ASSESSING INVERTEBRATE PREY PRODUCTION IN THE SKOKOMISH ESTUARY

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1 USGS - Page 1 of 15 Western Ecological Research Center San Francisco Bay Estuary Field Station, 55 Azuar Drive, Vallejo, CA ASSESSING INVERTEBRATE PREY PRODUCTION IN THE SKOKOMISH ESTUARY JANUARY 214 Report to: Shannon Kirby, Skokomish Tribe From: Ashley Smith, Isa Woo, John Takekawa INTRODUCTION We assessed foraging opportunity and capacity for juvenile Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) salmon from an estuarine restoration by comparing invertebrate prey availability with salmonid diet in the Skokomish estuary. A percent similarity index (PSI) was used to examine the similarity between the composition of the Chinook diet samples and the composition of the terrestrially available insects from each sampling station (Gray et al. 22). Preliminary research was supported in its first year in 211 by Skokomish Tribe, and continued in 212 with additional support from the Tribe. Here we summarize the sample collection, processing, and data analysis results for the 212 sampling period. METHODS We sampled terrestrial invertebrates that fall into the water from the aerial environment (fallout traps), and salmon diet (by gastric lavage). We collected and processed fallout trap samples to characterize terrestrial invertebrate abundance in a restoration site in the Skokomish estuary. Eight sampling stations were established throughout the estuary and were collected monthly from March September 212. Fish diet samples were collected over the same time period and sampling area. Suggested citation: Smith, A. L., I. Woo, and J. Y. Takekawa Assessing invertebrate prey production in the Skokomish Estuary. Data Summary Report, U. S. Geological Survey, Western Ecological Research Center, Vallejo, CA. 15 pp.

2 USGS - Page 2 of 15 Field Collection Insect fallout traps were deployed in the emergent marsh, along slough edges (Figure 1). They are approximately.25 m², 55-cm x 38-cm rectangular plastic basins filled with soapy water and attached on each corner to vertical polyvinyl chloride (PVC) poles installed along the edge of the tidal channel (Simenstad et al. 21). These traps measure the direct input of invertebrates from the marsh to the aquatic system by capturing insects that fall or settle onto the surface of the water (Gray et al. 22). Traps were deployed at eight stations in March 212 and were left to sample for 48 hours over an entire tidal cycle before being collected, sieved on a US No. 35 sieve (.5 mm mesh) and preserved in 7% ethanol. Three replicate traps were established at each sampling location and were collected monthly from March September 212. Fish diet samples were collected by the Skokomish Tribe by trapping fish via beach seine in the tidal sloughs of the Skokomish estuary. Stomach contents were collected via gastric lavage in the field by the Skokomish Tribe. Gastric lavage is a non-destructive method for obtaining gut contents where a plastic tube with a lavage tip is inserted into the mouth of the live specimen and the stomach contents are flushed out with filtered water. Flushing occurred over a sieve so that the contents collect on the top of the sieve. All contents were then transferred from the sieve to a sample jar filled with ethanol for preservation. Laboratory Methods Preserved stomach contents and insect fallout traps were then shipped to USGS San Francisco Bay Estuary Field station for final processing. Fallout trap and lavage invertebrate samples were spread out among petri dishes and sorted under stereo dissection microscopes at a magnification range of 7-35x. Invertebrates were identified by expert invertebrate biologists and prey densities were recorded. Abundances from fallout trap samples have been standardized to area and are reported as mean density/m². Non-detected taxa were represented as zero for any given sample. All samples had QA/QC reviews by an expert invertebrate biologist. We obtained biomass (g dry weight) for all gastric lavage samples by placing diet contents into aluminum weigh boats and oven-dried to a constant weight (24 hrs at 8C). Samples were allowed to cool for 3 minutes in a desiccator and weighed using the A&D HR-22i microbalance to the nearest.1 mg.

