SANCOR Newsletter Issue #170: June 2002
STUDENTS CORNER
Aging four Catshark species from the Southwestern Cape, South Africa
(And a fond farewell)
Alison Dainty, Zoology Department, UCT
As this is the last issue of the SANCOR newsletter where I’m editor of the ‘Student’s Corner’ (my Masters thesis will be finished by June!), I felt it was necessary to at least discuss some of the research I have been doing these last two years. A portion of my thesis is dedicated to the aging of the pyjama shark (Poroderma africanum), leopard catshark (P. pantherinum), puffadder shyshark (Haploblepharus edwardsii) and dark shyshark (H. pictus). These species are small, demersal sharks and are endemic to Southern Africa. Vertebrae are generally used when ageing sharks because of their lack of other hard parts besides teeth or spines (in some species). Depending on the technique used, growth rings are apparent on the vertebrae (much like the rings in trees) that consist of a dense, hyaline band (presumed to be summer growth) and a light, more translucent band (presumed to be winter growth). The goal of this portion of my project was to see if I could successfully process vertebrae to reveal growth rings, and then assess whether or not these rings were deposited annually.
In order to age these critters, samples, obviously, were a necessity. A small team of ‘expert’ shark catchers (basically trusted divers/friends from UCT) and I would capture these sharks with bait bags at various sites in the southwestern Cape (mostly in False Bay). Nothing could stop our ‘arrive and dive’ team (a phrase coined by a former dive instructor due to our ability to rock up at a site with the expectation of all our gear to be completely ready for use). And for two years, we always underestimated the time these dive trips would take us. I think we half expected that it would take us a total of 5 minutes from the time we ‘arrived’ at the site until we‘dived’. This included putting on wetsuits, checking gear, surveying the site for a good entry point, discussing the goals of the dive, dive times and safety precautions, and then actually walking in full kit to the entry point. Hey, it was possible. We incurred many a bruised limb attempting some not-so-exciting dives (or at least I always thought so). Rain, (so what?) gale force winds (bring it on!), cold temperatures (ha! We laughed in the face of excruciating ice cream headaches!) and washing machine conditions (did my wet suit just rip from being bashed against a rock?) could not stop us. We were an efficient diving machine (that is just in case the former said dive instructor is reading this). Really, we were safe and trusted each other, albeit there were some ‘interesting’ events that occurred in our little group. But I digress…
OK, back to the science bit of the story (yes, some work was involved during the project). After the sharks were captured and brought back to the aquarium at UCT, the specimens were kept for a short period for other project uses, and then sacrificed. The vertebrae were excised and cleaned in commercial bleach to remove any excess tissue. This was the tricky part; if the vertebrae were left in bleach for too long, ligaments that kept them together would dissolve, and I was left with little, individual vertebrae that were extremely difficult to process because of their size (generally around 5 mm). Once a string of vertebrae were embedded in resin, longitudinally sectioned, glued on slides and then sectioned again to reveal a thin section of cartilage, the slide could be viewed under a transmitting microscope. Growth rings were apparent on most specimens. The hyaline and opaque bands together were presumed to represent one year of growth.
Resin embedding proved to be the best processing method to see any substantial growth rings on the faces of the vertebrae once they were sectioned. Wax embedding, freeze dry sectioning, X-Ray and using a Scanning Electron Microscope (SEM) all gave unsatisfactory results. Vertebrae were ‘read’ up to four times and if the readings matched or were close to one another (no more than four‘years’ apart), an average was taken as the final age. I’m still in the process of analysis and comparing data from recaptured specimens, so I have yet to verify whether these sharks deposit annual rings. I know your interest has peaked at this point regarding my results and I’ve left you without a definitive answer. When the project is completely finished, I’ll be able to reveal more results. Maybe I’ll send another article for the next issue, but at that point, I’ll be writing from my home country, the USA.
Just some closing remarks about my time here and what it has meant to me (it is so great being the editor, I can write what I want! Well, with boundaries, of course). And maybe I can pass on some helpful tips to those students who have struggled or are struggling with their research. Firstly, I’ve enjoyed my time here immensely. Although I’ve, unfortunately, seen very little of this country, from what I have seen, it really is a special place. I plan to return many times. Now for the advice, if I may. Conducting research for a degree is painstaking, frustrating (to the point where beating your head against a wall starts to feel good), tiresome, and at some times, mind numbing. But, try not to lose sight of the big picture. You will have a degree in the end (!) and no one can take that away from you. All the sweat and hard work is worth it, although it may not feel like it at (many) times throughout your project. And one lesson I have learned (unfortunately only at the end) is that it really doesn’t matter if your data is perfect, or if your project outline is perfect (because believe me, it most likely will not be), it’s how you explain what did and did not happen in your results. Explain, explain, explain. Thoroughly describe the mistakes, make it known that you are aware of them and discuss every possible reason as to why what happened, happened. Please excuse me if you know this already, but for some reason it took me two years to figure this out! All that matters is if you can express what you know (and even what you do not) in a logical manner. And, if you can say to yourself, "If I only knew then what I know now…" then you’ve learned something. And, isn’t that the point? OK, I’m stepping down from the soapbox now. Good luck everyone!
What lies ahead for Cape Anchovy in a changing climate?
