Applying hedonic property models in the planning and evaluation of shoreline management

According to the Millennium Ecosystem Assessment’s chapter “Coastal Systems” (Agardy and Alder 2005), 40% of the world population falls within 100 km of the coast. Agardy and Alder report that population densities in coastal regions are three times those of inland regions and demographic forecasts suggest a continued rise in coastal populations. These high population levels can be partially traced to the abundance of ecosystem services provided in the coastal zone. While populations benefit from an abundance of services, population pressure also degrades existing services and leads to increased susceptibility of property and human life to natural hazards. In the face of these challenges, environmental administrators on the coast must pursue agendas which reflect the difficult balance between private and public interests. These decisions include maintaining economic prosperity and personal freedoms, protecting or enhancing the existing flow of ecosystem services to society, and mitigating potential losses from natural hazards. (PDF contains 5 pages)

Fishery resource surveys: beyond length-weight relationship models

Fisheries resource surveys are regular management tools for rational exploitation of commercial fisheries. In a growing number of cases, the use of these resource surveys has been largely restricted to assessment of the relative well being of fish stocks and the potential yields of such fisheries. This paper seeks to demonstrate that the data from such surveys can also be easily used to evaluate species diversity of such fisheries, both in terms of species richness and equitability of distribution. Using published data on two freshwater and two marine fisheries as case studies, Shannon-Wiener Diversity Function and Simpson's Index were computed for each of these fisheries. These biodiversity indices gave a deeper insight into the environmental status of each of these fisheries, beyond what the length-weight relationship models can reveal. Generally, while the marine fisheries showed more species richness, the freshwater fisheries apparently had more stable and equilibrated fish communities

The potential use of time-area closures to reduce catches of bigeye tuna (Thunnus obesus) in the purse-seine fishery of the eastern Pacific Ocean

Skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye (Thunnus obesus) tunas are caught by purse-seine vessels in the eastern Pacific Ocean (EPO). Although there is no evidence to indicate that current levels of fishing-induced mortality will affect the sustainability of skipjack or yellowfin tunas, fishing mortality on juvenile (younger than 5 years of age) bigeye tuna has increased, and overall fishing mortality is greater than that necessary to produce the maximum sustainable yield of this species. We investigated whether time-area closures have the potential to reduce purse-seine bigeye catches without significantly reducing skipjack catches. Using catch and effort data for 1995–2002, we identified regions where the ratio of bigeye to skipjack tuna catches was high and applied simple closed-area models to investigate the possible benefits of time-area closures. We estimated that the most optimistic and operationally feasible 3-month closures, covering the equatorial region of the EPO during the third quarter of the year, could reduce bigeye catches by 11.5%, while reducing skipjack tuna catches by 4.3%. Because this level of bigeye tuna catch reduction is insufficient to address sustainability concerns, and larger and longer closures would reduce catches of this species signficantly, we recommend that future research be directed toward gear technology solutions because these have been successful in many other fisheries. In particular, because over 50% of purse-seine catches of bigeye tuna are taken in sets in which bigeye tuna are the dominant species, methods to allow the determination of the species composition of aggregations around floating objects may be important.

Pinniped diet composition: a comparison of estimation models

Along the west coast of the United States, the potential impact of increasing pinniped populations on declining salmonid (Oncorhynchus spp.) stocks has become an issue of concern. Fisheries managers need species-specific estimates of consumption by pinnipeds to evaluate their impact on salmonid stocks. To estimate consumption, we developed a model that estimates diet composition by reconstructing prey biomass from fecal samples. We applied the model to data collected from harbor seals (Phoca vitulina) that are present year-round in the lower Columbia River where endangered stocks of salmonids pass as returning adults and as seaward-migrating smolts. Using the same data, we applied the split-sample frequency of occurrence model, which avoids reconstructing biomass by assuming that each fecal sample represents an equal volume of consumption and that within each sample each prey item represents an equal proportion of the volume. The two models for estimating diet composition yielded size-specific differences in consumption estimates that were as large as tenfold for the smallest and largest prey. Conclusions about the impact of harbor seal predation on adult salmonids, some of their largest prey species, remain uncertain without some appropriate rationale or further information (e.g. empirical captive studies) to discriminate between these models.