Removing observational noise from fisheries-independent time series data using ARIMA models

Abundance indices derived from fishery-independent surveys typically exhibit much higher interannual variability than is consistent with the within-survey variance or the life history of a species. This extra variability is essentially observation noise (i.e. measurement error); it probably reflects environmentally driven factors that affect catchability over time. Unfortunately, high observation noise reduces the ability to detect important changes in the underlying population abundance. In our study, a noise-reduction technique for uncorrelated observation noise that is based on autoregressive integrated moving average (ARIMA) time series modeling is investigated. The approach is applied to 18 time series of finfish abundance, which were derived from trawl survey data from the U.S. northeast continental shelf. Although the a priori assumption of a random-walk-plus-uncorrelated-noise model generally yielded a smoothed result that is pleasing to the eye, we recommend that the most appropriate ARIMA model be identified for the observed time series if the smoothed time series will be used for further analysis of the population dynamics of a species.

Use of a fishery independant index to predict recruitment and catches of the spiny lobster

This paper presents a review of recruitment and catch predictions based on an index of abundance of juveniles and pre-recruits (fishery independent index) in the Cuban lobster fisheries. This methodology can provide information based on fisheries data that can improve the management of the fishery.

Estimating exploitable stock biomass for the Maine green sea urchin (Strongylocentrotus droebachiensis) fishery using a spatial statistics approach

The objective of this study was to investigate the spatial patterns in green sea urchin (Strongylocentrotus droebachiensis) density off the coast of Maine, using data from a fishery-independent survey program, to estimate the exploitable biomass of this species. The dependence of sea urchin variables on the environment, the lack of stationarity, and the presence of discontinuities in the study area made intrinsic geostatistics inappropriate for the study; therefore, we used triangulated irregular networks (TINs) to characterize the large-scale patterns in sea urchin density. The resulting density surfaces were modified to include only areas of the appropriate substrate type and depth zone, and were used to calculate total biomass. Exploitable biomass was estimated by using two different sea urchin density threshold values, which made different assumptions about the fishing industry. We observed considerable spatial variability on both small and large scales, including large-scale patterns in sea urchin density related to depth and fishing pressure. We conclude that the TIN method provides a reasonable spatial approach for generating biomass estimates for a fishery unsuited to geostatistics, but we suggest further studies into uncertainty estimation and the selection of threshold density values.

The Northern Rockfish, Sebastes polyspinis, in Alaska: Commercial Fishery, Distribution, and Biology

The northern rockfish, Sebastes polyspinis, is the second most abundant rockfish in Alaska, and it supports a valuable trawl fishery. Little information is available, however, on either the biology of this species or its commercial fishery. To provide a synopsis of information on northern rockfish in Alaska, this study examined data for this species from commercial fishery observations in 1990–98 and from fishery-independent trawl surveys in 1980–99. Nearly all the commercial catch came from bottom trawling, mostly by large factory-trawlers, although smaller shore-based trawlers in recent years took an increasing portion of the catch in the Gulf of Alaska. Most of the northern rockfish catch in the Gulf of Alaska was taken by a directed fishery, whereas that of the Aleutian Islands predominantly came as discarded bycatch in the Atka mackerel fishery. In both regions, most of the catch was taken from a number of relatively small and discrete fishing grounds at depths of 75–150 m in the Gulf of Alaska and 75–175 m in the Aleutian Islands. These grounds, especially in the Gulf of Alaska, are on shallow rises or banks located on the outer continental shelf, and often are surrounded by deeper water. Five fishing grounds were identified in the Gulf of Alaska, and eleven in the Aleutian Islands. One fishing ground in the Gulf of Alaska, the “Snakehead” south of Kodiak Island, accounted for 46% of the total northern rockfish catch in this region. Analysis of the survey data generally revealed similar patterns of geographic distribution as those seen in the fishery, although some of the commercial fishing grounds did not stand out as areas of special abundance in the surveys. The surveys also found two areas of abundance that were not evident in the fishery data. Relatively few juvenile northern rockfish were caught in any of the surveys, but those taken in the Gulf of Alaska tended to occur more inshore and at shallower depths than adults. Individual size of northern rockfish was substantially larger in the Gulf of Alaska than in the Aleutian Islands according to both fishery and survey data. Analysis of age data from each region supports this, as Gulf of Alaska fish were found to grow significantly faster and reach a larger maximum length than those in the Aleutian Islands. Sex ratio in the Gulf of Alaska was nearly 50:50, but females predominated in the Aleutian Islands by a ratio of 57:43. In both regions, size of females was significantly larger than males.

