Reproductive Ecology and Body Burden of Resident ... - The Love Lab

sider the ecology of species of interest that utilize the platform including the degree of connectivity between
platform and natural habitat. Juvenile fish recruiting to a platform may utilize the platform for a period
of time and emigrate to other habitat or remain at the platform throughout adult life. Adults may migrate
between platforms and natural areas. A “platform fingerprint,” an otolith microchemical marker, ultimately
can be used to estimate the degree to which adult fish or juvenile fish that have used platforms as nursery
habitat migrate to local and perhaps regional populations in natural areas off California. This goal of this
study is to determine whether fishes, residing in the mid-water habitat or bottom habitat of platforms, possess
unique otolith microchemical signatures—platform fingerprints.
The specific objectives of this study were:
1. To determine if otolith microchemistry can be used to distinguish fishes that reside at platforms
from those that reside at natural habitat; and
2. To determine whether otolith chemistry is related to the water chemistry of the environment
where fishes reside.
Methods
Fish and seawater sample collection
Adult and subadult specimens of kelp rockfish (Sebastes atrovirens) and Pacific sanddab (Citharichthys
sordidus) were sampled from six platforms and twelve natural areas (Table 1). Both species reside at the
platforms and natural sites during all seasons and were sufficient in number to be selected for this study. We
collected kelp rockfish on the platform structure at midwater depths and in kelp forests of rocky reef habitat.
We collected the bottom-dwelling Pacific sanddab on soft sediment within 100m of the platforms and
at natural sites at least 3 km away from the platform. Given that circulation patterns in the Santa Barbara
Channel region are complex and different water masses with unique element composition are expected to
be distributed within the study region at any one time, we (1) selected platforms located in several different
water masses; (2) selected natural habitat sites that were outside of the sphere of influence of discharges
from platform operations; and (3) paired each platform and natural site within the same water mass to
partition variability due to the effect of natural water mass differences within pairs that might confound our
test for a platform effect on otolith elemental signatures (Figure 1, Table 1). Platforms and natural habitat
sites were located in six geographic areas that we designated: Point Conception (PTC), west Santa Barbara
(WSB), east Santa Barbara (ESB), east entrance of the Santa Barbara Channel (EEC), offshore east Channel
(OEC), and Southern California Bight south of the Channel (SCB).
Kelp rockfish were collected by spear using SCUBA at four platforms at midwater depths at six kelp
forest habitat sites (Table 1). Pacific sanddab were collected by hook and line at six platforms and six natural
habitat sites. At each collection site, fish were bagged together in a plastic bag and kept on ice for up to ten
hours. The fish were either processed in the laboratory on the collection day or the whole body samples
were frozen until they were thawed and processed several weeks later. We measured fish total length (TL)
and standard length (SL) to the nearest millimeter (mm), and weighed fish to the nearest gram (g). Sagittal
otoliths were extracted from 8-10 fish specimens per site, rinsed in DI water, and stored dry in a clean plastic
snap cap vial until the time of preparation for otolith microchemistry. The otoliths were measured along the
axis of the sulcus to the nearest 0.05 mm and weighed to the nearest 0.001 mg.
We collected seawater samples at the study sites to examine the relationship between otolith chemistry
and seawater chemistry. Seawater samples were collected at the time of sampling fish for the otolith microchemistry
analysis. Three seawater samples were collected near the depth fish were sampled from separate
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