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2014 and 2015 Juvenile Green Sturgeon Capture Feasibility Study

Technical Report

Prepared by:

Joshua J. Gruber, William R. Poytress*, Chad E. Praetorius and David J. Ryan

U.S. Fish and Wildlife Service

Red Bluff Fish and Wildlife Office 10950 Tyler Rd

Red Bluff, CA 96080

*Corresponding author: bill_poytress@fws.gov

February 2017

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Disclaimer The mention of trade names or commercial products in this report does not constitute

endorsement or recommendation for use by the federal government.

Cover Photo: Two juvenile Green Sturgeon captured using a benthic trawl on the Sacramento River, California on September 22, 2015. The correct citation for this report is:

Gruber J.J., W.R. Poytress, C.E. Praetorius and D.J. Ryan. 2017. 2014 and 2015 Juvenile Green Sturgeon Capture Feasibility Study. Red Bluff Fish and Wildlife Office, Anadromous Fish Restoration Program, U.S. Fish and Wildlife Service, Red Bluff, California.

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Preface

The following is the final report for the U.S. Fish and Wildlife Service’s investigations on the feasibility of capturing juvenile Green Sturgeon on the Sacramento River, funded by the Central Valley Project Improvement Act (CVPIA) Anadromous Fish Restoration Program in Fiscal Year 2014/2015. Title 34, Section 3406(b)(1) of the CVPIA, Public Law 102-575, requires the Secretary of the Interior to develop within three years of enactment and implement a program which makes all reasonable efforts to ensure that, by the year 2002, natural production of anadromous fish in Central Valley rivers and streams will be sustainable, on a long-term basis, at levels not less than twice the average levels attained during the period of 1967-1991. The purpose of this investigation is to provide scientific information to the Central Valley Project Improvement Act Anadromous Fish Restoration Program to assist in developing restoration recommendations that will help meet program objectives and achieve its anadromous fish doubling goal.

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2014 and 2015 Juvenile Green Sturgeon Capture Feasibility Study

Joshua J. Gruber, William R. Poytress, Chad E. Praetorius and David J. Ryan

U.S. Fish and Wildlife Service, Red Bluff Fish and Wildlife Office, 10950 Tyler Rd, Red Bluff, CA 96080, USA

Abstract.—A variety of sampling methods have been used to collect juvenile sturgeon nationally and worldwide. Captures of juvenile Green Sturgeon within the Sacramento River system have been incidental and anecdotal using standard salmonid monitoring techniques widely employed within the Central Valley. We tested the feasibility of collecting age-0 juvenile Green Sturgeon through the use of two passive (hoop and gill nets) and one active (benthic trawl) sampling techniques. Two different types of benthic trawls (2.4-m Siamese and 4.9-m Sacramento River Trawls) and three different time strata (daytime, early night, and late night) were tested to compare size and catch rates of juvenile Green Sturgeon.

Of the three different gear types tested, active sampling using a benthic trawl was the one gear type that collected juvenile Green Sturgeon (n=41). Juvenile Green Sturgeon caught within the 2.4-m Siamese (n=6) and 4.9-m Sacramento River Trawl (n=35) had mean total lengths of 125 and 231 mm, respectively. Sample gear comparisons of juvenile Green Sturgeon catch were problematic due to small sample sizes and differing temporal distribution of sampling effort between the two nets. Catch per unit effort of trawls (measured in sturgeon per wetted net minute) during the evaluation period was highest from the late night period (CPUE=0.026), followed by the early night (CPUE=0.023) and daytime (CPUE=0.005). Subsequent fall sampling efforts focused on the early night period with a CPUE of 0.021. River temperatures ranged between 14.0 and 17.9 °C in areas where sturgeon were sampled.

We believe the active nature of the benthic trawl sampling gear allowed us to sample for sturgeon utilizing their rearing habitat. Future sampling efforts should continue to use a benthic trawl in areas where juvenile Green Sturgeon were collected in 2015 or where river temperatures are between 14-18 °C. Additionally juvenile Green Sturgeon sampled in good physical condition >150 mm in total length could be tagged and tracked using micro-acoustic tag implantation techniques to determine the extent of juvenile rearing areas, identify habitat preferences, and downstream migration cues and timing.

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Table of Contents Preface ......................................................................................................................................iii Abstract .....................................................................................................................................iv List of Tables .............................................................................................................................vi List of Figures ............................................................................................................................vii Introduction ..............................................................................................................................1 Objectives..................................................................................................................................1 Study Area .................................................................................................................................2 Methods ....................................................................................................................................2 Results .......................................................................................................................................4 Discussion..................................................................................................................................6 Conclusions and Recommendations .........................................................................................8 Acknowledgments.....................................................................................................................9 Literature Cited .........................................................................................................................10 Tables…… ...................................................................................................................................13 Figures .......................................................................................................................................23

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List of Tables

Table Page 1. Gear specifications for (a) hoop and (b) gill nets used during the 2014 and 2015

juvenile Green Sturgeon capture feasibility study on the Sacramento River, California ..................................................................................................................... 14

2. Summary of (a) hoop and (b) gill net sampling effort in wetted net minutes (WNM) by site during 2014 on the Sacramento River, California ........................................... 15

3. Fish species capture by hoop and gill nets during juvenile Green Sturgeon capture feasibility study on the Sacramento River, California during 2014 and 2015 ............ 16

4. Summary of 2014 juvenile Green Sturgeon trawling effort on the Sacramento River, California. Summary effort by site sampled, wetted net minutes (WNM), catch of juvenile Green Sturgeon, and relative abundance as catch per unit of effort (CPUE) expressed in Green Sturgeon per WNM ..................................................................... 17

5. Fish species captured by 2.4-m Siamese and 4.9-m SRT trawl during juvenile Green Sturgeon capture feasibility study on the Sacramento River, California ................... 18

6. Summary of sampling effort in wetted net minutes (WNM) for gill nets during 2015 on the Sacramento River, California. Catch per unit effort (CPUE) expressed in Green Sturgeon per WNM ..................................................................................................... 19

7. Environmental data for each sampling gear type. Values in parentheses () indicate values associated with juvenile Green Sturgeon captures ......................................... 20

8. Summary of 2015 juvenile Green Sturgeon trawling effort on the Sacramento River, California. Summary effort by site sampled, wetted net minutes (WNM), total number of juvenile Green Sturgeon sampled, and relative abundance as catch per unit of effort (CPUE) expressed in Green Sturgeon per WNM ................................... 21

