i
ii

Most NOAA Technical Memorandums NMFS-NWFSC are

available on-line at the Northwest Fisheries Science Center

web site (http://www.nwfsc.noaa.gov)

Copies are also available from:

National Technical Information Service

5285 Pot Royal Road

Springfield, VA 22161

phone orders (1-800-553-6847)

e-mail orders (orders@ntis.fedworld.gov)
iii

EXECUTIVE SUMMARY

Trestle Bay is 11.3 RKm upstream from the mouth of the Columbia River in Oregon.

The 244-ha bay consists of shallow subtidal and intertidal mudflats and intertidal marsh habitats.

Trestle Bay formed as a result of the initial construction of the Columbia River south jetty which

took place from 1885 to 1895. Sand accumulation around the jetty created the bay, which is

surrounded by land on the west, south, and east sides and separated from the mainstem of the

Columbia River by a 2,682-m rock jetty along the north side. Although the rock jetty is

permeable to water, it has likely discouraged resident and migratory juvenile fishes (e.g.,

salmonids) from entering the bay.

In August 1995, the jetty was modified by removing a 152-m section of rock, creating an

unobstructed passageway between the bay and the lower Columbia River estuary. This allowed

better flushing and made Trestle Bay available as foraging habitat for many marine and estuarine

fishes and shellfish, and ultimately reestablished the bay as an integral part of the lower

Columbia River estuarine ecosystem. In 1994, the U.S. Army Corps of Engineers contracted

with the National Marine Fisheries Service to conduct pre- (1994) and post-breach (1996-97)

surveys in and adjacent to Trestle Bay, to determine any physical or biological changes caused by

the jetty breach.

Resource agencies were particularly interested in the use of the bay by juvenile salmonid

species and changes in their benthic and epibenthic invertebrate prey after the breach. This is a

concern because the Columbia River is critical habitat for several endangered salmonid species.

Biological sampling was conducted to assess benthic and epibenthic invertebrate populations,

fish species compositions, and sediment characteristics before and after the jetty was breached.

Sampling was also conducted outside and adjacent to Trestle Bay to provide reference

information.

Estuaries and associated wetlands provide critical habitat for many marine and estuarine

fish and shellfish species. The primary producers (algae and eelgrass) within these areas provide

extensive cover and foraging habitat. Prior to the jetty breach, biological surveys within Trestle

Bay found very high densities of benthic and epibenthic invertebrate species that are prey for

many fishes that rear in the Columbia River estuary, yet few of those fishes were found inside the

bay. In particular, no juvenile salmonids were captured in the bay during the pre-breach sampling

period.

The effects of jetty modification were most apparent in the benthic invertebrate and fish

populations in Trestle Bay, although the effects were difficult to discern because of confounding

interactions. For benthic invertebrates, the decline in pre-breach to post-breach density inside the

bay was more than twice that of the decline outside the bay, indicating a causal factor other than

normal natural variation. Possibilities include either increased foraging activities by fishes after

the jetty breach, or there was a physical disruption of the fauna related to a sustained freshwater

flood that reduced salinities. For fishes, more species were common between the two sampling
iv

areas (in Trestle Bay and in the reference area) during post-breach surveys than during pre-breach

surveys. This indicates that the jetty acted as a barrier, ultimately affecting the ability or

willingness of some fish species to enter and utilize the Bay as foraging habitat. Juvenile

salmonids, for example, were captured inside Trestle Bay only in surveys conducted after the

jetty was breached. Fish densities were also more similar between the two sampling areas after

the jetty was breached.

Although epibenthic invertebrate densities declined from 1994 to 1997, the breach did not

appear to affect them significantly. Similarly, sediment characteristics remained essentially

unchanged between the pre- and post-breach surveys.

The Trestle Bay project provided a rare opportunity to return ecologically functioning

estuarine marshes, intertidal, and shallow subtidal habitats back to an estuary. The primary goal

of restoring fish access to the bay, particularly for salmonids which could include federally listed

endangered and threatened salmonid species, appears to have been met. Resource agencies

should continue to look for similar project sites that could be modified at minimum cost, yet have

long-term benefits for associated ecosystems.
v

CONTENTS

EXECUTIVE SUMMARY ...........................................................................................................iii

INTRODUCTION .......................................................................................................................... 1

METHODS ..................................................................................................................................... 3

Sampling ............................................................................................................................. 3

Benthic Invertebrates and Sediment ................................................................................... 3

Epibenthic Invertebrates ..................................................................................................... 3

Fishes .................................................................................................................................. 4

Data Analyses ..................................................................................................................... 4

Benthic Invertebrates .............................................................................................. 4

Epibenthic Invertebrates ......................................................................................... 6

Sediment ................................................................................................................. 6

Fishes ...................................................................................................................... 6

RESULTS ....................................................................................................................................... 9

Benthic Invertebrates .......................................................................................................... 9

Epibenthic Invertebrates ................................................................................................... 15

Sediment ........................................................................................................................... 21

Fishes ................................................................................................................................ 21

DISCUSSION ............................................................................................................................... 31

CONCLUSIONS .......................................................................................................................... 35

ACKNOWLEDGMENTS ............................................................................................................ 37

CITATIONS .................................................................................................................................. 39

APPENDIX A: FIGURES ............................................................................................................ 43

APPENDIX B: TABLES ............................................................................................................. 53
vi
vii

Figure 1. Locations of benthic and epibenthic invertebrate and sediment sampling stations in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary........................................................ 2

Figure 2. Locations of purse seine (PS) and trapnet (TN) stations in and adjacent to Trestle Bay,

Columbia River estuary. ................................................................................................................. 5

Figure 3. Median grain size, percent silt/clay, and percent volatile solids at sediment sampling

stations located in and adjacent to Trestle Bay, Columbia River estuary. .................................... 22

Figure 4. Average monthly river discharges for the Columbia River during 1993-97 at Beaver

Army Terminal near Quincy, Oregon, and average monthly salinities in Trestle Bay, Columbia

River estuary. ................................................................................................................................ 32

LIST OF FIGURES
viii
ix

Table 1. Numbers of taxa/categories of benthic invertebrate at sampling stations located in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.......................................................10

Table 2. Mean densities (number/m2

) of benthic invertebrates at sampling stations in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.......................................................11

Table 3. Summary of densities (mean number/m2) for major benthic invertebrate taxa found in

and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary................................................12

Table 4. Diversities (H) of benthic invertebrates at sampling stations in and adjacent to Trestle

Bay (RKm 11.3), Columbia River estuary.....................................................................................13

Table 5. Equitabilities (E) of benthic invertebrates at sampling stations in and adjacent to Trestle

Bay (RKm 11.3), Columbia River estuary.....................................................................................14

Table 6. Numbers of taxa/categories of epibenthic invertebrates at sampling stations in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.......................................................16

Table 7. Mean densities (number/m2) of epibenthic invertebrates at sampling stations in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.......................................................17

Table 8. Summary of densities (mean number/m2) for major epibenthic invertebrate taxa/

categories found in and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.................18

Table 9. Diversities (H) of epibenthic invertebrates at sampling stations in and adjacent to

Trestle Bay (RKm 11.3), Columbia River estuary.........................................................................20

