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Sub Sampling Recording Errors

Posted: Tue Sep 26, 2017 10:40 am
by dabbott
Hi everyone,

By far the most common errors we see on data sheets relates to recoding subsampling, so I thought I would post this to try to clear up some of the confusion.

First, it's all about DENSITY! On the invert and algae transects the data you are collecting is the density of our indicator species:


Number of Organisms
Area Counted

Most of this time that area is just the 30m x 2m (60m2) of our transect but in the case of subsampling, it is a smaller area, which you need to record by noting the distance along the transect that you searched. The key is that we need both numbers, the number of organisms AND the area you counted to determine the density. On the invert and algae datasheets there are two boxes for abundant species, put the total in one, and the distance traveled in the second one which has an "m" in it (for meter). If it doesn't fit in the box, or it's just not clear, feel free to write it out. For example: 53@12.4 meters.

Often what happens is that it's really unclear what one or both of these numbers are. Sometimes due to just the sheer amount of writing in that species' area. There might be a ton of numbers, commas, circles, and it hard to know which one is the number counted and which one is the area searched. Put it in the correct box or write it out.

Other times, one or both of these numbers is missing. Maybe you totaled the number but forgot to write the area, or at least write it in the correct spot. Or the area is noted but not the number. We need both, number and area.

Lastly, we all know that to subsample we have to count at least 50 but remember it is always ok to count more. Also remember that if you count your 50th urchin right before the 12-meter mark, but there are seven more before the mark you need to count those too. Whatever area you record you need to count everything in that area. I can't just assume that if you wrote a distance, you counted exactly 50. Additionally, if you count 50 or more but don't subsample, go ahead and write 30m so the data entry person knows you didn't make a mistake and just leave it out.

We never subsample fish, abalone, or kelp stipes (kelp plants ok)

Here are some (real) examples of incorrect subsampling recording:
27 m
max out @ 9 m
50 < 5 m
more than 50 @ 7m
27 @ 36

Corrected examples:
53 @ 30 m
50 @ 27m
50 @ 9m
64 @ 4m
62 @ 7 m
298 @ 5m
50 @ 17 m

I hope that clarifies it a bit!

Re: Sub Sampling Recording Errors

Posted: Fri Jun 29, 2018 9:32 pm
by Colleen Callan
Thank you for the reminders on recording sub samples. Looking forward to learning more skills on the ocean tomorrow!