development of a refined conceptual model for aquatic food webs in san francisco bay rmp 2007...

Development of a refined conceptual model for aquatic food webs in San

Francisco Bay

RMP 2007 Proposed Special Study

Overarching questions

• How is the SF Bay food web organized?

• What is the relative role of sediments vs. the water column as transport pathways of contaminants to biota?

• Is there food-web driven spatial variation in contaminant uptake?

Source: Bridges et al. 2006

Source: Bridges et al. 2006

Species Prey types Contaminant pathways

Spatial variation in diet

Shiner surfperch

Epibenthic invertebrates Sediment and boundary layer

No

White croaker Benthic and epibenthic invertebrates and small fish

Sediment and boundary layer

No

Topsmelt Algae and zooplankton Water column No

Silverside Epibenthic, terrestrial invertebrates, and zooplankton

Sediment and water column

No

Least tern Small pelagic forage fish (e.g., topsmelt, silverside)

Water column Yes

(prey types)

Harbor seal Large pelagic forage fish Water column Yes

(prey types)

Hypotheses:

Approach

• Review literature and local data ($5,000)

• Field sample collection ($2,000)

• Gut content analysis of fishes ($10,000)

• Communication of results ($3,000)

Review literature and local information

• Focus on updating or refining conceptual model for key species– Is the model accurate? Is it likely to vary spatially?

• Harbor seals, least terns, surfperch, croaker, small fish

• Multiple data sources– Previous unpublished studies on surfperch, croaker (Port of

Oakland, Regional Board/MLML, DFG historic studies)– Harbor seals publications – Dianne Kopec, Emma Grigg – Least tern diets – Meredith Elliot, USFWS, SFBNWR, Calfed

Project– IEP and IRWMP silverside diets– Literature review

Field sample collection

• Collection will have to be opportunistic due to budgetary limitations

• Leveraged from other projects– RMP Fish 2006 - Shiner perch and croaker– EEPS small fish Hg 2006 and 2007 – topsmelt and

silverside– EEPS endocrine effects to small fish 2007 (Kevin

Kelley) – surfperch– IEP trawl surveys– USFWS Beach seine surveys

• Picking up fish and fixing stomachs

Laboratory gut content analysis

• Target fish species• Focus on sufficient information to determine

proportion benthic vs. pelagic prey– ID to order or family level– Some estimates of relative mass or volume– Trade off between number of fish vs. detail level of

information• If field sampling is sufficient, will examine

spatial variation in prey types• Details to be worked out with subcontractor

Communication of results

• Focus on interaction and communication with RB and other interested stakeholders– Summary presentation of findings and

discussion of future research directions

• Short (approximately 5 pp.) technical memo

Possible next steps in future years

• Refine estimates of sediment vs. surface water in contaminant uptake

• Incorporate refined dietary estimates into food web model

• Combine food web and fate models – Role of sediments vs. water column – Spatial variation in sources