Table 10. Numbers of fish and shellfish species collected by purse seine at sampling stations in

and adjacent to Trestle Bay(RKm 11.3), Columbia River estuary.................................................23

Table 11. Densities (numbers/hectare) of fish and shellfish species collected by purse seine at

sampling stations in and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary...............24

Table 12. Densities (number/hectare) by year of fish and shellfish captured by purse seine in

Trestle Bay (RKm 11.3), Columbia River estuary.........................................................................25

Table 13. Densities (number/hectare) by year of fishes captured by purse seine at the reference

area outside Trestle Bay (RKm 11.3) Columbia River estuary......................................................26

Table 14. Diversities (H) of fish and shellfish captured by purse seine at sampling stations in and

adjacent to Trestle Bay...................................................................................................................28

Table 15. Equitabilities (E) of fish and shellfish captured by purse seine at sampling stations in

and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary................................................29

Table 16. Yearly total numbers of fish and shellfish captured by trapnet stations in Trestle Bay

(RKm 11.3), Columbia River estuary.............................................................................................30

LIST OF TABLES
x
xi

Appendix Figure A1. Differences in monthly means of benthic invertebrates for numbers of

species and densities. .................................................................................................................... 45

Appendix Figure A2. Differences in monthly means of epbenthic invertebrates for numbers of

species and densities. .................................................................................................................... 46

Appendix Figure A3. Differences in monthly means of fish and shellfish for numbers of species

and densities. ................................................................................................................................ 47

Appendix Figure A4. Length-frequency histograms for Pacific herring collected by purse seine

in Trestle Bay in July-August 1996. ............................................................................................. 48

Appendix Figure A5. Length-frequency histograms for shiner perch collected by trapnet in

Trestle Bay in May-September 1994. ........................................................................................... 49

Appendix Figure A6. Length-frequency histograms for shiner perch collected by trapnet in

Trestle Bay in May-September 1996. ........................................................................................... 50

Appendix Figure A7. Length-frequency histograms for shiner perch collected by trapnet in

Trestle Bay in May-September 1997. ........................................................................................... 51

LIST OF FIGURES IN APPENDIX A
xii
xiii

LIST OF TABLES IN APPENDIX B

Appendix Table B1. Geographic locations of benthic invertebrate, sediment, purse seine, and

trapnet sampling stations for Trestle Bay surveys 1994 and 1997. .............................................. 55

Appendix Table B2. Summary of benthic invertebrate taxa/categories at sampling stations in and

adjacent to Trestle Bay, Columbia River estuary. ......................................................................... 56

Appendix Table B3. Summary of epibenthic invertebrate taxa/categories at sampling stations

located in and adjacent to Trestle Bay, Columbia River estuary................................................... 59

Appendix Table B4. Median grain sizes at sediment sampling stations in and adjacent to Trestle

Bay (RKm 11.3), Columbia River estuary. ................................................................................... 63

Appendix Table B5. Percent silt/clay at sediment sampling stations in and adjacent to Trestle

Bay, Columbia River estuary. ....................................................................................................... 64

Appendix Table B6. Percent volatile solids at sediment sampling stations in and adjacent to

Trestle Bay, Columbia River estuary. ........................................................................................... 65

Appendix Table B7. Summary of fish and shellfish captured by purse seine at stations in and

adjacent to Trestle Bay, Columbia River estuary. ......................................................................... 66

Appendix Table B8. Total numbers of fish and shellfish captured at trapnet sampling stations in

Trestle Bay, Columbia River estuary. ........................................................................................... 70
1

INTRODUCTION

Trestle Bay is a 244-ha (603 acre) area consisting of shallow subtidal and intertidal

mudflats and intertidal marsh habitats located in the northwest corner of Oregon, near the mouth

of the Columbia River, at River Kilometer (RKm) 11.3. The bay is bordered on the south, west,

and east by Fort Stevens State Park and to the north by the Columbia River estuary (Fig. 1).

Trestle Bay formed after the initial construction of the Columbia River south jetty was completed

(1885 to 1895). The placement of the jetty caused sand to accumulate near its base, resulting in

the formation of Clatsop Spit and Trestle Bay. The development of Clatsop Spit ultimately

shifted the operational portion of the south jetty 3 miles toward the west of the original jetty base.

Trestle Bay lies between the Clatsop Spit formation and the original jetty base. Approximately

2,682 m (8,800 ft) of the South Jetty separates Trestle Bay from the Columbia River. Although

permeable to water the large rock jetty can hinder the export of detritus from the marshes to the

river, and seemed to discourage passage into the bay by juvenile fishes residing in the lower

Columbia River estuary.

In the late 1980s, discussions began among local groups and regional and national agency

representatives regarding a modification to the south jetty to restore fish access into Trestle Bay.

The intent of the modification (breaching the jetty) would be to create a passage between the bay

and the lower Columbia River estuary, permitting better water exchange, making foraging habitat

available for many marine and estuarine fishes and shellfishes, and ultimately reestablishing

Trestle Bay as an integral part of the lower Columbia River estuarine ecosystem. In 1995, the

Trestle Bay Enhancement Project, as it had become known, was determined to meet the

requirements under Section 1135(b) of the Authority of the Water Resources Development Act

(namely, the project entailed the physical modification of a structure operated and maintained by

the COE). The act also has streamlined requirements regarding reporting and implementation

compared to other processes and requires a local non-federal sponsor to share 25% of the total

cost. The Oregon Parks and Recreation Department agreed to take the cost-sharing

responsibility.

In 1995, with local, state, and federal agencies in agreement, the COE issued a contract

for modification of the jetty structure near the original base to take place in the form of a breach,

which occurred in August 1995. The breach consisted of lowering a 152-m portion of the jetty to

1.7 m below mean sea level, and placing the removed stone in three mounds 18-30 m riverward

of the existing structure.

In 1994, the COE contracted the National Marine Fisheries Service (NMFS) to conduct

biological surveys in and adjacent to Trestle Bay. Because the Columbia River is recognized as

critical habitat for salmonids including several listed and endangered species, particular interest

was placed on use of the bay by juvenile salmonids and their benthic and epibenthic invertebrate

prey. Sampling consisted of assessing benthic and epibenthic invertebrate populations, fish

species compositions, and sediment characteristics inside and outside Trestle Bay before and

after the jetty was breached.
2
3

METHODS

Sampling

Fish, benthic and epibenthic invertebrate, and sediment sampling station locations

(latitude and longitude) were established using a Global Positioning System, which allowed

stations to be easily reoccupied (Appendix Table 1).

Benthic Invertebrates and Sediment

Thirteen stations inside and three stations outside Trestle Bay were sampled for benthic

invertebrates and sediments (Fig. 1). Benthic invertebrate samples were collected in April, June,

and August of 1994 and 1997. Sediment samples were collected in August 1993, April and June

1994, and June and August 1997. A polyvinyl chloride (PVC) coring device with an inside

diameter of 3.85 cm and a penetrating depth of 15 cm (volume of 174.6-cm3

) was used to collect

benthic invertebrate and sediment samples (Hinton et. al 1995). Samples were collected by

scuba diving or snorkeling. For benthic invertebrates, ten core samples (replicates) from each

station were placed in labeled jars and preserved in a buffered formaldehyde solution (> 4%)

containing rose bengal, a protein stain. In the laboratory, samples were washed with water

through a 0.5-mm screen, organisms were sorted from the remaining residue, identified to the

lowest practical taxon/category (category represents a group of related organisms), counted, and

stored in vials with 70% ethanol. One sediment sample from each station was placed in a labeled

plastic bag and refrigerated until delivery to COE North Pacific Division Materials Laboratory,

Troutdale, Oregon, and AGRA Earth & Environmental, Inc., Portland, Oregon, for grain size and

percent organics analyses.

