Disruption of Marine Ecosystems

The reduction of targeted fish populations may have significant ecological flow-on effects. These impacts are not well understood. Large scale purse seining of inshore species such as kahawai, jack mackerel and trevally may have reduced food for seabirds such as white-fronted terns and Huttons and fluttering shearwaters which typically feed in association with schooling fish. These larger schooling fish drive the smaller fish to the surface where they can be captured by these seabirds.

Squid is an important part of the diet of many bird species, toothed whales, dolphins, seals and sea lions. Harvesting large quantities of squid may have an impact on these species, but the effects are poorly understood. ¹⁸³⁹

Reductions in targeted fish populations can impact on the entire food web. When top predators are removed, their prey species may increase in number, in turn increasing predation further down the food web. Research on the marine habitat at Mimiwhangata Marine Park and Paparahi Point in the northern part of the Auckland region has indicated that because predators such as snapper and crayfish have been extensively fished in nearby coastal areas, numbers of their prey kina (sea-urchin) have increased dramatically. ¹⁸⁴⁰  Kina graze on kelp, and their increase in numbers has resulted in some rocky reefs being stripped bare of their kelp forests – referred to as ‘kina barrens’. ¹⁸⁴¹

Last updated at 1:38PM on February 25, 2015