Somewhere between land and sea lie intertidal habitats such as sandflats, mudflats and rocky reefs. These in-between places provide a wide range of valuable services including fisheries, recreation, buffers to sea-level rise and storm protection. Yet the distribution of these habitats, and therefore how well they are protected in reserves, remain unknown at a national level, below a 10km resolution.

​Of course, mapping the distribution of a habitat which is repeatedly inundated can be remarkably complex, even using remote sensing. That’s a big part of the reason we know so little about the distribution of these habitats. With Landsat imagery for example, images (which are taken only every 16 days) must coincide with the highest and lowest astronomical tides on a day without cloud, to create a map. Finding suitable images at a national level is therefore difficult, but not impossible.

In our study, we were able to combine 15 years of images to produce the first map of intertidal habitats for Australia at a 30m resolution (the shapefile can be found at https://doi.pangaea.de/10.1594/PANGAEA.845726) (Dhanjal-Adams et al, 2016). The method we used to map the extent and distribution of intertidal habitats in Australia was based on a continental-scale mapping project conducted across Asia by Nick Murray and colleagues (Murray et al, 2012; and see Decision Point #81).

Of the 9,856 km2 of mapped habitat, we discovered large intertidal areas, particularly in Western Australia, Queensland and South Australia, along embayed coastlines and river mouths. Furthermore, we discovered that 39% of mapped intertidal habitats fell under the jurisdiction of one protected area designation or another (fig. 2).

​Levels of protection varied considerably between states ranging from 80% in Victoria to 6% in the Northern Territory. We were also surprised to discover that some states mainly protected intertidal habitats as part of marine protected areas (eg, Queensland), and others as part of terrestrial protected areas (eg, Victoria). In some cases, 3% intertidal habitats were protected both by marine and a terrestrial protected areas (10% in South Australia).

​Given the importance of intertidal habitats, there is a strong need to better understand how these designations can impact management of intertidal species. Intuitively, we might expect such designations to lead to better protection with both marine and terrestrial protected area managers collaborating. However, there is also the potential for confusion, with neither organisation sure who should take the burden of responsibility.

The protection of intertidal habitats is undeniably blurred, but with great potential for improvement. By providing the most accurate map of intertidal habitats to date, our research provides the data needed to better align protected area boundaries with intertidal habitats. In so doing we can improve the protection afforded to the many amazing species these habitats support.

This is a post I wrote for the Journal of Applied Ecology on my recent paper ‘Optimizing disturbance management for wildlife protection: the enforcement allocation problem’

Determining where and when to carry out enforcement patrols can be a complex issue. Imagine for instance that you have 10 sites that you want to visit between 0 and 5 times…There would be a grand total of 60,466,176 possible combinations of site visits. So how do you figure out which one of these 60,466,176 possible combinations works best for you?

Then of course there is the issue of how effective the enforcement actually is. Maybe people are stubborn and don’t want to change their behaviour to follow regulations. Or maybe they are very fearful, and go somewhere else to avoid patrols. If people are fearful and avoid patrols, it is both expensive and useless to keep patrolling the same site when no one is there. There is therefore a sweet spot, in other words an optimal number of visits, which ensures a site is not being visited so little that enforcement has no effect, or visited so much that money is wasted.

​Our recent paper in the Journal of Applied Ecology examines these trade-offs and investigates where managers should patrol, and how often. The problem can be broken into two parts. Firstly, what is the benefit of enforcing regulations? And secondly, what is the cost of enforcing regulations?

Because we are birders and we live in Australia, we use the case study of declining migratory shorebirds and dogs on beaches to illustrate our approach. Indeed, the shorebirds that we see here migrate 11,000 kilometres, all the way from Alaska and Russia, to spend the summer feeding on worms, shells and crabs in the intertidal zone. Dogs, though cute, have a tendency to chase birds. One dog can cause hundreds of birds to take flight, and if this occurs regularly, the birds cannot feed and gain the weight necessary to complete their long-distance migrations.

​Enforcement is very simple. It involves increasing the number of dogs on leashes. Like I said before, there are two parts to the problem: the benefit of enforcement, and the cost of enforcement. Benefit here can be thought of as the number of birds no longer being disturbed. Cost is simply that of travelling to a given shorebird site and time spent enforcing.

Because we are unsure, without extensive fieldwork, how effective enforcement is (i.e. how many people actually continue putting their dog on a leash after enforcement), we tested two scenarios. One where people are stubborn, and don’t want to put their dog on a leash, and another where people immediately start putting their dog on a leash. The results are surprisingly similar between the two scenarios, many of the same sites appear important in both. What varies is the number of times these sites are visited.

​Quite intuitively, if people are reluctant to follow regulations, a site must be visited more often, while if people are willing to follow regulations, money should be invested visiting lots of sites a small number of times. This shows that the methods we develop make sense, but to figure out the exact number of visits to a site, it remains essential to do the maths. No pain, no gain!