Why did DEFRA decide not to adopt the IEP recommendation of continuing to use cull-sample-matching?

In the report on the first year of badger culling in the Somerset and Gloucestershire cull zones, the Independent Expert Panel recommended that the use of cull-sample-matching should be continued.¹ In fact the IEP stated the following

The cull-sample-matching approach represents the most reliable way in which to assess the effectiveness of any future culling operations.
...
in any future culling operations, in the pilot areas or elsewhere, hair trapping and genotyping effort should be at least as great as in the pilot culls.

See Ref 1 in Section 10.6.9 of Page 7.

In response to this recommendation, DEFRA stated the following to explain why it decided NOT to adopt the IEP recommendation in the second year of culling in 2014.

We note the conclusions of the IEP that the cull sample matching methodology is the most reliable way for determining the proportional reduction in a population. However, it is an expensive Government intervention involving pre-cull fieldwork every year and is potentially affected by interference with hair-traps by those seeking to prevent the culls.

Defra will work with Natural England and AHVLA to adopt more cost-effective methodologies to assess effectiveness of culling, that do not rely solely on measurement of population numbers. We will aim to take a more cost-effective approach to monitor progress of the cull. Rather than focusing primarily on pre-cull numerical targets based on population estimates which we now know are subject to considerable uncertainty, we will focus on more useful indicators of progress of the cull.

Does cull-sample-matching rely on pre-cull numerical targets based on population estimates?

This is in fact not the case as explained in Ref 2 in Section 4.2.4 on Page 9. Although capture-mark-recapture relies on estimating pre-cull population size, cull-sample-matching does not. This statement regarding dependence on population estimates is misleading because cull-sample-matching is a remarkably simple method which just uses the proportion of hair-trapped badgers that were culled. This proportion directly gives effectiveness.

Regarding DEFRA's stated concern regarding "interference with hair-traps by those seeking to prevent the culls", the IEP concluded in Reference 2 (see Section 4.4.14 on Page 17) that protestor activity may have biased down population estimates in the capture-mark-recapture analysis but is unlikely to have introduced bias into the cull-sample-matching method.

Regarding cost, Reference 4 concludes that hair-trapping is not prohibitively expensive. It was this aspect of the work which was omitted in the second cull carried out in 2014. Indeed Reference 5 states that in that cull dispatched badgers were received each day at the PM facility, where carcases had their ear tips removed and sent for DNA analysis.

As an added bonus of using the cull-sample-matching method, population size may be derived by dividing the number of badgers culled by this proportion. As such, cull-sample-matching is a very simple and powerful scientific tool. Unlike all other methods which are available today and used in the Randomised Badger Culling Trial (RBCT), it's use relies on very little human judgement. In view of this CSM should be playing an important role in helping to understand the benefits or otherwise of culling. In my view, analyse of the effectiveness of culling in the pilots should be based on CSM.

Further background is given in Reference 3 which asks the following question:

Will cull-sample-matching (CSM) be used in the fourth year to allow badger number reductions to be examined in another year in each cull zone and to allow badger numbers in the first and last years to be compared?

References

1. Defra response. Pilot Badger Culls in Somerset and Gloucestershire: Report by the Independent Expert Panel. April 2014.
2. Pilot Badger Culls in Somerset and Gloucestershire. Report by the Independent Expert Panel. Chair: Professor Ranald Munro. Presented to DEFRA Secretary of State Owen Paterson MP, March 2014.
3. Pilot badger culls in Somerset and Gloucestershire and their value in planning future policy.
4. Estimating social group size of Eurasian badgers Meles meles by genotyping remotely plucked single hairs. LJ Thomas et al. Source: Wildlife Biology, 13(2):195-207. Published By: Nordic Board for Wildlife Research. 2007.
5. Audit report for the 2014 badger control project. Conducted and prepared by: Independent Principal Auditor Dr. Martine Wahl, Clinical Research & Communication (CRC). Submitted to: Bovine TB Programme, Defra 16/12/2014.