GREAT BARRIER REEF
// Outlook Report 2014
The condition and trend in phytoplankton abundance are monitored through indicators such as chlorophyll a, which is now recorded in the Region via remote sensing as well as in situ sampling.150,151,152,153,154,155,156,157 For the years 2010 to 2012, differences were recorded in the abundance and diversity of the phytoplankton between the northern third of the Region and areas further south, although there is not yet sufficient data to detect trends.157 While there is still limited information about the condition and trend of zooplankton in the Region, there is now increased data collection158,159.
There are about 1600 species of bony fish in the Region. This diversity of species is recognised in the world heritage listing of the Great Barrier Reef.23 Decades of research have improved understanding of fish biology and ecology, particularly commercial species, but very little is known about the status of most species.142 There is long-term monitoring of 214 species of coral reef fish populations160,161 (Figure 2.9). Fisheries-dependent monitoring provides some information on the trend of a number of species targeted by fishers162; however, there is limited fisheriesindependent monitoring. There has been no comprehensive analysis of the long-term trends in the populations of the coral reef fish species that are monitored. Populations of the coral reef fish species are likely to have been affected by the declines in their habitats163,164 especially in the southern two-thirds of the Region. Current understanding of fishing activities suggests targeted species are under significantly more pressure in the southern two-thirds of the Region (Section 5.4). These patterns are likely to be similar for nontargeted fish species that interact with the fishery. The condition of northern populations of targeted and non-targeted species is not well known. Of the species targeted in fishing activities, decades of fishing pressure have reduced the size of individual fish, reduced abundances, and contributed to population declines — at least for the more heavily fished species.165 This is likely to have been exacerbated by extreme weather, reduced habitat availability and declining water quality.166 Selective fishing can also lead to potentially irreversible evolutionary changes in populations of targeted fish species.167,168 Zoning arrangements within the Region have been shown to affect the abundance and biomass of targeted species.169,170,171 The biomass of coral trout, one of the most commonly targeted reef fishes, is greater in no-take zones than in zones open to fishing165,172 (Figure 2.10). Life history traits, habitat preferences and cumulative pressures mean that populations of some targeted species may be particularly vulnerable. The vulnerability of two species of threadfin salmon has been assessed as ‘high’.173 The vulnerability of grey mackerel has been assessed as ‘medium’, with concerns about the future sustainability of stocks in the Region.174 Stock assessments undertaken as part of fisheries management provide an indication of the condition of some targeted species. The stock of snapper has been assessed as ‘overfished’ (where harvest may be exceeding sustainable levels and/or yields may be higher in the long term if the effort is reduced) for the past three years.142 The stock status of Spanish mackerel could be approaching ‘overfished’.175 In 2012, the stock status of coral trout moved from ‘sustainably fished’ to ‘uncertain’ due to low catches and catch rates.142 The ecological consequences of reduced fish populations and biomass, for example flow-on effects to other trophic levels, are largely unknown. The biology of some of these fishes (for example being long-lived, late maturing or forming aggregations for spawning) makes them vulnerable to depletion.176 In addition, fishing activity, including illegal fishing in zones closed to fishing, has contributed to population declines of some targeted fish species.171