Won’t protected areas just displace effort?

We’ve seen what happens when our favourite fishing spots get discovered by the masses. They get hammered by dozens of boats until it’s all gone.

The new SeaChange proposal suggests 13 new protected areas—10 areas of 'high protection’ and 3 areas that allow fishing but protect the seafloor from dredging and trawling—and 2 extensions of existing protected areas. Are these new protections just going munt the surrounding reefs?

This is part of the pros and cons of marine protection, so we should consider not only the benefit to the protected area, but also the effect on the unprotected area surrounding it. Fortunately, there has been a fair bit of scientific work on this, and a lot of it in the New Zealand context. So let’s look at this more closely. When a marine protected areas is established, three things happen…

1. DISPLACEMENT OF EFFORT

First, fishing effort is almost immediately displaced to the surrounding area, and usually to habitat that matches that from where the fishers were displaced.

This makes sense: Protect Burgess Island at the Mokes and the fisho is probably going to head to Fanal Island or Maori Rocks in the same group, rather than take up cockling at Shakespeare Bay.

This puts additional pressure on the surrounding area, but the impact of that depends largely on how resilient that ecosystem is and the size of the catchment area in relation to the protected area.

Scientific modelling suggests that the protected area will need to be at least twice as productive when protected to make up for this displaced effort… though this modelling assumes even fishing effort, and it’s less certain what happens when displaced effort is concentrated into hotspots—more on this below.

2. INCREASE IN ABUNDANCE

The second thing that happens is that the abundance of fish in the protected area increases rapidly.

A study conducted at the Poor Knights before and after it was closed for fishing found that the abundance of snapper increased 740% within just four years. Snapper do not stay entirely within the protected area, but radiate out from it into adjacent areas, in part compensating for the displaced fishing effort—this is called the halo effect.

The graphic below shows the size distribution and abundance for snapper in the Leigh Marine Reserve, and outside it, reflecting not only the power of protection but also how different the unprotected stock is from a ‘natural’ population.

Graphic modelled on data from inside and outside Leigh Marine Reserve. (Allard, Haggitt, Shears)

Bag limits in unprotected areas can incrementally increase abundance over time, but it’s a very slow process because fishing pressure remains, and large fish are targeted. Closing an area, however, creates a rapid increase to a very high abundance, and the size of fish is also significantly bigger on average, resulting in far more eggs spawned. It’s like night and day.

3. EXPORT OF LARVAE

The same study also discovered that the ‘daily batch fecundity’ (the number of eggs released) increased 18-fold over the same period. Basically, snapper breed like rabbits when given half a chance, with larger fish releasing more eggs. Using data from Poor Knights study, the productivity of a marine reserve looks like this:

Graphic modelled on batch fecundity data from before and after the Poor Knights Marine Reserve. Willis et al, 2003

A study at Leigh Marine Reserve found that just 1.4% of this larvae actually stayed in the reserve, the rest drifting some 40–50 kilometres into unprotected waters north and south… an export of fish from the reserve scientists call a ‘larval subsidy’; like the dividend from an investment. They discovered that more than 10% of snapper in the surrounding 400 square kilometres of the Gulf were ‘exported’ from the Leigh Marine Reserve, which is just 4 square kilometres in extent. The biophysical model looks like this;

Larvae distributed from the Leigh Marine Reserve (green area at centre) 50km north and south. LePort et al 2017

This is all good and well, in theory, but there is a period of a couple of years between when protection is declared, and when productivity in those protected areas has increased to a point that it compensates for that protection. This danger zone between displacement and productivity is a difficult one.

We also need to consider that not every protected area is going to respond in the same way as the Poor Knights or Leigh Marine Reserve. Anecdotal evidence suggests that Long Bay Marine Reserve may never reach fish densities that are seven times greater than the surrounding area.

There is no question that we need protection in some places to save all places from the ravages of overfishing, so we need to carefully consider where displaced effort from each protected area will go and what we can do to ensure those areas with greater effort don’t suffer unsustainable pressure.

Recreational snapper catch in the Hauraki Gulf. Bruce Hartill/NIWA

The second concern is that fishing effort is not evenly distributed, and will not be displaced evenly either. With Burgess Island and the top of Little Barrier/Hauturu protected, Fanal Island and Katherine Bay are going to take a hiding, right? And with the south side of Tiri protected, the 1200 boats that fish there each year will head to the north side which already sustains double that pressure. That can’t be good.

This is true, but it’s also moderated by ‘network effects’—the way in which a distributed system of protection serves better than a single massive one.

Having highly productive areas distributed around the Gulf creates a network of ‘fish pumps’ that export larvae up to 50km from each reserve; reaching pretty much everywhere.

Not every area is going to respond to marine protection in the same way. Some will see more modest increases in abundance due to external factors such as sedimentation—which may be the case with Long Bay Okura Marine Reserve which has ‘only’ reached 6.7-times the abundance of snapper as outside the reserve. Some will be more limited in the halo effect—such as the Poor Knights where all the reef habitat is within the reserve. So this is where available data can point us in a direction more than give us specific answers.

We can’t model the outcomes precisely, but we can build something of a ‘mud map’ of what larval subsidies from protected areas look like under the SeaChange proposal. This looks only at the range of influence of each area to see how larvae exported from protected areas overlaps. To be more accurate we would need to conduct biophysical modelling to see where larvae actually goes and account for the habitat types more comprehensively, as the flats are not as productive as reefs. University of Auckland is working on developing a more robust model that accounts for larval dispersal and habitat types to fill in the picture.

The large protected areas will likely produce the greatest larval subsidy simply because there can be more fish within their boundaries, but small areas that overlap suggest that almost every inch of the Hauraki Gulf could see the benefit of this network of fish pumps.

Larval subsidy areas of influence from proposed protected areas (SeaChange), by area.

There are a lot of legitimate concerns around protection, but the alternative is managing the fishery at an extremely low level.

The scientific models suggest that the 18-times productivity of protected areas will more than compensate for displaced effort and result in substantially higher abundances—and better fishing—even in unprotected areas. The risk is the sudden increase in pressure on nearby spots in the short term.

How can the new rules respond to this new problem? How can we reduce the impact? The success or failure of SeaChange may rest on our answers to these questions.