9. Summary of 2.4-m Siamese and 4.9-m SRT trawling effort in wetted net minutes (WNM) during evaluation (July 21–September 4, 2015) and fall sampling period (September 14–October 27, 2015). Data includes juvenile Green Sturgeon catch with relative abundance in Green Sturgeon per WNM (CPUE) summarized by net type and strata ............................................................................................................ 22

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List of Figures

Figure Page 1. Map of juvenile Green Sturgeon capture feasibility study area on the Sacramento

River, California ........................................................................................................... 24 2. Length frequency distribution of all fish species collected in 2.4-m Siamese and 4.9-

m SRT trawls during 2014 and 2015 sampling ............................................................ 25

3. Date and total length of juvenile Green Sturgeon collected in 2.4-m Siamese (black square) and 4.9-m SRT (red triangle) trawl during 2015 ............................................ 26

4. Weight and length relationship(s) developed from juvenile Green Sturgeon captured

using benthic trawls in 2015 on the Sacramento River, California ............................ 27 5. Mean daily water temperatures observed at the Red Bluff Diversion Dam from 2000-

2012 (historic average), 2014, and 2015. Vertical bars represent the estimated larval to juvenile rearing period for Green Sturgeon ........................................................... 28

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2014 and 2015 Juvenile Green Sturgeon Capture Feasibility Study

Introduction

Juvenile sturgeon, Acipenser spp., sampling has been conducted through parts of the United States with varied success using a variety of gear types. Young of the year or age-0 Green Sturgeon Acipenser medirostris and White Sturgeon A. transmontanus have been difficult to locate within the Sacramento River system and are only sporadically detected through numerous river and Delta monitoring projects and salvage from pumping facilities. Limited studies and information exist regarding the rearing and foraging areas utilized by Southern Distinct Population Segment (SDPS) of the North American Green Sturgeon1. Habitat preference of juvenile Green Sturgeon was listed as a key life history stage to research (NMFS 2015). Larval sturgeons are typically described as fish that are not completely morphologically developed (e.g., lateral scutes not fully formed; Detlaff et al. 1993). Juvenile sturgeon are typically described as being those fish greater than 35 days post hatch (dph; Van Eenennaam et al. 2001) and fully developed so they can be field identified to the species level using non-lethal techniques (Detlaff et al. 1993). Rotary screw traps and benthic D-nets employed by the Red Bluff Fish and Wildlife Office (RBFWO) have been successful at sampling larval Green Sturgeon (Gaines and Martin 2002; Brown 2007; and Poytress et al. 2009-2012, 2014). Rotary traps have occasionally sampled juvenile Green Sturgeon (Poytress et al. 2014), but capture frequency has been episodic using this passive sampling technique. Juvenile sturgeon sampling using other passive techniques, such as gill nets, have been successful for White Sturgeon (Glova et al. 2008-2010), Lake Sturgeon A. fulvescens (Barth et al. 2001; Haxton 2011), and Gulf Sturgeon A. oxyrinchus desotoi, a subspecies of the Atlantic Sturgeon A. o. oxyrinchus (Sulak and Clugston 1998). Benthic or bottom trawls have been used successfully to sample White Sturgeon (Parsely et al. 1993) and more recently Pallid Scaphirhynchus albus and Shovelnose sturgeon S. platorynchus (Herzog et al. 2005; Phelps et al. 2009; Steffensen et al. 2015).

Objectives The objectives of this juvenile Green Sturgeon capture feasibility study were to: 1) acquire and deploy two passive and one active gear types in an attempt to capture juvenile sturgeon, 2) determine if gear types could result in non-lethal or low injury rates of captured sturgeon, and 3) measure length and weight of captured individuals to determine if future

1 The Southern Distinct Population Segment (SDPS) of North American Green Sturgeon was federally listed as a Threatened species under the Endangered Species Act (ESA) on April 7, 2006 (71 FR 17757). Critical habitat was designated October 9, 2009 (74 FR 52300). A 5-year status review (77 FR 64959) was completed August 25, 2015 resulting in no change of classification from Threatened status.

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efforts using acoustic tagging techniques could provide greater information on juvenile sturgeon habitat use and migration characteristics.

Study Area

The Sacramento River originates in Northern California near Mt. Shasta from the springs of Mt. Eddy (Hallock et al. 1961). It flows south through 600 kilometers of the state draining numerous slopes of the Coast, Klamath, Cascade, and Sierra Nevada mountain ranges and eventually reaches the Pacific Ocean via the San Francisco Bay (Figure 1). Shasta Dam and its associated downstream flow regulating structure, Keswick Dam, have formed a complete barrier to upstream anadromous fish passage since 1943 (Moffett 1949). The 94-river kilometer (rkm) reach between Keswick Dam (rkm 485; measured from the confluence with the San Joaquin River at Collinsville) and RBDD (rkm 391) supports areas of intact riparian vegetation and largely remains unobstructed. Below RBDD, the river encounters greater anthropogenic influence as it flows south to the Sacramento-San Joaquin Delta. Exploratory sampling using a variety of gear types occurred within a 154 rkm reach of the Sacramento River (Figure 1) from the mouth of Ink’s Creek (rkm 426) to Butte City Bridge (rkm 272) with RBDD (rkm 391) being an area of emphasis primarily due to logistical reasons.

Methods

Passive (hoop and gill nets) and active (benthic trawl) gear types were used to target juvenile Green Sturgeon within and downstream of their known spawning habitat in the Sacramento River (Poytress et al. 2015). Juvenile sampling was scheduled to occur during the late summer and fall, encompassing a period of 180 dph from estimated Green Sturgeon spawning activities and when river temperatures decreased to 10°C or below (Kynard et al. 2005). Previous studies on the Sacramento River, as well as laboratory studies, indicate Green Sturgeon peak activity and migration periods occur during nocturnal hours (Kynard et al. 2005; Poytress et al. 2011). Therefore, sample sites were selected to facilitate safe transit and sampling operations at night. Hoop net surveys.—Turtle style hoop nets were set and left to sample in and around the vicinity of the RBDD to sample a variety of depths, velocities, and substrate types along river margins and backwater areas in an attempt to capture foraging juvenile Green Sturgeon. Four different types of hoop nets were used and allowed to settle on the river bottom with openings facing downstream (Table 1a). Net sets were designed to sample between 0830 and 2030 hours (morning) or 2030 and 0830 hours (evening). Morning/evening set and retrieve cycles were repeated twice daily between rkm 391 and 373 (Figure 1). A float line of varying length was attached to the downstream hoop to manually orient the net and serve as a visual marker for retrieval crews. The upstream hoop of the net was weighted with steel plates to prevent downstream movement of the net. Two, 1.2-m lengths of 1.9-cm diameter Schedule 40 PVC set 180° apart ran the length of the net to keep the hoops

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separated and net fishing properly. A baited, mesh chum-bag was tied within the net onto the hoop just forward of the net’s cod end. A variety of baits were used including: bloodworms, Silver Cup® fish feed pellets, salmon carcasses, sardines, and anchovies.