3 USGS - Page 3 of 15 RESULTS Prey Availability in Fallout Traps Terrestrial invertebrate density in the fallout traps was lowest in March (x = 58/m²) and steadily increased until peaking in July (x = 2,9/m²; Figure 2). Springtails (Collembola) were the most dominant taxa detected in fallout traps over the sampling period (x = 63/m²). Long-legged flies (Dolichopodidae) had the second highest density (x = 24/m²), followed by midges (Chironomidae, x = 185/m²). The terrestrial invertebrate community was characterized by other dipteran flies (Ephydridae, Ceratopogonidae, Cecidomyiidae, and Tipulidae), as well as true insects (Cercopoidae, Cicadellidae and Saldidae). Other terrestrial invertebrates commonly detected at the site were Coleoptera, Hymenoptera, Thysanoptera, Psocoptera, and Arachnids (Figure 2). Taxa comprising <.1% of total abundance are included in our analysis as Other (Orthoptera, Lepidoptera, Gastropoda, Oligochaeta, Taltridae (Amphipoda), Hemigrapsis (Brachyura), Zygoptera). Springtail abundance was greatest in June and July (x = 1,2/m² and 1,1/m², respectively) and lowest in March and September (x = 6/m² and 1/m², respectively). Long-legged flies were most common in July and August (x = 6/m², both months), while abundance of the smaller fly, Chironomidae, peaked in April and May (x = 32/m² and 38/m², respectively). Chironomidae were the only taxa to have peak abundance in the spring, as all other taxa were most abundant in the summer months (Figure 2). Community composition and abundance varied between sampling stations. Station CASPM2 had by far the greatest terrestrial fallout invertebrate density (x = 4,3/m²), followed by (x = 2,3/m²). All other stations had similar densities (x = 8 13/m²). Springtails were the most prominent taxa at three of the eight sampling stations (CAPH1, CASPM2 and ). Chironomids were the dominant taxa at three of the sampling locations (CASPM9, CAPL1, and CASPL11) in the earlier months (March May), and Dolichopodidae was the dominant taxa in the summer months (June September). Juvenile Chinook and Coho Diet Juvenile Chinook and Coho diet samples were highly variable during the sampling period from March August 212, within and between sites (Figures 4-7). The capture efficiency varied between taxa, with juvenile Chinook samples only captured in May and June. We obtained a total of 21 juvenile Chinook gastric lavage samples in May and 8 in June (Figure 4). Coho were caught earlier on in the season (April, n=4), but we received fewer samples per month than compared to the juvenile Chinook (May, n=2; June, n=1; July, n=5; August, n=7; Figure 6).

4 USGS - Page 4 of 15 The Coho lavage samples from the early season (April May) were primarily comprised of benthic and aquatic invertebrates, including Amphipoda and Mysida (Figure 6). The majority of diet items in June samples were terrestrially available prey resources (9%) including the shorefly, Ephydridae, and the midge, Chironomidae, however benthic and neustonic invertebrates were also detected in the samples. We observed the highest abundance of prey items in the July lavage samples, which was primarily attributed to the large abundance of barkflies (Psocoptera) in four of the five samples that were collected (Figure 6). Barkfly density in the fallout samples peaked in July, however they were not a prominent taxa detected at any of the sampling stations. August Coho lavage samples had high variation in density, with individual guts containing between and 15 prey items. Gut samples from August had a diverse array of prey items, primarily consisting of benthic dipteran larvae. Hemipterans were prevalent throughout the August samples, along with the Dipteran flies, Chironomidae, Ceratopogonidae and Dolichopodidae (Figure 6). The prey availability sampling within the Skokomish estuary revealed that there are ample prey resources in the summer months, despite the low detection of prey items found in the Coho diet samples in June and August (Figure 2, 6). Coho diet biomass varied greatly over the sampling period, and was greatest in April due to the large amphipods and mysids detected in the gut samples (Figure 7). The shorefly, Ephydridae was the primary biomass contributor in June lavage samples and was present in six of the ten samples. Ephydridae density was greatest in June in the prey availability samples. Although the lavage samples contained up to 15 Psocopterans each, they are small and contributed little biomass. August biomass was relatively low and the majority of the biomass was attributed to Chironomidae and Dolichopodidae. Chinook diet contents in this study were drastically different than the prey resources found in the Coho samples. Two of the 21 samples contained >3 items per sample, however, five were empty and the remaining 14 had fewer than ten items each. The majority of prey items in May Chinook samples were copepods and Crustacea nauplii. By June, the diet contents shifted to more terrestrially available invertebrates including biting midges, Ceratopogonidae, non-biting midges, Chironomidae, and Brachycerans. Gut content biomass in May was variable, and was relatively high in a few samples primarily due to the presence of Mysids, crustacean larvae and Other. In this case, the Other category represented partially digested, unidentifiable pieces of tissue. A percent similarity index (PSI) was used to examine the similarity between the composition of the salmonid diet samples and the composition of the fallout samples from each site (Gray et al. 22). A high PSI value for a given sampling location indicates that the diet composition of the fish is similar to the composition of the sampled invertebrate population. PSI was calculated using the following formula (Hurlbert 1978, Yoklavich et al. 1991):

