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My experiences on a fisheries trawl survey
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I was invited to join a team of scientists from the Department of Agriculture, Forestry and Fisheries (DAFF) for the first leg of the annual South Coast Demersal Survey that usually takes place in September upon the RV Africana.
This particular survey has not been conducted in recent years due to the RV Africana being out of service. Fortunately, with the Africana finally being back in the water, DAFF could take her out to proceed with the survey.
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The primary objective was to conduct a swept area demersal trawl survey to assess the abundance and distribution of hake, horse mackerel, squid and other key demersal trawl species on the shelf and upper slope of the South Coast. Other objectives included collecting hydrographic data using a CTD (an oceanography instrument used to determine the conductivity, temperature, and depth of the ocean) and to fulfil other sample requests from external scientists as well as scientists from other sections within the DAFF Fisheries Research Chief Directorate.
The intention was to successfully sample a minimum of 120 trawl stations during the survey, which were selected using a pseudo-random stratified sampling design. This survey includes deeper stations in the 500-1000 m depth range, as has been conducted since January 2011, to encompass the deeper trawl grounds that are exploited by the deep-sea trawl fishery.
My first taste of “trawl-life”
The voyage started by departing Cape Town harbour around 4pm on the Thursday and setting sail for the South Coast. The work began the next morning with a bang!
The first few trawls had a good catch size, filled with all sorts of fish and invertebrates. Along with ten other scientists representing DAFF, I represented SAEON as the “Invert Lady”. I was assigned to identify, sort out, weigh and count all marine invertebrates caught in the trawl nets. If any of the invertebrates were rarely found, I was requested to retain and collect them for further identification.
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The first couple of days were a bit of a challenge as this was my very first time doing this kind of work and being exposed to the “trawl-life”. After the first few trawls, I found a rhythm and the work became a lot more interesting as we continued to find some extraordinary creatures.
As we moved further offshore we noticed a distinct change in the catch composition of fish and invertebrates. I was pleased to see that in some of the catches we managed to collect quite a few specimens that had been rarely found prior to this survey.
Obstacles
Although most of the trip went according to plan, achieving four to five trawls a day, we faced a few obstacles along the way. Firstly, weather conditions were marginal at times. About half way through the first leg of the voyage, a cold front came through churning the sea up, preventing us from being able to work. We had to set anchor inshore along the Witsand/Breede River mouth.
Secondly, the trawl net got caught on hard ground, causing some damage to the net and gear. However, once we had evaded the bad weather and repaired the net, we continued the rest of the survey without further incidents.
During the first leg of the cruise the vessel worked its way from west to east, starting from the western part of the survey area (20°E, in line with Cape Agulhas) towards Mossel Bay. Once we docked at the Mossel Bay harbour, most of our team disembarked and the first change-over occurred.
A shuttle was organised to take us back to Cape Town. As we disembarked, the next team got on board. They were scheduled to work eastwards to Port Elizabeth and then back to Cape Town.
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Opportunity to observe and learn
I really enjoyed the opportunity of joining DAFF in this survey, especially as I got to observe and learn, not only from the invertebrate aspect, but also by assisting the other scientists during my free time with sexing species including hake, sharks and rays; measuring and weighing fish; and capturing data.
I am grateful to have met such an amazing group of people who are as passionate about marine life as I am. It was a pleasure being on board the RV Africana. I would like to thank the Captain and crew for a safe journey and for the hospitality they displayed.
A huge thank you to the DAFF team and to my mentors and manager at SAEON for allowing me this opportunity of learning and working in an environment that I am so passionate about.
Watch a video of Leila’s experiences: Africana_vid2Sept2016.mp4