Characteristics of capture fishery resources, their assessment and management

There are two groups of factors, namely fishery independent factors such as current, temperature and salinity and fishery dependent factors such as types of fishing, namely trawling, gill netting etc. with different mesh sizes and intensity of fishing indicating the number of units of each type of fishing. Hence assessment of capture fishery resources remains a puzzle even today. However, attempts have been made to develop suitable mathematical and statistical models for assessing them and for offering suggestions for judicious management of the resources. This paper indicates in brief the important characteristics of the capture fisheries, their assessment and management with particular reference to India.

Spatial abundance patterns and recruitment of a virus-affected commercial mollusc fishery

 Infectious pathogens figure prominently among those factors threatening marine wildlife. Mass mortality events caused by pathogens can fundamentally alter the structure of wild fish stocks and depress recruitment rates and yield. In the most severe instances, this can precipitate stock collapses resulting in dramatic economic losses to once valuable commercial fisheries. An outbreak of a herpes-like virus among commercially fished abalone populations in the south-west fishery of Victoria, Australia, during 2006-2007, has been associated with high mortality rates among all cohorts. Long-term records from fishery-independent surveys of blacklip abalone Haliotis rubra (Leach) enabled abundance from pre- and post-viral periods to be analysed to estimate stock density and biomass. The spatial distribution of abundance in relation to physical habitat variables derived from high-resolution bathymetric LiDAR data was investigated. Significant differences were observed in both measures between pre- and post-viral periods. Although there was some limited evidence of gradual stock improvement in recent years, disease-affected reefs have remained below productivity rates prior to the disease outbreak suggesting a reduction in larval availability or settlement success. This was corroborated by trends in sublegal sized blacklip abalone abundance that has yet to show substantial recovery post-disease. Abundance data were modelled as a function of habitat variables using a generalised additive model (GAM) and indicated that high abundance was associated with complex reef structures of coastal waters (<15 m). This study highlights the importance of long-term surveys to understand abalone recovery following mass mortality and the links between stock abundance and seafloor variability.

Efficient designs for sampling and subsampling in fisheries research based on ranked sets

Sampling strategies are developed based on the idea of ranked set sampling (RSS) to increase efficiency and therefore to reduce the cost of sampling in fishery research. The RSS incorporates information on concomitant variables that are correlated with the variable of interest in the selection of samples. For example, estimating a monitoring survey abundance index would be more efficient if the sampling sites were selected based on the information from previous surveys or catch rates of the fishery. We use two practical fishery examples to demonstrate the approach: site selection for a fishery-independent monitoring survey in the Australian northern prawn fishery (NPF) and fish age prediction by simple linear regression modelling a short-lived tropical clupeoid. The relative efficiencies of the new designs were derived analytically and compared with the traditional simple random sampling (SRS). Optimal sampling schemes were measured by different optimality criteria. For the NPF monitoring survey, the efficiency in terms of variance or mean squared errors of the estimated mean abundance index ranged from 114 to 199% compared with the SRS. In the case of a fish ageing study for Tenualosa ilisha in Bangladesh, the efficiency of age prediction from fish body weight reached 140%.

A new data source for fisheries resource assessment: genetic estimates of the effective number of spawners. Final Report to the Fisheries Research and Development Corporation.

