The effect of riverine discharge on the distribution …...1 Department of Marine Sciences, University of South Alabama & the Dauphin Island Sea Lab, 101 Bienville Blvd., Dauphin Island,

The effect of riverine discharge on the distribution of marine and estuarine fishes and crabs of the Copper River Delta, Alaska

Final Report for the Prince William Sound Oil Spill Recovery Institute

OSRI Graduate Fellowship: Monica J. Dozier and Charles H. Peterson

Institute of Marine Sciences, University of North Carolina at Chapel Hill, 3431 Arendell Street, Morehead City, North Carolina 28775 USA

In collaboration with

Sean P. Powers1, and Mary Anne Bishop2

1 Department of Marine Sciences, University of South Alabama & the Dauphin Island Sea Lab, 101 Bienville Blvd., Dauphin Island, Alabama 3668 USA

2Prince William Sound Science Center, P.O. Box 705, Cordova, Alaska 99754 USA

Abstract: Vast expanses of intertidal sand/mudflats serve as a critical link in the food web of nearshore communities along the southcentral Alaska coastline. The rich abundance of benthic invertebrates residing within the sediments of intertidal flats and the large network of subtidal channels that bisect these flats provide a significant prey resource for numerous species of fish, crabs, birds, and marine mammals. One of the largest expanses of intertidal mud/sand flats occurs in the Copper River Delta and southeastern Prince William Sound (Orca Inlet). From April 2002 through October 2003, we performed the first study of the demersal fish and mobile invertebrate community of the estuarine/marine waters of the Copper River Delta and adjacent Orca Inlet (southeastern Prince William Sound). At seven stations located throughout Orca Inlet and the Western Copper River Delta monthly otter trawl surveys were performed from April through October of 2002 and 2003. A diverse fish assemblage dominated by flatfish, sculpins, snake prickleback and Crangon shrimp is present on the Copper River Delta. Several of the demersal fish species and one crab species that occur within the Copper River Delta are of significant value to recreational and commercial fisheries. Pacific halibut, lingcod, English sole, and Dungeness crab appear to use the extensive network of sloughs and presumably the tidal flats as nursery habitat. Spatial variability in the demersal fish and invertebrate community reflect two principal factors: distance from the Copper River and abundance of sea otters.

Introduction Nearshore habitats (e.g., intertidal and subtidal mudflats, rocky outcropings, seagrass meadows and kelp beds) are an integral component of the Gulf of Alaska ecosystem serving as essential nursery and feeding grounds for numerous marine, anadramous, avian and terrestrial species (Peterson 2001). Nearshore habitats are often characterized by high densities of invertebrate prey that, in turn, provide a critical prey resource for fish, crabs, shorebirds, water fowl and mammals (Powers et al. 2002). Although the productivity of Alaskan nearshore habitats is well recognized, much of the area has not been studied. In particular, shallow-water (0 – 20 m) areas of the Alaska coast have received little attention as a result of the logistic difficulties (e.g., large tidal regime, geographically isolated) and high financial costs associated with conducting research in many of these areas. Here, we present the findings of the first field survey of the demersal fish and invertebrate community of the Copper River Delta, Alaska. The study also represents one of the few investigations of the 0-20m nearshore area of southcentral Alaska. Vast expanses of intertidal and shallow subtidal mudflats are a ubiquitous feature of the southcentral Alaskan coastline and in many areas represent the dominant nearshore marine habitat. One of the largest expanses of intertidal and shallow subtidal flats occurs at the terminus of the Copper River. Large expanses of mudflats also occur throughout Cook Inlet, and Controller Bay with more modest expanses of interidal mudlftas scattered throughout small embayment along the Alaska coastline. Located at the eastern edge of Prince William Sound near the port of Cordova, the vast 500-km2 mudflats of the Copper River Delta stretch almost continuously for 80 km from Egg Island to Castle Island, and from Kokinhenik Island to Softuk Bar (Figure 1). Extensive mudflats also occur in Orca Inlet, a large bay in southeast Prince William Sound influenced by the Copper River. The vast network of intertidal mudflats and shallow sloughs that meander through the tidal flats serve as a critical connection between the Gulf of Alaska and the vast expanse of freshwater wetlands, rivers, lakes and glaciers of the Copper River watershed. The tidal flats of the Copper River Delta provide foraging habitat for a variety of migratory (shorebirds and salmonid fish) and resident demersal species (e.g., Dungeness crabs, Pacific halibut, lingcod). During high tide, the inundated tidal flats provide rich foraging habitat for demersal fish and crabs. As the tide ebbs and tidal flats become exposed, fish and mobile invertebrates retreat to a network of deeper water channels and sloughs that meander through the tidal flats. During periods of exposure, tidal flats are visited by avian and terrestrial consumers that feed on benthic invertebrates or shallow water fishes. Over 4 million shorebirds, the largest spring concentration of shorebirds in

