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| Black surfperch (Embiotoca jacksoni). Credit: Credit: Clint Nelson |
By ScienceDaily, September 27, 2012
Thanks to studies of
a fish that gives birth to live young and is not fished commercially,
scientists at UC Santa Barbara have discovered that food availability is a
critical limiting factor in the health of fish populations.
The scientists were
able to attach numbers to this idea, based on 16 years of data. They discovered
that the availability of enough food can drive up to a 10-fold increase in the
per capita birthrate of fish. And, with adequate food, the young are up to 10
times more likely to survive than those without it.
This research,
published this week in the Proceedings of the Royal Society B, is expected to
be useful for managers involved in maintaining sustainable fisheries.
The scientists used
a remarkable set of black surfperch population data -- collected from 1993 to
2008 -- to develop these statistics. Divers collected the data by monitoring a
fish population off Santa Cruz Island, near Santa Barbara. Russell J. Schmitt
and Sally J. Holbrook, both professors in UCSB's Department of Ecology, Evolution,
and Marine Biology and UCSB's Marine Science Institute, head the team of
scientists.
First author Daniel
K. Okamoto, a Ph.D. student in UCSB's Department of Ecology, Evolution, and
Marine Biology, explained that there has been a lack of information about how
survival and birthrates are influenced by food availability, which is known to
fluctuate through time. Black surfperch, found off the Pacific Coast from
central Baja California northward to Fort Bragg, feed on small crustaceans and
worms.
"If a management
procedure has called for a certain harvest rate that is constant through time,
that would be like saying we should harvest the same amount of corn through
time, even though we know that corn can be influenced by things like
drought," said Okamoto.
The scientists
consider the black surfperch (Embiotoca jacksoni) to be a model species because
it is not fished commercially, making it easier to assess the effects of food
availability on fish mortality and reproduction.
A key feature of
the black surfperch is the fact that this fish gives birth to live young that
remain on the reef, allowing for its population to be counted accurately from
year to year.
"The
individual fish stay on their natal reef; they have low emigration- immigration
rates, so we can actually track cohorts through time," said Okamoto.
"An adult gives birth to live, capable young, instead of laying eggs.
Those young stay on the reef where the adults were, which is a really nice
property. We can go to a reef in a given year, survey it for adults, then go to
that reef again the next year and see the young that are there and know, for
the most part, that those young came from the adults that were there the year
before." By contrast, most fish are dispersed into open water when they
are in the larval stage.
Okamoto said that
not including food availability in calculating benchmarks for species
conservation may leave out a critical element in fisheries management.
Daniel
Reed, a research biologist with UCSB's Marine Science Institute and the principal
investigator for the Santa Barbara Coastal Long Term Ecological Research
Program, is also a co-author of the study. The National Science Foundation
provided funding for the research.
Story Source:
The above story is reprinted from materials provided by University of California - Santa Barbara.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- D. K. Okamoto, R. J. Schmitt, S. J. Holbrook, D. C. Reed.Fluctuations in food supply drive recruitment variation in a marine fish. Proceedings of the Royal Society B: Biological Sciences, 2012; DOI: 10.1098/rspb.2012.1862
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