Collected samples were field sorted with the amount and type of debris recorded. All fish captured were identified, enumerated, and lengths (fork and total) measured to the nearest millimeter (mm). Green Sturgeon incidental mortalities were retained in 95% EtOH for genetic archiving (Anderson et al. in press). Live Green Sturgeon in good condition were weighed to the nearest gram before being returned to the river. Captured salmonids were identified to the species level and all Chinook Salmon Oncorhynchus tshawytscha were identified to race using length-at-date criteria developed by Greene1 (1992). Other (i.e., by-catch) fish were identified to at least the genus level. Catch per unit effort (CPUE) was calculated as the number of Green Sturgeon caught per wetted net minutes (WNM). Effort and environmental data collected for each sample included: set and retrieve date and time, turbidity, temperature, and discharge. River water samples for turbidity analysis were collected at the beginning of the each sample. Turbidity was measured in nephelometric turbidity units (NTUs) in the lab using a Hach model 2100P turbidimeter. River temperatures were recorded using Onset® Tidbit Temp Data Loggers. Two loggers, per site, recorded hourly water temperature at the RBDD (rkm 391), Tehama Bridge (rkm 366.5), Woodson Bridge (rkm 352), Gianella Bridge (rkm 320.6), and Butte City Bridge (rkm 272). River discharge was obtained from the California Department of Water Resources California Data Exchange Center which maintains gaging stations at the following locations: Bend Bridge (BND; rkm 415), RBDD (RDB; rkm 391), Tehama Bridge (TEH; rkm 366.5 ), Woodson Bridge (VIN; rkm 352), Gianella Bridge (HMC; rkm 320.6), and Butte City Bridge (BTC; 272). Gill net surveys.—Gill nets were sampled between RBDD (rkm 391) and Butte City Bridge (rkm 272; Figure 1) to test the feasibility of capturing juvenile Green Sturgeon in river margin and backwater areas of the Sacramento River. Sinking gill nets were made of either monofilament or multifilament nylon mesh of various sizes with a 0.95 cm foam-core float line and 0.64 cm lead-core bottom line (Table 1b). Nets were either sampled independently or joined together. Sampling effort was designed to occur for 200 WNM during the afternoons and evening. Sample collection, as well as, environmental and effort data were processed with the methods described for the hoop net surveys. Benthic trawl surveys.—Benthic trawl nets were used to actively target fish moving or rearing along the river bottom between Ink’s Creek (rkm 426) and Butte City Bridge (rkm 272; Figure 1). Sample sites were determined after scanning areas both visually and with a Humminbird® 1198C SI side imaging and dual-beam sonar. Sonar allowed for coarse resolution imaging of river bottom features to assess areas where the net could likely be deployed and retrieved without becoming snagged. Areas with large woody debris, boulder, or bedrock substrates were avoided. Trawl duration in WNM varied within and between sites and was limited by linear distance containing adequate depths within each sample site and number of

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obstructions. Three different time strata (Daytime 0800-1400; Early Night 2000-0200; Late Night 2400-0600) were evaluated by CPUE to determine if capture rates varied between strata. Two benthic trawl net configurations were evaluated. The first configuration was a small 2.4-m Siamese Trawl that was comprised of a 3.2-mm mesh body with a double-cod bag consisting of 15.9-mm mesh inner bag and 3.2-mm mesh outer bag that separated fish by size. The second configuration was a larger 4.9-m Sacramento River Trawl (SRT) made from 15.9-mm mesh body with a single 3.2-mm mesh cod bag. Both nets were equipped with a large trash door zipper to remove debris and a chafe skirt to protect the cod bags. Trawl nets were deployed from the bow of a boat and towed downstream while making S curves through any given sample area. Tow speeds varied due to river depth and velocity but were generally faster than ambient river velocities yet slow enough to maintain contact with the river bottom (~3-5 rkm/hr). Both trawling nets were towed by 0.95-cm braided floating line with otter boards used to open the mouth of the net. Otter boards for the Siamese and SRT trawls were constructed of marine-grade plywood reinforced with steel measuring 50.8 cm x 30.5 cm and 76.2 cm x 38.1 cm, respectively. Cod ends were tied closed to prevent fish escapement. A tail rope with float was also tied to the cod end to serve as a visual reference of net location and to free the net when it became snagged. Sample collection, as well as, environmental and effort data were processed with the methods described for the hoop net surveys.

Results 2014 Hoop net surveys.—Hoop net sampling occurred between August 8 and October 2 at four locations between rkm 391 and rkm 373.5. Effort for all sites combined totaled 49,341 WNM (822.4 h; Table 2a). Ninety-five percent of the sample effort focused within 2-river kilometers of the RBDD. Sample habitats consisted of eddies and backwater areas with sand and cobble substrates along edges of aquatic vegetation. Fish captured (n=6) ranged in size from 110 to 325 mm (mean=211 mm) but zero Green Sturgeon were sampled by this gear type (Table 3). Gill net surveys.—Gill net sampling occurred between September 8 and October 11 at three locations between rkm 389 and rkm 373.5. Net set durations ranged from 10 to 835 minutes. Effort for all sites combined totaled 4,300 WNM (71.7 h; Table 2b). Sample effort was divided nearly equally between the 3.8 cm and experimental multi-meshed nets at 2,036 and 2,268 WNM, respectively. Nets were placed within backwater and riffle habitats, along bank and gravel bar edges over substrates consisting of sand and cobble. Fish captured (n=17) ranged in size from 205 to 450 mm (mean=302 mm), but zero Green Sturgeon were sampled by this gear type (Table 3).