the Western Hemisphere (Isleib 1979, Bishop et al. 2000) visit the Copper River flats annually between late April and mid-May on their way to breeding grounds in western Alaska. The Copper River Delta also supports a substantial commercial and subsistence fishery that is an integral element of the local economy: some 549 gillnet fishers commercially harvest 3 species of salmon, sockeye (Oncorhyncus nerka), coho (O. kisutch) and chinook (O. tshawytscha), in the estuarine portion of Copper River Delta. Equally important, subsistence fishing provides an important food source for residents of Cordova and the upper Copper River watershed. The tidal flats serve as both an entry and exit corridor for these salmon. The fish migrate through the delta first as smolts (i.e., late-stage juveniles) leaving freshwater habitats and then again as adults attempting to return to the same freshwater habitats to spawn (Christensen et al., 2000). Beyond its importance as a salmon fishery, little is known about the fish and mobile invertebrate community of the estuarine waters of the Copper River Delta. From April 2002 through October 2003, we performed the first study of the demersal fish and mobile invertebrate community of the estuarine/marine waters of the Copper River Delta and adjacent Orca Inlet (southeastern Prince William Sound). The objectives of this study were to: (1) characterize spatial and temporal variability in the demersal fish and invertebrate community, (2) determine the influence of river discharge on community composition, and (3) asses the relative importance of the Copper River Delta as a nursery habitat for fisheries species. Materials and methods Site Description.

All field surveys were conducted in the estuarine/marine waters of the western portion of the Copper River Delta and Orca Inlet in southeastern Prince William Sound (Fig.1). The Copper River Delta, the largest contiguous coastal wetland system on the West Coast of North America (Thilenius 1995), contains 500 km2 of intertidal sand/mud and an extensive network of sloughs that bisect the flats. The Copper River provides the largest supply of freshwater and associated sediment load to the delta. Brabets (1997) reported the delivery of 62 million metric tons (69 million tons) of suspended sediments annually to the delta from the 63,000 km2 drainage basin of the Copper River. Much of this delivery follows spring ice melt (May-July) and continues into the warmer summer months when discharge rate of the river can be as high as 5,300 m3s-1 (Brabets 1997). Additional freshwater inputs into the delta result from discharge of three smaller rivers (Scott, Sheridan, and Eyak) as well as a series of sloughs that drain the extensive network of freshwater marshes that occur on the delta. The Scott and Sheridan Rivers flows are dominated by glacial silts whereas the Eyak River, which drains Eyak Lake, delivers freshwater with relatively little suspended solids. Saltwater from the Gulf of Alaska enters through three primary channels, Strawberry, Egg Island, and Pete Dahl, which bisect a string of barrier islands that protect the delta’s mudlfat from waves and currents in the Gulf Alaska.

Water clarity within the study area is influenced by the high suspended sediment

load of river discharge as well as storm induced resuspension of silt/clay sediments. Turbidity during summer months is lowest, less than 20 NTU (nephlometer turbidity units), at Hartney Bay where phytoplankton and some suspended sediment control turbidity levels and increases as distance to the Copper River decreases. Turbidity ranges from 200 and 400 NTU’s near the Copper River (Powers et al. 2004).

Tidal flats of the Copper River Delta are dominated by silt-clay sediments, a

result of the glacial silt delivered by the Copper, Sheridan and Scott Rivers. Fine sands increase in sediments as distance decreases to the Gulf of Alaska or Prince William Sound. A low diversity benthic infauna characterizes tidal flat area of the Copper River Delta where 5 species account for > 95% of infaunal biomass (Powers et al. 2002, 2004). The deposit-feeding bivalve Macoma balthica accounts for 80-90% of infaunal biomass within the sediments of the Delta. Infaunal diversity increases from east to west with highest diversity present within tidal flats present in Hartney Bay (Orca Inlet). M. balthica, Mytilus trossulus, a suspension feeding mussel, and Mya arenaria, a suspension feeding infaunal clam, account for the majority of benthic biomass at Hartney Bay (Powers et al. 2004). Bottom sediments within most of the study area lack biogenic structure with the exception of eel grass (Zostera marina) beds near Orca Inlet and mussels beds (Mytilus trossulus) within Orca Inlet.

