NEUS survey has wgt and area_swept but wgt_cpua is set to 0

[federico-maioli]

Hi,
While working with the NEUS survey data, I noticed an inconsistency that I wanted to clarify. Specifically:
• The dataset contains valid entries for area_swept and wgt, but the corresponding wgt_cpua values are consistently set to 0.
• This behavior seems unexpected given the presence of the other fields.
See image below.

Could you confirm if this is the intended behavior or if it might indicate an issue in the data processing pipeline?

[AquaAuma]

Hi Frederico,

I'm tagging @afredston and @zoekitchel to help with this who've worked on that particular survey before. They will get back to you. Thank you, Aurore

[zoekitchel]

Hi @federico-maioli, thanks for reaching out. We describe this issue in the survey metadata, but I have added text to further clarify.

We intentionally did not calculate those columns. There was a change in gear and survey methods for the NEUS survey in 2008/2009. The wgt and num values have been adjusted in order to account for this change using conversion factors. Additionally, the trawl footprint (area_swept) has been standardized at 0.0384 km^2. However, haul duration (haul_dur) has not been adjusted. We did not calculate wgt_cpua or wgt_cpue values, as we want to make sure that care is taken to ensure a haul is a standard length (in time) haul before calculating the effort based metrics. These are the steps I took to reduce to high quality tows in a recent analysis, "The sampling methods and gear changed in the NEUS survey in 2009, so we applied calibration factors from Miller et al. 2010 to tows from 2009 onward. We removed all tows that were more than 5 minutes longer or shorter than the target tow duration of 30 minutes (before 2009) or 20 minutes (after 2008). To calculate catch per unit effort from raw biomass data, we divided by the average tow area of 0.0384 km2 (personal communication with S. Lucey, Northeast Fisheries Science Center)."

However, the effort cells should be marked as NA instead of 0, and I apologize for the discrepancy. See issue 47 for details. We are still working to resolve this issue.

For now, if you want effort based metrics, I recommend 1) Ignoring current 0 values, 2) removing tows with haul_dur outside of a range (I used +/- 5 min of intended haul duration which was 30 min before 2009 and 20 minutes after 2009), and finally, 3) calculating effort metrics by dividing by 0.0384 km2 or by 0.5 hr (all species observations calibrated to standard pre 2009 half hour tow).

Let me know if you have any further questions.

References
Miller, T.J., Das, C., Politis, P.J., Miller, A.S., Lucey, S.M., Legault, C.M., Brown, R.W., & Rago, P.J. (2010). Estimation of Albatross IV to Henry B. Bigelow calibration factors. Northeast Fisheries Science Center Ref Doc. 10-05; 233 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/nefsc/publications/