Epibenthic Invertebrates

Thirteen stations inside and three stations outside the bay were sampled for epibenthic

invertebrates (Fig. 1). Sampling occurred in April, June, and August of 1994 and 1997. These

invertebrates were collected using an epibenthic pump that consisted of a base (15.2-cm

diameter by 25.4-cm-high PVC pipe with 10 3.8-cm holes covered with 130-micron nitex

screen), a bilge pump, and a 3.05-meter handle made from 3.2-cm PVC pipe with a control

switch at the upper end. The epibenthic pump sampled an area of approximately 181.5 cm2..

The bilge pump was powered by a 12-volt battery, and the outflow was filtered through a 130-

micron plankton net. Each sample consisted of placing the pump base vertically on the bottom

while pumping water through a plankton net for 1 minute. The plankton net was then washed

down and the residue collected in the cup was placed in a labeled jar and preserved with a

formaldehyde solution. In the laboratory, organisms were sorted, identified to the lowest

practical taxon, counted, and stored in 70% alcohol. Three replicates were taken at each station.
4

Fishes

In 1994 (pre-breach) and 1997 (post-breach), fishes were sampled monthly, May through

September, at seven purse-seine stations inside and three stations outside the bay, as well as three

trapnet stations inside the bay (Fig. 2). In 1996 (post-breach), only stations inside the bay were

sampled. Because of the shallow and confined nature of the bay prior to the jetty breach, options

for sampling fishes were limited. Therefore a small shallow-water purse seine was designed to

effectively sample the area. The purse seine was 36.6 by 3.4 m with variable mesh (9.5-, 12.7-,

and 19.0-mm stretched) and knotless web in the bunt to reduce descaling. The purse seine

sampled an area of approximately a 106.5 m2. The sampling was conducted using the round-haul

technique. One end of the seine was held in place by an anchor and deployed by backing away in

a large circle while feeding the net off a platform on the bow of the boat. Once the circle was

complete the net was pursed and brought back onboard in a manner that collected the fish in the

bunt. Fishes were then quickly transferred to tubs for holding until they could be processed.

Three trapnet stations were established inside Trestle Bay (Fig. 2). The nets were

attached to pilings (inside the bay) adjacent to the rock jetty and extended perpendicular to the

jetty. Each trapnet consisted of six collapsible frames, constructed as follows: the lead wing was

15.2 m long by 0.9 m high with 19.0-mm stretched mesh; the body was 4.9 m long and consisted

of two 1.8- by 0.9-m rectangular metal frames followed by four 0.7-m-diameter circular frames;

the frames were covered with 19.0-mm stretched knotless mesh. A 6.8-kg weight attached to the

cod end held the net in position. Trapnets were set for approximately 24 hours. At retrieval,

fishes were collected into the cod end and transferred to tubs for processing.

All captured fishes were identified to lowest practical taxonomic level, counted, and a

maximum of 50 individuals of each species was measured (total length in mm). Juvenile

salmonids were anesthetized using benzocaine (ethyl-p-aminobenzoate) solution prior to any

handling and were allowed to fully recover before being released.

Data Analysis

Benthic Invertebrates

Benthic invertebrate data were analyzed by station to determine species composition,

densities (by taxon and total), and community structure (diversity and equitability). The

Shannon-Wiener function (H) was used to determine diversity (Krebs 1978), which was

expressed as follows:

s

H = - Σ (pi

)(log2pi)

i=1
5
6

where pi = ni/N (ni is the number of individuals of the ith taxon in the sample, and N is the total

number of all individuals in the sample) and s = number of taxa. Equitability (E) was the second

community structure index determined; E measures proportional abundances among the various

taxa in a sample (Krebs 1978) and ranges from 0.00 to 1.00, with 1.00 indicating all taxa in the

sample are numerically equal. Equitability is expressed as follows:

E = H/log2s

where H = Shannon-Wiener function and s = number of taxa. Both H and E were calculated

from each sampling station.

Mean numbers of species and total benthic invertebrate densities were compared between

areas (i.e., inside Trestle Bay and reference stations outside the bay) and years (i.e., pre- and postjetty breach) using two-way analysis of variance (ANOVA) (Cruze and Hartzell 1991);

invertebrate densities were transformed (log10) prior to performing the ANOVA. Statistical tests

were performed on the means from the 10 samples collected at each station.

Epibenthic Invertebrates

Epibenthic invertebrate data were analyzed by station to determine species composition

and densities (by taxon and total). Diversity (H) was also determined for each station. Means

from the three samples collected at each station provided the data for analysis.

Mean numbers of species and total epibenthic invertebrate densities were compared

between areas (i.e., inside Trestle Bay and reference stations outside the bay) and years (i.e., preand post-jetty breach) using two-way analysis of variance (ANOVA); epibenthic invertebrate

densities were transformed (log10) prior to performing the ANOVA. Statistical tests were

performed on the means from the three samples collected at each station.

Sediment

For each sediment sample, median grain size, percent silt/clay, and percent volatile solids

were determined. No statistical comparisons were performed on the sediment characteristics

because of the non-normal distribution of the data and the lack of a satisfactory data

transformation.

Fishes

For each purse-seine station, individual species and total fish densities (number/ha) were

determined using the catch data and area sampled. The two previously described community

structure indices, H and E, were also calculated for each station.
7

Monthly mean numbers of species and densities (numbers/ha) were compared between

areas (i.e., inside Trestle Bay and reference stations outside the bay) and years (i.e., pre- and postjetty breach) using two-way analysis of variance (ANOVA); fish densities were transformed

(log10 (density + 1)) prior to performing the ANOVA. Means were obtained by combining all

stations for each area (seven in Trestle Bay, three outside the bay) by month.
8
9

RESULTS

Benthic Invertebrates

The total numbers of taxa/categories collected at benthic invertebrate sampling stations in

Trestle Bay (three surveys/year) ranged from 12 to 22 in 1994, and 6 to 12 in 1997 (Table 1,

Appendix Table 2). At the reference stations outside Trestle Bay, taxa/categories ranged from 8

to 18 in 1994 and 4 to 14 in 1997. Mean benthic invertebrate densities (number organisms/m2) in

Trestle Bay ranged from 58,068 to 356,653 in 1994, and 2,921 to 42,950 in 1997 (Table 2). At

the reference stations, mean benthic invertebrate densities ranged from 5,068 to 114,332 in 1994,

and 1,976 to 30,752 in 1997.

At sampling locations both inside and outside Trestle Bay, the number of taxa/categories

and mean benthic invertebrate density both decreased significantly after the jetty breach

(ANOVA, P < 0.05). Although areas inside the bay and in the outside reference area both

showed a decreasing trend from 1994 to 1997, the decrease in benthic invertebrate densities was

greater inside the bay than in the reference area. Some of the steeper decrease can be attributed

to habitat changes caused by the breaching of the jetty (Appendix Fig. 1). Subtracting the

decrease that could be attributed to natural variation (i.e., the differences between surveys

observed in the reference area) indicated that benthic invertebrate densities inside the bay

decreased by about one-half as a result of the jetty breach. A similar analysis indicated that there

was a loss of three or four taxa from inside Trestle Bay that may be attributed to the breach.

