Amy Y. Then

Recommendations for Catch-Curve Analysis

Abstract Three common cross-sectional catch-curve methods for estimating total mortality rate (Z) are the Chapman–Robson, regression, and Heincke estimators. There are five unresolved methodological issues: (1) which is the best estimator, (2) how one should determine the first age-group to use in the analysis, (3) how the variance estimators perform; and, for regression estimators, (4) how the observations should be weighted, including (5) whether and how the oldest ages should be truncated. We used analytical methods and Monte Carlo simulation to evaluate the three catch-curve methods, including unweighted and weighted versions of the regression estimator. We evaluated four criteria for specifying the first age-class used. Regression estimators were evaluated with four different methods of right data truncation. Heinckes method performed poorly and is generally not recommended. The two-tailed χ2 test and one-tailed z-test for full selectivity described by Chapman and Robson did not perform as well as s...

Comparison of Two Length-Based Estimators of Total Mortality: A Simulation Approach

AbstractLength-based methods for estimating the total mortality rate, Z, are appealing due to their potential application in data-poor situations, particularly when assessing tropical and invertebrate fisheries where age composition data are lacking. We evaluated two length-based estimators attributed to Beverton and Holt (1956) and to Ehrhardt and Ault (1992) for precision and accuracy when applied to simulated length data generated under varying combinations of Z rates, growth rates, variability in length at age, and the degree of length truncation imposed by the data analyst. The Beverton–Holt method generally overestimated Z, with bias ranging from −5% to +40%, when the abundance of the oldest age-groups is less than that associated with a constant mortality rate. The bias in the Ehrhardt–Ault method ranged from −80% to +140%, depending on the combinations of Z and the von Bertalanffy growth coefficient K, the degree of imposed length truncation, and the method for mean length calculation. In general,...

Estimating fishing and natural mortality rates, and catchability coefficient, from a series of observations on mean length and fishing effort

Estimating fishing and natural mortality rates, and catchability coefficient, from a series of observations on mean length and fishing effort Amy Y. Then*, John M. Hoenig, and Quang C. Huynh Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia Virginia Institute of Marine Science, College of William and Mary, PO Box 1346, Gloucester Point, VA 23062, USA *Corresponding author: tel: þ60 379 674 368; fax: þ60 379 674 178; e-mail: amythen79@gmail.com or amy_then@um.edu.my.

Results of evaluating the performance of empirical estimators of natural mortality rate

This document has been issued as VIMS Data Report 62 and provides additional results and analyses for: Then, A. Y., Hoenig, J. M., Hall, N. G., Hewitt, D.. 2015. Evaluating the predictive performance of empirical estimators of natural mortality rate using information on over 200 fish species. ICES Journal of Marine Science 72(1): 82-92.

Seasonality, habitat type and locality influenced bird assemblage structure in Nigeria

This is the first report of the avian assemblage in the study area of Dutse, Nigeria. In addition to recording bird species, the effects of season, dominant vegetation structure, locality and anthropogenic activities on bird abundance, species richness and diversity were investigated. Using the point transect method, 264 points on 48 km of transect were used to count birds between 06:30 and 11:00 from August 2015 to February 2016. A total of 122 bird species of 41 families were recorded. Highest bird species richness was recorded in Warwade, highest abundance in Model, and highest diversity in Malamawa. The dry season and woodland habitat showed higher bird species richness, abundance and diversity than the wet season and shrubland habitat. Tree density was more important in increasing bird abundance than shrub density. Small-scale anthropogenic activities and habitat modification, such as farming, grazing, wood removal and human interference did not appear to have impacted the birds; however, loss of high tree-density woodland habitats may pose a major threat to the bird community in Dutse. The presence of birds of concern in the area suggests the need for conservation efforts of avifauna and as well as the forested habitats in Dutse.

Fish Ontology framework for taxonomy-based fish recognition

Life science ontologies play an important role in Semantic Web. Given the diversity in fish species and the associated wealth of information, it is imperative to develop an ontology capable of linking and integrating this information in an automated fashion. As such, we introduce the Fish Ontology (FO), an automated classification architecture of existing fish taxa which provides taxonomic information on unknown fish based on metadata restrictions. It is designed to support knowledge discovery, provide semantic annotation of fish and fisheries resources, data integration, and information retrieval. Automated classification for unknown specimens is a unique feature that currently does not appear to exist in other known ontologies. Examples of automated classification for major groups of fish are demonstrated, showing the inferred information by introducing several restrictions at the species or specimen level. The current version of FO has 1,830 classes, includes widely used fisheries terminology, and models major aspects of fish taxonomy, grouping, and character. With more than 30,000 known fish species globally, the FO will be an indispensable tool for fish scientists and other interested users.