Understanding the impact of fishing on the marine environment is a complex science. As yet, our reporting programme cannot draw firm conclusions about the full ecological impact of fishing on wider marine ecosystems.
The data we reported in this chapter provide a partial picture of fishing pressures. While it is good news that commercial dredging and bottom trawling are decreasing, there were still more than 72,000 trawl tows in 2014. Knowledge on the ecological implications of trawling and dredging and the consequences for the productivity of fish stock for New Zealand is incomplete.
The 17 percent of New Zealand’s commercial fish stock assessed as overfished in 2015 compares favourably to international data on overfished fish stocks. However, the purpose of the fish stock data are to inform good management decisions within QMS; the data are not intended for environmental reporting on the ecological sustainability of fisheries or wider ecosystems.
MTI indicates no determinable change in the abundance of demersal fish in the Chatham Rise over the past few decades. Having similar data across other fishing grounds in the wider EEZ would provide more information on the impact of fishing and other pressures on marine ecosystems.
Data on commercial bycatch of seabirds and marine mammals reported in the chapter Our marine birds and mammals show that while bycatch is decreasing, it is still an important cause of death for some threatened seabird and marine mammal species.
To provide a fuller picture of the impact of fishing, future reports would need to include data on the bycatch of other non-target species, and pressures on fisheries and marine ecosystems from recreational and customary fishing.
The role of phytoplankton in supporting marine life and our fisheries
Phytoplankton, microscopic organisms at the base of the food chain, use a pigment called chlorophyll-a to capture energy and grow via photosynthesis. These phytoplankton then become food for other marine organisms, including commercial fish species. As the marine environment’s primary producers, phytoplankton are critical for the productivity and abundance of other marine life, and the overall health of the marine ecosystem. They also influence other important aspects such as carbon dioxide uptake by the ocean.
Primary productivity is the synthesis of new organic material from nutrients and sunlight by phytoplankton, and can be measured by satellite observations of concentrations of chlorophyll-a. Primary productivity is often high along coastlines and in underwater continental shelf areas – one reason these areas are also productive fishing grounds. Figure 11 shows the relatively high primary productivity of the Chatham Rise, one of the most important commercial fishing grounds in New Zealand’s EEZ.
This map illustrates variation in the primary productivity of New Zealand’s waters between 1997 and 2016. Visit the MfE data service for the full breakdown of the data.
For more detail see: Environmental indicators Te taiao Aotearoa: Primary productivity.