I AQUATIC INVASIONS of the NSELENI RIVER SYSTEM
Total Page：16
File Type：pdf, Size：1020Kb
AQUATIC INVASIONS OF THE NSELENI RIVER SYSTEM: CAUSES, CONSEQUENCES AND CONTROL Thesis A thesis submitted in fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY of RHODES UNIVERSITY by Roy William Jones Department of Zoology and Entomology Rhodes University P.O. Box 94 Grahamstown 6140 Date: December 2014 i Frontispiece Richards Bay – 1937 (T.Ott – Richards Bay Minerals) Richards Bay – 2012 (Google Earth) ii QUOTATION “We May Be Brothers After All”. In 1854, The Great White Chief in Washington made an offer for a large area of Indian land and promised a “Reservation” for the Indian people. Chief Seattle’s reply to the offer was: “How can you buy or sell the sky, the warmth of the land? The idea is strange to us. If we do not own the freshness of the air and the sparkle of the water, how can you buy them? Every part of this earth is sacred to my people. Every shining pine needle, every sand shore, every mist in the dark woods, every clearing and humming insect is holy in the memory and experience of my people. The sap which courses through the trees carries memories of the red man. The white man’s dead forget the country of their birth when they go to walk amongst the stars. Our dead never forget this beautiful earth, for it is the mother of the red man. We are of the earth and it is part of us. The perfumed flowers are our sisters; the deer, the horses, the great eagle, these are our brothers. The rocky crests, the juices in the meadows, the body heat of the pony, and man – all belong to the same family. So when the Great White Chief in Washington sends word that he wishes to buy our land, he asks much of us. The Great White Chief sends word he will reserve us a place so that we can live comfortably to ourselves. He will be our father and we will be his children. So we consider your offer to buy our land, but it will not be easy. For this land is sacred to us. This shining water that moves in the streams and rivers is not just water but the blood of our ancestors. If we sell you our land, you must remember that it is sacred, and you must teach your children that it is sacred and that each ghostly reflection in the iii clear water of the lakes tells of events and memories in the life of my people. The water murmur is the voice of my father’s father. The rivers are our brothers, they quench our thirst. The rivers carry our canoes, and feed our children. If we sell our land, you must remember, and teach your children, that the rivers are our brothers, and yours, and you must henceforth give the rivers the kindness you would give your brother. … But in you perishing you will shine brightly, fired by the strength of the God who brought you to this land and for some special purpose gave you dominion over this land and over the red man. That destiny is a mystery to us, for we do not understand when the buffalo are all slaughtered, the wild horses are tamed, the secret corners of the forest heavy with scent of many men, and the view of the ripe hills blotted by talking wires. Where is the thicket? Gone! Where is the eagle? Gone! The end of living and the beginning of survival”. Chief Seattle (an Anglicization of Si'ahl) 1854 iv IN MEMORY OF THE LATE Esther Joyce Amy Jones (9 June 1927 - 1 September 2011) You may no longer walk the world as we know it, but you will never be forgotten, as you look down on us from amongst the stars. Thank you for all your encouragement in allowing me to pursue my interests, even though it took me far from home, at an early age. Thank you for everything you did for our family, especially during the tough times. v Mbazwane Mhlongo (15 October1956 – 22 June 2012) Mbazwane joined the then Natal Parks Board, now KZN Wildlife, on the 1st of October 1976 and had always been stationed at the Enseleni Nature Reserve. Mbazwane started as a general assistant and worked his way up through the ranks to a Senior Field Ranger. All of his Officers-in-Charge saw the potential in him to progress within the conservation structure. At the time of his death, Mbazwane had 36-years of unbroken service. I was busy attempting to get him promoted to a Principal Field Ranger at the time of his untimely death. Mbazwane died in the line of duty when he and a colleague drowned on Lake Nhlabane, while recovering illegal gill nets. Mbazwane took every opportunity to join me on the river while carrying out various research, assisting students with research projects or boat patrols. Mbazwane showed a keen interest in controlling water hyacinth on the Nseleni River, not because it was his job, but because he knew the negative effect it was having on biodiversity. Mbazwane was fascinated by the biological control agents that had been introduced and always asked deep penetrating