| Description |
Description
Life history diversity buffers salmon populations over space (e.g. the use of natal and
non-natal rearing habitats and time (e.g. variable migration timing resulting in greater
probability of meeting optimal ocean conditions). Historically the Sacramento-San
Joaquin Delta provided critical salmon rearing habitat, but urban expansion, water
diversions and species introductions have resulted in inhospitable conditions unlikely to
meet rearing needs. This study fills critical data gaps regarding Delta rearing by juvenile
Chinook salmon – primarily to determine the annual migrant portfolio (proportion of
different populations and life stages) and the relative success of Delta vs. natal rearing
(inferred by rearing duration, growth rate, diet and condition). We quantify the extent to
which Delta rearing contributes to salmon population resiliency under different
environmental conditions, including drought (2014-15) and flood conditions (2017,
2019), and provide baseline data to provide insights into population-level responses to
future habitat restoration and climate change. The study uses annual collections of fall &
late fall run salmon samples from sites upstream (Mossdale/Sherwood Harbor), within,
and downstream (Chipps Island) of the Delta sampled by the IEP Delta Juvenile Fish
Monitoring Program (DJFMP).
Need
Annual monitoring surveys routinely sample salmon entering and leaving the Delta, but
the extent to which these juveniles rear there is virtually unknown, and has been
highlighted as a critical data gap for parameterizing the NMFS Chinook salmon life cycle
model (S. Lindley NOAA pers. comm.). There are limited tools available to monitor
habitat use by native fishes, with most efforts providing a snapshot of fish
presence/absence or abundance. Tagging studies provide key information about
migratory pathways and survival through stretches of the Delta, but are typically limited
to larger individuals and often use hatchery smolts with different rearing needs and seareadiness to the smaller individuals most likely to use Delta habitats. Otoliths represent
a unique tool to reconstruct fish age, natal origin, growth history, movement patterns,
and habitat use, even in fry <40mm fork length.
Objectives
We will use juvenile salmon collected by the IEP Delta Juvenile Fish Monitoring
Program to assess:
1. Contributions of different rivers & hatcheries to sites upstream, within &
downstream of the Delta.
2. Delta habitat use (frequency, duration) and success (growth rates, condition and
diet).
3. Mechanisms governing juvenile salmon outmigration timing from the natal
tributary. |