Benthic invertebrate species compositions changed between the pre- and post-breach

surveys both inside and outside the bay (Table 3). In Trestle Bay in 1994, the most abundant

taxonomic category was Polychaeta, comprising 55% of the overall species composition,

followed by Oligochaetes (24%) and Arthropoda (18%). In 1997, the most abundant taxonomic

category in the bay was Arthropoda (46%) followed by Polychaeta (29%) and Oligochaeta

(17%). Changes in the reference area species composition also occurred between years. In 1994,

the most abundant benthic taxon was Oligochaeta (44%) followed by Polychaeta (37%),

Arthropoda (8%), and Mollusca (7%). In 1997, dominant benthic taxa included Arthropoda

(53%), Polychaeta (38%), and Mollusca (7%). Several dominant species in 1994 virtually

disappeared by 1997. In the bay, these included the estuarine anemone Nematostella vectensis,

the polychaetes Pygospio elegans and Manyunkia aestuarina, and the amphipod Eogammarus

confervicolus. At the reference stations there were large changes in the numbers of Turbellaria,

spionid polychaetes, and oligochaetes between 1994 and 1997.

Benthic invertebrate diversities (H) were similar between monthly surveys and areas

within each year (Table 4). In 1994, station diversity ranged from 0.99 to 3.55 inside the bay, and

2.03 to 3.12 at the reference area. In 1997, H ranged from 1.28 to 2.93 inside the bay, and 1.12 to

3.02 at the reference area. Equitability (E) was also similar among surveys and areas for each

year (Table 5). The mean E values for each survey and area indicated there were no dominant

benthic invertebrate species. Mean equitability values in 1994 for each survey ranged from 0.52
10

Table 1. Numbers of taxa/categories of benthic invertebrate at sampling stations located in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was conducted

in April, June, and August of 1994 (pre-breach) and 1997 (post-breach). The jetty was

breached in August 1995. Stations 1-10, 14, and 15 were located inside the bay, and

Stations 11c-13c were located outside and adjacent to the bay.
11

Table 2. Mean densities (number/m2) of benthic invertebrates at sampling stations in and djacent

to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was conducted in April,

June, and August of 1994 (pre-breach) and 1997 (post-breach). The jetty was breached

in August 1995. Stations 1-10, 14, and 15 were located inside the bay, and Stations 11c13c were located outside and adjacent to the bay.
12

Table 3. Summary of densities (mean number/m2) for major benthic invertebrate taxa found in

and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Monthly surveys

(April, June, and August) were combined for each year and area. Stations 1-10, 14, and

15 were located inside the bay; and Reference Stations (Ref.) 11c-13c were located

outside and adjacent to the bay.
13

Table 4. Diversities (H) of benthic invertebrates at sampling stations in and adjacent to Trestle

Bay (RKm 11.3), Columbia River estuary. Sampling was conducted in April, June, and

August of 1994 (pre-breach) and 1997 (post-breach). The jetty was breached in August

1995. Stations 1-10, 14, and 15 were located inside the bay, and Stations 11c-13c were

located outside and adjacent to the bay.
14

Table 5. Equitabilities (E) of benthic invertebrates at sampling stations in and adjacent to Trestle

Bay (RKm 11.3), Columbia River estuary. Sampling was conducted in April, June, and

August of 1994 (pre-breach) and 1997 (post-breach). The jetty was breached in August

1995. Stations 1-10, 14, and 15 were located inside the bay, and Stations 11c-13c were

located outside and adjacent to the bay.
15

to 0.69 in the bay and 0.58 to 0.78 in the reference area. Mean values in 1997 for each survey

ranged from 0.70 to 0.76 in the bay and 0.56 to 0.71 in the reference area.

Summaries by station for benthic invertebrate surveys are available upon request from

NMFS, Northwest Fisheries Science Center, Point Adams Biological Field Station, P.O. Box

155, Hammond, OR, 97121-0155.

Epibenthic Invertebrates

The mean numbers of epibenthic invertebrate taxa/categories (by monthly survey) were

slightly lower in 1997 than in 1994 for both Trestle Bay and the reference areas (Table 6,

Appendix Table 3). In 1994, mean numbers of taxa ranged from 24 to 31 per station, whereas in

1997 mean numbers ranged from 20 to 27 per station. Mean epibenthic densities were higher in

1994 than in 1997 in both the bay and the reference area. Mean epibenthic densities in 1994

ranged from 51,876 to 119,894 organisms/m2, and in 1997 from 19,591 to 36,056 organisms/m2

(Table 7).

There were no significant differences in taxa/categories or densities when comparing

results from the pre- and post-breach surveys for areas inside and outside Trestle Bay (ANOVA

P > 0.05) (Appendix Fig. 2). Therefore, changes in epibenthic species and densities were within

the natural variation of these communities, and the jetty breach had no significant effect.

Although taxa/categories were similar in Trestle Bay and the reference area, there were

differences in mean epibenthic densities when comparing the same areas and the two surveys

(1994 and 1997) (Table 8). Nearly every taxon/category showed a reduction in densities between

1994 and 1997, with the exception of a few harpacticoid and cyclopoid copepod species.

Crustaceans, primarily unidentified juvenile copepod nauplii and harpacticoids, remained the

dominant taxonomic categories each year, comprising 56-84% of the overall epibenthic densities

for both areas.

Epibenthic diversity (H) values were generally higher in 1994 than in 1997 for stations in

Trestle Bay and in the reference area (Table 9). In the bay, mean H values ranged from 3.08 to

3.35 in 1994, and 2.19 to 2.61 in 1997. At the reference area, mean H values were 2.33 to 3.05

in 1994, and 1.90 to 2.50 in 1997.

Summaries by station for epibenthic invertebrate surveys are available upon request from

NMFS, Northwest Fisheries Science Center, Point Adams Biological Field Station, P.O. Box

155, Hammond, OR, 97121-0155.
16

Table 6. Numbers of taxa/categories of epibenthic invertebrates at sampling stations in and

adjacent to trestle Bay (RKm 11.3), Columbia River estuary. Sampling was conducted

in April, June, and August of 1994 (pre-breach) and 1997 (post-breach). The jetty was

breached in August 1995. Stations 1-10, 14, and 15 were located inside the bay, and

Stations 11c-13c were located outside and adjacent to the bay.
17

Table 7. Mean densities (number/m2) of epibenthic invertebrates at sampling stations in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was conducted

in April, June, and August of 1994 (pre-breach) and 1997 (post-breach). the jetty was

breached in August 1995. Stations 1-10, 14, and 15 were located inside the bay, and

Stations 11c-13c were located outside and adjacent to the bay.
18

Table 8. Summary of densities (mean number/m2) for major epibenthic invertebrate taxa/

categories found in and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.

Monthly surveys (April, June, and August) were combined for each year and area.