Weather on the delta is maritime with mild wet summers (July mean air

temperature 12 ºC) and cool wet winters (January mean air temperature -5 ºC). Average annual precipitation on the Copper River Delta (based on Cordova, Alaska airport) is 236 cm and annual snowfall is 302 cm (Western Regional Climate Center, http://www.wrcc.dri.edu). Average annual snowfall is 302 cm. Although snow and ice may cover the supralittoral areas of the delta intermittently from October to late April, above-freezing temperatures and precipitation limit snow and ice accumulation. Hydrographic data Hydrographic data were collected at all stations where fish were collected. In 2002 and 2003, surface salinity and temperature were measured at each of the seven trawl stations (see below) prior to trawl operations. Salinity was measured using a refractometer and temperature with a mercury thermometer. In 2003, the hydrographic sampling was greatly expanded to include 11 stations where vertical profiles of salinity, temperature, and depth were measured using a Seabird CTD. Measurements of sediment grain size near most of the trawl stations were available from a companion study on benthic invertebrate dynamics (see Powers et al. 2002, 2004). Qualitative information on substrate characteristics (sediment type, seagrass or macroalgae presence, mussel beds) were recorded based on material retained in the trawl net. Fish and mobile invertebrate collections

Bottom trawl surveys were conducted monthly from April through September 2002 and from April through October 2003. At each of 7 sampling stations, three replicate 10 min otter trawl tows were performed. From west to east the station were named Hartney Bay, Eel grass, west hump, seal bar, Johnson’s hole, racetrack and Pete Dahl (Fig. 1). The otter trawl measured 4-m wide (when fully opened) with two 10 lb doors (0.6 m long x 0.3 m tall) on each side. Mesh size was 1.5 cm on the wings and body of the net and 6-mm on the cod end. All trawls were performed from the F/V Sage, a 30 ft gillnet boat with jet drive, captained by Dan Bilderback. Trawls were pulled from the bow of the boat as the boat went stern first against the tide at 2 to 4 km h-1. At each station trawling was conducted in well-defined channels or slough at or near low tide when animals would be more concentrated as they sought refuge from exposed tidal flats. Trawling operations occurred over two to three days within a seven day period. This distribution of effort was necessary to insure that all trawls were conducted at or near low tide. Replicate trawls were spaced to avoid trawling over areas that were previously trawled during the other tows. Starting and ending time, GPS location, boat speed, bottom depth, tidal stage, and weather conditions were recorded for each replicate trawl. All fish and mobile invertebrates collected in the trawls were identified to species counted and an aggregate weight by species determined. For a representative subsample of twenty individuals of each species, total length (TL) was measured to the nearest mm for all fish. Carapace width and length were recorded for all crabs. All fish were kept in saltwater-filled buckets during data collection and the majority of fish were then release unharmed after processing. All collections were performed under collection permits issued by the Alaska Department of Fish and Game and the International Pacific Halibut Commission. Data analysis Hydrographic data were used to characterize the study area as well as to determine if abiotic factors could predict spatial patterns of fish and crab abundance. Spatial and temporal patterns of riverine influence were examined through interpolation of salinity and temperature data using Arcview/GIS-based approach for spatial analysis. Interpolations of surface and bottom salinity and temperature measurements within our study area were made for each monthly sampling period. Regressions, both linear and non-linear, were performed between selected hydrographic variables (bottom-water salinity, bottom-water temperature, and depth) and fish and crab abundances (total catch per unit effort [CPUE] and CPUE of selected taxa). CPUE is reported as number of fish or biomass of fish captured per 10 minute trawl. Multivariate analyses were performed to examine spatial and temporal changes in fish and mobile invertebrate community structure. Dendograms of the seven trawl stations were constructed based on the average similarity between mean annual CPUE for 38 species of fish and mobile invertebrates. Results