The development of innovative methods of stock assessment is a priority for State and Commonwealth fisheries agencies. It is driven by the need to facilitate sustainable exploitation of naturally occurring fisheries resources for the current and future economic, social and environmental well being of Australia. This project was initiated in this context and took advantage of considerable recent achievements in genomics that are shaping our comprehension of the DNA of humans and animals. The basic idea behind this project was that genetic estimates of effective population size, which can be made from empirical measurements of genetic drift, were equivalent to estimates of the successful number of spawners that is an important parameter in process of fisheries stock assessment. The broad objectives of this study were to 1. Critically evaluate a variety of mathematical methods of calculating effective spawner numbers (Ne) by a. conducting comprehensive computer simulations, and by b. analysis of empirical data collected from the Moreton Bay population of tiger prawns (P. esculentus). 2. Lay the groundwork for the application of the technology in the northern prawn fishery (NPF). 3. Produce software for the calculation of Ne, and to make it widely available. The project pulled together a range of mathematical models for estimating current effective population size from diverse sources. Some of them had been recently implemented with the latest statistical methods (eg. Bayesian framework Berthier, Beaumont et al. 2002), while others had lower profiles (eg. Pudovkin, Zaykin et al. 1996; Rousset and Raymond 1995). Computer code and later software with a user-friendly interface (NeEstimator) was produced to implement the methods. This was used as a basis for simulation experiments to evaluate the performance of the methods with an individual-based model of a prawn population. Following the guidelines suggested by computer simulations, the tiger prawn population in Moreton Bay (south-east Queensland) was sampled for genetic analysis with eight microsatellite loci in three successive spring spawning seasons in 2001, 2002 and 2003. As predicted by the simulations, the estimates had non-infinite upper confidence limits, which is a major achievement for the application of the method to a naturally-occurring, short generation, highly fecund invertebrate species. The genetic estimate of the number of successful spawners was around 1000 individuals in two consecutive years. This contrasts with about 500,000 prawns participating in spawning. It is not possible to distinguish successful from non-successful spawners so we suggest a high level of protection for the entire spawning population. We interpret the difference in numbers between successful and non-successful spawners as a large variation in the number of offspring per family that survive – a large number of families have no surviving offspring, while a few have a large number. We explored various ways in which Ne can be useful in fisheries management. It can be a surrogate for spawning population size, assuming the ratio between Ne and spawning population size has been previously calculated for that species. Alternatively, it can be a surrogate for recruitment, again assuming that the ratio between Ne and recruitment has been previously determined. The number of species that can be analysed in this way, however, is likely to be small because of species-specific life history requirements that need to be satisfied for accuracy. The most universal approach would be to integrate Ne with spawning stock-recruitment models, so that these models are more accurate when applied to fisheries populations. A pathway to achieve this was established in this project, which we predict will significantly improve fisheries sustainability in the future. Regardless of the success of integrating Ne into spawning stock-recruitment models, Ne could be used as a fisheries monitoring tool. Declines in spawning stock size or increases in natural or harvest mortality would be reflected by a decline in Ne. This would be good for data-poor fisheries and provides fishery independent information, however, we suggest a species-by-species approach. Some species may be too numerous or experiencing too much migration for the method to work. During the project two important theoretical studies of the simultaneous estimation of effective population size and migration were published (Vitalis and Couvet 2001b; Wang and Whitlock 2003). These methods, combined with collection of preliminary genetic data from the tiger prawn population in southern Gulf of Carpentaria population and a computer simulation study that evaluated the effect of differing reproductive strategies on genetic estimates, suggest that this technology could make an important contribution to the stock assessment process in the northern prawn fishery (NPF). Advances in the genomics world are rapid and already a cheaper, more reliable substitute for microsatellite loci in this technology is available. Digital data from single nucleotide polymorphisms (SNPs) are likely to super cede ‘analogue’ microsatellite data, making it cheaper and easier to apply the method to species with large population sizes.

