by Dr.Warren Potts
TIMES have changed. The media, no doubt, has contributed. No longer are fishermen solely feverishly pursuing and killing their victims. Rather, there seems to be a need to understand, a will to appreciate and a hope to conserve their quarry.
I obtained overwhelming evidence of this after I published an article entitled “Leervis and the curious angler — Looking for answers to Southern African migration” (see SKI-BOAT November/December 2007). This article was written in response to questions raised by Johan Smal in the previous issue of this magazine.
In his article, Johan speculated that the leervis in the Western Cape actually come from Angolan waters. I had been conducting research on the biology and movement of the southern Angolan leervis for some time and was also interested to find out.
In the article I proposed a potential solution to the problem using a genetic analysis. I therefore asked interested anglers in South Africa and Namibia to collect a small piece of fin of the leervis that they had captured for a genetic analysis. Well, the response to the article was fantastic and I fielded many calls and emails from eager anglers, all with their opinions on the movement of the leervis. They offered their help and I gladly accepted it.
At this point I’d like to thank the anglers who agreed to collect genetic samples for me from all over the region. These included Johan Smal (Western Cape), Lourentius Bellingham (Western Cape), Chis Schultz (Eastern Cape), Dave Drennan (Eastern Cape), Mike Karron (KwaZulu-Natal), Jorg Walter (Namibia) and Stephen “Spyker” Kruger (Namibia). Without the help of these gentlemen, we would not be able to answer some interesting questions about one of our favourite species.
Well, we finally managed to collect a total of 985 genetic samples from the three countries and the results are back. A PhD student from the Royal Holloway University has conducted various analyses on the samples and this is what she said:
“The network assessments for the leervis showed that all genes revealed a clear distinctive break between samples from Angola/Namibia and South Africa, thus supporting the idea of a dispersion barrier between these countries.”
What she is trying to say in fishermen’s language is that there is no shared genetic material between leervis from South Africa and the Angolan/Namibian leervis. The cold water of the Benguela Current acts as a barrier to the southward and northward migration. The Angolan and South African leervis have been completely isolated for about two million years. So, adult fish do not make that arduous journey south from Angola to the South African coast, or vice versa. Eggs are not transported south from southern Angola through Namibia and into South African waters because of the northward flowing Benguela, and eggs cannot make it from South Africa to Namibia as they spawn a long way away in KZN waters.
I also recently received some exciting news from a good friend of mine, “Spyker” Kruger, who is a fishing guide from Hentiesbaai, Namibia. While fishing near the Winston Wreck in February, Spyker recaptured one of our tagged leervis. This fish was originally tagged at Flamingo Lodge (Angola) on 2nd June 2009 and recaptured on 13th February 2010, having made the 780km journey in no more than 256 days.
Just for interest, the fish had grown from 56cm fork length (1.9kg) to 67cm fork length (3.5kg) during that short time. This really provided confirmation of our genetic results, which suggested that the Angolan and Namibian leervis were one population.
So.....what does this all mean for us?
Firstly, the south African leervis can be managed as an independant population. We don't need to get into political deliberations with Angolan and Namibian governments over how to conserve this species. The South African leervis rersource is ours and we are wholly responsible for it.
Given the recent alarming news from Daniel Smith and Bruce Mann (in the Oceanographic Research Institute Tagging News No.22) whose research has shown that our leervis stock has collapsed to 14% of it's pristine biomass, we as anglers have to act immediately.
There appear to be two major problems for the leervis in South Africa. Firstly there is the problem of massive adult mortality. This occurs primarily in Kwazulu Natal during the annual sardine run. In fact, in Daniel Smith's MSc thesis which looked at the movement and health of the population, he showed that the numbers of fish arriving in Kwazulu-Natal each year in winter far exceeds the numbers that return at the end of the sardine run.
The second problem for the leervis is their dependance on estuaries when they are juveniles (10cm-70cm). There can be no argument that our estuaries are in very poor health at the moment. One of the major causes is the utilisation of large amountsof river waterfor farming, industry and human consumption.
This has drastically reduced the freshwater flow into our estuaries. In many cases, with the lack of freshwater flow, estuaries are no longer permanently open to the sea. In Kwazulu-Natal in particular, the estuaries are in very poor health and this has forced the juvenile leervis predominantly into the Transkei and Eastern Cape estuaries.
Unfortunately, one of the consequences of the beach vehicle ban, particularly in the Eastern Cape, has been a dramatic increase in the amount of fishing effort in estuaries. Certainly the increase in recreational, subsistance and illegal fishing (gillnets) in this region is having a major impact on the juvenile leervis population.
So, what can we do to protect the leervis? With government wheels generally quite slow to turn, it is unlikely that the regulations for this species will change very soon. In my opinion, when they are amended, the best option for protecting the adult fish should be a closed season over at least a portion of the sardine run.
For the juveniles, I would like to see improved water management of whole river systems for important estuaries (but I fear this is just a dream) and a clampdown on illegal fishing activities (by all sectors) for this species.
WHAT CAN WE DO TO PROTECT THE LEERVIS?
- Release more fish. One fish over 70cm is more than enough for the table, so don't always kill your limit.
- Use fish friendly capture techniques (especially when targeting juveniles in estuaries)
- Replace your treble hooks with barbless singles.These are sharper, penetrate deeper (so often hook the fish better), but are also easier to get out, and cause less damage to the fish.
- Improve your handling practices. Usea wet cloth to handle your fish, don't touch their eyes and don't let them touch a hot boat deck or dry beach sand.
- Have a camera ready and waiting, so that the photo is taken quickly.
- Be vigilant. Chastise fellow anglers who don't adhere to the regulations. They are after all, killing your resource. Report any illegal activities to the relevant authorities.
Without this type of attitude and practice, we are likely to knock the leervis out of it's rightful place as a dominant predator in the surf zone and estuaries, and condemn it to the shadows where it merely struggles for survival.
Article courtesy of: Skiboat Magazine