Hydrographic data Salinity varies both temporally in relation to discharge from rivers and sloughs as well as spatially with distance from the Gulf of Alaska, Prince William Sound and the plume of the Copper River. CTD profiles at 11 stations within the study area performed monthly from April through October 2003 documented the extensive spatial influence of the Copper River’s freshwater discharge on near shore areas of the delta and adjacent water bodies, Gulf of Alaska and Prince William Sound. Surface and bottom water salinities (Fig. 2) throughout the delta and Orca Inlet are significantly reduced during the summer in response to the large input of freshwater from the Copper River. From May to September, salinity was lowest (0-10 psu) in areas near the Eyak, Sheridan, Scott and Copper Rivers and highest (32 psu) at CTD stations within Orca Inlet. Salinity was most variable in those areas that were influenced by riverine discharge with highest values in April (prior to ice-break up in the rivers) and lowest during July (coincident with high river discharge). Salinity was relatively stable in most of Orca Inlet ranging from 27 to 32 psu. In summary, a west-east gradient of decreasing salinity was present from late spring to fall of 2002 and 2003 within Orca Inlet and the Copper River Delta. For the fish collection stations this gradient resulted in the generalized salinity pattern of Hartney Bay > eel grass = west hump > seal bar > Johnson’s hole = racetrack = Pete Dahl. The strength of this gradient appeared to vary as a result of seasonal changes in riverine discharge. Temperature measurements revealed a strong seasonal change in surface and bottom-water temperatures. Lowest temperatures were recorded in April of 2002 and averaged 5.8 ºC across all sites. Lowest temperatures in 2003 were also recorded in April but averaged 8.5 ºC. Highest water temperatures were recorded in July and averaged 14.5 ºC in 2002 and 15.8 ºC in 2003. In contrast to salinity values, no strong east-west gradient in temperature was evident. For CTD stations in water depths less than 10 m surface and bottom temperatures were similar with bottom temperature averaging 0.5ºC cooler than surface waters. For CTD stations located at water depth greater than 10-m surface and bottom water temperatures differed by 1-3ºC. Largest differences in surface and bottom-water temperature and salinity were observed in June and July of 2003. Differences in bottom habitat characteristics were evident among the seven fish collection stations. Sediments at the four stations within the Copper River Delta area (seal bar, Johnson’s hole, racetrack, and Pete Dahl) were dominated by silts and clays with some fine sands present. No emergent structure (seagrass or mussel beds) were found at or near any of these four stations. Mean water depth during trawl collection was highest at Pete Dahl (4.0 ± 1.5 m; mean ± 1 standard deviation), followed by Johnson’s Hole (3.8 ± 1.4 m) seal bar (3.7 ± 2.0 m) and racetrack (2.6 ± 0.8 m). As its name implies, the eel grass station had large quantities of submerged grass, Z. marina, with occasional clumps of mussels. The station was also the deepest with an average water depth during trawling of 5.7 ± 3.8 m. West hump, named because of its proximity to a shallow shoal called the “hump”, which is impassable to fishing boats at low tide, was most similar to the eel grass station. Bottom sediments at the west hump station were

dominated by fine sands. Occasional clumps of eel grass and mussels were collected at this mid-depth station (3.5 ± 1.7 m). Bottom sediments at Hartney Bay were dominated by fine-course sands with large quantities of wood fragments and detritus. On a few occasions small quantities of eel grass and mussels were collected in the trawl. Depth during trawling averaged 4.1 ± 1.8 m. Fish and mobile invertebrate collections A total of 38 species of fish and 5 species of mobile invertebrates were collected during the 2 year study. Half of the fish species collected were members of three families: families Pleuronectidae (flatfish, 9 species), Cottidae (sculpins 6 species) and Hexagrammidae (lingcod and greenlings, 5 species). The remaining 18 species represented 10 families (Table 1). For mobile invertebrates, Dungeness crab (Cancer magister) and crangonid shrimp were the most common taxa collected. Numerically, crangonid shrimp were the dominant taxa collected in the trawl in 2002 and 2003. Excluding crnagonid shrimp, the four dominant species by abundance and biomass were starry flounder (Platichthys stellatus), snake prickleback (Lumpenus sagitta), Pacific staghorn sculpin (Leptocottus armatus), and Dungeness crabs. Although the rank order within this top 4 varied, these same four species were the dominants in 2002 and 2003 (Tables 2 and 3). Spatial differences in the abundances of fish and mobile invertebrate species were evident when average CPUE of stations was arranged by each stations relative position along a west to east transect across the study area. For both the 2002 and 2003 (Fig. 3), the highest CPUE for Dungeness crabs was recorded at the two sites furthest east and closest to the Copper River, racetrack (average CPUE = 45.1 crabs) and Pete Dahl (average CPUE = 21.2). Dungeness crabs were found occasionally at seal bar and Johnson’s hole (average CPUE = 2.3), but were extremely rare (average CPUE < 1.0 ) at the west hump, eel grass and Hartney bay stations. Highest CPUE of hexagrammids (primarily white-spotted greenling and lingcod) were found at the west hump and eel grass stations with few hexagrammids captured east of seal bar. For the two anadramous species collected in the trawls (primarily eulachon and coho salmon smolt), higher CPUE were found east of the west hump station. Flatfish (Family Pleuronectidae) were common throughout the Delta and Orca Inlet (Fig. 3). Four species accounted for 95% of the flatfish collected, starry flounder, English sole (Parophrys vetulus), sand sole (Psettichthys melanostictus) and Pacific halibut (Hippoglossus stenolepis) (Fig. 4). Although CPUE of starry flounder were high throughout the study area, abundances peaked near the racetrack and Johnson’s hole stations. English sole were rare at stations east of the west hump station in 2002 and 2003 (Fig. 5). CPUE for Pacific halibut and sand sole were slightly higher near the west hump station in 2002 and 2003, although both species were found throughout the study area. Cluster analysis based on the mean abundances of all 38 species of fish and Dungeness crab collected within the study area, demonstrated greatest similarity between the four stations in closest proximity to the Copper River: racetrack, Johnson’s hole, seal

