Healthy watersheds provide valuable services to society, including the supply and purification of fresh water. Because these natural ecosystem services lie outside the traditional domain of commercial markets, they are undervalued and underprotected. With population and development pressures leading to the rapid modification of watershed lands, valuable hydrological services are being lost, which poses risks to the quality and cost of drinking water and the reliability of water supplies. Increasing the scale and scope of programmes to protect hydrological services requires policies that harmonize land uses in watersheds with the provision of these important natural services. This article summarizes key attributes of hydrological services and their economic benefits; presents a spectrum of institutional mechanisms for safeguarding those services; discusses programmes in Quito (Ecuador), Costa Rica and New York City; and offers some lessons learned and recommendations for achieving higher levels of watershed protection.

[1] Freshwater scarcity has been cited as the major crisis of the 21st century, but it is surprisingly hard to describe the nature of the global water crisis. We conducted a metaanalysis of 22 coupled human-water system case studies, using qualitative comparison analysis (QCA) to identify water resource system outcomes and the factors that drive them. The cases exhibited different outcomes for human wellbeing that could be grouped into a six "syndromes": groundwater depletion, ecological destruction, drought-driven conflicts, unmet subsistence needs, resource capture by elite, and water reallocation to nature. For syndromes that were not successful adaptations, three characteristics gave cause for concern: (1) unsustainability-a decline in the water stock or ecosystem function that could result in a long-term steep decline in future human wellbeing; (2) vulnerability-high variability in water resource availability combined with inadequate coping capacity, leading to temporary drops in human wellbeing; (3) chronic scarcity-persistent inadequate access and hence low conditions of human wellbeing. All syndromes could be explained by a limited set of causal factors that fell into four categories: demand changes, supply changes, governance systems, and infrastructure/technology. By considering basins as members of syndrome classes and tracing common causal pathways of water crises, water resource analysts and planners might develop improved water policies aimed at reducing vulnerability, inequity, and unsustainability of freshwater systems.

The index of biotic integrity (IBI) integrates 12 measures of stream fish assemblages for assessing water resource quality. Initially developed and tested in the Midwest, the IBI recently was adapted for use in western Oregon, northeastern Colorado, New England, the Appalachians of West Virginia and Virginia, and northern California. The concept also was extended to Louisiana estuaries. In regions of low species richness, the IBI proved difficult to apply and often required extensive modification. Adapting the 1BI to those regions required that metrics be replaced, deleted, or added to accommodate regional differences in fish distribution and assemblage structure and function. Frequently replaced metrics include: proportion of individuals as green sunfish (Lepomis cyanellus), proportion of individuals as insectivorous cyprinids, proportion of individuals as hybrids, and number and identity of sunfish and darter species. The proportion of individuals as top carnivore metric was often deleted. Metrics added include total fish biomass and the number and identity of minnow species. These modifications generally followed the original IBI concept and its theoretical underpinnings. Problems remain in establishing tolerance rankings and scoring criteria, and adjusting scoring criteria for gradient differences in streams of similar size. The IBI holds promise for direct biological monitoring because of its strong ecological foundation and flexibility. Vermont, Tennessee Valley Authority, Ohio, Kentucky, and Illinois have incorporated the IBI into their monitoring or standards programs. The IBI thus serves as a quantitative, biological goal for water resource management.

Although the basic concepts of factor analysis are roughly a century old (see Spearman, 1904), more recent extensions of the exploratory factor analysis (EFA) concepts have created the basic methods for confirmatory factor analysis (CFA; see Joreskog, 1969). Both EFA and CFA are part of the general linear model (GLM). Thus, many of the concepts introduced previously with regard to EFA apply in CFA as well. Indeed, an important emphasis in this book is elaborating the similarities between EFA and CFA as part of a single underlying GLM, while also highlighting the differences in the two sets of methods.Of course, the basic difference in CFA is that one or more underlying models (i.e., how many factors, which measured variables are thought to reflect which latent variables, whether the factors are correlated) must be specified even to run the analysis. There are also statistical analyses that are possible in CFA but impossible in EFA (e.g., allowing error variances to be correlated).And some procedures that are routine in EFA, such as factor rotation, are irrelevant in CFA. This is because the a priori models themselves typically specify simple structure, by constraining certain factor pattern coefficients to be zero while freeing other pattern coefficients to be estimated.Confirmatory factor analysis is a very important component within a broader class of methods called structural equation modeling (SEM), or some 109

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Interaction between institutional change and technological change poses important constraints on transitions of urban water systems to a state that can meet future needs. Research on urban water and other technologydependent systems provides insights that are valuable to technology researchers interested in assuring that their efforts will have an impact. In the context of research on institutional change, innovation is the development, application, diffusion, and utilization of new knowledge and technology. This definition is intentionally inclusive: technological innovation will play a key role in reinvention of urban water systems, but is only part of what is necessary. Innovation usually depends on context, such that major changes to infrastructure include not only the technological inventions that drive greater efficiencies and physical transformations of water treatment and delivery systems, but also the political, cultural, social, and economic factors that hinder and enable such changes. On the basis of past and present changes in urban water systems, institutional innovation will be of similar importance to technological innovation in urban water reinvention. To solve current urban water infrastructure challenges, technology-focused researchers need to recognize the intertwined nature of technologies and institutions and the social systems that control change.

Age and growth rates of bull shark Carcharhinus leucas [n ¼ 255; 555-2230 mm fork length (L F )] from the northern Gulf of Mexico were estimated from ring counts on vertebral sections collected from fishery-dependent and -independent surveys. Two growth models were fitted to observed data: the von Bertalanffy growth model (VBGM) with t 0 as the third parameter and a modified version of the VBGM using a fixed size-at-birth intercept as the third parameter. To address the variability in size-at-birth, a Monte Carlo simulation was incorporated into the sizeat-birth intercept. The sex-specific growth models were not significantly different, allowing a sexes combined model to be generated. The traditional VBGM predicted a theoretical maximum size (L 1 ) of 3007Á1 mm L F , a growth coefficient (K) of 0Á042 year À1 and a theoretical age at zero length (t 0 ) of -6Á844 years. The modified VBGM with a fixed size-at-birth intercept of 565 mm L F predicted an L 1 of 2289Á2 mm L F and a K value of 0Á089 year À1 . When comparing model estimates to previously published information, the traditional VBGM predicted a significantly lower theoretical maximum size and a higher growth coefficient than those produced using data collected during the 1980s. Overall, results obtained using the VBGM with a fixed size-at-birth produced more biologically realistic parameters than that of the VBGM with t 0 . The Monte-Carlo simulation incorporating variability in size-at-birth produced similar results to the VBGM using a fixed size-at-birth. This study provides the first attempt to incorporate variability at size-at-birth and provide measurements of variability around the individual parameter estimates for an elasmobranch. # 2005 The Fisheries Society of the British Isles