larvae. Marine Ecology
Progress Series 51: 19-33.

Hanisko, David. 2004. Personal communication. NOAA. National Marine
Fisheries Service, Paspagoula Laboratory, Mississippi. Personal comm.
2004.

Runge, J.A. and R.J. Jones. PULSE: A Cooperative Partnership for Coastal
Ocean Ecosystem Monitoring in the Gulf of Maine. Award # NA16FL2452,
Northeast Consortium. Data available online at  HYPERLINK
"http://www.cooa.unh.edu/data/boats/zooplankton/bongoNetsDensity/index.j
sp"
http://www.cooa.unh.edu/data/boats/zooplankton/bongoNetsDensity/index.js
p . Accessed on January 13, 2009.

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