bar and Pete Dahl (Fig 6). Eel grass and west hump stations had little overall similarity to the four stations near the Copper River Delta or to each other. Despite its greater proximity to the eel grass and west hump stations, the fauna at the Hartney Bay station had greater overall similarities to sites near the Copper River in both 2002 and 2003. Intra and interannual changes in the abundance of fish and mobile invertebrates were evident during the sampling period. The most noteworthy of which was the July-August peak in abundance of Dungeness crab (Fig. 7) in 2002 and 2003. Dungeness crab between 20 and 220 mm carapace width (CW) were collected primarily from the racetrack and Pete Dahl sites (Fig. 8). Interannual difference in the abundance of Pacific halibut was also seen in the temporal plots of flatfish CPUE (Fig. 7). Examination of the length-frequency diagrams for Pacific halibut for 2002 and 2003, coupled with fish age estimates of Pacific halibut conducted for our project by the International Pacific Halibut Commission, suggest that differences between years may reflect differences in recruitment of young of the year halibut. In 2002, a strong pulse of 0+ yr old halibut entered the study area in August-September. Age 1+ and 2+ fish were also present. Assuming a similar size range for year classes in 2003 (IPHC has not completed otolith annuli counts for 2003), few 0+ halibut recruited to the study area in 2002 whereas age 1+ and 2+ halibut abundances remained relatively similar to 2002. Discussion In an effort to document the abundance and distribution of demersal fish and crabs, we conducted replicate otter trawl surveys monthly at 7 stations within the estuarine/marine waters of the Copper River Delta and adjacent Orca Inlet from April through September 2002 and April through October 2003. A diverse fish assemblage (Table 1) dominated by flatfish, sculpins, snake prickleback and Crangon shrimp is present on the Copper River Delta. Several of the demersal fish species and one crab species that occur within the Copper River Delta are of significant value to recreational and commercial fisheries. Pacific halibut, lingcod, English sole, and Dungeness crab appear to use the extensive network of sloughs and presumably the tidal flats as nursery habitat. Spatial variability is evident in the demersal fish and crab distributions. For example, Dungeness cabs were most abundant east of Orca Inlet. This pattern appears to reflect the abundance pattern of sea otters: higher numbers of sea otters are found in Orca Inlet compared to the Copper River Delta sites. Our data also suggests that the absence of larger, harvestable sizes of Dungeness crabs in Prince William Sound and the Copper River Delta is not explained by lack of juvenile recruitment. The lack of spatial overlap between Dungeness crab and sea otters observed in our study, coupled with the temporal coincidence of sea otter increases and collapse of the Dungeness crab fishery in the 1970’s, offer strong support that top-down effects by sea otters are controlling the Dungeness crab populations in the area.

The unique interface of land, sea and air characteristic of intertidal habitats serves to promote high biological productivity within the intertidal and adjacent subtidal habitats. The land provides a substratum for the occupation of intertidal organisms, the seawater facilitates import and export of nutrients and larvae, and the air provides a medium for passage of solar energy and a source of physical stress (Peterson 2001). Whereas tidal energy and wind subsidize the intertidal zone with planktonic foods produced in the photic zone, freshwater runoff injects inorganic nutrients from terrestrial communities (Nixon et al. 1986, Peterson 2001). This mix of nutrients coupled with high solar energy levels results in high primary production that is readily transferred to higher trophic levels through a sizeable benthic invertebrate prey base (Powers et al. 2002). The results of this study, coupled with a companion study on diets of demersal fish on the Copper River Delta, provide strong evidence that this energy is transferred to a rich demersal fish and crab fauna. Many of the factors that contribute to the high biological productivity also result in heightened sensitivity of intertidal systems to natural and anthropogenic change. Short and long-term changes in sea level resulting from annual or decadal changes in atmospheric pressure and global warming result in changes in tidal inundation, which can result in changes in the location of the land-sea interface. Changes in habitat boundaries may also result from subsidence and/or elevation of flat areas resulting from tectonic activity (e.g. the 1964 Good Friday Earthquake, Plafker 1990). Spatial and temporal variation in coastal circulation patterns or upwelling/downwelling intensity can result in shifts in temperature regime or delivery of oceanic nutrients and significantly modify species distributions, primary production and trophic transfer (Andersen and Piatt 1999, Zheng and Kruse 2000, Clark and Hare 2002). Patterns of freshwater inputs, which affect both nutrient levels, ambient salinities, and fish distributions can vary in response to climatic oscillation that in turn effect precipitation levels and transgression or regression of glaciers. A variety of direct and indirect effects on marine community structure may result from the propagation of these changes up or down coastal food chains. Adding to the heightened sensitivity of intertidal habitats is the fact that these areas are often the repository for contaminants released in coastal areas (Short and Heintz 1997, Short et al. 1999, Peterson 2001). As with changes caused by variation in natural forcings, a host of direct and indirect effects may result from acute and chronic exposure to contaminants that ultimately modify the complex ecological network of a coastal system (Peterson 2001). The detection of these effects is often difficult and requires long-term field research that incorporates a web of ecological interactions (Underwood and Peterson 1984, Underwood 1992). While the acute response of intertidal communities to large-scale releases of contaminants has received a considerable amount of study, chronic exposure often resulting in sublethal effects on organisms (e.g., changes in fitness or fecundity) has proven difficult to study as a result of the paucity of long-term data sets (National Research Council 1985, Peterson and Holland-Bartels 2002). Data collected during this project will contribute to establishing the baseline biological data, and more importantly understudying of ecosystem function, to assess future disturbances to the Copper River Delta ecosystem.

