What’s a Zooplankton Hole?

4th July 2017

A recent journal article in the Nature Ecology and Evolution journal titled, “Widely used seismic survey air gun operations negatively impact zooplankton” (Robert D. McCauley et al) investigated the effects of seismic surveys on zooplankton.

Zooplankton underpin the health and productivity of global marine ecosystems.  Zooplankton are a group of small animals including organisms whose complete life cycle lies within the plankton (holoplankton) as well as organisms that spend part of their lives in the plankton before moving to the bottom (meroplankton).  Zooplankton are primarily transported by water currents but many have locomotion used to avoid predators or capture prey.

 

 

 

 

Seismic surveys are used to produce detailed images to determine the location and size of possible oil and gas reservoirs.  Sound waves emitted by seismic equipment are bounced off underground rock formations and the waves that reflect back to a vessel where they are captured by recording sensors for later analysis.

In March 2015 the study took place at Storm Bay off southern Tasmania.  It used plankton nets to collect live and dead zooplankton before and after a simulated seismic survey.  The study found the simulated survey created a 2km wide “hole” up to 30m deep in the zooplankton population where abundance dropped by two-thirds and the number of dead zooplankton increased two to three times.

The study did not investigate why this was occurring but did speculate that exposure to seismic waves may have damaged sensitive hairs that zooplankton use for locomotion.

Zooplankton are “R” selected meaning they have high growth rates, short life cycles, high reproductive rates and very low survival to adults.  These populations may only be affected for a short time by seismic surveys because they can bounce back quickly.   However, the study noted that commercial fish species are also a significant component of zooplankton.  Commercial fish species rely heavily on annual recruitment events and are not true R selected species.

South East Trawl fishermen have always known that once a fishing ground has a seismic survey that it becomes unproductive for a period of months.  The zooplankton hole theory might explain this with a period of unproductivity occuring until the short life cycle of these organisms and oceanic mixing backfills the hole.

In 2014 oil and gas exploratory company ION proposed the largest seismic survey in Australia’s history effectively covering all of south-east Australia (see below).  Thankfully this survey was cancelled for commercial reasons.

In spite of recent research about the potential negative effects that seismic surveys have on zoooplankton, scallops and crayfish, SETFIA members are consumers of oil, acknowledge the importance of Australia’s energy security and want to act as good neighbours.  For these reasons SETFIA continues to assist the oil and gas industry to plan and run their activities in a way in which the fishing industry present the lowest possible risk and the disruption to fishing businesses is minimised.