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Benthic trawl surveys.—Trawling occurred between September 10 and October 23 at nine locations between rkm 426 and 272. Effort for both net configurations totaled 564 WNM (9.4 h; Table 4). Sample effort was split between the Siamese and SRT trawls at 365 and 199 WNM, respectively. A variety of fish were sampled, however, no juvenile Green Sturgeon were captured (Table 5). Fork lengths of the fish captured ranged between 21 and 145 mm (mean=65 mm). Of the 212 fish captured, 9 were recorded as mortalities, none of which were ESA-listed species (Table 5). 2015 Gill net surveys.—Gill nets were deployed at rkm 352, rkm 320.6, and rkm 272 between June 10 and June 25. Nets were generally set between 2000 and 2400 hrs. Effort for all sites totaled 5,626 WNM (93.8 h; Table 6c). Nets were placed along banks, gravel bar edges, and within backwater areas consisting of sand and cobble substrates. A variety of fish were sampled, but no juvenile Green Sturgeon were captured by any of the gill nets (Table 3). Turbidity values derived from surface grab samples ranged from 2.4 to 4.9 NTU (mean=3.6 NTU; Table 7). Benthic trawl surveys.—Benthic trawling efforts began on July 21 and concluded on October 27. Effort for both net configurations (Siamese and SRT) totaled 2,232 WNM (37.2 h) from seventeen sampling locations between rkm 405.5 and rkm 352 (Table 8). Sample effort was greater with the SRT (74.1%) than the Siamese (25.9%) trawl. In total, 41 juvenile Green Sturgeon were collected from eight sample sites over a 30-rkm reach (Table 8). Of the 41 juvenile sturgeons collected, two were incidental mortalities (Table 5). During the time strata evaluation period (July 21-September 4, 2015) combined sample effort for the two trawl nets totaled 1,586 WNM (26.4 h; Table 9). Twenty-five of the 28 juvenile Green Sturgeon (89%) were collected at night during the evaluation period. The remaining 11% were sampled during daytime (CPUE=0.005). CPUE was highest during the late night period (CPUE=0.026), slightly greater than the early night period (CPUE=0.023). Fall sampling (September 14–October 27, 2015) occurred exclusively during the early night period and collected 13 juvenile Green Sturgeon. Fall sampling CPUE was 0.021, similar to the evaluation period (Table 9). Size of fish captured varied between the two trawl nets. Lengths of fish collected by the 2.4-m Siamese net (n=349) ranged from 21 to 190 mm (mean=55; median=50). Lengths of fish collected by the 4.9-m SRT net (n=1,316) ranged from 35 to 830 mm (mean=127; median=84; Figure 2). Total lengths of juvenile Green Sturgeon collected by the 2.4-m Siamese net (n=6) ranged from 77 to 204 mm (mean=125; median=98.5) whereas those collected by the 4.9-m SRT net (n=35) ranged from 73 to 344 mm (mean=231; median=239; Figure 3). Juvenile Green Sturgeon captured by the 2.4-m Siamese net weighed between 4 and 36 grams (mean=14; median=5). Juvenile Green Sturgeon captured by the 4.9-m SRT net weighed between 2 and 153 grams (mean=68; median=71). A polynomial growth curve was fitted to the total length

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and weight measurements for the juvenile Green Sturgeon captured by both nets resulting in a strong relationship between the two variables (r2=0.98, df=40, P=<0.001; Figure 4). Sacramento River flows ranged from 169 to 211 m3s-1 (mean=200 m3s-1) during the sample period. Sacramento River temperatures were monitored at rkm 391, rkm 369, and rkm 351 within our 53.5-rkm sampling reach. Sacramento River temperatures remained the same between rkm 391 and 369, however, temperatures increased between rkm 369 and rkm 351. Temperatures at rkm 391 and rkm 369 ranged from 14 to 17.9°C (mean=15.9°C) whereas temperatures at rkm 351 ranged from 14.6 to 19.8 °C (mean=17.1°C). There was a 1.2°C increase in mean daily temperatures between rkm 392 and rkm 351 between July 21 and October 27. Daily turbidity values derived from surface grab samples ranged from 1.7 to 4.4 NTUs (Table 7).

Discussion

Active versus passive gear.—Two passive (hoop and gill nets) and one active (benthic trawl) gear types were used in 2014 and 2015 to determine a feasible method for collecting juvenile Green Sturgeon. Of the three different gear types tested during late-summer and fall periods, active sampling using a benthic trawl was the one gear type that collected juvenile Green Sturgeon (n=41). Considering the limited amount of information known about this species during the juvenile life stage, we believe the active nature of the trawling gear allowed us to sample for sturgeon utilizing their rearing habitat. Passive gear types seem better suited for sampling sturgeon during downstream migration periods. Although the passive gear types (gill and hoop nets) were sampled within the same reach of river as the one active gear type, they did not capture any juvenile sturgeon. Gill nets have been an effective means for capturing other juvenile sturgeon species including White Sturgeon (Glova et al. 2008-2010), Lake Sturgeon (Barth et al. 2011; Haxton 2011) and Gulf Sturgeon (Sulak and Clugston 1998). In our study, gill nets were not sampled within the same mesohabitats where juvenile Green Sturgeon were collected with the benthic trawl; primarily due to high water velocities and depths. Additionally, loading of gill nets with aquatic vegetation reduced the amount of time nets could sample and their overall effectiveness. Initial efforts quickly determined that sampling areas of high water velocity, when feasible to sample, would have negative impacts in terms of capture and incidental mortality to a variety of ESA-listed salmonids present in the area. Gill nets may remain a viable option and have proven somewhat successful in the Sacramento-San Joaquin Delta by other researchers for juvenile Green and White Sturgeon (M. Thomas, UCD, personal communication). Future sampling efforts may occur in areas that aren’t conducive to sampling with a benthic trawl, but would need to be monitored closely to prevent excessive impacts to Federal ESA-listed species. Of the 23 different fish species collected using a benthic trawl, 3 of those species were listed as Threatened or Endangered under the ESA (Table 5). Impacts to listed species was low with one juvenile winter Chinook and two juvenile Green Sturgeon captures observed as direct mortalities during our sampling efforts.

