A prior for steepness in stock-recruitment relationships, based on an evolutionary persistence principle

Priors are existing information or beliefs that are needed in Bayesian analysis. Informative priors are important in obtaining the Bayesian posterior distributions for estimated parameters in stock assessment. In the case of the steepness parameter (h), the need for an informative prior is particularly important because it determines the stock-recruitment relationships in the model. However, specifications of the priors for the h parameter are often subjective. We used a simple population model to derive h priors based on life history considerations. The model was based on the evolutionary principle that persistence of any species, given its life history (i.e., natural mortality rate) and its exposure to recruitment variability, requires a minimum recruitment compensation that enables the species to rebound consistently from low critical abundances (Nc). Using the model, we derived the prior probability distributions of the h parameter for fish species that have a range of natural mortality, recruitment variabilities, and Nt values

Interactions of age-dependent mortality and selectivity functions in age-based stock assessment models

The natural mortality rate (M) of fish varies with size and age, although it is often assumed to be constant in stock assessments. Misspecification of M may bias important assessment quantities. We simulated fishery data, using an age-based population model, and then conducted stock assessments on the simulated data. Results were compared to known values. Misspecification of M had a negligible effect on the estimation of relative stock depletion; however, misspecification of M had a large effect on the estimation of parameters describing the stock recruitment relationship, age-specific selectivity, and catchability. If high M occurs in juvenile and old fish, but is misspecified in the assessment model, virgin biomass and catchability are often poorly estimated. In addition, stock recruitment relationships are often very difficult to estimate, and steepness values are commonly estimated at the upper bound (1.0) and overfishing limits tend to be biased low. Natural mortality can be estimated in assessment models if M is constant across ages or if selectivity is asymptotic. However if M is higher in old fish and selectivity is dome-shaped, M and the selectivity cannot both be adequately estimated because of strong interactions between M and selectivity

Pacific bonito management information document

Management of Pacific bonito in California is examined in this Management Information Document by a State-Federal team of scientists. Abundance of Pacific bonito in southern California has fallen dramatically between the 1963-1969 period and the 1974-1977 period. Since 1976 the commercia1 fleet has found few large fish in southern California, and has caught fish in the size range of 15 to 57 cm (1.2 to 4.7 pounds). This fact, coupled with the low abundance indices, point out the need for a more active management regime. To develop management measures for the California bonito fishery both a surplus yield analysis and a yield-per-recruit analysis were performed. A maximum sustained yield of 10,000 short tons was estimated for the fishery in southern California, while the whole fishery, including Baja California, has an estimated MSY of 13,000 tons. In order to achieve this level of catch, however, the stock abundance must be increased by a factor of five. Yield-per-recruit considerations suggest that a minimum size limit in the commercial fishery has two important effects. A three-pound size limit could result in a slight increase in yield-per-recruit. If the size limit is increased to 5 or 7.5 lbs, the yield-per-recruit would fall significantly. Offsetting the effect on yield-per-recruit, however, would be a substantial increase in average amount of spawning per recruit which should result in a proportional increase in recruitment. With the current depressed stock abundance both a reduced annual take and a minimum size limit on commercial catch would confer substantial benefits in the form of an increase in the future stock size. After considering seven different types of management measures, the team finds that three types -- an annual commercial catch quota, a commercial size limit, and a recreational bag limit -- appear desirable. Re-establishment of the stock in southern California was the major consideration in this evaluation because the stock is currently depressed. All segments of the fishery will benefit from a more abundant resource. The difficult issues for policy, however, concern the rate of rebuilding, the degree of risk that is acceptable, and the distribution of benefits among user groups. By judicious choice among the options discussed here, a variety of positions can be established with respect to these issues. The greater the size limit, for instance, the more benefit is provided the recreational sector while difficulties are imposed upon commercial fishermen. The higher the quotas adopted, the slower the stock rebuilding and the greater the risk of continued stock depletion. A final reconciliation of the management options involves social, political and legal considerations which must be thoroughly incorporated by decision-makers before adoption of a management plan. (93pp.

The principal affordance of publishing texts online: Possible implications for the bibliographic universe model

In this presentation, I argue for focusing the attention of classification theorists on the implications of what I argue to be the principal affordance of publishing texts online, in contrast to their publication on paper, and that is the capability for an author or creator to update an online text without the text having to be republished as a new physical edition. This affordance is a result of the possibilities provided for by a shift in the materiality of textual carrier from physical to digital. I examine the implications of this capability for the WEMI model and argue that its starting point in terms of online “things” in the bibliographic universe should be modeled more granularly

