Since January 2011, I am working as postdoctoral fellow at the Marine Research Institute (Ma-Re), University of Cape Town (UCT). My current research focuses on the assessment of the South African linefishery resource and is conducted under the supervision of Prof. Colin Attwood from the Zoology Department, UCT, and in close collaboration with Dr. Sven Kerwath from the Inshore Resources Research Unit at the Department of Agriculture, Forestry and Fishery.
In South Africa, the term ‘linefishery’ is used to denote a multi-species, multi-user, multi-area cluster of low to medium technology fisheries that make use of hand-lines and rods and reels from the shore and from boats. In the late 1990’s, spawner-biomass per-recruit assessments produced alarming results for the majority of linefish species, which subsequently lead to the declaration of the state of emergency in this fishery in 2000, accompanied with a significant reduction in commercial effort. To date, a decade later, quantitative assessments of the impact of these management interventions, which were designed to allow stock recovery, are long overdue. The aim of my current research project is therefore to develop age-structured assessment models that allow the integration of (i) life history parameters, (ii) total catch estimates, (iii) catch and effort time series (1985 – 2010), (iv) information on the population size structure and (V) historical baseline reference points into a quantitative stock assessment framework for important South African linefish species. These include, for example, important commercial species such as silver kob Argyrosomus inodorus, geelbek Atractoscion aequidens, carpenter Argyrozona argyrozona, snoek Thyrsites atun and slinger Chrysoblephus puniceus.
My general research interests could be placed within the wider field of fisheries ecology and specifically revolve around life history adaptation, population dynamics, catch-per-unit-effort standardization based on generalized linear and additive models, bootstrap methods and stochastic age-structured fisheries models.
During my MSc thesis at the University of Plymouth (2005), I investigated the long-term population response of commercially important fish stocks to exploitation, covering several ICES and NAFO areas of the North Atlantic. The thesis was conducted in collaboration with the FishBase Team and was primarily supervised by FishBase founder Dr. Rainer Froese. Subsequently, Dr Froese employed me as researcher in the European INCOFISH project (www.incofish.org) at the Leibniz Institute for Marine Science in Kiel (IFM), Germany (2006). During this period, my research focus was on developing indicators for ecosystem-based fisheries management. Following my employment in Kiel, I decided to conduct my PhD at the Dept. of Ichthyology and Fisheries at Rhodes University also with the perspective to gain valuable experience in sampling design, fisheries modelling and stock assessment under the mentorship of Dr. Olaf Weyl and Prof. Tony Booth. In April 2011, I was awarded the PhD in Ichthyology and Fisheries Sciences.
Froese R, Stern-Pirlot A, Winker H, Gascuel D.(2008). Size matters: How single-species management can contribute to ecosystem-based fisheries management. Fisheries Research 92: 231-241
Götz A, Cowley PD, Winker H (2008). Selected fishery and population parameters of eight angling species in the Tsitsikamma National Park no-take marine reserve. African Journal of Marine Science 30: 519-532
Teske PR, Winker H, McQuaid CD, Barker NP (2009).Tropical/subtropical biogeographic disjunction in southeastern Africa separates two evolutionarily significant units of estuarine prawn. Journal of Marine Biology 156: 1265-1275
Winker H, Ellender BR, Weyl OLF, Booth AJ (2010) Validation of growth zone deposition in otoliths of two endemic large cyprinids in Lake Gariep, South Africa. African Zoology 40:
Ellender BR, Weyl OLF, Winker H, Stelzhammer H, Traas, GRL (2010). Estimating angling effort and participation in a multi-user inland fishery. Fisheries Management and Ecology 17: 19-27
Ellender BR, Weyl OLF, Winker H, Booth AJ (2010). Quantifying annual harvests from South Africa’s largest impoundment. Water SA 36: 45-51
Winker H, Weyl OLF, Booth AJ, Ellender, BR (2010) Validating and corroborating the deposition of two annual growth zones in asteriscus otoliths of common carp Cyprinus carpio from South Africa’s largest impoundment. Journal of Fish Biology 77 2210-2228