sansou
05-29-2009, 03:44 PM
Sport Fishing Hammering Large Male Sheephead
Researcher:
Jennifer Caselle
Marine Science Institute
University of California
Santa Barbara
E.: caselle@msi.ucsb.edu (caselle@msi.ucsb.edu)
T.: (805) 893-5144
Scott Hamilton
Marine Science Institute
University of California
Santa Barbara
E.: s_hamilt@lifesci.ucsb.edu (s_hamilt@lifesci.ucsb.edu)
T.: (805) 893-7397
Christopher Lowe
Dept. of Biological Sciences
CSU Long Beach
E.: clowe@csulb.edu (clowe@csulb.edu)
T.: (562) 985-4918 www.csulb.edu/web/labs/sharklab
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Revised:
April 22, 2009
http://www-csgc.ucsd.edu/NEWSROOM/NEWSRELEASES/RESOURCES/2009/Sheephead/800px-Fishmarket_01-m.jpg A male California sheephead at the fishmarket in Ensenada,
Baja California, México. Credit: Wikipedia/Tomás Castelazo
April 20, 2008
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
SANTA BARBARA — All California sheephead are born female. When large enough to defend a territory and harem, females undergo hormonal changes that transform them into males.
That (curious as it may be) is old news. Scientists even have a name for the life-history characteristic – sequential hermaphrodism or, more precisely, protogynous hermaphrodism.
The news, and it’s bad news for future generations of Semicossyphus pulcher, is that big strong males are conspicuously absent at Catalina Island, located 20 miles from Los Angeles, the most visited of the Channel Islands.
“We see lots of tiny, midget males, which is not the case historically,” says UC Santa Barbara postdoctoral researcher Scott Hamilton, who is working with UC Santa Barbara researcher Jennifer Caselle on the Ocean Protection Council-funded project. CSU Long Beach scientists Christopher Lowe and Kelly Young are co-investigators on the project, slated to end in 2010.
The scientifically defensible explanation for the lack of buff sheephead dudes is that sport fishing has selectively removed the “trophy” fish, which for sheephead means the males almost exclusively, Caselle says. The commercial fishery targets live smaller solid-red females that command the highest prices in Asian markets.
Sex change in females is suppressed by aggressive interactions with dominant males, she explains. When alpha males are removed, females are socially cued to switch sex. If this occurs over a large enough scale, the result is a precipitous drop in total egg production as females spend less of their life producing eggs and because older, bigger females produce exponentially more eggs.
Female sheephead off Catalina in 2007 were observed to be turning male at ages as young as five and at “standard lengths” as short as 24 centimeters, the scientists found. The youngest, smallest males observed in 2007 off San Nicolas Island, in contrast, were 9 years and 40 centimeters respectively. In 1980, when scientists say San Nicolas was relatively un-exploited, sheephead were switching sex between the ages of 13 and 14 and at lengths of about 48 centimeters.
“The fish keep getting smaller and they are changing sex earlier,” Hamilton says. “The bright spot is that we are seeing a recovery off San Nicolas.”
San Nicolas, besides being the most remote of the Channel Islands, is controlled by the Navy as a weapons-testing facility. Post 9-11, access to the island has been greatly restricted. This combined with rising fuel prices and new regulations on commercial fishing has greatly reduced sheephead landings in the last decade.
In 1998, at the peak of the commercial sheephead fishery off San Nicolas, sex change was occurring at 7 and 8 years and at lengths of 30 centimeters at the island, the scientists report.
“What we see is that the fish do come back once the fishing pressure is reduced,” Hamilton says.
The ICUN lists the California sheephead as "vulnerable," meaning the species is likely to become endangered unless the circumstances threatening its survival and reproduction improve.
The worry is for places like Catalina, where fishing pressure is holding steady. Size limits may no longer protect both genders. “We think in some places you could literally fish out the entire male population legally,” Hamilton says.
The scientists are recommending that state biologists implement slot limits, which would establish upper and lower bounds on legal-size sheephead. The usual fisheries management techniques don’t work for a species that switches sex midway through life, Hamilton adds.
The ICUN (International Union for the Conservation of Nature and Natural Resources) lists the California sheephead as "vulnerable," meaning the species is likely to become endangered unless the circumstances threatening its survival and reproduction improve.