Effects of fishing on tropical reef associated shark populations on the Great Barrier Reef

Three data sets were examined to define the level of interaction of reef associated sharks with the commercial Coral Reef Fin Fish Fishery within the Great Barrier Reef (GBR). Data were examined from fishery logbooks, an observer program within the fishery and a fishery-independent survey conducted as part of the Effects of Line Fishing (ELF) Experiment. The majority of the identified catch was comprised of grey reef (62-72%), whitetip reef (16-29%) and blacktip reef (6-13%) sharks. Logbook data revealed spatially and temporally variable landings of shark from the GBR. Catch per unit effort (CPUE) through time was stable for the period from 1989 to 2006 with no evidence of increase or decline. Data from observer and ELF data sets indicated no differences in CPUE among regions. The ELF data set demonstrated that CPUE was higher in Marine National Park zones (no fishing) when compared to General Use zones (open to fishing). The ongoing and consistent catches of reef sharks in the fishery and effectiveness of no-fishing zones suggest that management zones within the GBR Marine Park are effective at protecting a portion of the reef shark population from exploitation.

EcoGIS – GIS tools for ecosystem approaches to fisheries management

Executive Summary: The EcoGIS project was launched in September 2004 to investigate how Geographic Information Systems (GIS), marine data, and custom analysis tools can better enable fisheries scientists and managers to adopt Ecosystem Approaches to Fisheries Management (EAFM). EcoGIS is a collaborative effort between NOAA’s National Ocean Service (NOS) and National Marine Fisheries Service (NMFS), and four regional Fishery Management Councils. The project has focused on four priority areas: Fishing Catch and Effort Analysis, Area Characterization, Bycatch Analysis, and Habitat Interactions. Of these four functional areas, the project team first focused on developing a working prototype for catch and effort analysis: the Fishery Mapper Tool. This ArcGIS extension creates time-and-area summarized maps of fishing catch and effort from logbook, observer, or fishery-independent survey data sets. Source data may come from Oracle, Microsoft Access, or other file formats. Feedback from beta-testers of the Fishery Mapper was used to debug the prototype, enhance performance, and add features. This report describes the four priority functional areas, the development of the Fishery Mapper tool, and several themes that emerged through the parallel evolution of the EcoGIS project, the concept and implementation of the broader field of Ecosystem Approaches to Management (EAM), data management practices, and other EAM toolsets. In addition, a set of six succinct recommendations are proposed on page 29. One major conclusion from this work is that there is no single “super-tool” to enable Ecosystem Approaches to Management; as such, tools should be developed for specific purposes with attention given to interoperability and automation. Future work should be coordinated with other GIS development projects in order to provide “value added” and minimize duplication of efforts. In addition to custom tools, the development of cross-cutting Regional Ecosystem Spatial Databases will enable access to quality data to support the analyses required by EAM. GIS tools will be useful in developing Integrated Ecosystem Assessments (IEAs) and providing pre- and post-processing capabilities for spatially-explicit ecosystem models. Continued funding will enable the EcoGIS project to develop GIS tools that are immediately applicable to today’s needs. These tools will enable simplified and efficient data query, the ability to visualize data over time, and ways to synthesize multidimensional data from diverse sources. These capabilities will provide new information for analyzing issues from an ecosystem perspective, which will ultimately result in better understanding of fisheries and better support for decision-making. (PDF file contains 45 pages.)

