Conservation Implications of Patterns of Horn Regeneration in Dehorned White Rhinos

The demand for rhino horn has led to drastic declines in numbers of rhinos in Asia and Africa. Although all trade in rhino products has been illegal since the mid-1970s, a lucrative illegal market flourishes and poaching continues. Horn removal from African rhinos has been conducted in Zimbabwe, Namibia, and Swaziland to deter poaching. Regeneration of horns following dehorning has created the potential for a sustainable harvest of rhino horn through dehorning programs. Establishment of a regulated legal market for rhino horn has been suggested to help fund rhino conservation programs in African countries. However, evaluation of an economic harvest of rhino horn from dehorning programs has been limited because few data on rates and form of horn regeneration exist. Because rate of horn regeneration will determine the interval at which rhino horns could be harvested profitably, we measured horn regrowth for two white rhino (Ceratotherium simum) populations studied in Zimbabwe between 1991–1995. Measurements of horn sizes were collected before and after dehorning, and mass to volume relationships were calculated. Von Bertalanffy growth curves were used to model horn size and rates of horn regrowth relative to age. Adult males had larger horn bases (p < 0.001) and faster rates of horn regrowth than adult females. Regenerated horn mass for adult males (>1.3 kg/yr) was almost twice the mass of adult females. Based on an economic model for profit maximization, intervals for dehorning range from 1.16 to 1.51 years and vary with both sex and age. We suggest managers use these values as minimum dehorning intervals to balance profits with longer-term management goals. Rates of horn regeneration are likely to be less important than law enforcement in determining the efficacy of dehorning as a deterrent to rhino poaching.     

Local vulnerability as an advantage: mangrove forest management in Pará state,north Brazil,under conditions of illegality

When ecosystems are threatened or scientific knowledge of the effects of human action is uncertain, legislative prohibition is often adopted. This paper examines how the criminalization of mangrove tree use affects ecosystem management outcomes. We explore the biological, economic and social sustainability effects of the legal ban on mangrove use on the coast of Bragança, Pará, north Brazil. There are two main categories of mangrove users in this area: firstly, local subsistence users who also derive some financial incomes from mangrove sale. Their mangrove use is intertwined with household livelihood strategies and they display self-initiated planning and action towards sustainable management; secondly, more mobile, purely commercial users who are responsible for most commercial mangrove exploitation and who employ regionally sequential, predatory resource exploitation strategies. These users are typically based at some distance from the exploited areas and share neither local livelihood strategies nor sustainability agendas. The current outright ban on any utilization of mangrove flora seems to undermine biological sustainability, is economically inefficient and generates normative insecurity, conflict and social polarization. The ineffectiveness of the outright legal prohibition of mangrove tree use in terms of sustainable coastal management leads us to investigate alternative management options. We suggest that the legalization of local mangrove utilization and the strengthening of local users rights and responsibilities to control outsiders in a co-management framework, as proposed in the Brazilian extractive reserves (RESEX) approach, is most likely to advance ecologically, economically and socially sustainable mangrove management. It is demonstrated that a legal recognition of local entitlements to mangrove trees would reduce social vulnerability and therefore move forest management outcomes into more desirable directions.

The advantages of accelerator-based radiocarbon measurements in geophysical research

This paper reviews methods for carbon-14 dating using accelerators. ¹⁴C is accelerated to high energies. Subsequently ¹⁴C is separated from ¹⁴N by passing it through a xenon gas cell or electrostatic separator. Advantages, limits and applications of the techniques are discussed.     

Effects of copper on the latency of lysosomal hexosaminidase in the digestive cells of Mytilus edulis

Mytilus edulis collected from Tomales Bay, California, USA, during mid-winter 1979 were exposed to increased concentrations of dissolved copper under controlled laboratory conditions. A dose-dependent reduction in the latency of lysosomal hexosaminidase activity in digestive cells was induced after a 30 d exposure to copper. The half-time of the hexosaminidase staining reaction in sections of digestive gland from control mussels was 15.5 min; for mussels exposed to 25, 50, and 75 g Cu l^-1 it was 11.8, 8.5 and 5.5 min, respectively. In addition, the dyecoupled reaction product was seen earlier in sections from individuals exposed to 50 and 75 g Cu l^-1 (after 30 s) and 25 g Cu l^-1 (1 min) than in sections from control individuals (2.5 min). Copper accumulations were demonstrated histochemically to have the same distribution as the hexosaminidase reaction product, indicating that copper is sequestered in lysosomes. Copper concentrations in digestive gland tissue, were related to the concentrations of copper in the water to which the mussels were exposed.     

Man-made and natural smog in California

The radiocarbon content in creosote bush in the greater Los Angeles area has been found to reflect the distribution of smog. Indications are that smog in the even larger air basin of the San Joaquin Valley of California may be caused in part by recent biospheric emissions rather than by fossil fuel combustion alone.     

Maternal investment in sons and daughters: problems of methodology

Summary The prediction that mothers should invest more in sons than daughters was briefly examined in American bison (Bison bison) by Wolff (1988). He concluded that (a) male calves suckle more than females, (b) cows that had previously produced sons were more likely to be barren, and (c) cows that had male calves became estrous later in the year than other cows. In this paper we present data from two long term studies at different sites to show that Wolff's conclusions are equivocal at best and difficult to reconcile with predictions of the hypothesis because of questionable methods and assumptions. Offprint requests to: W.C.H. Green