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The following e-mail was posted to various mailing lists on 12/5/99.
Date: Sun, 05 Dec 1999 08:13:16
To: abnet@uct.ac.za, abalone_action-list@lists.sonic.net
From: Rocky Daniels
Subject: Rickettsia, withering syndrome, and aquaculture
Cc: ba_diving@lists1.best.com, freedive-list@freediver.net,
cal_diving@lists.sonic.net
In 1998, California's abalone fishery south of San Francisco was closed indefinitely by legislative action. That same action also instituted a revenue stream dedicated for work on abalone by imposing an annual fee on recreational abalone harvesters north of San Francisco. Expenditures from that funding source are overseen by the Recreational Abalone Advisory Committee composed of recreational and ex-commercial divers, marine biologists, and game wardens; the RAAC meets at least once a year. At last September's meeting, information was presented that's likely of interest to folks associated with the abalone aquaculture industry. Since September, there have been additional relevant developments.
At the September meeting, it was reported that the causative agent of Withering Syndrome has been confirmed to be the Rickettsia-like bacteria strongly suspected for the past few years. My understanding is that the appropriate scientific write ups are already in progress. For additional information on this and the following information, I'd refer the reader to Carolyn Friedman at the Bodega Bay Marine Lab.
Prior to September's meeting, it was reported that aquaculture facilities throughout California are infested with Rickettsia. Having also determined that Rickettsia are water borne and do not require physical proximity for transmission, samples of wild stocks from Central and Southern California waters were checked for Withering Syndrome and Rickettsia. As a result, Withering Syndrome has been confirmed in wild stocks off California north of Monterey with Rickettsia found in the wild almost to the Oregon border (i.e., about as far north in California as you can get). This bad news had been limited to a few wild sites near aquaculture facility outflows; samples taken from other Central and Northern California locations came back negative until recently. The latest development is that sampling of wild stocks was expanded to include wild locations remote from aquaculture facilities where abalone outplanting experiments using aquaculture seed animals were undertaken in 1995. One abalone has turned up Rickettsia-positive at one of these sites (though I'm not clear on how many of the five outplant locations have been sampled so far).
Considering that Withering Syndrome resulted in mortalities approaching 100% in some Southern California stocks, these are rather dismal developments. The best hope of scientists today is that Rickettsia infested abalone require temperature stressing before full blown Withering Syndrome can make an appearance. It's equally likely, however, that colder water simply retards the inevitable development of Withering Syndrome.
Earlier this year, a Sabellid motivated exchange I had with a prominent scientist raised the question of whether Withering Syndrome might turn out to be the result of an exotic species introduction complements of the aquaculture industry. Other scientists at the time challenged the motivations of such a question. Some of those other scientists are now the ones making discoveries that make that question ever more plausible.
At this point, wild and cultured California abalone are potential vectors for the spread of Withering Syndrome to abalone stocks elsewhere in the world. Has any work been done to determine if cultured abalone are infected in areas besides California and Mexico? Also, has there been any work to determine whether the identified Rickettsia are naturally occurring in any wild stocks anywhere?
Rocky Daniels
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Last Modified on December 20, 1999
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