Tagging and recovery of tropical tunas 1955-1959

ENGLISH: Yellowfin and skipjack tuna occur in commercial quantities in the Eastern Pacific Ocean from California to Chile. They are captured in the high seas at distances from the mainland up to several hundred miles (see Alverson, 1960). The Inter-American Tropical Tuna Commission has been engaged for several years in research on the biology, ecology, and population dynamics of the stocks of these species supporting the commercial fishery, in order to elucidate the effects of the fishery and of fishery independent factors on their abundance and behavior, to provide the scientific basis for rational management of the fishery. An important aspect of this research is the investigation of the migrations of these species in the Eastern Pacific, and the determination of whether each consists of but a single population or is composed of various sub-populations. One direct means of approaching these problems is the tagging, and subsequent recovery, of specimens in the region of the commercial fishery. This also provides direct information on growth rates, by comparison of sizes of specimens at tagging and upon later recovery, and can furnish the basis of estimating rates of mortality. These are two of the important elements of the vital statistics of the tuna populations. SPANISH: El atún aleta amarilla y el barrilete se encuentran en cantidades comerciales en el Océano Pacífico Oriental, desde California hasta Chile. Estos peces son capturados en alta mar a varios cientos de millas de distancia de tierra firme (ver Alverson, 1960). La Comisión Interamericana del Atún Tropical ha estado dedicada durante varios años a la investigación de la biología, ecología y dinámica de las poblaciones de los stocks de las indicadas especies que mantienen la pesquería comercial, a fin de elucidar los efectos de ésta y de los factores independientes de la explotación sobre la abundancia y hábitos de estos peces, para obtener una base científica que permita una administración racional de la pesquería. Un aspecto importante de esta investigación es el estudio de los movimientos migratorios de estas especies en el Pacífico Oriental, y la determinación de que si cada una constituye una sola población o está compuesta de varias subpoblaciones. Un medio directo de abordar estos problemas es el de la marcación, y subsecuente recuperación, de especímenes en la región de la pesquería comercial. Esto también proporciona una información directa sobre la tasa de crecimiento, por la comparación de los tamaños de los especímenes al ser marcados y recuperados más tarde y puede proveer la base para estimar las tasas de mortalidad. Estos son dos de los elementos importantes de las estadísticas vitales de las poblaciones de atún.

Some factors affecting the distribution and apparent abundance of yellowfin and skipjack tuna in the Eastern Pacific Ocean

ENGLISH: Since 1951, the Inter-American Tropical Tuna Commission has been investigating the biology, ecology and population dynamics of the yellowfin tuna, Thunnus albacares, and the skipjack tuna, Katsuwonus pelamis, in the Eastern Pacific Ocean. Of particular importance has been the study of the effects of fishing and of fishery-independent factors on the abundance and distribution of these tunas. For yellowfin tuna there is, on the average, an inverse relationship between total fishing effort and apparent abundance (Schaefer, 1957a). For skipjack there is no evidence to suggest that fishing effort has ever been sufficiently intense to affect measurably the abundance (Schaefer, 1961). Rather, it appears that the year-to-year fluctuations in apparent abundance are independent of the activities of the fishing fleets. SPANISH: Desde 1951 la Comisión Interamericana del Atún Tropical se ha dedicado a la investigación de la biología, ecología y la dinámica de las poblaciones del atún aleta amarilla, Thunnus albacares, y del barrilete, Katsuwonus pelamis, en el Océano Pacífico del Este. De importancia especial ha sido el estudio de los efectos de la pesca y de los factores independientes de las pesquerías sobre la abundancia y la distribución de esos atunes. En cuanto al atún aleta amarilla, existe, en promedio, una relación inversa entre el esfuerzo total de pesca y la abundancia aparente (Schaefer, 1957a) . Con respecto al barrilete, no hay evidencia que haga pensar que el esfuerzo de pesca haya sido nunca lo suficientemente intenso como para afectar sensiblemente la abundancia (Schaefer, 1961). Más bien parece que las fluctuaciones de un año a otro en su abundancia aparente, son independientes de las actividades de las flotas pesqueras.

Widow rockfish: Proceedings of a workshop, Tiburon, California, December 11-12, 1980