Shona Young, Environmental and Geographical Science Department, UCT
Changes to global climate systems, as predicted by many climatologists, will impact on ecosystems in numerous ways. The nutrient-rich waters of marine upwelling environments enable prolific growth, which in turn support large shoals of pelagic fish. The nutrient supply is dependent on the strength and direction of winds, which govern the upwelling process as well as turbulence. A change in climate may thus affect the food supply and feeding conditions required by pelagic fish populations.
Both climate change and the Cape anchovy (Engraulis capensis) in the southern Benguela System are very topical issues at the moment - climate change because of the sudden and dramatic changes we are seeing over such a small temporal scale and anchovy because of the large catch observed in 2000 which exceeded any catches ever recorded in the past. My research examined the effects of a change in climate, according to a climate model, on anchovy in the southern Benguela upwelling system.
General circulation models (GCMs) have been developed to simulate past climate change, by attempting to understand the processes that produce climate, and to project future trends. The model used in the study is called the National Center for Atmospheric Research (NCAR) Climate System Model, which is a global coupled ocean-atmosphere model. Specific data are obtained from five grid cells in the southern Benguela system (Fig. 1), covering the southern Benguela upwelling system and the area in which anchovy spawn and recruit. The major spawning ground for anchovy is the area east of Cape Point to Cape Agulhas on the western Agulhas Bank, although the major spawning area has shifted further east in recent years. Once anchovy have spawned their eggs, the larvae are carried in a north-westerly direction by the prevailing currents to the recruitment area on
the West Coast. After six months, when the anchovy are sexually mature, they begin their return migration southwards back to the western Agulhas Bank spawning grounds.
According to the results from the model, wind speeds and turbulence off the Agulhas Bank are expected to remain suitable and potentially become even more conducive to spawning in the future. The results show similar mean wind speeds to present day values, a decrease in turbulence, a decrease in the frequency of extreme wind speeds and a decrease in the frequency of extreme turbulence during the anchovy spawning season. An increase in Lasker events (the number and duration of calm periods) is expected at the Eastern Bank Grid Cell, which suggests that this area may become the preferred spawning habitat in the future. The Cape Town Grid Cell also shows suitable conditions in the future simulation for anchovy spawning and may thus become an alternative spawning location. The West Coast shows an increase in alongshore wind stress and thus an increase in upwelling in the future simulation from November–February. This is likely to increase planktonic food availability and ultimately anchovy recruitment.
Output data from the Climate System Model thus show that to the best of our present knowledge and understanding of climate change, anchovy will continue to spawn on the eastern and western Agulhas Bank during the spring and summer months, and that conditions in these areas may even improve. Global climate models are continually being upgraded and replaced with newer models. Future research could utilise the latest models for generating climatic predictions and run comparisons with the data presented in this study. In this way the fisheries industry can keep track of the best available predictions for climate change as well as the possible implications for anchovy recruitment.
Fig. 1: The five grid cells investigated in the southern Benguela system
Visit to the Cabrillo Marine Aquarium, San Pedro,California
By Ashok Bali (University of the Western Cape)
Recent evidence suggests that the jellyfish, Chrysaora hysocella, has become abundant (compared to 30 years ago) in the waters of the northern Benguela ecosystem. Populations of jellyfish are now so large that they may prevent the recovery of the once abundant pelagic fish populations, which has serious economic implications.
distribution of Chrysaora, basic biological information for this species is lacking. This is partly due to the difficulties in capturing and maintaining specimens in laboratory conditions.I have recently started a M.Sc. thesis on the reproduction and growth of Chrysaora hysocella, in an effort to gain a better understanding of this species’ biological functions. This (and future) research will be based on the factors that contribute to planula settlement, scyphistoma persistence, strobilation and medusa growth. This study will also include aspects of feeding biology and tolerance to low oxygen bottom water.
The first stage of the project is to establish viable laboratory polyps. This requires me to breed this species in captivity, as the polyp stages have not been observed in situ. In order to successfully breed this species, expertise was sought with a partner institution, the Cabrillo Marine Aquarium (CMA), San Pedro, U.S.A. funded by the Royal Society-NRF SET programme in Biodiversity at UWC, I was able to take a three-week visit to the aquarium. The objectives of the venture were to learn jellyfish husbandry, pre and post breeding protocols, maintenance, tank design and feeding regimes.
Mike Schaadt is director of the aquarium and co-ordinates the Aquaculture Laboratory, which serves as the breeding grounds for animals in the aquarium. He supervises the work of students and volunteers. Larry Fukuhara, the Programmes Director, co-ordinates events such as the famous grunion run, gray whale and dolphin watching and lectures at the CMA. I also had the opportunity to meet Dr. M. P. Franklin who is the Life Science co-ordinator at California State University, Bakersfield and Research Associate Co-ordinator at the Southern California Marine Institute. He hosts an online tertiary course on biology, which is also broadcasted on a nation-wide cable channel, and I had the privilege of appearing on the programme for an interview.
Being a foreigner in the most powerful country in the world, one could expect to feel estranged, however, the residents of California are amongst the friendliest people I have ever met, whether it was at the beaches, malls or bus stops. California is truly the "melting pot" of the world and exudes cultural and racial diversity. If I could single out one impression that California has given me, is that of the word "metropolitan". I would definitely return for another fifteen minutes of fame.
The Cabrillo Marine Aquarium (CMA), San Pedro, U.S.A.