5 USGS - Page 5 of 15 (1) PSI = Σ minimum (p 1i, p 2i ), where p1i is the percentage of individuals from a taxonomic grouping in sample 1 and p2i is the percentage of individuals from a taxonomic grouping in sample 2. PSI values for all months were relatively low for both Coho and Chinook diet samples. Chinook PSI values were similar in the two sampling months (May=18.5%; June=17.9%; Table 2). In both months, Chironomidae was the highest contributor to the PSI (9.4%, 7.8%, respectively). Greatest mean PSI values were detected in Coho gut contents in August (31.5%; Table 3). Lowest PSI values were detected in April (3.%) due to the large number of aquatic organisms we recorded in those diet samples. The community similarity increased from April to May (15.3%), and again from May to June (28.5%). The high PSI values in June are largely attributed to the high number of Dolichopodidae and Chironomidae found in the availability and diet samples during this time period. Community similarity in July was lower (6.9%), partially due to the overwhelmingly abundant Psocoptera that was hardly detected in the diet samples. Community similarity peaked in August (31.5%) due to the high presence of Dolichopodidae, Chironomidae and Hemipterans in both sample types. CONCLUSION The invertebrate fallout data and salmonid diet data indicate that the juvenile salmon are able to utilize prey resources provided in multiple strata, as their diet shifted from aquatic invertebrates in early spring to terrestrial food sources as the season progresses. Further studies that include neustonic and benthic prey sampling will help to understand more about prey availability from terrestrial inputs and within the water column and benthos to explain shifts in prey sources throughout the outmigration season. REFERENCES Gray, A., C. a. Simenstad, D. L. Bottom, and T. J. Cornwell. 22. Contrasting Functional Performance of Juvenile Salmon Habitat in Recovering Wetlands of the Salmon River Estuary, Oregon, U.S.A. Restoration Ecology 1: Hurlbert, S. H The measurement of niche overlap and some relatives. Ecology 59: Simenstad, C. A., A. J. Wick, J. R. Cordell, R. M. Thom, and G. D. Williams. 21. Decadal Development of a Created Slough in the Chehalis River Estuary : Year 2 Results. Report to U.S. Army Corps of Engineers, Seattle District. Yoklavich, M. M., G. M. Cailliet, J. P. Barry, D. a. Ambrose, and B. S. Antrim Temporal and Spatial Patterns in Abundance and Diversity of Fish Assemblages in Elkhorn Slough, California. Estuaries 14:465.

6 USGS - Page 6 of 15 Table 1. Terrestrial invertebrate density (individuals/m²) by sampling area and time period in the Skokomish estuary (Mar-Sep 212). March 212 April 212 Taxa ID CASPH1 CASPH14 CASPL1 CASPL11 CASPM2 CASPM5 CASPM9 CASPH1 CASPH14 CASPL1 CASPL11 CASPM2 CASPM5 CASPM9 Brachycera, other Dolichopodidae Ephydridae Nematocera, other Chironomidae Ceratopogonidae Cecidomyiidae 2 Tipulidae Hemiptera, other Cercopoidae Cicadellidae Saldidae Coleoptera Hymenoptera Thysanoptera Psocoptera 2 Collembola , , Araneae Acari Other

7 USGS - Page 7 of 15 Table 1 continued May 212 June 212 Taxa ID CASPH1 CASPH14 CASPL1 CASPL11 CASPM2 CASPM5 CASPM9 CASPH1 CASPH14 CASPL1 CASPL11 CASPM2 CASPM5 CASPM9 Brachycera, other Dolichopodidae Ephydridae Nematocera, other Chironomidae , Ceratopogonidae Cecidomyiidae Tipulidae Hemiptera, other Cercopoidae Cicadellidae Saldidae Coleoptera Hymenoptera Thysanoptera Psocoptera Collembola 1, , , , , , Araneae Acari , Other

8 USGS - Page 8 of 15 Table 1 continued July 212 August 212 September 212 Taxa ID CASPH1 CASPH14 CASPL1 CASPL11 CASPM2 CASPM5 CASPM9 CASPH1 CASPM2 CASPM5 CASPM9 CASPH14 CASPL1 CASPL11 Brachycera, other Dolichopodidae 35 1,71 1, , Ephydridae Nematocera, other Chironomidae Ceratopogonidae Cecidomyiidae Tipulidae Hemiptera, other Cercopoidae Cicadellidae Saldidae Coleoptera Hymenoptera Thysanoptera Psocoptera Collembola 1, , , , Araneae Acari , Other