Stations 1-10, 14, and 15 were located inside the bay, and Stations 11c-13c were located

outside and adjacent to the bay.
19

Table 8. Continued.
20

Table 9. Diversities (H) of epibenthic invertebrates at sampling stations in and adjacent to

Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was conducted in April,

June, and August of 1994 (pre-breach) and 1997 (post-breach). The jetty was breached

in August 1995. Stations 1-10, 14, and 15 were located in side the bay, and Stations

11c-13c were located outside and adjacent to the bay.
21

Sediment

With few exceptions, sediment characteristics (median grain size, percent silt/clay, and

percent volatile solids) remained fairly constant at each station during the pre- and post-breach

studies (Fig. 3). Even though median grain size varied at each station for each survey, the

sediment type usually remained the same (Appendix Tables 4-6). Percentages of silt/clay and

volatile solids were higher in sediment from inside Trestle Bay than in the reference area because

of the reduced currents and water circulation in the bay. There were no apparent effects of the

jetty breach on sediment characteristics in the bay or reference area.

Fishes

In 1994 (pre-breach), monthly mean numbers of fish and shellfish species collected at

each purse-seine sampling station ranged from two to three in Trestle Bay and one to three at the

reference stations (Table 10, Appendix Table 7). Monthly mean fish species numbers during the

two post-breach studies in the bay ranged from two to three, and from three to four at the

reference stations (1997 only). There was no significant difference in the number of species

between pre- and post-breach surveys for either of the two areas (Appendix Fig. 3).

Monthly mean fish and shellfish densities (number/hectare) in Trestle Bay varied most

during the pre-breach study (1,698 to 25,606) (Table 11). During the two post-breach studies

(1996-97), mean fish and shellfish densities were less variable between months and years (876 to

2,655). Variation in mean monthly fish and shellfish densities during the pre-breach survey was

primarily a result of the large number of threespine sticklebacks (Gasterosteus aculeatus) that

were captured in September 1994 (Table 12).

In Trestle Bay, Dungeness crab (Cancer magister) was the only species captured by purse

seine in 1994 that was not found in 1996 or 1997. However the following eight species were

captured during one or both of the post-breach studies and not in 1994: American shad (Alosa

sapidissima), Pacific herring (Clupea pallasi), chinook salmon (Oncorhynchus tshawytscha),

juvenile smelt (Osmeridae), banded killifish (Fundulus diaphanus), largemouth bass

(Micropterus salmoides), larval flatfish (Pleuronectidae), and yellow shore crab (Hemigrapsus

oregonensis)(Table 12). Densities of Pacific herring and surf smelt (Hypomesus pretiosus) were

underestimated, in the post-breach surveys, particularly in 1997, because nearly all the

individuals of these two species were approximately 2-3 months old (postlarval stage) and

readily swam through the 9.5- to 19.0-mm mesh of the purse seine. Length-frequency histograms

for Pacific herring showed that most were 30-65 mm long (Appendix Fig. 4).

At the reference stations, mean monthly fish and shellfish densities were usually lower

than in Trestle Bay, ranging from 220 to 3,900 in 1994 and 817 to 1,509 in 1997 (Table 11).

Although similar species were caught between the pre- and post-breach studies, the proportional

abundances of those species changed (Table 13). In 1994, shiner perch (Cymatogaster
22

Figure 3. Median grain size, percent silt/clay, and percent volatile solids at sediment sampling

stations located in and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary.

Sampling was conducted August 1993, April and June 1994 (pre-breach), and June and

August 1997 (post-breach). Stations 1-10, 14, and 15 were located inside the bay, and

Stations 11C-13C were located outside and adjacent to the bay. The jetty was breached

in August 1995.
23
24
25

Table 12. Densities (number/hectare) by year of fish and shellfish captured by purse seine in

Trestle Bay (RKm 11.3), Columbia River estuary. Totals are the average for each year

(five months, May-September, seven stations/month). Sampling was conducted in

1994, 1996, and 1997. The jetty was breached in August 1995.
26

Table 13. Densities (number/hectare) by year of fishes captured by purse seine at the reference

area outside Trestle Bay (RKm 11.3) Columbia River estuary. Totals are the average

for each year (five months, May-September, three stations/month). Sampling was

conducted in 1994 and 1997. No purse seine sampling was conducted in the reference

area in 1996. The jetty was breached in August 1995.
27

aggregata) and English sole (Parophrys vetulus) were the dominant species, while in 1997

subyearling chinook salmon and surf smelt were the most abundant species. Three species were

captured by purse seine at the reference stations only in 1994: Pacific sandlance (Ammodytes

hexapterus), cabezon (Scorpaenichthys marmoratus), and English sole. Five species were

captured only in 1997: American shad, coho salmon (Oncorhynchus kisutch), surf smelt, starry

flounder (Platichthys stellatus), and yellow shore crab.

Fish densities (numbers/hectare) were significantly different (P < 0.05) between the preand post-breach surveys for both areas. This was primarily a result of the decline in fish

densities inside the bay and indicates that the breach affected fish. Although fish densities in

Trestle Bay decreased between surveys, fish densities in the outside reference area increased

(Appendix Fig. 3). The significant decline in density in Trestle Bay was most likely influenced

by the large number of threespine sticklebacks captured in 1994 that were not observed in 1997.

As such, it is difficult to determine the degree of impact that the jetty breach had on fish densities

inside Trestle Bay because they naturally are highly variable and are influenced by many biotic

and abiotic factors (i.e., species schooling tendencies, recruitment success, sampling gear

efficiency, etc.). However, some effect is seen in the commonality of fish species observed

between the two areas before and after the breach occurred. During the 1994 sampling period,

55% of the fish species observed in the bay were also found outside the bay, whereas in 1997,

80% of the fish species were common between the two areas.

Diversity (H) was low for both sampling areas and for all surveys, ranging from 0.27 to

1.58 (Table 14). The low values are a result of few fish species captured at each station, and the

occasional sampling efforts when no fish were captured. Mean monthly values for Equitability

(E) in Trestle Bay for all surveys ranged from 0.24 to 0.81, with most values less than 0.60. The

lower values indicate that the number of individuals captured were not equally distributed

between species (Table 15). E values were also influenced by sampling efforts that produced no

fish.

Total numbers of fishes captured by trapnets (three stations combined for five sampling

months) were similar between the pre- (1994) and post-breach (1997) studies (Table 16,

Appendix Table 8). Even though six of the 18 fish and shellfish species found in trapnets were

found throughout all three studies, the overall numbers of those species varied between surveys.