This workshop was organized because of the increase between 1978 and 1980 in coastwide landings of widow rockfish, from less than 1,000 mt to more than 20,000 mt, and because of scientists' concern with the lack of knowledge both of the fishery and biology of the species. Most scientists active in research on Pacific groundfish, as well as some members of the fishing industry and fishery managers, attended the workshop. These proceedings contain the report of the workshop discussion panel, status reports on California, Oregon, and Washington fisheries through 1980, and a collection of seven papers presented at the workshop. The status reports provide an historical perspective of the development of an important fishery. The papers present a fairly complete survey of biological knowledge of widow rockfish, economic status of the fishery, and fishery-independent methods for estimation of abundance. The papers also contain some information developed after the workshop. Since the workshop, the fishery has matured. Largest landings were made in 1981, when more than 28,000 mt were landed. Maximum sustainable yield (MSY) is estimated to be slightly less than 10,000 mt, and the stock appeared to be at about the MSY level in 1985. The Pacific Fishery Management Council and National Marine Fisheries Service have implemented regulations that have maintained landings since 1983 at approximately the maximum sustainable yield level. Fishery-dependent stock assessments are being made on an annual basis for the Pacific Fishery Management Council. While these assessments are considered to be the best possible with available data, scientists responsible for the assessment have chosen to delay their publication in the formal scientific literature until more data are obtained. However, the stock assessment reports are available from the Pacific Fishery Management Council. In addition to the papers in this collection, three papers have been published on widow rockfish since 1980. BoehIert, Barss, and Lamberson (1982) estimate fecundity of the species off Oregon; Gunderson (1984) describes the fishery and management actions; and Laroche and Richardson (1981) describe the morphology and distribution of juvenile widow rockfish off Oregon. During the past decade, the fishery for widow rockfish has developed from a minor fishery to one of the more important on the Pacific Coast. Our knowledge of the biology and dynamics of the species has progressed from minimal to relatively extensive for a groundfish species. It is our intention in preparing this collection of papers to make this knowledge readily available to the scientific community. (PDF file contains 63 pages.)

Blue Crab target setting: final report

We have developed a hierarchy of target levels, designated to address sustainability, efficiency, and recovery scenarios. Targets were derived from: 1) reported catches and effort in the commercial fishery, 2) statistics from fishery-independent surveys, and 3) knowledge of the biology of blue crab. Targets that are recommended include population sizes, catches, and effort levels, as well as reference fishing mortality rates. They are intended to be conservative and risk-averse. (PDF contains 182 pages)

Population dynamics of the skipjack tuna (Katsuwonus pelamis) of the Eastern Pacific Ocean

