Why fisheries collapse and what to do about it.

With the collapse of fisheries in many parts of the world causing widespread economic harm, attention is focused on a possible cause and remedy of fishery collapse. Economic theory for managing a renewable resource, such as a fishery, leads to an ecologically unstable equilibrium as difficult to maintain as balancing a marble on top of a dome. A fishery should be managed for ecological stability instead--in the analogy, as easy to maintain as keeping a marble near the base of a bowl. The goal of ecological stability is achieved if the target stock is above that producing maximum sustainable yield and harvested at less than the maximum sustainable yield. The cost of managing for ecological stability, termed "natural insurance," is low if the fishery is sufficiently productive. This cost is shown to pay for itself over the long term in a variable and uncertain environment. An ecologically stable target stock may be attained either with annually variable quotas following current practice or, preferably, through a market mechanism whereby fish are taxed at dockside if caught when the stock was below target and are untaxed otherwise. In this regulatory environment, the goal of maximizing short-term revenue coincides with the goal of ecological stability, thereby also maximizing long-term revenue. This new approach to fishery management is illustrated with the recently collapsed Newfoundland fishing industry. The Newfoundland cod fishery is expected to rebuild to an ecologically stable level in about 9 years and thereafter support an annual harvest of about 75% of the 1981-1990 average.

Increase in the Quantum Yield of Photoinhibition Contributes to Copper Toxicity in Vivo1

The effect of copper on photoinhibition of photosystem II in vivo was studied in bean (Phaseolus vulgaris L. cv Dufrix). The plants were grown hydroponically in the presence of various concentrations of Cu2+ ranging from the optimum 0.3 μm (control) to 15 μm. The copper concentration of leaves varied according to the nutrient medium from a control value of 13 mg kg−1 dry weight to 76 mg kg−1 dry weight. Leaf samples were illuminated in the presence and absence of lincomycin at different light intensities (500–1500 μmol photons m−2 s−1). Lincomycin prevents the concurrent repair of photoinhibitory damage by blocking chloroplast protein synthesis. The photoinhibitory decrease in the light-saturated rate of O2 evolution measured from thylakoids isolated from treated leaves correlated well with the decrease in the ratio of variable to maximum fluorescence measured from the leaf discs; therefore, the fluorescence ratio was used as a routine measurement of photoinhibition in vivo. Excess copper was found to affect the equilibrium between photoinhibition and repair, resulting in a decrease in the steady-state concentration of active photosystem II centers of illuminated leaves. This shift in equilibrium apparently resulted from an increase in the quantum yield of photoinhibition (ΦPI) induced by excess copper. The kinetic pattern of photoinhibition and the independence of ΦPI on photon flux density were not affected by excess copper. An increase in ΦPI may contribute substantially to Cu2+ toxicity in certain plant species.