1

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. 
2

We also prepared a map of SEAMAP sampling locations (copied here as Appendix A) that colorcoded 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.
3

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).
4
5
6
7

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
8

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 
9

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. 
10

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 http://www.cooa.unh.edu/data/boats/zooplankton/bongoNetsDensity/index.jsp. 

Accessed on January 13, 2009.