1 Topic by James Dargie

  • James Dargie
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  • Registered: 10-02-2010
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Topic: Abundance measures in MR - Numbers per square Metre

Does anybody else collect data as numbers of individuals per square metre?

SNH have recently received data from a contractor who has recorded some data as numbers of individuals per square metre.  Speaking with our survey team it is clear that they forsee we may have further such data in the future.

According to the manual (printed page 77, digital page 78) and the MR interface the only permissable abundance measures are SACFORN, Present/ Not present, Percentage, Score (0-5) & Count. In theory it is not therefore possible to enter Number per square metre data to MR.

When they have entered the data they have chosen to put the number per square metre values into MR as if they were Count values; I don't think that is the correct thing to do [and I suspect it is at least partly (due to presence of decimal values in Count field) the cause of an export to the NBN Gateway failing]. I'd suggest that the appropriate action would have been to convert the number per square metre to a SACFOR value as per the MNCR Rationale & Methods; though clearly this looses information.

I'm slightly confused as the MR snapshot seems to have a Number per square metre field  but there is no documentation to describe how this is populated; I assume it is a field calculated when a device area is also recorded, as not all count values in the snapshot have a Number per square metre value?

2 Reply by James Dargie

  • James Dargie
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Re: Abundance measures in MR - Numbers per square Metre

I suspect that assuming we don't want a new abundance measure added to MR that the appropriate way to handle such data is either to:

- aggregate it up to semi-quantitative SACFORN values (not my preference)

or to:

- enter it as a genuine count along with the 'device' area & number of deployments. Once that is done,  I assume MR auto-populates the snapshot NumPerSqm field with a caluclated value when the MR snapshot is generated. That approach though relies on contractors recording genuine count values and 'device' area & number of deployments.

Any thoughts?

N.B. I'm putting 'device' in quotes as in many of the cases I've noted in our data there was no device simply an area within 5m radius of the station coordinates that had conspicuous species noted - so the device was simply a visual observation. Clearly this was designed for cores but I can't see why it can't work for visual observations.

3 Reply by Lynn Heeley

  • Lynn Heeley
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Re: Abundance measures in MR - Numbers per square Metre

You are correct James the snapshot calculates the number per square metre: NumPerSqm = [TotalArea]/[SpCount].
i think the advice to contractors should be your second option.

Best Wishes,
Lynn