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

Task 2: Otolith Elemental Signatures of Kelp Rockfish (Sebastes atrovirens)
and Pacific Sanddab (Citharichthys sordidus) from Offshore Oil Platforms
and Natural Areas in the Southern California Bight
Mary M. Nishimoto and Milton S. Love
Abstract
The goal of this study was to determine if fishes, residing in the mid-water habitat or bottom habitat
of platforms, possess unique otolith microchemical signatures. 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) determine whether otolith chemistry is related to the water chemistry
of the environment where fishes reside. We sampled 98 kelp rockfish and 108 Pacific sanddab collected
from six offshore oil platforms and 12 natural areas during 2005 and 2006 for microchemical analysis of
19 elements in otoliths. The otolith composition of kelp rockfish and Pacific sanddab differed between the
two habitat types—the sampled platforms and natural sites—and among geographic areas. Kelp rockfish
collected from platforms tended to incorporate higher concentrations of Mg and Ba and lower concentration
of Sr in otoliths compared to fish from natural habitat. In comparison, Pacific sanddab collected from
platforms tended to have lower concentrations of Ba and Fe in otoliths compared to fish from natural
habitat. Sr Ca -1 in otoliths of kelp rockfish tended to decrease eastward along the coastal shelf from Point
Conception through the east Channel. Mn Ca -1 in otoliths of sanddab from both habitat types was lower
in the three westernmost geographic areas (Point Conception, west Santa Barbara, and east Santa Barbara)
than in the eastern and southern areas (east channel entrance, offshore east channel, and Southern California
Bight). Mn Ca -1 was not detectable in kelp rockfish otoliths. The success rate of correctly assigning
fish to habitat type (platform or natural habitat) using a canonical discriminant function based on otolith
element signatures differed between species. Ninety-four percent of kelp rockfish individuals were correctly
assigned to habitat type based on the otolith signature of Mg Ca -1 , Ba Ca -1 , and Sr Ca -1 . A lower proportion,
64%, of Pacific sanddab correctly grouped into habitat type based on the otolith signature of Mg Ca -1 , Sr Ca -
1
, Mn Ca -1 , Cu Ca -1 , and Ba Ca -1 —otolith element concentrations that individually varied between sanddab
habitat types and/or areas. Success in discriminating otoliths of either species from the two different habitat
types was not associated with seawater element concentrations. Results from this study imply that platform
habitat “fingerprints,” unique microchemical markers, may be identifiable in kelp rockfish (although not
for Pacific sanddab) along the time-keeping, growth trajectory of the otolith to reconstruct the history of
platform habitat use during the lifetime of individuals. Such reconstructions will require more study on the
spatial variability of platform elemental signatures from all existing platforms and the temporal stability of
platform markers.
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