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Sample period comparison.—Catch rates using the benthic trawl were substantially lower during daytime hours as compared to nighttime (Table 9). Standardized CPUE varied slightly between early night and late night sampling at 0.023 and 0.026 fish/WNM, respectively (Table 9). Fall sampling occurred during the early night sample period with a similar resultant CPUE of 0.021 fish/WNM. We determined that the most productive sampling effort for juvenile Green Sturgeon in the freshwater river environment occurred during the early and late night periods (Table 9); similar to prior larval sampling efforts (Poytress et al. 2011). Direct observations in laboratory studies indicated that larval sturgeon become more active during night time hours (Van Eenennaam et al. 2001; Kynard et al. 2005). Poytress et al. (2011) sampling with a benthic D-net (passive gear type) found that larval catch increased after nightfall, peaking around midnight as diurnal temperatures began to descend from daily peak values. Sampling for juvenile sturgeon on the Missouri River using a benthic trawl occurs during daylight hours with high levels of success. However, water clarity is much different between the two river systems. Secchi disk readings on the Missouri River were <0.5 m compared to the Sacramento River where readings typically exceed 3 meters (Herzhog 2004; D. Killam, California Department of Fish and Wildlife, personal communication). Water clarity and associated increased net avoidance are a possible reason for different catch rates during day and night time hours. Field crewmembers noted a change in fish abundance and diversity between tows that were conducted before and immediately after sunset. Three juvenile sturgeons were collected during daylight hours, however at least one piece of large cobble was also found within the trawl. The water clarity on the Sacramento River may require these juvenile fish to hide under larger substrate to avoid predation during daylight hours. Shortly after nightfall, as their activity level increases likely due to foraging activity, they may become more susceptible to the trawl as they move away from the larger substrate that is typically avoided during trawling operations. This hypothesis is consistent with laboratory observations indicating that Green Sturgeon are voracious nocturnal feeders and hid in rocks during the day (Kynard et al. 2005). Trawl net comparison.— From the sampling efforts in 2014 and 2015, multiple samples were collected in the same locations switching between the 2.4-m Siamese and 4.9-m SRT nets on consecutive tows. Debris, substrate, and size of all fish species entrained varied between net types. Typically, the 2.4-m Siamese net collected more aquatic debris, contained finer substrates and more fish <50 mm in FL. The 4.9-m SRT net collected larger substrates and more fish >200 mm in FL (Figure 2). Our results mirrored that of Phelps et al. (2009) who compared catch rates between comparably designed benthic trawls. At least two theories exist about the differences in catch observed between the two trawl nets. One is that larger fish have increased abilities to avoid the smaller 2.4-m Siamese trawl compared to the larger mouth 4.9-m SRT trawl. The second theory relates to the difference in mesh size between the two trawls. The 2.4-m Siamese trawl has 3.2-mm mesh whereas the 4.9-m SRT trawl has 15.9-mm mesh allowing small fish to escape. Both theories likely have relevance.

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Juvenile Green Sturgeon caught by the 2.4-m Siamese and 4.9-m SRT trawl nets during the 2015 sampling period had mean total lengths of 125 and 231 mm, respectively. Comparisons between the two gear types is problematic because of the relatively small sample sizes available for comparison (n = 6 & n=35) and differing temporal distribution of sampling effort between the two nets. In 2015, sampling effort prior to August 20 was distributed equally between the two trawls and juvenile sturgeons of similar lengths were being collected using both trawls (Figure 3). After August 20, 2015, sampling effort favored the 4.9-m SRT net (1,125 WNM) over the 2.4-m Siamese net (20 WNM) due to the 4.9-m SRT net’s larger trawling area and ease of retrieval due to the larger mesh which filtered out fine sediments and debris. The limited effort (i.e., 3 tows) with the 2.4-m Siamese trawl reduced our opportunities to collect juvenile sturgeon of a larger relative size later in the season. This assumption is based on the idea that as fish growth occurs over time, the size of the fish in the population and, thus, the fish catch by the trawl, could be larger. Water temperature effects on habitat selection.—Exogenous feeding age-0 Green Sturgeon larvae initially disperse from egg incubation and hatching areas at approximately 18-25 days post hatch in search of food and rearing habitat (Kynard et al. 2005; Poytress et al. 2012). Food resources, as well as temperatures, can affect the distribution of fish through available habitats (Jobling 1981; Hurst and Conover 2002). Water temperature in the upper Sacramento River is managed by the USBR for the purposes of protecting winter-run Chinook Salmon spawning and rearing habitat annually from ~May 15 - October 31 (NMFS 2009). From WY 2000-2012 mean daily river temperatures at the Red Bluff Diversion Dam (rkm 391) ranged between 12.8 and 14.8°C during the water temperature management period. Several years of low precipitation (i.e., drought conditions) within the Sacramento Valley resulted in lower than average amounts of cold water storage within Shasta Reservoir between 2013 and 2015. As a result, mean daily water temperatures at rkm 391 averaged 16.6°C during the same period in 2014 and 2015 (Figure 5). Maximum daily temperatures reached 18.1 and 18.7°C in 2014 and 2015, respectively (Figure 5), which fell within the optimal bioenergetics performance range of 15-19°C (Mayfield and Cech 2004) as determined in the laboratory for age-0 Green Sturgeon. A long term monitoring rotary trapping project at the RBDD collects significant numbers of larval sturgeon, yet prior to 2014 only three juvenile sturgeon >100 mm had been collected. In contrast, 3 and 18 juvenile Green Sturgeon >100 mm TL were collected at this sample site in 2014 and 2015, respectively (USFWS, unpublished data). The increased catch of juvenile sturgeon by the rotary traps during 2014 and 2015 could indicate that water temperatures between 14-18 °C may be preferred by juvenile sturgeon for rearing habitat (Table 7). Comparison of catch and growth rates from years when water temperature management for salmon are more effective may elucidate this assumption.

Conclusions and Future Recommendations

Prior to this study, captures of juvenile sturgeon of either species have been incidental and anecdotal using standard salmonid monitoring techniques widely employed within the Central Valley. The primary objective of this study was to identify a feasible method for

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collecting age-0 juvenile Green Sturgeon. Determining a cost effective, suitable technique that would result in little to no impact on ESA-listed as Threatened SDPS Green Sturgeon was a secondary objective. The use of an active gear type, the benthic trawl towed for short durations, was found to be feasible for simple capture and low impact to Green Sturgeon in the upper Sacramento River. Future sampling efforts should continue to use a benthic trawl in areas where juvenile Green Sturgeon were collected in 2015 to test which physical variables or biological variables are associated with in-river rearing habitat. The third objective of determining if fish captured by a given gear type were of suitable size for acoustic tag implantation was also met. For future years study, juvenile Green Sturgeon sampled in good physical condition >150 mm in total length (Figure 4) could be tagged and tracked using micro-acoustic tag implantation techniques, assuming a 2% tag burden (Winter 1996). The use of this technology on Green Sturgeon could help determine the extent of juvenile rearing areas, identify habitat preferences and downstream migration cues and timing. In the event juvenile sturgeons are not collected in future efforts in habitats that were occupied in 2015, sampling should focus on areas where river temperatures are between 15-19 °C as noted by Mayfield and Cech (2004), which typically exist downstream of the 2015 sample areas when temperature and flow targets are met for winter-run Chinook salmon.

