Over the years the jigging fishery has experienced large fluctuations in catches. It is thought that these fluctuations are the result of environmental influences. In 1991 the SFRI installed a permanent mooring in St Francis Bay to investigate the environmental factors that influence the arrival of squid on the spawning grounds the survival of eggs and hatchlings. The mooring contains instruments that measure currents, temperature and the turbidity, or clarity, of the water. Good catches of squid correspond to low temperatures of the coastal water.
Poor catches occur when bottom turbidity is high on the benthic spawning grounds.
Squid eggs develop faster in warmer temperatures, resulting in higher hatch rates. The behaviour of squid during spawning affects their residence time on the spawning grounds, and thus catch rates by the jigging fishery. Research with acoustic tags has shown that females remain near the egg bed longer than males, especially at night. It is therefore likely that more females are caught at night. If it becomes necessary to limit fishing effort to protect the squid resource, this would be most beneficial at night.