TEMPLATE DESIGN © 2008

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Non-insect abundance and their contributions to salmonid parasites in the Deschutes River, Oregon

INTRODUCTION RESULTS DISCUSSION

Black spot infection observed on a lower Deschutes River Rainbow Trout. Infection is determined by the presence of uncharacteristic black spots, often found on the white underbelly which is usually free of spots in trout. Photo credit: Amy Hazel March 3, 2018

CONCLUSIONS •  The observed shift in the invertebrate community

(predominantly non-insect) is consistent with changes

in water quality to eutrophic conditions.

•  Polychaete worms were the dominant taxon at Dizney

Riffle and were present at both sites.

•  Snails were the dominant taxon at Kaskela in 60% of

sample events and occurred in high abundance at both sites.

•  The overall macroinvertebrate community composition

indicates “poor” stream conditions.

•  The snails and polychaete worm observed in this study

contribute to the life cycle of salmonid parasites.

RECOMMENDATIONS

•  Reduce surface water releases from Lake Billy Chinook to

reduce nutrient inputs and improve water quality in the

lower Deschutes River. Improvements to water quality

may ameliorate parasite infection rates in salmonids by

reducing invertebrate host abundance (e.g. snails & worms).

•  Continue benthic macroinvertebrate monitoring in the lower

Deschutes River to track abundance of non-insect taxa and

intermediate hosts of salmonid parasites.

•  Continue to implement monitoring studies in the lower

Deschutes River to determine infection levels in salmonids

of both black spot and C. shasta.

ACKNOWLEDGEMENTS The Deschutes River Alliance thanks our generous

supporters and Steve Pribyl for his input on this project.

Beginning in late 2009, a structural modification was made at

the Pelton-Round Butte Hydroelectric Project that resulted in

increased nutrient loads and entrained algae being

discharged into the lower Deschutes River (Eilers & Vache

2019). Declines in water quality can lead to shifts in the

aquatic macroinvertebrate community (Barbour et al. 1999).

The shift towards a non-insect dominated macroinvertebrate

community has occurred in the lower Deschutes River

(Edwards 2018). Aquatic non-insects including a polychaete

worm Manayunkia speciosa and snails can act as hosts for

parasites that affect the health of salmonids. M. speciosa is

host to Ceratonova (syn.: Ceratomyxa) shasta and snails can

host a worm-like fluke that causes undesired black spots on

fish. C. shasta has been cited as the primary cause for

salmon mortality in the Klamath River (Schakau et al. 2019).

Black spot infection is reported to reduce over-winter survival

of Coho Salmon (Cairns et al. 2005) but the effects on other

salmonids are less understood. Recent studies in the lower

Deschutes River and its tributaries suggest that C. shasta is

causing mortality in returning adult spring Chinook Salmon

(Boostrom & Baker 2017) and that black spot infection is

present in >50% of trout sampled (ODFW unpub. pres. July

2019).

OBJECTIVES

Determine the abundance of non-insects that host salmonid

parasites using benthic sampling (ODEQ 2009)

Characterize the macroinvertebrate community at two sites

using Multi-Metric Index scores (EPA 2016)

STUDY SITE Lower Deschutes River, OR (Jefferson and Wasco counties)

Non-insect abundance (primarily worms & snails) exceeded insect abundance in all samples (>50% total abundance).

The polychaete worm Manayunkia speciosa was the dominant taxon at Dizney Riffle in all samples followed by the snails Vorticifex effusa and Fluminicola sp.

At Kaskela snails dominated invertebrate abundance in October 2015 and March/September 2016, while segmented worms (Oligochaeta) were the dominant taxon in May and July 2016. Multi-Metric Index (MMI) scores were calculated for the Western Mountains Ecoregion using methods developed by the EPA National Rivers and Streams Assessment (EPA 2016)

All MMI scores fell into the “poor” stream condition category, except for one sample that scored in the “fair” condition category (Kaskela: July 2016).

M. speciosa is the intermediate host to C. shasta. Infection prevalence of the C. shasta parasite is low in M. speciosa, <5% of individuals infected (ODFW pers. comm. Oct. 2019), although in-situ water samples detected spore counts for C. shasta high enough to cause mortality in salmonids (>10 spores/Liter)(ODFW 2016). Declines in Klamath River adult Chinook Salmon returns are attributed to the C. shasta parasite (Schakau et al. 2019). Snails are an intermediate host to the black spot causing Neascus spp. parasite. Neascus sp. life cycle:

Image Source: https://novascotia.ca/fish/documents/special-management-areas-reports/

Parasite_brochure_on_Blackspot.pdf

Prior studies suggest that as the abundance of the host snail increases so will the infection rate of juvenile trout (Schaff 2017). One plausible explanation for the increase in observed black spot infection in lower Deschutes River trout is that snail abundance has increased in response to declines in water quality as we have seen. Lower Deschutes River Bull Trout with black spot.

Wesley Noone, Rick Hafele, Greg McMillan—Deschutes River Alliance