Trawling for predators? Predator Trawling vs Line Catching

We've been thinking again.  There is an interesting analogy to be drawn between how we catch fish and how we catch predators.

We think trying to catch predators using traps is similar to line fishing. Every fisherman knows you need a good lure on your hook and then you need to hope that a hungry fish comes along, chooses to take the bait, and gets caught.  But even the most skilled fisherman knows that, even with the finest bait, a hook won't catch a fish every time and it certainly won't catch all the fish - no matter how many hooks you cast into the sea (in the case of fish, you certainly wouldn't want to catch them all). 

If you have read any of our previous work you know just how many predators walk past baited traps. We suspect there is no combination of great baits/traps that will ever make it possible to catch every last predator. Just as you would not be able to catch ALL the fish in an area with just line fishing. We may need something of a more industrial scale to achieve total predator elimination. Obviously poisons are a proven method of reducing populations fast but they are not suitable for use everywhere and we still need more effective tools in combination with poisons (especially when trying to catch the last few survivors).

Selective predator trawling

Trawling for fish is certainly a method that has been proved to completely crash fish populations (with lots of other nasty side effects too).   But what if trawling could be selective?  We have been thinking about how we could “trawl” for predators in a given area. Obviously we can’t drag a net through the bush like you can in the ocean, but we could guide predators into openings along key geographic features and have a much higher catch rate.  Our idea is to have a portable fence that guides predators to an opening and then have a selective method to catch only the things we are interested in. The method is a combination of the active predator fence and the open architecture traps we have been developing. 

Some things to consider.

Trawling in the sea for fish is easier than trawling for predators in the bush because:

  • You can actively move through a large area with one device
  • Fish clump together in schools and can be tracked

Predator trawling in the bush has some advantages over trawling in the sea because:

  • The bush is mostly two dimensional and when predators move about they tend to walk along the bush floor (though it is possible some rats may never come down from trees)
  • Predators tend to follow natural paths so you may not have to trawl an entire area - just key landscape features along ridges, streams etc.
  • It is much easier to have selective elimination where you use intelligent devices to decide what to catch and what to let through

Predator trawling has some key advantages over trapping (line catching):

  • You are more likely to interact with ALL the predators in an area
  • Differences in a predator's preferences for baits and lures do not matter
  • Just like ocean trawling you may not even need to bait at all (yes this does seem controversial given the effort put into developing baits but we've seen quite a few predators wander into unbaited open architecture traps)
  • Predator trawling could be used to catch all types of predators rather than having lots of different trap types each targeting a different species

When predators have GPS tracking during research studies it is clear how often they walk past baited traps. It is also clear that predators use many of the same paths consistently. They also seem to follow features of the landscape so we suspect a skilled trapper could set up key active fences to guide the predators through. In just a few days all the predators could have wandered into the “nets” and been caught.  The "nets" could then be moved to the next area (in the same way a fishing fleet doesn't just sit in one spot in the ocean).  With this method you have the potential to sweep through and completely clear an area of predators.

We are busy developing the key parts of the technology that will allow us to test these ideas. We'd love to hear what you think about this approach - leave a comment below or email us at




Publication Date: 
Thursday, 2 December 2021