Acknowledgments. This research was funded by grants from the Prince William Sound Oil Spill Recovery Institute (OSRI) and the Exxon Valdez Oil Spill Trustee Council’s Gulf Ecosystem Monitoring Program (EVOS-GEM) to S.P. Powers and M.A. Bishop. Funding for M.J. Dozier was provided by an OSRI graduate fellowship. Dan Bilderback (Sage Charters) was critical to the success of this project by providing the vessel for trawling and navigation skills for the field sites. We also acknowledge the help of J. Grabowski, E. Clesceri, K. Gregalis, D. Gaskill during field collections and T. Ellis for his assistance in the processing of samples.

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Table 1. Fish and mobile invertebrate species collected in 333, 10-minute otter trawls performed in 2002 and 2003 in estuarine/marine water of the Copper River Delta and Orca Inlet (southeast Prince William Sound). Classification scheme for fishes is based on Fishes of Alaska (2002) and for mobile invertebrates on Southeast Alaska's Rocky Shores (1998). Family Species Common Name Size Range (mmTL)

FishesClupeidae Clupea pallasii Pacific herring 112-170Osmeridae Osmerus mordax Rainbow smelt 57-160

Thaleichthys pacificus Eulachon (smelt) 39-192Salmonidae Oncorhynchus kisutch Coho salmon 155Gadidae Gadus macrocephalus Pacifc cod 177

Microgadus proximus Pacific tomcod 55-997Gasterosteidae Gasterosteus aculeatus Three-spine stickleback 75-84Syngnathidae Syngnathus leptorhynchus Bay pipefish 106-260Hexagrammidae Ophiodon elongatus Lingcod 89-224

Hexagrammos decagrammus Kelp greenling 79-145Hexagrammos lagocephalus Rock greenling 65-82Hexagrammos octogrammus Masked greenling 66-135Hexagrammos stelleri Whitespotted greenling 22-235

Cottidae Enophyrs bison Buffalo sculpin 86-169Enophrys diceraus Antlered sculpin 74-180Icelinus borealis Northern sculpin 45-102Leptocottus armatus Pacific staghorn sculpin 50-271Myoxocephalus polyacanthocephalus Great sculpin 250Myoxocephalus scorpius Shorthorn sculpin 106

Hemitripteridae Blepsias bilobus Crested sculpin 110Agonidae Pallasina barbata Tubenose poacher 85-105

Podothecus accipenserinus Sturgeon poacher 60-240Zoarcidae Eel pouts 135Stichaeidae Stichaeus punctatus Arctic shanny -

Lumpenus sagitta Snake prickleback 55-300Pholidae Pholis laeta Crescent gunnel 118-140Trichodontidae Trichodon trichodon Pacific sandfish 69-190Ammodytidae Ammodytes hexapterus Pacific sand lance 65-145Gobiidae Lepidogobius lepidus Bay goby 52Pleuronectidae Hippoglossus stenolepis Pacific halibut 80-352

Hippoglossoides elassodon Flathead sole -Psettichthys melanostictus Sand sole 20-299Isopsetta isolepis Butter sole 150Lepidopsetta bilineata Rock sole (southern) 56-461Limanda aspera Yellowfin sole 55-260Parophrys vetulus English sole 48-248Platichthys stellatus Starry flounder 41-1116Pleuronectes quadrituberculatus Alaska plaice 69-162

Mobile invertebrates

Crangonidae Crangonid shrimp 48-101Majidae Pugettia producta Northern kelp crab 21-22Atelecyclidae Telmessus cheiragonus Helmet crab 69Cancridae Cancer magister Dungeness crab 12-219Grapsidae Hemigrapsus oregonensis Yellow shore crab -

Table 2. Rank order by numeric abundance of the 20 dominant species (excluding

crangonid shrimp) collected in 192, 10-min otter trawls performed from April through

September 2002 in estuarine/marine water of the Copper River Delta and Orca Inlet

(southeast Prince William Sound).