There were large declines between the pre- and post breach studies in numbers of threespine

stickleback, Pacific staghorn sculpin, and Dungeness crab. Shiner perch was the only fish

species that had a major increase in abundance from 1994 to 1997. Monthly length-frequency

histograms of shiner perch revealed a similar growth pattern for each year, suggesting that they

consistently used Trestle Bay as rearing habitat (Appendix Figs. 5-7)

Summaries by station for fish surveys are available upon request from NMFS, Northwest

Fisheries Science Center, Point Adams Biological Field Station, P.O. Box 155, Hammond, OR,

97121-0155.
28
29
30

Table 16. Yearly total numbers of fish and shellfish captured by trapnet stations in Trestle Bay

(RKm 11.3), Columbia River estuary. Values are totals derived from three trapnet

sampling stations/month for five months (May-September). Sampling was conducted

in 1994, 1996, and 1997. The jetty was breached in August 1995.
31

DISCUSSION

Removing a section of the Trestle Bay jetty created an unobstructed passageway between

the bay and the lower Columbia River estuary, essentially returning 244 ha of marsh and

intertidal habitat to the estuarine system. The effects of the modification on Trestle Bay were

apparent for benthic invertebrate and fish populations; however, epibenthic invertebrate

populations were not influenced significantly, and sediment characteristics were virtually

unchanged. Benthic invertebrate populations showed a significant decline in density and changes

in species compositions both inside the bay and in the reference area from 1994 to 1997, yet the

decline was twice as great inside the bay. Something other than normal natural variation also

reduced invertebrate densities in Trestle Bay after the breach. Two likely explanations for the

declines are 1) an increase in predation by fishes, and/or 2) a physical disruption of the local

fauna related to the sustained high Columbia River flows beginning in February 1996. The

permeability of the jetty allows the interior of Trestle Bay to experience the same tidal influence

and salinities as the shallow subtidal estuarine habitat outside the bay. In February 1996, major

and minor tributaries to the Columbia River experienced some of the highest flows recorded

since the introduction of flood-control dams in the 1940-50s (Oregon Climate Service 1997).

High river flows continued for much of 1996 and into 1997 (Fig. 4) (U.S. Geological Survey

1992). These high freshwater flows lowered salinity levels inside Trestle Bay long enough to

eliminate or reduce invertebrate species that were less tolerant of sustained low salinity

conditions. Even though invertebrate densities inside Trestle Bay were less in 1997 than in 1994,

they were still similar to densities in other intertidal and subtidal benthic invertebrate surveys

conducted in the lower Columbia River estuary (Hinton et al. 1990).

Although epibenthic invertebrate populations experienced declines in species numbers

and densities similar to the benthic invertebrates, an impact attributed to breaching the jetty was

not observed. In addition, no change was indicated from sediment analysis. Circulation patterns

within the bay did not appear to change between the pre- and post-breach studies, because most

stations maintained their original sediment classification after the breach.

Changes in overall fish densities in Trestle Bay were primarily influenced by the capture

of a large number of threespine sticklebacks in 1994. Therefore, the degree to which the jetty

breach influenced changes in fish densities is uncertain. However, a possible effect of the breach

was revealed by increased similarity in composition and densities of fishes inside and outside the

bay after the jetty was breached.

 The 1994 surveys revealed that the habitat inside Trestle Bay contained many of the

positive biological attributes of estuaries and wetlands. By furnishing important prey, foraging

habitat, and cover, estuaries and wetlands provide critical habitat for migrating juvenile

salmonids (Healey 1982, Simenstad et al. 1982, Fisher and Pearcy 1989, Miller and Simenstad

1997) and various other anadromous and marine fishes, such as American shad, surf smelt,

English sole, Pacific herring (Bottom et al. 1984, Schiewe et al. 1989), and shellfish (Armstrong

and Gunderson 1985, Emmett and Durkin 1985). Shallow-water estuarine habitats have high
32
33

primary productivity rates, which in turn support high densities of secondary consumers. Detrital

food webs also add to this secondary production.

During this study Trestle Bay contained extensive marshes, several large eelgrass beds

(Zostera spp.), and high benthic and epibenthic invertebrate populations. The benthic

invertebrate densities inside Trestle Bay in 1994 were some of the highest observed in the lower

Columbia River estuary (Holton 1984; Emmett et al. 1986; Hinton et al. 1990; Hinton et al.

1992; McCabe and Hinton 1993; McCabe et al. 1993a, 1993b; McCabe and Hinton 1996;

McCabe et al. 1996). Benthic and epibenthic populations in Trestle Bay during both surveys

consisted of many prey organisms juvenile fishes are known to consume during their resident

times in an estuary. Most of the copepods, amphipods, and several polychaete species found in

Trestle Bay are important prey for many estuarine fish species, including post-larval and juvenile

stages of Pacific herring, surf smelt, starry flounder, and salmonids (Hart 1973, Meyer et al.

1981, Durkin 1982, Pearce et al. 1982, Kirn et al. 1986, McCabe et al. 1982, Nicholas and Lorz

1984, Emmett et al. 1991).

Despite the positive attributes within Trestle Bay, results from the 1994 fish sampling

suggested that many juvenile fishes of the Columbia River estuary were not taking advantage of

the cover and foraging habitat available inside the bay because of the barrier created by the rock

jetty. Passage into Trestle Bay by some fish species (e.g., schooling fishes and juvenile

salmonids) appeared to be inhibited by the rock jetty, perhaps because of the low light levels

within the rock jetty itself. Research at hydropower dams suggests that light affects the

willingness of salmonids to pass into or through orifices and gatewells of fish bypass systems

(Marquette et al. 1970, Ebel et al. 1971). Salmonid passage was increased when orifices were

lighted. Even though the rock jetty was extremely permeable, the thickness of the structure (up

to 5 m at the base) created a dark tunnel effect that probably discouraged juvenile salmonids and

possibly other estuarine fish species from passing through. Results from the pre- and post-breach

fish sampling support this hypothesis. Pacific herring, chinook salmon, surf smelt, and starry

flounder took advantage of the new opening. These species were either absent or had low

numbers inside the bay prior to the breach. Therefore, the removal of the rock jetty positively

affected the ability of estuarine fishes to utilize Trestle Bay.
34
35

CONCLUSIONS

Trestle Bay provided a rare opportunity to observe the biological impact of returning

valuable wetland and intertidal and shallow subtidal habitats to an estuary that has seen a decline

in similar habitats as a result of urban and industrial development and pollution. Breaching the

jetty created an unobstructed passageway allowing access of fishes to the highly productive

habitats within Trestle Bay. The main goal of this project was to restore fish access to the bay

primarily for juveniles salmonids which potentially includes federally listed endangered and

threatened species. This goal appears to have been met, as evidenced by the observed increase in

use of the bay by juvenile salmonids. In addition, the breach improved forage conditions for

other important recreational and commercial fishes of the lower Columbia River estuary. No

apparent adverse effects on environmental conditions within Trestle Bay were observed as a

result of the jetty breach. Resource agencies should continue to look for similar project sites

which could be modified and returned to the ecosystem (with minimum cost) and that would

provide long-term benefits for natural resources.
36
37

ACKNOWLEDGMENTS

Thank you to all those involved with this project since the voluntary beginning study of

1993. Without your vision and persistence such a positive project would not have been possible.

Thank you to Paul Bentley, George T. McCabe, Jr., and Dennis Umphfres for their valuable

assistance in the field. Thanks also to Pat Oxley and Fort Stevens Park Service for sponsoring

and gaining the public obligation to secure project funding, and to Geoff Dorsey of the COE for

successfully implementing and seeing the project through the federal process.
38
39

CITATIONS

Armstrong, D. A. and D. R. Gunderson. 1985. The role of estuaries in Dungeness crab early life

history: a case study in Grays Harbor, Washington. Proceedings of the Symposium on

Dungeness Crab Biology and Management. Alaska Sea Grant Rep. 85-3:145-170.

Bottom, D. L., K. K. Jones, and M. J. Herring. 1984. Fishes of the Columbia River estuary.

