1. Growth Trajectories of Wild California Steelhead Parr David Swank 1,2, Will Satterthwaite 1, Michael Beakes 1, Susan Sogard 2, Marc Mangel 1, Rob Titus 3, Joe Merz 4 1 UC-Santa Cruz; 2 National Marine Fisheries Service; 3 California Dept of Fish and Game; 4 East Bay Municipal Utilities District

2. Previous work (Thorpe et. al. 1998) on the life-history of Atlantic salmon has shown that: In juvenile development, maturation in the stream as a resident parr and smolting are mutually exclusive. The fastest-growing juveniles in a cohort mature as resident parr, the next fastest become smolts, while the slowest remain immature parr in stream for another year. A decision window occurs in the fall preceding smolting, during which the juvenile salmon decides which pathway to follow.

3. Hypothesis O. mykiss follow life-history decision rules similar to Atlantic salmon. Stream temperatures, stream flows, and food availability differ between coastal California and Central Valley streams, and will affect juvenile growth. The resulting differences in juvenile growth rates should result in significant differences in life-histories among these populations.

4. Objectives Characterize growth rates and life-history pathways of juvenile steelhead in two coastal California populations and two Central Valley populations. Incorporate these data as part of a model that predicts how changes in flows on managed rivers can affect growth rates and therefore life-histories of wild steelhead populations.

5. Scotts Creek Soquel Creek American R. Mokelumne R.

6. Scotts Creek Soquel Creek

8. Coastal Estuaries = Critical Nursery Habitat

9. Lower American River Lower Mokelumne River

11. Methods Juvenile steelhead were sampled by seasonal (June, Oct., Dec.) electrofishing at four sites on Scotts Creek from 2006-2007 and four sites on Soquel Creek from 2003-2007. –Additional samples came from a smolt trap on Scotts Creek, and seining in Scotts Creek Lagoon. Juvenile steelhead were sampled by seine and hook and line at three sites on the American River, and two sites on the Mokelumne River. –Additional data came from boom electrofishing by EBMUD on the Mokelumne River.

12. Methods Elastomer tags were placed on all steelhead 64mm FL. Length, weight, and scale sample Gastric lavage on a subsample of fish Invertebrate drift samples (monthly) Benthic samples (quarterly)

15. Average length over a year for steelhead parr in the four study streams based on PIT tag recaptures; all periods and sites combined.

16. Aug 2 nd 2006, Sunrise (American River) 126mm FL and 60mm FL

17. Growth among sites Scotts CreekSoquel Creek

18. Growth rates (mm/day), by site and time period for PIT tagged juvenile steelhead in Scotts Creek, 2006-2007. Error bars are +/- 2 standard errors. Growth among time periods – Scotts Creek

19. Growth rates (mm/day), by site and time period for PIT tagged juvenile steelhead in Soquel Creek, 2006-2007. Error bars are +/- 2 standard errors. Growth among time periods – Soquel Creek

20. Length at capture of juvenile steelhead caught in the Scotts Creek smolt trap. Each point represents a single capture event. Only the last capture for each fish was in the smolt trap.

21. StreamSiten% Ripe Males Scotts Creek Swanton270.0% Upper Scotts362.8% Big Creek320.0% Lower Scotts150.0% Soquel Creek Badger Springs3511.4% Ashbury515.9% Girl Scout Falls5911.9% Lion's Park420.0%

22. Soquel Creek: Partial Barriers

23. Presumed resident steelhead from Soquel Creek. This individual was age-2 at first capture, age-5 at last capture, and gained only 50mm over three years.

24. Mokelumne River adult O. mykiss; Presumed resident rainbow trout.

26. Results Central Valley steelhead populations were found to have much higher growth rates than coastal populations. Steelhead parr reach smolt size in only one year on the American and Mokelumne Rivers. Significant growth in Coastal California steelhead occurs mostly during winter and spring. Many fish actually lose weight over the summer and fall, when streamflow is very low. Temperatures do not appear to be limiting. Coastal juveniles will still emigrate downstream even after little to no growth for many months. However, most are emigrating to the lagoon for further growth before smolting. Lowest site on each coastal stream stands out as high growth site, somewhat similar to lagoons. Resident rainbow trout are common in the Mokelumne River, rare below barriers in the coastal streams.

27. Seining in Soquel Creek Lagoon for PIT tagged emigrants from upstream sites

28. PIT tag antenna on Soquel Creek to record emigrants

29. Acoustic tagging wild steelhead/rainbow trout on Lower American River to track emigration/residency

30. Lab Growth Experiment Treatment Schedule Treatment 1: Aug 1 – Sept 26 Treatment 2: Sept 27 – Nov 22 Treatment 3: Nov 23 – Jan 18 Treatment 4: Jan 19 – Mar 16.

32. Comments Early life-history decisions in juvenile salmonids include whether to mature as a parr, become a smolt and emigrate, or remain a parr. Scotts Creek and Soquel Creek are small coastal California streams that are heavily forested, have high gradients, and stream flows that are heavily precipitation dependent. The Lower American and Mokelumne Rivers are large Central Valley Rivers with coldwater habitat present below impassable dams. Stream flows and temperatures are relatively stable year-round. Most American River steelhead achieve lengths greater than 150mm FL in their first year, and many reach lengths greater than 200mm FL. Length at capture of juvenile steelhead caught in the Scotts Creek smolt trap. Each point represents a single capture event. Only the last capture for each fish was in the smolt trap. Mean monthly stream temperatures (˚C) in the four study streams, 2006-2007. The dashed line at 16 degrees indicates an ideal temperature for growth of juvenile steelhead. Upper Soquel Creek sites are all further from ocean and at higher elevation than any Scotts Creek site. Mokelumne river “adult” resident rainbow trout, n = 289 over 2 years, most in 220 to 520 mm FL range. 3 ripes males (all <385 mm) and 7 females (all < 450 mm, so not sea-run)

33. mature parr Age-1 smolt Age-1 parr Fry Age-0 parr maturity decision smolt decision

34. Outline Introduction –Theory Methods –Sites and their habitats Results –Growth rates from PIT tagged juveniles –Residency Ongoing sampling projects –PIT tag antennae –Lagoon seining –Acoustic tagging

36. Mean individual growth rate (mm/day) was significantly related to stream flow (cfs) in Scotts Creek (ANOVA; p<.01 at all sites).

37. PIT Tagging Stream No. Marked No. Recaptured 1x No. Recaptured 2x+ American R.451101 Mokelumne R.479130 Scotts Creek1,51721121 Soquel Creek1,89323050