Acknowledgements

This project was funded by the Anadromous Fish Restoration Program under the authority of the Central Valley Project Improvement Act (P.L. 102-575). Numerous individuals helped with literature reviews, gear testing, and project development including (but not limited to) Samantha Adams, Casey Collins, Robert Larson, Scott Voss, and Travis Webster. Special thanks to the Columbia Fish and Wildlife Office and Innovative Net Systems for gear consultation and construction. Tricia Parker-Hamelberg, Jim Smith, and Valerie Emge provided programmatic support within AFRP and RBFWO. Thank you to Zac Jackson and others for providing critical reviews of earlier drafts of this document.

10

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Brown, K. 2007. Evidence of spawning by Green Sturgeon, Acipenser medirostris, in the upper

Sacramento River, California. Environmental Biology of Fishes 79:297-303. Crossman, J.A., K.T Scribner, C.A. Davis, P.S. Forsythe and E.A. Baker. 2014. Survival and

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Gaines, P.D. and C.D. Martin. 2002. Abundance and seasonal, spatial and diel distribution

patterns of juvenile salmonids passing the Red Bluff Diversion Dam, Sacramento River. Red Bluff Research Pumping Plant Report Series, Volume 14, U.S. Fish and Wildlife Service, Red Bluff, CA.

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Sturgeon habitat use in the Lower Fraser River, 2007-2008. Prepared for the Fraser River Sturgeon Conservation Society, Vancouver, BC. May 2008.

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Sturgeon abundance and habitat use in the lower gravel reach of the Lower Fraser River, 2009-2010. Prepared for the Fraser River Sturgeon Conservation Society. September 2010.

Hallock, R.J., W.F. Van Woert, and L. Shapolov. 1961. An evaluation of stocking hatchery-

reared Steelhead Rainbow Trout (Salmo gairdnerii gairdnerii) in the Sacramento River System. California Department of Fish and Game. Fish Bulletin 114. 74 p.

Haxton, T. 2011. Depth selectivity and spatial distribution of juvenile Lake Sturgeon in a large,

fragmented river. Journal of Applied Ichthology 27:45-52. Herzog, D. P. 2004. Capture efficiency and habitat use of Sturgeon Chub (Macrhybopsis gelida)

and Sicklefin Chub (Macrhybopsis meeki) in the Mississippi River. Master’s thesis. Southeast Missouri State University, Cape Girardeau.

11

Herzog, D.P, V.A. Barko, J.S Scheibe, R.A. Hrabik and D.E. Ostendorf. 2005. Efficacy of a benthic

trawl for sampling small-bodied fishes in large river systems, North American Journal of Fisheries Management 25:2, 594-603.

Hurst, T.P., and D.O. Conover. 2002. Effects of temperature and salinity on survival of young-

of-the year Hudson River striped bass (Morone saxatilis) implications for optimal overwintering habitats. Canadian Journal of Fisheries and Aquatic Sciences 59:787–795.

Jobling, M. 1981. Temperature tolerance and the final preferendum – rapid methods for the

assessment of optimum growth temperatures. Journal of Fish Biology 19:439–455. Kynard, B., E. Parker, and T. Parker. 2005. Behavior of early Life intervals of Klamath River

Green Sturgeon, Acipenser medirostris, with a note on body color. Environmental Biology of Fishes 72:85-97.

Kohlhorst, D.W. 1976. Sturgeon spawning in the Sacramento River in 1973, as determined by

distribution of larvae. California Department of Fish and Game 62:32–40. Mayfield, R.B., and J.J Cech. 2004. Temperature effects on green sturgeon bioenergetics.

Transactions of the American Fisheries Society 133:961–970. Moffett, J.W. 1949. The first four years of King Salmon Maintenance below Shasta Dam,

Sacramento River, California. California Department of Fish and Game 35(2): 77-102. NMFS (National Marine Fisheries Service). 2009. Biological opinion on the long-term central

valley project and state water project operations criteria and plan. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southwest Fisheries Service Center, Long Beach, California.

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Parsley, M.J., L.G. Beckman, and G. T. McCabe Jr. 1993 Spawning and Rearing Habitat Use by

White Sturgeons in the Columbia River Downstream from McNary Dam. Transactions of the American Fisheries Society 122:217-227.

Phelps, Q.E., D.P Herzog, R.C. Brooks, V.A. Barko, D.E. Ostendorf, J.W. Ridings, S.J. Tripp, R.E.

Colombo, J.E. Garvey and R.A. Hrabik. 2009. Seasonal comparison of catch rates and size structure using three gear types to sample sturgeon in the middle Mississippi River. North American Journal of Fisheries Management 29:5, 1487-1495.

Poytress, W.R., J.J. Gruber, D.A. Trachtenbarg, and J.P. Van Eenennaam. 2009. 2008 Upper

Sacramento River Green Sturgeon spawning habitat and larval migration surveys.

12

Annual Report of U.S. Fish and Wildlife Service to US Bureau of Reclamation, Red Bluff, CA.

Poytress, W.R., J.J. Gruber, and J.P. Van Eenennaam. 2010. 2009 Upper Sacramento River

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Green Sturgeon spawning habitat and larval migration surveys. Annual Report of U.S. Fish and Wildlife Service to U.S. Bureau of Reclamation, Red Bluff, CA.

Poytress, W.R., J.J. Gruber, and J.P. Van Eenennaam. 2012. 2011 Upper Sacramento River

Green Sturgeon spawning habitat and larval migration surveys. Annual Report of U.S. Fish and Wildlife Service to U.S. Bureau of Reclamation, Red Bluff, CA.

Poytress, W.R., J.J. Gruber, C.E. Praetorius, and J.P. Van Eenennaam. 2013. 2012 Upper

Sacramento River Green Sturgeon spawning habitat and young-of-the year migration surveys. Annual Report of U.S. Fish and Wildlife Service to U.S. Bureau of Reclamation, Red Bluff, CA.

Poytress, W.R., J.J. Gruber, F.D. Carrillo and S.D. Voss. 2014. Compendium report of Red Bluff

Diversion Dam rotary trap juvenile anadromous fish production indices for years 2002-2012. Report of U.S. Fish and Wildlife Service to California Department of Fish and Wildlife and U.S. Bureau of Reclamation.

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distribution of spawning events and spawning habitat characteristics of Sacramento River Green Sturgeon. Transactions of the American Fisheries Society 144:6, 1129-1142.

Steffensen, K.D, J.J. Wilhelm, J.D. Haas and J.D Adams. 2015 Conditional capture probability of

Pallid Sturgeon in benthic trawls. North American Journal of Fisheries Management, 35:4, 626-631.

Sulak, K.J., and J.P. Clugston. 1998. Early life-history stages of Gulf Sturgeon in the Suwannee

River, Florida. Transactions of the American Fisheries Society 127:758–771. Van Eenennaam J.P., M.A.H. Webb, X. Deng, S.I. Doroshov, R.B. Mayfield, J.J Cech Jr, D.C.

