DOI: 10.5061/dryad.h70rxwdjn
title: Coldwater fish in a warm water world: implications for predation of salmon smolts during estuary transit

description: Predator-prey systems face intensifying pressure from human exploitation
 and a warming climate with implications for where and how natural resource
 management can successfully intervene. We hypothesized young salmon
 migrating to the Pacific Ocean face a seasonally intensifying predator
 gauntlet when warming water temperature intensifies a multiple predator
 effect (MPE) from Striped Bass Morone saxatilis, and Largemouth Bass
 Micropterus salmoides. We evaluated this hypothesis using data synthesis
 and simulation modeling. 2. Contemporary studies based on
 acoustically-tagged fish reaffirmed older observations that Chinook Salmon
 smolts must transit the Delta before water temperature reaches 20°C or
 mortality will be nearly 100%. Striped Bass attack rates on tethered
 smolts were insensitive to distance from shore and water temperature
 whereas Largemouth Bass attack rates were highest near shorelines in warm
 water, supporting the temporal aspect of the hypothesis. Whether the
 combined effects of the two predators produces an MPE remains unconfirmed
 due to limitations on quantifying salmon behavior. 4. We used multiple
 simulation models to try to reconstruct the empirical relationship between
 smolt survival and water temperature. Simulations reinforced attack rate
 results, but could not recreate the temperature dependence in smolt
 survival except at higher than observed temperatures. We propose three
 hypotheses for why and recommend discerning among them should be a focus
 of research. 5. We found significant linear relationships between monthly
 mean inflow to the Delta from each of its two largest tributaries and
 monthly mean water temperatures along associated salmon migration routes,
 but these relationships can be nonlinear, with most of the correlation
 occurring at low inflows when water temperature is largely controlled by
 air temperature and day length. As the global climate warms, changed
 circumstances in predator-prey relationships may present important
 challenges when managing species vulnerable to extinction in addition to
 presently more abundant species. --
description: This data set is a mixture of Microsoft Excel files where data
 were compiled and then coverted into .csv files that were analyzed in the
 R environment and simulation model code in R that generates its own data
 and does not require an external data source. The field data come from
 various websites and previously published studies of Chinook salmon smolt
 survival in California's Sacramento-San Joaquin Delta.
 Each Excel file has an associated ReadMe included as the first
 tab in the workbook. The ReadMe files for the .csv's derived from the
 Excel files are in an Excel file called CSV_ReadMe.xlsx. The ReadMe's
 for the R scripts are included as #comments interspersed with the active
 code. Raw flow data for the Sacramento-San Joaquin
 Delta can be downloaded
 here: https://data.cnra.ca.gov/dataset/dayflow Raw
 temperature used in our study can be extracted from the 20-mm Survey and
 Spring Kodiak Trawl Survey databases housed
 here: https://iep.ca.gov/Data/IEP-Survey-Data We
 apologize but the second link above does not match what is in the paper.
 These fish survey data were migrated to the link above while our
 manuscript was in press and we did not notice the update until after we
 had finalized the page proofs.
description: The excel files should guide the user through them sufficiently
 well for others to reproduce the analyses that come from them. The R code
 creates some of its own data. In other places, a user is pointed to
 particular associated .csv files.