Trap Nights - bit of confusion

Kia ora, just wanting some clarification on how Trap NZ calculates trap nights in relation to submissions - e.g. I have two DOC250 traps (BD35 and BRCD01). BD35 was uploaded onto the system on 25/11/23 while BRCD01 was uploaded on the 24/11/23. Neither trap was sprung however BR35 had three more entries (still set, bait ok) added which I think impacted the trap night calculations.

BD35 - 67 trap nights

BRCD01 - 70 trap nights - 5 entries (could only embed one image).

How do submissions impact trap night calculations? I believe BRCD01 is correct with 70 trap nights but shouldn’t BD35 be 69? Since there is only a night difference and the traps both caught nothing? BRCD01 was checked daily but entries were only made for rebaiting. BR35 had rebaiting entries and three more checks submitted. Any help for this confused human is much appreciated.

BRCD01 - 70 trap nights

Hi Kat,

Trap nights is fairly complicated under the hood, but the basic formula is calculated as the number of days between the dates in the period modified as follows:

If anything is logged as caught on a record (Species Caught is not None and Strikes > 0) then the trap nights from the date of the previous record to the date of the record with the catch is halved. For example, if you check a trap once per week on Monday mornings and there is no catch, the trap nights for the previous week is 7. If there is a catch, the trap nights for that period is 3.5.

Once something has been caught, the trap is no longer active and able to catch anything else. We don’t know when ecactly the catch actually happened (it could have been any night that week), so we just average out to the middle of that period and assume that the trap was active for half the time between checks.

Second, if a record sets Rebaited to False, then trap nights from that record date will be zero until a record is logged with Rebaited set to True. If a trap has no bait, it is not considered active, and does not get counted in trap nights for that period.

Finally Status is factored in. Sprung means that it has a catch, any of the 3 Still Set statuses mean that it is active, and any other status is treated as inactive.

I’m not sure what time period you were looking at, but I suspect your difference will be due to one or more of these factors.

Hope that helps!


1 Like

ohhhh this is very interesting @scottw - I knew about the nights being halved when a catch is input, but not about the bait. We don’t replace bait every check as we have a variety of longlasting baits, so only put in that we have rebaited when we change/refresh the lure. I’m guessing this means that our trap night data will be wildly inaccurate?

We don’t actively use that data for reporting at the moment but do look at it every now and again just to check it out.

Scott - We also run a number of traps with no bait - run through traps. On our other traps, we also dont rebait every trap check - long life baits. So that will also muck up our trap night calculation big time. We will probably have to do it manually from a spreadhseet download and use date of install.