Final report on the fish work unit of the Columbia River Estuary Data Development

Program. Oregon Dept. Fish Wild., Portland, OR. 113 p. plus appendices. (Available

from Columbia River Estuary Taskforce, 748 Commercial St., Astoria, OR 97103)

Cruze, E., and B. Hartzell. 1991. Minitab reference manual, PC version, release 8. Quickset

Inc., Rosemont, PA.

Durkin, J. T. 1982. Migration characteristics of coho salmon (Oncorhynchus kisutch) smolts in

the Columbia River and its estuary. In V. S. Kennedy (editor), Estuarine Comparisons, p.

365-376. Academic Press, New York.

Ebel, W. J., H. L. Raymond, C. W. Long, W. M. Marquette, R. Krcma, and D. Park. 1971.

Progress report on fish-protective facilities at Little Goose Dam and summaries of other

studies relating to the various measures taken by the Corps of Engineers to reduce losses

of salmon and steelhead in the Columbia and Snake Rivers. Final report to the U.S.

Army Corps of Engineers, Contract no. DACW68-71-C-0093, 40 p. plus appendices.

(Available from Northwest Fisheries Science Center, 2725 Montlake Blvd.E., Seattle WA

98112.)

Emmett, R. L., and J. T. Durkin. 1985. The Columbia River estuary: an important nursery for

Dungeness crabs, Cancer magister. Mar. Fish. Rev. 47(3):21-25.

Emmett, R. L., G. T. McCabe, Jr., T. C. Coley, R. J. McConnell, and W. D. Muir. 1986. Benthic

sampling in Cathlamet Bay, Oregon - 1984. Final report to U.S. Army Corps of

Engineers, Portland District, Contract no. DACW57-84-F-0348, 11 p. plus appendices.

(Available from Northwest Fisheries Science Center, 2725 Montlake Blvd.E., Seattle WA

98112.)

Emmett, R. L., S. L. Stone, S. A. Hinton, and M. E. Monaco. 1991. Distribution and abundance

of fishes and invertebrates in west coast estuaries, Volume II: species life history

summaries. Estuarine Living Marine Resources Program Rep. no. 8. NOAA/NOS

Strategic Environmental Assessments Division, Rockville, MD, 329 p.

Fisher, J. P., and W. G. Pearcy. 1989. Distribution and residence times of juvenile fall and spring

chinook salmon in Coos Bay, Oregon. Fish. Bull., U.S. 88(1):51-58.

Hart, J. L. 1973. Pacific Fishes of Canada. Fish. Res. Board of Canada., Bull. 180:1-740.
40

Healey, M. C. 1982. Juvenile Pacific salmon in estuaries: the life support system. In V. S.

Kennedy (editor), Estuarine Comparisons, 315-341 p. Academic Press, New York.

Hinton, S. A., G. T. McCabe, Jr., and R. L. Emmett. 1990. Fishes, benthic invertebrate, and

sediment characteristics in intertidal and subtidal habitats at five areas in the Columbia

River estuary. Final report to U.S. Army Corps of Engineers, Portland District, Contract

no. E86880158, E8690107, and E86900048. 92 p. plus appendices. (Available from

Northwest Fisheries Science Center, 2725 Montlake Blvd.E., Seattle WA 98112.)

Hinton, S. A., R. L. Emmett, and G. T. McCabe, Jr. 1992. Fishes, shrimp, benthic invertebrates,

and sediment characteristics in intertidal and subtidal habitats at Rice Island and Miller

Sands, Columbia River estuary, 1991. Final report to U.S. Army Corps. of Engineers,

Portland District, Contract no. E96910025. 44 p. plus appendices. (Available from

Northwest Fisheries Science Center, 2725 Montlake Blvd.E., Seattle WA 98112.)

Hinton, S. A., G. T. McCabe, Jr., and R. L. Emmett. 1995. In-water restoration between Miller

Sands and Pillar Rock Island, Columbia River: environmental surveys, 1992-1993. U.S.

Dep. Commer., NOAA Tech. Memo. NMFS-NWFSC-23, 47 p.

Holton, R. L. 1984. Benthic infauna of the Columbia River estuary. Final report on the Benthic

Infauna Work Unit of the Columbia River Estuary Data Development Program. 179 p.

plus appendices. College of Ocean. Oregon State Univ. Corvallis, OR. (Available from

Columbia River Estuary Taskforce, 748 Commercial St., Astoria, OR 97103.)

Kirn, R. A., R. D. Ledgerwood, and A. L. Jensen. 1986. Diet of subyearling chinook salmon

(Oncorhynchus tshawytscha) in the Columbia River estuary and changes effected by the

1980 eruption of Mount St. Helens. Northwest. Sci., 60(3):191-196.

Krebs, C. J. 1978. Ecology: the experimental analysis of distribution and abundance. Harper

and Row, New York, 678 p.

Marquette, W., F. Ossiander, R. Duncan, and C. Long. 1970. Research on gate-well - sluice

method of by-passing downstream migrants around low-head dams. Final report to U.S.

Army Corps of Engineers, Walla Walla District, Contract no. DACW68-69-C-0082, 32 p.

(Available from U.S. Army Corps of Engineers, Portland District, P.O. Box 2946,

Portland, OR 97208.)

McCabe, G. T., Jr., R. L. Emmett, W. D. Muir, and T. H. Blahm. 1982. Utilization of the

Columbia River estuary by subyearling chinook salmon. Northwest. Sci., 60(2):113-124.
41

McCabe, G. T., Jr., and S. A. Hinton. 1993. Benthic invertebrates and sediments in vegetated

and nonvegetated habitats at three intertidal areas of the Columbia River estuary, 1993.

Final report to U.S. Army Corps of Engineers, Portland District, Contract no. E9592012,

16 p. plus appendices. (Available from Northwest Fisheries Science Center, 2725

Montlake Blvd. E., Seattle WA 98112.)

McCabe, G. T., Jr., and S. A. Hinton. 1996. Benthic invertebrates and sediment characteristics

in freshwater, beach habitats of the lower Columbia River, 1994-95. U.S. Dep. Commer.,

NOAA Tech. Memo. NMFS-NWFSC-26, 111 p.

McCabe, G. T. Jr., S. A. Hinton, and R. L. Emmett. 1993a. Benthic and epibenthic

invertebrates, fishes, and sediments at and adjacent to a proposed new site for Area D, an

in-water dredged-material disposal site in the lower Columbia River, 1991. Final report

to U.S. Army Corps of Engineers, Portland District, Contract no. E96910017 and

E96910040, 27 p. plus appendices. (Available from Northwest Fisheries Science Center,

2725 Montlake Blvd. E., Seattle WA 98112.)

McCabe, G. T., Jr., S. A. Hinton, and R. L. Emmett. 1993b. In-water restoration between Miller

Sands and Pillar Rock Island, Columbia River: biological surveys, 1992. Final report to

U.S. Army Corps of Engineers, Portland District, 26 p. plus appendices. (Available from

Northwest Fisheries Science Center, 2725 Montlake Blvd. E., Seattle WA 98112.)

McCabe, G. T., Jr., S. A. Hinton, and R. L. Emmett. 1996. Benthic invertebrates and sediment

characteristics in subtidal areas adjacent to Rice Island and Miller Sands, 1993-1994.