Percent Rank Common Name Abundance Catch1 Snake prickleback 6056 29.752 Starry flounder 4791 23.543 Dungeness crab 1806 8.874 Pacific staghorn sculpin 1541 7.575 Pacific tomcod 1346 6.616 Eulachon (smelt) 1242 6.107 Sand sole 1073 5.278 English sole 988 4.859 Whitespotted greenling 354 1.7410 Pacific halibut 376 1.8511 Rock sole (southern) 245 1.2012 Yellowfin sole 128 0.6313 Pacific sand lance 111 0.5514 Pacific sandfish 88 0.4315 Rainbow smelt 53 0.2616 Northern sculpin 29 0.1417 Crescent gunnel 24 0.1218 Pacific herring 18 0.0919 Sturgeon poacher 17 0.0820 Three-spine stickleback 11 0.05

Total *Dominant Species 20297 99.72Total Catch 20354 100.00

Table 3. Rank order by numeric abundance of the 20 dominant species (excluding

crangonid shrimp) collected in 141, 10-min otter trawls performed from April through

October 2003 in estuarine/marine water of the Copper River Delta and Orca Inlet

(southeast Prince William Sound).

Percent PercentRank Common Name Abundance Catch Biomass (kg) Catch1 Starry flounder 3568 22.55 230.12 52.852 Snake prickleback 3326 21.02 44.40 10.203 English sole 2700 17.07 20.04 4.604 Pacific staghorn sculpin 1558 9.85 57.36 13.175 Eulachon (smelt) 1454 9.19 2.05 0.476 Dungeness crab 1061 6.71 24.53 5.637 Pacific tomcod 973 6.15 16.02 3.688 Sand sole 329 2.08 12.10 2.789 Pacific halibut 275 1.74 12.36 2.8410 Yellowfin sole 82 0.52 1.91 0.4411 Sturgeon poacher 74 0.47 1.28 0.2912 Pacific sand lance 72 0.46 0.16 0.0413 Whitespotted greenling 64 0.40 2.88 0.6614 Pacifc cod 48 0.30 0.04 0.0115 Lingcod 45 0.28 1.32 0.3016 Rainbow smelt 41 0.26 0.43 0.1017 Kelp greenling 39 0.25 0.18 0.0418 Pacific sandfish 31 0.20 0.70 0.1619 Rock sole (southern) 24 0.15 6.54 1.5020 Northern sculpin 15 0.09 0.11 0.02

Total *Dominant Species 15734 99.45 435 99.89Total 15821 100 435.41 100.00

Figure Legends

Figure 1. Aerial image of the western Copper River Delta showing the spatial extent of the Copper River outflow (cloudy, gray water vs. deep black water) and the network of mudflat through out the brackish water portions of the Delta and Orca Inlet. Sampling station for CTD, nutrient and chlorophyll water column measurements (filled circles) and demersal fish trawls (filled squares) are noted on the image. From west to east demersal fish sampling stations are as follows: Hartney Bay, Eel grass, West Hump, East Hump, Sea Bar, Johnson’s Hole, Racetrack, and Pete Dahl. Figure 2. Interpolated bottom salinity maps by month for the Copper River Delta study area. Note the large influence of the Copper River outflow in July during peak outflow. Figure 3. Average catch per unit effort (CPUE) by station for selected groups of fish and crabs in 2002 (upper) and 2003 (lower). Stations are arranged along a west to east transect across the study area. Figure 4. Percent composition based on numeric abundance of flatfish for 2002 (upper) and 2003 (lower). Figure 5. Average catch per unit effort (CPUE) by station for flatfish species in 2002 (upper) and 2003 (lower). Stations are arranged along a west to east transect across the study area. Figure 6. Dendograms illustrating overall similarity in average CPUE of 38 species for the seven trawl stations in 2002 (upper) and 2003 (lower). Figure 7. Average catch per unit effort (CPUE) by month for selected fish and crab groups (upper) and flatfish species (lower) in 2002 and 2003 at the seven trawl stations. CPUE for October 2002 and March 2003 are interpolated from September 2002 and April 2003 data. Figure 8. Size frequencies for Dungeness crabs collected within the Copper River estuary in 2002 (upper) and 2003 (lower). Figure 9. Size frequencies for Pacific halibut collected within the Copper River estuary and Orca Inlet in 2002 (upper) and 2003 (lower). Estimated ages of halibut by size range are based on otolith annuli counts performed by the International Pacific Halibut Commission. The square represents the standard deviation around the mean size (denoted by the vertical line) for the specific age class and the horizontal lines outside the box represent the size range for the given age class. Ages for Pacific halibut collected in 2003 are not yet available.