Hillemeier and T.E. Wilson. 2001. Artificial spawning and larval rearing of Klamath River Green Sturgeon. Transactions of the American Fisheries Society 130:159-165.

Winter, J. 1996. Advances in underwater biotelemetry. Pages 555–585 in B.R. Murphy and

D.W. Willis, editors. Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.

13

Tables

14

Table 1. Gear specifications for (a) hoop and (b) gill nets used during the 2014 and 2015 juvenile Green Sturgeon capture feasibility study on the Sacramento River, California.

Hoops (#) Mesh (cm) Length (m) Hoop (cm)

3 5.1 2.1 76.2 3 3.8 2.1 76.2 3 2.5 2.1 76.2

4 1.3 1.8 61

Material Mesh (cm) Length (m) Height (cm)

Multifilament 3.8 11.0 90 3.8 15.5 90

2.5, 3.2, 3.8 15.5 90

Monofilament 3.8 11.0 90

3.8 15.5 90

2.5, 3.2, 3.8 15.5 90

(a)

(b)

15

Table 2. Summary of (a) hoop and (b) gill net sampling effort in wetted net minutes (WNM) by site during 2014 on the Sacramento River, California. Hoop Net Mesh Size (cm) Total

(WNM)

Catch

CPUE Site 1.3 2.5 3.8 5.1 rkm 391 - 13,198 19,260 4,844 37,302 0 0.000 rkm 389 - 5,174 - 4,266 9,440 0 0.000 rkm 382 1,305 - - - 1,305 0 0.000 rkm 373.5 1,294 - - - 1,294 0 0.000 Total (WNM) 2,599 18,372 19,260 9,110 49,341 0 0.000

Gill Net Mesh Size (cm) Total (WNM)

Catch

CPUE Site 3.8 Experimental

rkm 389 820 913 1,733 0 0.000 rkm 382 10 153 163 0 0.000 rkm 373.5 1,202 1,202 2,404 0 0.000 Total (WNM) 2,036 2,268 4,300 0 0.000

(a)

(b)

16

Table 3. Fish species capture by hoop and gill nets during juvenile Green Sturgeon capture feasibility study on the Sacramento River, California during 2014 and 2015.

2014

2015

Hoop

Gill

Gill

Common Name Scientific Name Alive Mort

Alive Mort

Alive Mort Hardhead Mylopharodon conocephalus - -

5 -

- -

Prickly Sculpin Cottus asper 1 -

- -

- - Steelhead/Trout Oncorhynchus mykiss - -

2 1

1 -

Sacramento Squawfish Ptychocheilus grandis 3 -

6 1

1 - Sacramento Sucker Catostomus occidentalis - -

2 -

3 -

Sacramento Splittail Pogonichthys macrolepidotus - -

- -

2 - Striped Bass Morone saxatillis - -

- -

3 1

Tule Perch Hysterocarpus traskii 2 -

- -

3 - Total 6 -

15 2

13 1

17

Table 4. Summary of 2014 juvenile Green Sturgeon trawling effort on the Sacramento River, California. Summary effort by site sampled, wetted net minutes (WNM), catch of juvenile Green Sturgeon, and relative abundance as catch per unit of effort (CPUE) expressed in Green Sturgeon per WNM.

2.4-m Siamese

4.9-m SRT

Site Start Date End Date Trawls WNM Catch CPUE

Start Date End Date Trawls WNM Catch CPUE rkm 426 9/11/2014 9/11/2014 7 61 0 0.000

- - - - - -

rkm 416 10/9/2014 10/9/2014 9 51 0 0.000

9/24/2014 9/24/2014 3 49 0 0.000 rkm 406 9/15/2014 9/15/2014 1 * 0 0.000

- - - - - -

rkm 400 9/15/2014 10/8/2014 16 128 0 0.000

10/22/2014 10/22/2014 12 65 0 0.000 rkm 389 9/15/2014 10/10/2014 6 23 0 0.000

- - - -

rkm 366.5 9/10/2014 9/10/2014 5 9 0 0.000

- - - - - - rkm 354 9/17/2014 9/17/2014 2 17 0 0.000

- - - - - -

rkm 322 9/17/2014 10/15/2014 11 60 0 0.000

10/23/2014 10/23/2014 10 48 0 0.000 rkm 272 9/18/2014 9/18/2014 2 16 0 0.000

10/16/2014 10/16/2014 8 37 0 0.000

Total 59 365 0 0.000 Total 33 199 0 0.000 * – sample times not recorded.

18

Table 5. Fish species captured by 2.4-m Siamese and 4.9-m SRT trawl during juvenile Green Sturgeon capture feasibility study on the Sacramento River, California. 2014 2015

Common Name Scientific Name Native ESA Status Alive Mort

Alive Mort Bluegill Lepomis macrochirus Non-native - 8 -

- -

Channel Catfish Ictalurus punctatus Non-native - 2 -

- - Winter Chinook Oncorhynchus tshawytscha Native Endangered 4 -

3 1

Fall Chinook Oncorhynchus tshawytscha Native - 1 -

4 1 Late Fall Chinook Oncorhynchus tshawytscha Native - 9 3

1 -

Cottus Fry -a Native - - -

82 3 Cyprinidae Fry -a Native - - 1

- -

Speckled Dace Rhinichthys osculus Native - - -

13 2 Green Sunfish Lepomis cyanellus Non-native - - -

1

Green Sturgeon Acipenser medirostris Native Threatened - -

39 2 Lamprey Fry -a Native - 2 -

4 -

Bigscale LogPerch Percina macrolepida Non-native - 1 -

2 - Prickly Sculpin Cottus asper Native - 35 -

- -

Steelhead/Trout Oncorhynchus mykiss Native Threatened 5 -

- - Redear Sunfish Lepomis microlophus Non-native - 3 -

- -

Riffle Sculpin Cottus gulosus Native - 10 3

56 - Sacramento Squawfish Ptychocheilus grandis Native - - -

12 -

Sacramento Sucker Catostomus occidentalis Native - 43 1

880 26 Sacramento Splittail Pogonichthys macrolepidotus Native - - -

3 -

Striped Bass Morone saxatillis Non-native - 1 -

2 - Tule Perch Hysterocarpus traskii Native - 53 -

217 5

Threespine Stickleback Gasterosteus aculeatus Native - 26 1

4 - White Catfish Ameiurus catus Non-native - - -

1 -

Total 203 9

1,324 40 a – multiple genus and/or species possible.