ENGLISH: Catches of skipjack tuna supporting major fisheries in parts of the western, central and eastern Pacific Ocean have increased in recent years; thus, it is important to examine the dynamics of the fishery to determine man's effect on the abundance of the stocks. A general linear hypothesis model was developed to standardize fishing effort to a single vessel size and gear type. Standardized effort was then used to compute an index of abundance which accounts for seasonal variability in the fishing area. The indices of abundance were highly variable from year to year in both the northern and southern areas of the fishery but indicated a generally higher abundance in the south. Data from 438 fish tagged and recovered in the eastern Pacific Ocean were used to compute growth curves. A least-squares technique was used to estimate the parameters of the von Bertalanffy growth function. Two estimates of the parameters were made by analyzing the same data in different ways. For the first set of estimates, K= 0.819 on an annual instantaneous basis and L= 729 mm; for the second, K = 0.431 and L=881. These compared well with estimates derived using the Chapman-Richards growth function, which includes the von Bertalanffy function as a special case. It was concluded that the latter function provided an adequate empirical fit to the skipjack data since the more complicated function did not significantly improve the fit. Tagging data from three cruises involving 8852 releases and 1777 returns were used to compute mortality rates during the time the fish were in the fishery. Two models were used in the analyses. The best estimates of the catchability coefficient (q) in the north and south were 8.4 X 10- 4 and 5.0 X 10- 5 respectively. The other loss rate (X), which included losses due to emigration, natural mortality and mortality due to carrying a tag, was 0.14 on an annual instantaneous basis for both areas. To detect the possible effect of fishing on abundance and total yield, the relation between abundance and effort and between total catch and effort was examined. It was found that at levels of intensity observed in the fishery, fishing does not appear to have had any measurable effect on the stocks. It was concluded therefore that the total catch could probably be increased by substantially increasing total effort beyond the present level, and that the fluctuations in abundance are fishery-independent. The estimates of growth, mortality and fishing effort were used to compute yield-per-recruitment isopleths for skipjack in both the northern and southern areas. For a size at first entry of about 425 mm, the yield per recruitment was calculated at 3 pounds in the north and 1.5 pounds in the south. In both areas it would be possible to increase the yield per recruitment by increasing fishing effort. It was not possible to assess potential production of the skipjack stocks fished in the eastern Pacific, except to note that the fishery had not affected their abundance and that they were certainly under-exploited. It was concluded that the northern and southern stocks could support increased harvests, especially the latter. SPANISH: Las capturas de atún barrilete que sostienen las pesquerías principales de la parte occidental, central y oriental del Océano Pacífico han aumentado en los últimos años; así que es importante examinar la dinámica de la pesquería para determinar el efecto que pueda tener sobre la abundancia de los stocks. Se desarrolló un modelo hipotético, lineal para standardizar el esfuerzo de pesca a un solo tamaño de barco y tipo de arte. Luego se usó el esfuerzo standardizado para computar un índice de la abundancia que pueda dar razón de la variabilidad estacional en el área de pesca. Los índices de la abundancia variaron mucho de un año a otro tanto en el área septentrional como en el área meridional de la pesquería, pero indicaron una abundancia generalmente superior en el sur. Se emplearon los datos de 438 peces marcados y recuperados en el Océano Pacífico oriental para computar las curvas de crecimiento. Una técnica de mínimos cuadrados fue usada para estimar los parámetros de la función de crecimiento de van Bertalanffy. Se hicieron dos estimativos de los parámetros mediante el análisis de los mismos datos, de diferente manera. Para el primer juego de estimativos, K=0.819 sobre una base anual instantánea y L∞=729 mm; para el segundo, K=0.431 y L∞=881. Estos se correlacionaron bien con los estimativos obtenidos usando la función de crecimiento de Chapman-Richards, que incluye la de von Bertalanffy como un caso especial. Se decidió que la última función proveía un ajuste empírico, adecuado a los datos del barrilete, ya que la función más complicada no mejoró significativamente el ajuste. Los datos de marcación de tres cruceros incluyendo 8852 liberaciones y 1777 retornos, fueron usados para computar las tasas de mortalidad durante el tiempo en que los peces estuvieron en la pesquería. Se usaron dos modelos en los análisis. Los mejores estimativos del coeficiente de capturabilidad (q) en el norte y en el sur fueron 8.4 X 10-4 y 5.0 X 10-5 , respectivamente. La otra tasa de pérdida (X), la cual incluyó pérdidas debidas a la emigración, mortalidad natural y mortalidad debida a llevar una marca, fue 0.14 sobre una base anual instantánea para las dos áreas. Con el fin de descubrir el efecto que posiblemente pueda tener la pesca sobre la abundancia y el rendimiento total, se examinó la relación entre la abundancia y el esfuerzo y entre la captura total y el esfuerzo. Se encontró que a los niveles de la intensidad observada en la pesquería, la pesca no parece haber tenido ningún efecto perceptible en los stocks. Por lo tanto se decidió que mediante un aumento substancial del esfuerzo total, más allá del nivel actual, la captura total probablemente podría aumentarse, y que las fluctuaciones de la abundancia son independientes de la pesquería. Los estimativos del crecimiento, mortalidad y esfuerzo de pesca fueron usados para computar las isopletas del rendimiento por recluta del barrilete, tanto en las áreas del norte como del sur. Para una talla de primera entrada de unos 425 mm, el rendimiento por recluta fue calculado en 3 libras en el norte y 1.5 libras en el sur. En ambas áreas sería posible aumentar el rendimiento por recluta mediante un aumento del esfuerzo de pesca. No fue posible determinar la producción potencial de los stocks del barrilete pescado en el Pacífico oriental, excepto para observar que la pesquería no ha afectado su abundancia y que ciertamente se encuentran subexplotados. Se concluyó que los stocks norte y sur pueden soportar un aumento en el rendimiento, especialmente este último. (PDF contains 274 pages.)