Biology Reference
In-Depth Information
State vessel conducts herring survey near the Bay Bridge. (Ryan Bartling)
mass. When a sea lion chases the herring, they can spin into a cyclone or
contract into a sphere, which appears as a dancing red ball onscreen.
“Any footage of schooling fish shows they almost act as one when they
move,” comments Becky Ota, who worked on the herring project for 10
years. “Once they spawn, they typically leave the bay within two tidal cy-
cles. It can be just a continuous revolving door through the Golden Gate,
with these schools coming in week after week through March.”
Once they find herring, the crew trawls a net through the school to
bring up samples. Back in the lab, scientists test the fish for ripeness (for
spawning), record length and sex, and remove otoliths (ear bones) to con-
firm a specimen's age. Most schools contain fish 2-6 years old. The otolith
is about the size of a kernel of rice and grows a new ring every year, just
like a tree. The strength of each year class is indicative of the potential
number of future spawners returning to the bay.
State crews also monitor where schools of herring go in the bay, and
they look at acoustic data to figure out which school spawned where. How
do they tell different schools apart? Each is dominated by one or two year
classes, associated with a specific location, and can be distinguished from
other schools by ripeness and how far along they are in the spawning
cycle.
The work does not all occur on the big boat. Biologists also climb into
the smaller skiff Ronquil (common name for a bottom fish) to survey
where and how much spawn—or roe—is being deposited. The crew first
maps a school's spawning episode, then samples it by working their way at
low tide out from the shore wielding a long rake. The raking and sampling
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