Synthesis of tailored ligands for radiopharmaceutical applications

An important aspect of clinical imaging techniques involves the use of complexed gamma or positron-emitting radionuclides, e.g. (^99m)Tc(γ, t1/2 = 6.02 h, 141 keV) for Single Photon Emission Tomography (SPET), (^62)Cu (β(^+),t1/2 = 9.74 min, 1.315 MeV) for Positron Emission Tomography (PET). With such radiopharmaceuticals in mind, two new classes of acyclic tetradentate ligands have been synthesised, featuring an N(_2)S(_2) donor system. This array of donor atoms is particularly attractive for its 'soft’ metal preference, favouring the complexation of radionuclides such as (^64)Cu and (^99m)Tc in diagnostic imaging of disease states, and (^186/188)Re (β(^-), t1/2 = 90h) in targeted radiotherapy. In both ligand systems the sulfur donor is adjacent to pentavalent phosphorus. Substitution at phosphorus allows easy modification of aryl or alkyl groups to vary the lipophilicity of the complex without affecting the binding properties. The first class of new ligands presented incorporate thiophosphinic acid groups which are more acidic than their corresponding phosphinates and carboxylates, increasing the stability of the complexes in acidic media. The synthetic routes to series of such ligands have been investigated and optimised. Initial attempts to access the aza- thiophosphinates via treatment of the sulfur-containing P(III) species with the diamine and paraformaldehyde failed to show any significant reaction. The best method of P=S bond formation was found to be via sulfur transfer to the corresponding P(V) phosphinate. The other class of ligands synthesised incorporate the dialkylthiophosphoryl group in conjunction with hydrazide or aminopyridyl moieties. The solid state structures of the ligands were determined by X-ray crystallography. The solution complexation behaviour of the ligands with a variety of metals, particularly copper and rhenium was studied. The thiophosphinic acid ligands form 1:1 complexes with copper(II) under dilute conditions and oligomeric complexes at high solution concentrations. The complexes formed with copper(II) and oxorhenium(V) appear to be charge neutral. Several of the dialkylthiophosphoryl ligands formed copper(I) complexes by spontaneous reduction of a copper(II) source, and redox behaviour was also shown towards oxorhenium(V). Some of the ligands radiolabel efficiently with technetium-99m and copper-64 and their preliminary evaluation shows promise for further development

Organization under digital inversion: A theory for cooperative librarian organizing practices for online textual artifacts

Theories can provide frameworks with which to construct models for cooperative professional practices. The knowledge organization theorizing of Cutter, Dewey and others leading up to and following the 1876 first meeting of the American Library Association set this precedent for over 130 years of professional librarianship. With the relatively recent advent of the possibility for publishing texts online, librarians are potentially at another epochal time when basic theoretical frameworks for cooperative professional practice are due for re-examination and possible wholesale changes. This paper provides a preliminary theoretical investigation of a framework, digital inversion theory, for thinking about possible the cooperative knowledge organization practices for the existing network of librarians

California's Pacific bonito resource, its status and management

Pacific bonito, Sarda chiliensis, have become increasingly important to California's sport and commercial fishermen since the early 1960's, but are now showing signs of decline. Recent investigations have revealed much about the bonito's life history and population dynamics. These recent discoveries have been brought together into a document which will serve as a guide to future management actions. Document has 44 pages

Potential use of offshore marine structures in rebuilding an overfished rockfish species, bocaccio (Sebastes paucispinis)

Although bocaccio (Sebastes paucispinis) was an economically important rockfish species along the west coast of North America, overfishing has reduced the stock to about 7.4% of its former unfished population. In 2003, using a manned research submersible, we conducted fish surveys around eight oil and gas platforms off southern California as part of an assessment of the potential value of these structures as fish habitat. From these surveys, we estimated that there was a minimum of 430,000 juvenile bocaccio at these eight structures. We determined this number to be about 20% of the average number of juvenile bocaccio that survive annually for the geographic range of the species. When these juveniles become adults, they will contribute about one percent (0.8%) of the additional amount of fish needed to rebuild the Pacific Coast population. By comparison, juvenile bocaccio recruitment to nearshore natural nursery grounds, as determined through regional scuba surveys, was low in the same year. This research demonstrates that a relatively small amount of artificial nursery habitat may be quite valuable in rebuilding an overfished species

A Theory for the Measurement of Internet Information Retrieval

The purpose of this study was to develop and evaluate a measurement model for Internet information retrieval strategy performance evaluation whose theoretical basis is a modification of the classical measurement model embodied in the Cranfield studies and their progeny. Though not the first, the Cranfield studies were the most influential of the early evaluation experiments. The general problem with this model was and continues to be the subjectivity of the concept of relevance. In cyberspace, information scientists are using quantitative measurement models for evaluating information retrieval performance that are based on the Cranfield model. This research modified this model by incorporating enduser relevance judgment rather than using objective relevance judgments, and by adopting a fundamental unit of measure developed for the cyberspace of Internet information retrieval rather than using recall and precision-type measures. The proposed measure, the Content-bearing Click (CBC) Ratio, was developed as a quantitative measure reflecting the performance of an Internet IR strategy. Since the hypertext "click" is common to many Internet IR strategies, it was chosen as the fundamental unit of measure rather than the "document." The CBC Ratio is a ratio of hypertext click counts that can be viewed as a false drop measure that determines the average number of irrelevant content-bearing clicks that an enduser check before retrieving relevant information. After measurement data were collected, they were used to evaluate the reliability of several methods for aggregating relevance judgments. After reliability coefficients were calculated, measurement model was used to compare web catalog and web database performance in an experimental setting. Conclusions were the reached concerning the reliability of the proposed measurement model and its ability to measure Internet IR performance, as well as implications for clinical use of the Internet and for future research in Information Science