Final report to U.S. Army Corps of Engineers, Portland District, Contract no. E96930052,

23 p. plus appendices. (Available from Northwest Fisheries Science Center, 2725

Montlake Blvd. E., Seattle WA 98112.)

Meyer, J. H., T. A. Pearce, and S. B. Patlan. 1981. Distribution and food habits of juvenile

salmonids in the Duwamish estuary, Washington, 1980. U.S. Dept. Interior and U.S.

Fish Wildlife Service. Olympia, WA. 39 p. plus appendices.

Miller, J. A., and C. A. Simenstad. 1997. A comparative assessment of a natural and created

estuarine slough as rearing habitat for juvenile chinook and coho salmon. Estuaries

20(4):792-806.

Nicholas, J. W., and H. V. Lorz. 1984. Stomach contents of juvenile wild chinook and juvenile

hatchery coho salmon in several Oregon estuaries. Oregon Dept. Fish Wildlife. Progress

Rep. no. 84-2. 9 p.

Oregon Climate Service. 1997-. http://www.ocs.orst.edu/reports/flood96/flood2.html

Pearce, T. A., J. H. Meyer, and R. L. Boomer. 1982. Distribution and food habits of juvenile

salmon in the Nisqually estuary, Washington, 1979-1980. U.S. Dept. Interior, U.S. Fish

Wildlife Service. Olympia, WA. 30 p. plus appendices.
42

Schiewe, M. H., D. M. Miller, E. M. Dawley, R. D. Ledgerwood, and R. L. Emmett. 1989.

Quality and behavior of juvenile salmonids in the Columbia River estuary and nearshore

ocean. Final report to Dept. Energy, Bonneville Power Admin, Div. Fish Wildlife.

Contract no. DE-AI79-88BP92866. 38 p.

Simenstad, C. A., K. L. Fresh, and E. O. Salo. 1982. The role of Puget Sound and Washington

coastal estuaries in the life history of Pacific salmon: an unappreciated function. In V. S.

Kennedy (editor), Estuarine Comparisons, 343-364 p. Academic Press, New York.

U.S. Geological Survey. 1992-.

http://waterdata.usgs.gov/nwis-w/OR/data.components/hist.cgi?statnum=14246900
43

APPENDIX A: FIGURES
44
45

Appendix Figure 1. Differences in monthly means of benthic invertebrates for numbers of

species and densities (log10 (mean number/m2)) from stations located in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was

conducted in April, June, and August of 1994 (pre-breach) and 1997 (postbreach). Stations 1-10, 14, and 15 were located inside the bay and Stations

11C-13C were located outside and adjacent to the bay. The jetty was

breached in August 1995.
46

Appendix Figure 2. Differences in monthly means of epibenthic invertebrates for numbers of

species and densities (log10 (mean number/m2)) from stations located in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was

conducted in April, June, and August of 1994 (pre-breach) and 1997 (postbreach). Stations 1-10, 14, and 15 were located inside the bay and Stations

11C-13C were located outside and adjacent to the bay. The jetty was

breached in August 1995.
47

Appendix Figure 3. Differences in monthly means of fish and shellfish for numbers of species

and densities (log10 (mean number/m2

)) from stations located in and adjacent

to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was

conducted in April, June, and August of 1994 (pre-breach) and 1997 (postbreach). Stations 1-7 were located inside the bay and Stations PE, PM, nd

PW were located outside and adjacent to the bay. The jetty was breached in

August 1995.
48

Appendix Figure 4. Length-frequency histograms for Pacific herring (Clupea pallasi), collected

by purse seine in Trestle Bay, Columbia River estuary, in July and August

1996.
49

Appendix Figure 5. Length-frequency histograms for shiner perch (Cymatogaster aggregata)

collected by trapnet in Trestle Bay, Columbia River estuary, in MaySeptember 1994. Data were combined for three trapnet stations for each

month.
50

Appendix Figure 6. Length-frequency histograms for shiner perch (Cymatogaster aggregata)

collected by trapnet in Trestle Bay, Columbia River estuary, in MaySeptember 1996. Data were combined for three trapnet stations for each

month.
51

Appendix Figure 7. Length-frequency histograms for shiner perch (Cymatogaster aggregata)

collected by trapnet in Trestle Bay, Columbia River estuary, in MaySeptember 1997. Data were combined for three trapnet staitons for each

month.
52
53

APPENDIX B: TABLES
54
55

Appendix Table 1. Geographic locations of benthic invertebrate, sediment, purse seine, and

trapnet sampling stations for Trestle Bay surveys 1994 and 1997.
56

Appendix Table 2. Summary of benthic invertebrate taxa/categories at sampling statinos in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Stations 1-10

were located in the bay and reference Stations 11c-13c were located outside

and adjacent to the bay. Sampling occurred in April, June, and August of

1994 and 1997. The jetty was breached in August 1995.
57

Appendix Table 2. Continued.
58

Appendix Table 2. Continued.
59

Appendix Table 3. Summary of epibenthic invertebrate taxa/categories at sampling statinos in

and adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Stations 1-

10 were located in the bay and reference Stations 11c-13c were located

outside and adjacent to the bay. Sampling occurred in April, June, and

August of 1994 and 1997. The jetty was breached in August 1995.
60

Appedix Table 3. Continued.
61

Appendix Table 3. Continued.
62

Appendix Table 3. Continued.
63

Appendix Table 4. Median grain sizes at sediment sampling stations in and adjacent to Trestle

Bay (RKm 11.3), Columbia River estuary. Sampling was conducted in

August 1993, April and June 1994 (pre-breach), and June and August 1997

(post-breach). Stations 1-10, 14, and 15 were located in the bay, and Stations

11c-13c were located outside and adjacent to the bay. The jetty was

breached in August 1995.
64

Appendix Table 5. Percent silt/clay at sediment sampling stations in and adjacent to Trestle Bay

(RKm 11.3), Columbia River estuary. Sampling was conducted in August

1993, April and June 1994 (pre-breach), and June and August 1997 (postbreach). Stations 1-10, 14, and 15 were located in the bay, and Stations 11c13c were located outside and adjacent to the bay. The jetty was breached in

August 1995.
65

Appendix Table 6. Percent volatile solids at sediment sampling stations in and adjacent to

Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was conducted

in August 1993, April and June 1994 (pre-breach), and June and August

1997 (post-breach). Stations 1-10, 14, and 15 were located in the bay, and

Stations 11c-13c were located outside and adjacent to the bay. The jetty was

breached in August 1995.
66

Appendix Table 7. Summary of fish and shellfish captured by purse seine at stations in and

adjacent to Trestle Bay (RKm 11.3), Columbia River estuary. Sampling was

conducted May-September, 1994, 1996, and 1997. No sampling was

conducted in the reference area in 1996. The jetty was breached in August

1995.
67

Appendix Table 7. Continued.
68

Appendix Table 7. Continued.
69

Appendix Table 7. Continued.
70

Appendix Table 8. Total numbers of fish and shellfish captured at trapnet sampling stations in

Trestle Bay (RKm 11.3), Columbia River estuary. Values are for three

trapnet stations combined by month. Sampling was conducted MaySeptember 1994, 1996, and 1997. The jetty was breached in August 1995.
71

Appendix Table 8. Continued.
72

Appendix Table 8. Continued.