(Originally published in the November/December 2019 issue of Ski-Boat)
By Bruce Mann
Oceanographic Research Institute (ORI)
I WAS recently contacted by Nick Nel from the Natal Deep Sea Angling Association who asked whether I thought it would be possible to include seventy-four (Polysteganus undulosus) as a target species in the 2019 Bottomfish Nationals scheduled to be fished from 11 to 16 August off Durban.
As most ski-boat anglers know, seventy-four are on the Prohibited List and may not be caught. However, the moratorium on this species has been in place since 1998 and there are indications that the population is slowly recovering.
In the absence of catch information, scientists need to explore alternative methods to assess the population trend of seventy-four. One novel way of determining whether the population is recovering — without having to kill any fish — is through genetics. A small fin clip (the size of a fingernail) taken from one of the pelvic fins and an accurate measurement of the fish is all that is needed. This can be done on a live fish which is then released back to the sea. Fortunately seventy-four seem to be able to survive the stresses of barotrauma (i.e. pressure change when being brought to the surface) better than some other reef fish species and this enables them to swim back down after being released.
After thinking about Nick’s suggestion I contacted Dr Denham Parker at the Department of Environment, Forestry and Fisheries (DEFF) and asked him whether involvement of ski-boat anglers in the collection of seventy-four genetic samples was a possibility. Denham managed to obtain permission for the 16 boats and anglers competing in the Nationals to collect seventy-four fin clips on condition that best handling practices and fish survival were prioritised.
Back at ORI we made up 16 sampling kits (one for each vessel) containing ten sample bottles filled with 95% ethanol, a tape measure, pencil, labels and pair of scissors, along with a clear instruction brochure explaining how to handle and measure the fish, take a fin clip, release the fish and record the data. These sampling kits were given to the skipper of each vessel at the briefing before the competition.
A sample of at least 50 fish is required to produce results that are statistically significant. While only 11 seventy-four were caught and sampled during the competition, this is a good start and a much-needed, positive collaboration between scientists and anglers.
Chris Wilke, a senior technician from the DEFF, was able to attend some of the weigh-ins in the afternoons and collected the samples that had been taken. Basically, what the geneticists will do is to get an estimate of the genetic variability (heterozygosity) of the population and compare this to a similar estimate that was made based on samples collected by ORI in 2006. An increase in heterozygosity is a good indication of an increasing population. This is particularly true in species that have suffered a population collapse (e.g. seventy-four) as genetic diversity is inherently low due to the relatively few breeding individuals. Similar attempts will be made to collect more fin clips over the next 12 months.