questions about them. Shortly before his death, Mbazwane received the highest award that a Field Ranger can receive, namely the Magqubu Ntombela Award for the Best Field Ranger in Ezemvelo KZN Wildlife. Hamba Kahle, Mbazwane. vi Abstract Globalization has seen an unprecedented dispersal of exotic and alien species worldwide resulting in worldwide homogenization and sometimes extinction of indigenous or endemic taxa. When an exotic species becomes established in a new habitat the invasive organisms are capable of having an impact on indigenous community dynamics and the overall structure and function of ecosystems. Furthermore, the impact of invasion is determined by the geographical range, abundance and the per-capita or per-biomass effect of the invader. However, the success of the introduced organisms is reliant on their ability to acclimate to the physiochemical conditions of the newly invaded environment. Freshwater ecosystems are especially vulnerable to invasions because there are numerous potential routes of introduction including intentional pathways such as stocking, and unintentional pathways such as the release of ballast water and aquarium releases. Efforts to limit the introduction of invasive species or to manage established exotic populations are often hindered by insufficient understanding of the natural history of problematic species. Relatively little is known regarding the physiological tolerances of many taxa. Knowledge about specific species ecophysiological constraints allows for the prediction of future patterns of invasion more accurately, including where an introduced organism would probably survive, thrive and disperse. Furthermore, data on the physiological tolerances of an introduced exotic organism may provide data necessary for effective management and control. This study investigated three invasive species in the Nseleni River system in a protected area in KwaZulu-Natal. The species studied were, Tarebia granifera (Quilted melania – Lamarck, 1822), Pterygoplichthys disjunctivus (Suckermouth armoured catfish - Weber, 1991) and Eichhornia crassipes (water hyacinth – (Martius) Solms-Laubach,). The Nseleni River flows into Lake Nsezi which is responsible for providing potable water to the surrounding towns and industry, as well as the surrounding rural communities. The Enseleni Nature reserve has become the centre for biodiversity dispersal in the immediate area, due to the change in landscape surrounding the protected area. vii An important step in developing alien invasive species management strategies in protected areas is determining their extent and invasive traits. Tarebia granifera is a prosobranch gastropod originally from South-East Asia that has become invasive in several countries around the world including South Africa. Snail populations were sampled at nine sites throughout the Nseleni/Mposa river system every six weeks over a twelve month period. The snail was abundant throughout the system, especially in shallow waters of less than 1m in depth. The first positive identification the loricariid catfish Pterygoplichthys disjunctivus for the Nseleni River was in 2006. The original introduction is believed to have been via the aquarium trade. The aim of the study was to assess the usefulness of the unified framework with regard to management of fish invasions by assessing the invasion stage of the loricariid population and identifying appropriate management actions using the Blackburn et al. (2011) framework. The fish were sampled at nine different sites and three different depths over a period of twelve months, as well as when two ichthyological surveys were carried out on the Nseleni River system. This invasive fish has been located throughout the system and both male and female fish were collected. The smallest fish sampled was a fingerling of a day or two old and the smallest pregnant female was a mere 270mm TL. This is a clear indication that this fish is breeding in the river system. Although T. granifera and P. disjunctivus were abundant in the Nseleni/Mposa river system, it was not clear what their role in the system was, and in particular if they were competing with any of the indigenous species. Therefore, isotope samples were collected from numerous taxa over a two week period, with the exception of Pterygoplichthys disjunctivus samples, which were collected over 12 months. The δ13C and δ15N signatures of all samples were determined. The niche overlap between the invasive and indigenous snails was effectively zero (1.02E-13%), indicating no shared food resources. The medium ranges of dNRb (7.14) and dCRb (9.07) for the invasive fish indicate that it utilizes a wider range of food resources and trophic levels than the majority of indigenous fish. A medium CDb value (2.34) for the invasive fish species, P.