Researcher:
Jennifer Caselle
Marine Science Institute
University of California
Santa Barbara
E.: caselle@msi.ucsb.edu (caselle@msi.ucsb.edu)
T.: (805) 893-5144
Scott Hamilton
Marine Science Institute
University of California
Santa Barbara
E.: s_hamilt@lifesci.ucsb.edu (s_hamilt@lifesci.ucsb.edu)
T.: (805) 893-7397
Christopher Lowe
Dept. of Biological Sciences
CSU Long Beach
E.: clowe@csulb.edu (clowe@csulb.edu)
T.: (562) 985-4918 www.csulb.edu/web/labs/sharklab
Tools:
Print this (javascript:print())http://www-csgc.ucsd.edu/NEWSROOM/images/document.gif (javascript:print())
Normal text (http://www-csgc.ucsd.edu/NEWSROOM/NEWSRELEASES/2009/Sheephead.html#)
Larger text (http://www-csgc.ucsd.edu/NEWSROOM/NEWSRELEASES/2009/Sheephead.html#)
Add me to California Sea Grant mailing list (https://seaserver.ucsd.edu/emailform/contactform.php) [/URL]
Email this http://www-csgc.ucsd.edu/NEWSROOM/images/mail.gif (javascript:send()) [URL="javascript:print()"]
Revised:
April 22, 2009
http://www-csgc.ucsd.edu/NEWSROOM/NEWSRELEASES/RESOURCES/2009/Sheephead/800px-Fishmarket_01-m.jpg A male California sheephead at the fishmarket in Ensenada,
Baja California, México. Credit: Wikipedia/Tomás Castelazo
April 20, 2008
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
SANTA BARBARA — All California sheephead are born female. When large enough to defend a territory and harem, females undergo hormonal changes that transform them into males.
That (curious as it may be) is old news. Scientists even have a name for the life-history characteristic – sequential hermaphrodism or, more precisely, protogynous hermaphrodism.
The news, and it’s bad news for future generations of Semicossyphus pulcher, is that big strong males are conspicuously absent at Catalina Island, located 20 miles from Los Angeles, the most visited of the Channel Islands.
“We see lots of tiny, midget males, which is not the case historically,” says UC Santa Barbara postdoctoral researcher Scott Hamilton, who is working with UC Santa Barbara researcher Jennifer Caselle on the Ocean Protection Council-funded project. CSU Long Beach scientists Christopher Lowe and Kelly Young are co-investigators on the project, slated to end in 2010.
The scientifically defensible explanation for the lack of buff sheephead dudes is that sport fishing has selectively removed the “trophy” fish, which for sheephead means the males almost exclusively, Caselle says. The commercial fishery targets live smaller solid-red females that command the highest prices in Asian markets.
Sex change in females is suppressed by aggressive interactions with dominant males, she explains. When alpha males are removed, females are socially cued to switch sex. If this occurs over a large enough scale, the result is a precipitous drop in total egg production as females spend less of their life producing eggs and because older, bigger females produce exponentially more eggs.
Female sheephead off Catalina in 2007 were observed to be turning male at ages as young as five and at “standard lengths” as short as 24 centimeters, the scientists found. The youngest, smallest males observed in 2007 off San Nicolas Island, in contrast, were 9 years and 40 centimeters respectively. In 1980, when scientists say San Nicolas was relatively un-exploited, sheephead were switching sex between the ages of 13 and 14 and at lengths of about 48 centimeters.
“The fish keep getting smaller and they are changing sex earlier,” Hamilton says. “The bright spot is that we are seeing a recovery off San Nicolas.”
San Nicolas, besides being the most remote of the Channel Islands, is controlled by the Navy as a weapons-testing facility. Post 9-11, access to the island has been greatly restricted. This combined with rising fuel prices and new regulations on commercial fishing has greatly reduced sheephead landings in the last decade.
In 1998, at the peak of the commercial sheephead fishery off San Nicolas, sex change was occurring at 7 and 8 years and at lengths of 30 centimeters at the island, the scientists report.
“What we see is that the fish do come back once the fishing pressure is reduced,” Hamilton says.
The ICUN lists the California sheephead as "vulnerable," meaning the species is likely to become endangered unless the circumstances threatening its survival and reproduction improve.
The worry is for places like Catalina, where fishing pressure is holding steady. Size limits may no longer protect both genders. “We think in some places you could literally fish out the entire male population legally,” Hamilton says.
The scientists are recommending that state biologists implement slot limits, which would establish upper and lower bounds on legal-size sheephead. The usual fisheries management techniques don’t work for a species that switches sex midway through life, Hamilton adds.
The ICUN (International Union for the Conservation of Nature and Natural Resources) lists the California sheephead as "vulnerable," meaning the species is likely to become endangered unless the circumstances threatening its survival and reproduction improve.