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Invasive mussels

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Affected water status definitions

Regarding the presence for quagga and/or zebra mussels, Utah Division of Wildlife Resources' classification system follows:

Unaffected water bodies

  1. Not tested: A water body has simply not been tested.
  2. Pending: Sample has either not yet been collected for the current year or is at the laboratory being analyzed.
  3. Not detected: No juvenile or adults mussels have been detected, and a plankton tow net sample analyzed via microscopy (FlowCam or cross-polarized microscopy followed by light microscopy) shows no evidence of larval form veligers.

Affected water bodies

  1. Suspected: A single sampling event at a water body, facility or water supply system reveals the presence of a mussel via visual identification or microscopy. The result of that sampling event is confirmed in two tests, each conducted at independent laboratories.
  2. Detected: Two consecutive sampling events at a water body, facility or water supply system reveal the presence of a mussel via visual identification or microscopy. The results of each sampling event are confirmed in two tests, each conducted at independent laboratories.
  3. Infested: Two or more consecutive sampling events at a water body, facility, water supply system or geographic region reveal the presence of multiple age classes of attached mussels via visual detection or microscopy. The result of each sampling event is confirmed in two tests, each conducted at independent laboratories. The Utah Wildlife Board must declare this classification as per Rule R657-60, Aquatic Invasive Species Interdiction.

Classification change

If an affected water body evidences no detections of quagga or zebra mussel life forms for an extended period of time (time varies based on classification), declassification may be considered at the end of the last assessment year, once all samples are analyzed; the year of discovery is the zero year. The mere passing of time with no detections for quagga or zebra mussel life forms is not a guarantee for declassification to occur. Natural resource managers are perpetually gaining experience and knowledge, all of which could affect the declassification process. Fortunately, it is not uncommon for aquatic animal transfers to require several introductions before a successful, self-sustaining population is established. So, aggressive containment management (inspect arriving boats, provide professional decontamination for departing boats, and market self-decontamination via Clean, Drain & Dry) at Utah's water bodies may result in fewer or no introductions causing initial introductions to fail.

Declassification to "not detected" for a quagga or zebra mussel affected water must follow an extended period of intensive sampling as follows:

  • Suspected: Must be intensively sampled for three consecutive years with no detections;
  • Detected: Must be intensively sampled for five consecutive years with no detections;
  • Infested: Must show seven consecutive years of intensive sampling with no detections.

See full definitions in Rule R657-60, Aquatic Invasive Species Interdiction.

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