Seasonally abundant marinelife
Since the early 1800's fishermen have worked the offshore waters of southern Western Australia, primarily in search of whales, bluefin tuna and the prized deepsea orange roughie.
Being passionately curious about our local marine environment, we have eagerly participated in research cruises that venture out over the continental shelf edge to see with our own eyes exactly what was out there.
Over the years we have noticed that the offshore waters over the continental shelf edge are typically low in surface activity with the occasional seabird following behind our vessel and very rarely are any fish captured on one of our trailing tuna lures.
This is in complete contrast to what we observe on the shelf itself where birds, tuna and bowriding dolphins abound.
Generally speaking, the inshore waters are far more abundant with surface activity than over the continental shelf edge.
We first noticed an exception to the rule back in summer 2006 when during a
survey looking at the abundance of southern bluefin tuna, we passed through
an area of extreme marine activity some 30 miles from shore and 6 miles over
the edge.
Consistent sightings of seabirds, sunfish, sharks, killer whales, tuna and schools
of tiny baitfish all seemed to indicated an area of unusually high productivity.
Year after year we observed the same activity in roughly the same geographical
location.
There are more than two dozen deepwater rifts running up to the continental
shelf edge along southern West Australia yet we have never heard of, read
about or seen anything like what we were observing near the Bremer canyon.
We figured that something must be causing the animals to gather in this
particular location, but what?
Surface blooms
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Around the same time the marine life is frequenting the area, we noticed massive plumes of "dirty water" stretching far across the surface.
We started researching aerial images of the location and eventually came across NASA's MODIS satellite program.
NASA's high resolution satellite photography has been ongoing since October 2004 and after trawling through hundreds of their images, we came to the conclusion that these blooms were possibly getting nutrition from something that was emanating from below, right in the area we were observing the activity.
Hydrocarbons
Continuing our research, we happened upon a report that was produced by GeoScience Australia, an Australian government agency looking for oil and gas accumulations during 2004.
They identified possible fuel reserves in a number of locations in offshore Western Australia ... including where we had consistently been seeing the killer whales.
Fast forward to December 2009 and an oil and gas explorer commenced a more extensive 2D seismic examination of the seafloor. Their survey positively identified a number of promising oil and gas prospects.
In addition, they encountered a number of killer, sperm and pilot whales .. right where we were observing them .. and at the same time of year.
Seafloor nutrient seepage
To understand what could be happening we needed to contemplate whether the fuel was leaking and somehow kickstarting the phytoplankton bloom, causing the animals we were observing to gather and feed.
We got in contact with an expert .. Norwegian scientist Dr Martin Hovland.
Martin's 30 years of research in the North Sea and Gulf of Mexico suggested light hydrocarbons (methane, propane, butane and other chemicals) are migrating toward the surface from these deep sub-seafloor oil and gas accumulations.
The hydrocarbons are used by bacteria who turn it into nitrogen which feeds into and benefit the entire food chain, beginning with the phytoplankton.
Check out this MARUM video which explains how these systems function.
There are upwards of three dozen deep water canyons along Southern Australia's continental shelf edge yet not all are as productive as Bremer Canyon. Our observed seasonal gathering of marine life appears to be concentrated within a portion of the massive oil and gas prospect.
So it seems Martin's theory could explain the way nutrients from a deepwater oil and gas deposit can effectively "fertilize" an area of ocean and therefore provide a reason for animals to gather.
But we believe there is more to this picture than leaking nutrients being carried to the seas surface by the upwelling of the nearby Bremer Canyon.
With nitrogen being a standard fertilizer, animals such as crabs, shrimps,mussels and prawns can now live on the methane hydrate reef far below. Crustaceans undertake spawning once a year (much like the Christmas Island red crabs) and we believe there may be a mass, seasonal spawning event occuring somewhere underneath the killer whales in summertime each year and this is amplifying the availability of food.
FURTHER INFORMATION:
MARUM: Methane Hydrates explained
Pozible Crowd Funding Campaign
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Bremer Canyon - History
Image copyright Martin Hovland