9 USGS - Page 9 of 15 Table 2. Percent similarity index (PSI) for juvenile Chinook diet and prey availability (fallout trap samples) in the Skokomish estuary in May and June 212. May 212 Jun 212 Brachycera, other.%.8% Dolichopodidae 1.7%.6% Ephydridae.%.% Nematocera, other.%.% Chironomidae 9.4% 7.8% Ceratopogonidae.9% 3.% Cecidomyiidae.%.% Tipulidae 1.2%.5% Hemiptera, other.% 1.% Cercopoidae.%.6% Cicadellidae.%.6% Saldidae.%.% Coleoptera.%.% Hymenoptera 1.% 1.7% Thysanoptera.%.% Psocoptera.%.% Collembola.%.% Araneae.9% 1.4% Acari 3.4%.% Other.1%.% Diptera larvae.%.% TOTAL 18.5% 17.9%

10 USGS - Page 1 of 15 Table 3. Percent similarity index (PSI) for juvenile Coho diet and prey availability (fallout trap samples) in the Skokomish estuary in April-August Apr May Jun Jul Aug Brachycera, other.6%.9%.8%.5%.% Dolichopodidae.%.% 5.8%.8% 16.3% Ephydridae.%.% 2.6%.%.% Nematocera, other.%.%.%.%.% Chironomidae.% 6.3% 7.8% 2.3% 5.2% Ceratopogonidae.%.% 3.% 1.% 1.1% Cecidomyiidae.%.%.%.%.% Tipulidae.%.%.%.%.% Hemiptera, other.%.%.%.2% 4.1% Cercopoidae.%.%.%.6%.% Cicadellidae.%.%.%.%.% Saldidae.%.%.8%.%.% Coleoptera.%.%.%.%.% Hymenoptera.%.% 4.5%.6% 2.3% Thysanoptera.%.% 1.9%.%.% Psocoptera.%.%.%.2%.% Collembola.%.%.%.%.% Araneae.% 1.9% 1.4%.2%.8% Acari 2.3% 6.3%.%.4% 1.7% Other.1%.%.%.%.% TOTAL 3.% 15.3% 28.5% 6.9% 31.5%

11 Figure 1. Fallout trap on slough edge at low tide.

12 USGS - Page 12 of 15 mean individuals/m² 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S Other Contaminant Acari Araneae Collembola Psocoptera Thysanoptera Hymenoptera Coleoptera Saldidae Cicadellidae Cercopoidae Hemiptera, other Tipulidae Cecidomyiidae Ceratopogonidae Chironomidae Nematocera, other Ephydridae Dolichopodidae Brachycera, other Figure 2. Mean terrestrial invertebrates (individuals/m²) in fallout traps across all sampling locations by month.

USGS - Page 13 of 15 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S 4,5 4, 3,5 3, 2,5 2,

3, 2,5 2, 1,5 1, 5 M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S CASPM2

M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S CASPL1 CASPL11 Figure 3.

13 USGS - Page 13 of 15 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S CAPH1 CASPH14 8, 7, 6, 5, 4, 3, 2, 1, M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S CASPM2 CASPM5 CASPM9 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 M A M J J A S CASPL1 CASPL11 Figure 3. Mean terrestrial invertebrates (individuals/m²) detected in fallout traps at each sampling station.

14 USGS - Page 14 of 15 invertebrates/lavage sample Mysida Crustacea larvae Copepoda Diptera larvae Araneae Acari Hymenoptera Hemiptera, other Tipulidae Ceratopogonidae Chironomidae Dolichopodidae Brachycera, other May June Figure 4. Invertebrate abundance in Chinook salmon gastric lavage samples (total invertebrates/sample). Biomass (mg, dry weight) May June Figure 5. Prey biomass (mg, dry weight) in Chinook salmon gastric lavage samples. Other Mysida Isopoda Crustacea larvae Copepoda Diptera larvae Araneae Acari Hymenoptera Hemiptera, other Tipulidae Ceratopogonidae Chironomidae Dolichopodidae Brachycera, other

15 USGS - Page 15 of 15 invertebrates/lavage sample 2 18 Mysida 16 Amphipoda 14 Diptera larvae Psocoptera 12 Araneae 1 Acari 8 Hymenoptera Hemiptera 6 Ephydridae 4 Ceratopogonidae 2 Chironomidae Dolichopodidae Brachycera, other April May June July August Figure 6. Invertebrate abundance in Coho salmon gastric lavage samples (total invertebrates/sample). Biomass (mg, dry weight) April May June July August Figure 7. Prey biomass (mg, dry weight) in Coho salmon gastric lavage samples. Mysida Amphipoda Diptera larvae Psocoptera Polychaeta Other insecta Araneae Acari Hymenoptera Hemiptera, other Ephydridae Ceratopogonidae Chironomidae Dolichopodidae Brachycera, other

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