Anthropogenic introduction of the etiological agent of withering syndrome into northern California abalone populations via conservation efforts

Populations of abalone have precipitously declined in California over the past several decades, largely as a result of fishing pressure and disease. Because of these declines, farmed seed abalone have been planted in an attempt to research and restore dwindling populations. Withering syndrome is a chronic disease responsible for mass mortalities of wild black abalone, Haliotis cracherodii, in southern and central California and is caused by the bacterium "Candidatus Xenohaliotis californiensis". This bacterium has been observed in wild populations of black and red (Haliotis rufescens) abalone south of Carmel and in farmed red abalone throughout the state. In an effort to elucidate the distribution and source of the bacterium in northern California, the presence or absence of the disease and bacterium was verified at 15 locations north of Carmel. This research revealed that both the bacterium and withering syndrome are present in abalone populations south of San Francisco. In addition, the bacterium (but not withering syndrome) is present at two locations in northern California, both associated with outplants of hatchery-reared abalone, suggesting a link between restoration efforts and the present distribution of this pathogen. These data highlight the need for careful assessment of animal health before restocking depleted populations.