19

Table 6. Summary of sampling effort in wetted net minutes (WNM) for gill nets during 2015 on the Sacramento River, California. Catch per unit effort (CPUE) expressed in Green Sturgeon per WNM. Gill Net Effort by Mesh Size (WNM)

Total Catch CPUE Site 3.8 (cm) Experimental rkm 352 1,352 221 1,573 0 0.000 rkm 320.6 1,902 504 2,406 0 0.000 rkm 272 919 728 1,647 0 0.000

Total 4,173 1,453 5,626 0 0.000

20

Table 7. Environmental data for each sampling gear type. Values in parentheses () indicate values associated with juvenile Green Sturgeon captures.

Flow (m3s-1) Temperature (°C) Turbidity (NTU)

Year Gear Site Sample Dates Range Mean Range Mean Range Mean

2014 Hoop rkm 391-373.5 Aug 12-Oct 3 154-251 (-) 214 (-) 15.7-17.6 (-) 16.6 (-) - -

Gill rkm 390-373.5 Sept 8-Oct 11 147-186 (-) 163 (-) 16.3-18.4 (-) 17.4 (-) - -

Trawl rkm 426-272 Sept 10-Oct 23 124-179 (-) 148 (-) 15.6-19.4 (-) 17.7 (-) - -

2015 Gill rkm 352-272 June 10-June 25 140-213 (-) 160 (-) 19.6-23.8 (-) 21.5 (-) 2.4-4.9 (-) 3.6 (-)

Trawl rkm 405.5-352 July 21-Oct 29 169-211 (169-211) 200 (201) 14.0-18.3 (14.0-17.9) 16.3 (16.0) 1.7-4.4 (1.7-4.4) 2.2 (2.4)

21

Table 8. Summary of 2015 juvenile Green Sturgeon trawling effort on the Sacramento River, California. Summary effort by site sampled, wetted net minutes (WNM), total number of juvenile Green Sturgeon sampled, and relative abundance as catch per unit of effort (CPUE) expressed in Green Sturgeon per WNM.

2.4-m Siamese

4.9-m SRT

Site Start Date End Date Trawls WNM Catch CPUE

Start Date End Date Trawls WNM Catch CPUE rkm 405.5 7/29/2015 7/29/2015 3 18 0 0.000

- - - - - -

rkm 400 7/21/2015 8/18/2015 18 120 0 0.000

7/29/2015 9/14/2015 24 135 2 0.015 rkm 394.5 7/21/2015 8/19/2015 18 161 3 0.019

7/29/2015 10/29/2015 44 359 13 0.036

rkm 393 8/19/2015 8/19/2015 9 63 0 0.000

8/20/2015 8/20/2015 1 13 0 0.000 rkm 390 - - - - - -

8/6/2015 10/13/2015 14 127 10 0.079

rkm 389 7/22/2015 7/22/2015 1 8 0 0.000

8/20/2015 10/30/2015 35 288 5 0.017 rkm 388 7/22/2015 7/30/2015 10 66 2 0.030

7/23/2015 10/15/2015 32 202 2 0.010

rkm 386 7/22/2015 9/16/2015 12 88 1 0.011

7/23/2015 9/3/2015 17 129 0 0.000 rkm 384 - - - - - -

9/3/2015 9/3/2015 3 13 0 0.000

rkm 380 7/30/2015 7/30/2015 4 22 0 0.000

8/27/2015 10/28/2015 17 126 2 0.016 rkm 377 7/23/2015 7/30/2015 8 25 0 0.000

7/30/2015 10/28/2015 13 59 0 0.000

rkm 373 7/23/2015 7/23/2015 2 8 0 0.000

7/31/2015 7/31/2015 4 16 0 0.000 rkm 370 - - - - - -

7/31/2015 10/28/2015 18 108 1 0.009

rkm 369 - - - - - -

9/24/2015 9/24/2015 2 20 0 0.000 rkm 368 - - - - - -

9/23/2015 9/23/2015 3 27 0 0.000

rkm 366.5 - - - - - -

9/23/2015 9/24/2015 3 8 0 0.000 rkm 352 - - - - - -

10/15/2015 10/15/2015 6 23 0 0.000

Total 85 579 6 0.010

Total 236 1,653 35 0.021

22

Table 9. Summary of 2.4-m Siamese and 4.9-m SRT trawling effort in wetted net minutes (WNM) during evaluation (July 21–September 4, 2015) and fall sampling period (September 14–October 27, 2015). Data includes juvenile Green Sturgeon catch with relative abundance in Green Sturgeon per WNM (CPUE) summarized by net type and strata.

Evaluation Period

Fall Sampling 2.4-m Siamese 4.9-m SRT Both Nets

Both Nets

Strata WNM Catch CPUE WNM Catch CPUE WNM Catch CPUE

WNM Catch CPUE

Daytime (0800 - 1400) 362 2 0.006 190 1 0.005 552 3 0.005

- - -

Early Night (2000 - 0200) 180 4 0.022 352 8 0.023 532 12 0.023

646 13 0.021

Late Night (2400 - 0600) 17 0 0.000 485 13 0.027 502 13 0.026

- - -

Total 559 6 0.011 1,027 22 0.021 1,586 28 0.018

646 13 0.021

23

Figures

24

Figure 1. Map of juvenile Green Sturgeon capture feasibility study area on the Sacramento River, California.

25

Figure 2. Length frequency distribution of all fish species collected in 2.4-m Siamese and 4.9-m SRT trawls during 2014 and 2015 sampling.

26

Figure 3. Date and total length of juvenile Green Sturgeon collected in 2.4-m Siamese (black square) and 4.9-m SRT (red triangle) trawl during 2015.

27

Figure 4. Weight and length relationship(s) developed from juvenile Green Sturgeon captured using benthic trawls in 2015 on the Sacramento River, California.

Weight (g)

0 20 40 60 80 100 120 140 160 180

Tota

l Len

gth

(mm

)

0

100

200

300

400

TL (mm) = 87.55 + (3.18 * Wt (g)) - (0.01 * Wt (g)2)

R2 = 0.98; df= 40; P < 0.001

Total Length (mm)

0 100 200 300 4000

20

40

60

80

100

120

140

160

180

Wei

ght (

g)

Weight (g) = 19.356 - (0.374 * TL (mm)) + (0.002 * TL (mm)2)

R2 = 0.98; df= 40; P < 0.001

28

Figure 5. Mean daily water temperatures observed at the Red Bluff Diversion Dam from 2000-2012 (historic average), 2014, and 2015. Vertical bars represent the estimated larval to juvenile rearing period for Green Sturgeon.