THOSE who angle make it their business to know where to find fish. They know fish seldom stray far from their food sources, but many species also require shelter to avoid being eaten themselves. What if the food and shelter both occur in the same place? Welcome to the reef.
Natural reefs are highly productive underwater bottom features formed either by hard rocky substrates, or biogenic (living) substrates such as shellfish or coral. Reefs of all three types tend to rise up vertically from the adjacent bottom, whether it be a foot or two in the case of shellfish reefs, many tens of metres in the case of rocky reefs, or hundreds of metres in the case of seamounts or coral reefs which rise from the depths of the open ocean. In each case, they interrupt currents, forming upwellings and eddies which can trap nutrients and kick start planktonic food chains, which attract baitfish. Small fish may also be attracted to natural reefs with high surface area, such as coral or shellfish reefs, because the large numbers of nooks and crannies (scientists call this feature rugosity or internal void area) which provides habitat for large numbers of shrimps, crabs and other invertebrate food items. Of course, whenever there are large numbers of invertebrates and baitfish in an area, the predatory fish will not be far away. Therefore, it is this increased surface area provided by natural rocky or biogenic reefs that drives their impressive fishery production.
Estuaries and inshore waters around the world have come under ever increasing pressure over the last century due to human population growth and its associated coastal development. This coastal development results in degradation of water quality (think runoff and sewage), which directly reduces the fisheries productivity of natural biogenic inshore reefs by smothering them with sediment and exposing them to excessive nutrients and various other waterborne pollutants. The increasing human population and declining natural reef condition in areas near those human population centres causes a “double whammy” effect which results in much damage to reefs and other fish habitat, which reduces fish populations and the “carrying capacity” of the system to sustainably produce the fish which support fisheries.
While some scientists and other interest groups continue to insist that these problems can be fixed by Marine Park Areas (MPAs) which exclude fishing from certain regions, in reality this does not work near human population centres. Why? Because the degradation of inshore water quality means that the damaged ecological function of the natural biogenic inshore reefs (and hence the lost “carrying capacity”) cannot be recovered without intensive restoration efforts (such as the restoration of shellfish reefs we are now seeing throughout Australia, see the reefbuilder programme. However, in many MPAs (Moreton Bay Marine Park in QLD is a good example), restoration of the damaged natural biogenic reefs is prohibited by marine parks legislation. In other words, the regulations managing MPAs in many parts of Australia may actually prevent meaningful recovery of fish stocks near areas of coastal development by prohibiting restoration of damaged natural reefs and other critical fisheries habitats.
This red tape preventing restoration of damaged habitat is one of the major downsides of poorly planned MPAs (and an embarrassing one which MPA proponents don’t seem to want to talk about much). In Moreton Bay the shellfish reef restoration trial in Pumicestone Passage resulted in an increase of 16.4 times more harvestable fish in the restoration area compared to the baseline 3 years earlier. This massive benefit from habitat restoration represents recovery of a mere fraction of lost “carrying capacity” in the restoration area, but it dwarfs the 2-3 or even 4 times greater fish numbers that are usually lauded as showing that sanctuary areas “work” in Moreton Bay Marine Park, including the green zones in Pumicestone Passage a few km north of the restoration site. Clearly this shellfish restoration trial in Pumicestone Passage has demonstrated beyond doubt that it is habitat quality that is the major driver of the health of fish populations in Moreton Bay, as shown by the fact that the 16.4 times increase in harvestable fish numbers occurred despite recreational fishing being permitted over the shellfish restoration area (though anchoring was discouraged as this damages the delicate shellfish reefs).
So it is an indisputable fact that habitat quality is king. Nevertheless, we also see similar issues when it comes to non-natural fish habitat enhancement structures, otherwise known as artificial reefs. In view of the increasing human population and widespread degradation of natural inshore reef habitat, and given that properly designed artificial reefs have been proven in many countries to greatly enhance carrying capacity and fisheries production beyond any scientific doubt (see the excellent report by Recfishwest on this at https://www.frdc.com.au/project?id=408), you would think that installation of artificial reefs would be encouraged by MPA legislation in order to regain lost carrying capacity and reduce the fishing pressure on natural reefs (or in some cases to compensate for loss of access to natural reefs captured in green zones). But again, this is generally not the case. Indeed, we see time and time again in Australia MPA legislation that makes it difficult if not impossible to perform habitat enhancement, not only in sanctuary or “green zones” but also often in the areas that remain open to fishing.
Clearly things need to change. Research in NSW estuaries has found that addition of artificial reefball reefs restored lost carrying capacity and increased total fish abundance without affecting fish numbers on nearby natural rocky‐reef sites – a result identical to that found after the restoration of the shellfish reefs in QLD. So when it comes to both restoration of natural reefs and deployment of artificial reefs, the jury is in on both counts. They work, and given the massive decline in fisheries carrying capacity within our estuaries and inshore areas close to population centres around Australia, we won’t be able to get enough of these reefs back into the water. While the MPA bandwagon rolls on, provided their legislation allows for fish habitat restoration (e.g. of lost shellfish reefs) and enhancement (via artificial reefs), we could end up with situations where we have many more fish in the restored and enhanced fishing zones than the degraded green zones, which MPA dogma require to be “left alone to look after themselves”. So as that famous slogan says. We need to “Just do it”.
For more on how restoration of lost shellfish reefs in a tiny 1.5 ha section of Pumicestone Passage increased fish numbers 16 times, see https://onlinelibrary.wiley.com/doi/abs/10.1111/rec.13413 and http://restorepumicestonepassage.org/wp-content/uploads/2021/05/USCfinalreport.pdf
For more on how artificial reefs increased overall carrying capacity and fish abundance in NSW estuaries, see https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2664.13666