Trawl station Benthic sampling station

Gulf of Alaska

12

3

4 5 6

CTD/Surface nutrient & chl a station

11

10

8 9

EyakRiver

Watershed nutrient & chl a station

AlaganikSlough

Scott River

Sheridan River

Copper River

River Low

Orca Inlet

Cordova

Egg Island

Hartney Bay

Gulf of Alaska

EyakRiver

AlaganikSlough

Scott River

Sheridan River

Copper River

Cordova

Egg Island

Hartney Bay

N

0

50

100

150

200

250

300

Hartney Bay Eel Grass West Hump Seal Bar J Hole Racetrack Pete Dahl

Trawl Station

CPU

E

Flatfish Pricklebacks Dungeness Crab SculpinGadids Anadromous Hexagrammids Other

0

50

100

150

200

250

300

Hartney Bay Eel Grass West Hump Seal Bar J Hole Racetrack Pete Dahl

Trawl Station

CPU

EFlatfish Pricklebacks Dungeness Crab SculpinGadids Anadromous Hexagrammids Other

Alaska plaice 0%

Sand sole 14%

Starry flounder

63%

nglish sole 13%

Pacific halibut 5%

Rock sole 3%Yellowfin sole

2%

Flathead sole 0%

2002

Starry flounder51%

Sand sole5%

English sole39%

Pacific halibut 4%

Butter sole0%

Alaska plaice0%Rock sole

0%

Yellowfin sole1%

2003

0

20

40

60

80

100

120

140

160

Hartney Bay Eel Grass West Hump Seal Bar J Hole Racetrack Pete Dahl

Trawl stations

CPU

E

Starry flounder Sand sole English sole Pacific halibut Rock soleYellowfin sole Alaska plaice Butter sole Flathead sole

2002

0

20

40

60

80

100

120

140

160

Hartney Bay Eel Grass West Hump Seal Bar J Hole Racetrack Pete Dahl

Trawl stations

CPU

E

Starry flounder Sand sole English sole Pacific halibut Rock soleYellowfin sole Alaska plaice Butter sole Flathead sole

2003

2002

Eel Grass

Hartney Bay

J Hole

Pete Dahl

Racetrack

Seal Bar

West Hump

Distance0 1 2 3 4 5 6 7 8

2002

Eel Grass

Hartney Bay

J Hole

Pete Dahl

Racetrack

Seal Bar

West Hump

Distance0 1 2 3 4 5 6 7 8

Distance0 1 2 3 4 5 6 7 8

Eel Grass

Hartney Bay

J Hole

Pete Dahl

Racetrack

Seal Bar

West Hump

Distance0 1 2 3 4 5 6 7 8

2003

Eel Grass

Hartney Bay

J Hole

Pete Dahl

Racetrack

Seal Bar

West Hump

Eel Grass

Hartney Bay

J Hole

Pete Dahl

Racetrack

Seal Bar

West Hump

Eel Grass

Hartney Bay

J Hole

Pete Dahl

Racetrack

Seal Bar

West Hump

Distance0 1 2 3 4 5 6 7 8

Distance0 1 2 3 4 5 6 7 8

2003

0.00

50.00

100.00

150.00

200.00

250.00

300.00

Apr-02

May-02

Jun-02

Jul-02

Aug-02

Sep-02

Oct-02

Nov-02

Dec-02

Jan-03

Feb-03

Mar-03

Apr-03

May-03

Jun-03

Jul-03

Aug-03

Sep-03

Oct-03

Month

CPU

EFlatfish Pricklebacks Dungeness Crab Sculpin

Gadids Anadromous Hexagrammids Other

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

Apr-02

May-02

Jun-02

Jul-02

Aug-02

Sep-02

Oct-02

Nov-02

Dec-02

Jan-03

Feb-03

Mar-03

Apr-03

May-03

Jun-03

Jul-03

Aug-03

Sep-03

Oct-03

Month

CPU

E

Starry flounder Sand sole English sole Pacific halibut Rock soleYellowfin sole Alaska plaice Butter sole Flathead sole

n = 526

0

20

40

60

80

100

120

140

160

Cou

nt

0 50 100 150 200 250 300

Dungeness Crab CW (mm)

2003

0

20

40

60

80

100

120

140

160C

ount

0 50 100 150 200 250 300

Dungeness Crab CW (mm)

2002

n = 440

0

10

20

30

40

50

60

Cou

nt

0 50 100 150 200 250 300 350 400

Pacific Halibut TL (mm)

n = 3120+

1+2+

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Pacific Halibut TL (mm)

2002

n = 3120+

1+2+

n = 3120+ 0+

1+2+

0

10

20

30

40

50

60

Cou

nt

0 50 100 150 200 250 300 350 400Pacific Halibut TL (mm)

2003

n = 149

0

10

20

30

40

50

60

Cou

nt

0 50 100 150 200 250 300 350 400Pacific Halibut TL (mm)

2003

n = 149