179 
NOAA 
National Marine 
Fisheries Service 
Abstract— Recent acoustic tagging of 
juvenile Chinook salmon ( Oncorhyn - 
chus tshawytscha ) in the southern 
portion of California’s Sacramen- 
to-San Joaquin Delta has revealed 
extremely low survival rates (<1%), 
possibly due to predation by piscivo- 
rous fishes. We evaluated predation 
as a cause of low survival by design- 
ing and testing freely floating GPS- 
enabled predation-event recorders 
(PERs) baited with juvenile Chinook 
salmon. We estimated predation 
rates and identified predation loca- 
tions within a 1-kilometer reach of 
the Lower San Joaquin River. We 
modeled the relationship between 
time to predation and environmen- 
tal variables with a Cox proportional 
hazards analysis that accounts for 
censored data. Our results indicated 
that an increase of 1 m/s in water 
velocity elevated the minute-by-min- 
ute hazard of predation by a factor 
of 9.6. Similarly, each increase in 
median depth decreased the preda- 
tion hazard by a factor of 0.5. The 
mean relative predation rate in the 
study area was 15.3% over 9 sam- 
pling events between March and 
May 2014. Waterproof video cameras 
attached to a subset (48 of 216) of 
PERs successfully identified preda- 
tor species 25% of the time. Our 
GPS-enabled PERs proved to be an 
inexpensive and reliable tool, which 
quantified predation, identified pre- 
dation locations, and provided com- 
plementary information for acoustic 
telemetry and predator diet studies. 
Manuscript submitted 9 July 2015. 
Manuscript accepted 3 February 2016. 
Fish. Bull. 114:179-185 (2016). 
Online publication date: 23 February 2016. 
doi: 10.7755/FB.114.2.5 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
fr established 1881 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Development of underwater recorders to 
quantify predation of juvenile Chinook 
salmon ( Oncorhynchus tshawytscha ) in a 
river environment 
Nicholas J. Demetras (contact author ) 1 
David D. Huff 2 
Cyril J. Michel 1 
Joseph M. Smith 3 
George R. Cutter 4 
Sean A. Hayes 5 
Steven T. Lindiey 5 
Email address for contact author: nicholas.demetras@noaa.gov 
1 University of California, Santa Cruz 
Affiliated with Southwest Fisheries Science 
Center 
National Marine Fisheries Service, NOAA 
1 10 Shaffer Road 
Santa Cruz, California 95060 
2 Point Adams Research Station 
Fish Ecology Division 
Northwest Fisheries Science Center, NOAA 
PO Box 155, Hammond, OR 97121 
3 School of Aquatic and Fishery Sciences 
University of Washington 
1 122 NE Boat Street 
Seattle, Washington 98105 
4 Fisheries Resource Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
8901 La Jolla Shores Drive 
La Jolla, California 92037-1508 
5 Fisheries Ecology Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
1 10 Shaffer Road 
Santa Cruz, California 95060 
Predation on juvenile Chinook salm- 
on (Oncorhynchus tshawytscha ) and 
other native fishes within Califor- 
nia’s Sacramento-San Joaquin Delta 
has raised considerable debate over 
the last several decades (Bennet and 
Moyle, 1996; Mount et al., 2012). Tra- 
ditionally, juvenile Chinook salmon 
survival within this delta has been 
estimated by using acoustic tagging 
data or coded-wire tag recoveries 
from mid-water trawls (Brandes and 
McLain, 2001; Newman and Rice, 
2002; Buchanan et al., 2013; Michel 
et al., 2013; Pyper et al., 2013; New- 
man, 2003; Newman 1 ). It is currently 
1 Newman, K. B. 2008. An evaluation of 
the four Sacramento-San Joaquin River 
Delta juvenile salmon survival studies, 
not clear what proportion of juvenile 
salmonid mortality may be directly 
attributed to fish predation. It is also 
difficult to interpret results regard- 
ing population-level survivorship in 
the Delta because these data have 
limited spatial scales, used various 
tagging methodologies, and do not 
clearly connect tag loss or mortality 
to predation (Grossman et al. 2 ). Be- 
181 p. U.S. Fish Wildl. Serv., Stockton, 
CA. [Available at website, accessed Oc- 
tober 2014.1 
2 Grossman, G. D., T. Essington, B. John- 
son, J. Miller, N. E. Monsen, and T. N. 
Pearsons. 2013. Effects of fish preda- 
tion on salmonids in the Sacramento 
River-San Joaquin Delta and associated 
ecosystems, 71 p. [Available at website, 
accessed October 2014.] 
