Tag-reporting levels for red drum (Sciaenops ocellatus) caught by anglers in South Carolina and Georgia estuaries

A total of 1784 legal-size (≥356 mm TL) hatchery-produced red drum (Sciaenops ocellatus) were tagged and released to estimate tag-reporting levels of recreational anglers in South Carolina (SC) and Georgia (GA). Twelve groups of legal-size fish (~150 fish/group) were released. Half of the fish of each group were tagged with an external tag with the message “reward” and the other half of the fish were implanted with tags with the message “$100 reward.” These fish were released into two estuaries in each state (n=4); three replicate groups were released at different sites within each estuary (n=12). From results obtained in previous tag return experiments conducted by wildlife and fisheries biologists, it was hypothesized that reporting would be maximized at a reward level of $100/tag. Reporting level for the “reward” tags was estimated by dividing the number of “reward” tags returned by the number of “$100 reward” tags returned. The cumulative return level for both tag messages was 22.7 (±1.9)% in SC and 25.8 (±4.1)% in GA. These return levels were typical of those recorded by other red drum tagging programs in the region. Return data were partitioned according to verbal survey information obtained from anglers who reported tagged fish. Based on this partitioned data set, 14.3 (±2.1)% of “reward” tags were returned in SC, and 25.5 (±2.3)% of “$100 reward” tags were returned. This finding indicates that only 56.7% of the fish captured with “reward” tags were reported in SC. The pattern was similar for GA where 19.1 (±10.6)% of “reward” message tags were returned as compared with 30.1 (±15.6)% for “$100 reward” message tags. This difference yielded a reporting level of 63% for “reward” tags in GA. Currently, 50% is used as the estimate for the angler reporting level in population models for red drum and a number of other coastal finfish species in the South Atlantic region of the United States. Based on results of our study, the commonly used reporting estimate may result in an overestimate of angler exploitation for red drum.

Fish tagging experiments: a prelude to an extensive tag-recovery programme on Lake Victoria

The present study is an early stage of this programme and examines several species of fishes under controlled conditions to delineate responses to tagging as a function of type of tag, species, size, and sex of fish, and position of tag placement. It is intimately related to another phase of research currently being conducted by the author on age and growth of several species important to the fishery of Lake Victoria (e.g. Tilapia spp., and several catfishes, Clarias mossambicus Peters and Bagrus docmac (Forskal). Data reported are both a reflection of growth studies and an attempt to achieve insight into tag loss, growth, and mortality that might be expected to occur in these species under lake conditions with reference to the above parameters.

Lessons from the breeding program of rohu

For the first time in India, selective breeding work has been initiated at the Central Institute of Freshwater Aquaculture, Bhubaneswar, India in collaboration with the Institute of Aquaculture Research (AKVAFORSK), Norway. Rohu has been chosen as the model species because it enjoys the highest consumer preference among Indian major carps (IMC) although its performance was observed to be slower than other IMC. As this was the first ever selection work on any Indian major carp, many procedures and techniques for successful implementation of the programs were standardized (i.e. production of full-sib groups, establishment of model hatchery for selective breeding of carps, rearing of full-sib groups in partitioned nursery ponds, individual tagging with the Passive Integrated Transponder (PIT) tag, communal rearing, sampling, data analysis, field testing and dissemination of improved rohu). After four generations of selection, an average of 17 per cent higher growth per generation was observed in improved rohu.

A method for estimating the rate of shedding of tags from yellowfin tuna

ENGLISH: The present paper describes a new method for estimating the shedding rate of tags. The method utilizes not only data on tagging and recovery of fish marked with two tags but also data from those marked with one. One important advantage of the new technique is that the estimates of the shedding rates are free from distortion caused by variations in fishing intensity during the total recovery period. The idea of this method appears to be implicit in a short note by Gulland (1963). This technique has been applied to the data obtained by the Inter-American Tropical Tuna Commission in a tagging cruise off the west coast of southern Baja California, during June 1963, at which time both single and double-tagged yellowfin tuna were released. Details of the tagging procedure and equipment have been described by Fink (1965b). The results presented in the present paper are for yellowfin tuna tagged with dart tags. Estimates of shedding should be made separately for each species investigated and also for each type of tag used, since these rates may be variable and often unexpectedly high (Springer and McErlean 1961, Chadwick 1963). SPANISH: El presente estudio describe un nuevo método para estimar las tasas del desprendimiento de marcas. El método emplea no solamente los datos sobre la marcación y recobro de peces marcados con dos marcas, pero también datos de los peces marcados con una marca. Una ventaja importante de la nueva técnica, es que las estimaciones de las tasas de desprendimiento son libres de alteración, causada por las variaciones en la intensidad de pesca durante el período total de recobro. La idea de este método parece ser implícita en un breve apunte por Gulland (1963). Esta técnica se ha aplicado a los datos obtenidos por la Comisión Interamericana del Atún Tropical, en un crucero de marcación efectuado frente a la costa occidental al sur de Baja California, en junio de 1963, tiempo en el cual fueron liberados atunes aleta amarilla marcados tanto con una como con dos marcas. Los detalles del procedimiento de la marcación y del equipo usado han sido descritos por Fink (1965b). Los resultados presentados en este estudio, pertenecen al atún aleta amarilla marcado con marcas de dardo. Las estimaciones del desprendimiento deben efectuarse separadamente para cada especie que ha sido investigada y también para cada tipo de marca usado, ya que estas tasas pueden ser vaiables, y a menudo inesperadamente altas (Springer y McErlean 1961, Chadwick 1963). (PDF contains 20 pages.)

Proceedings of the International Workshop on age determination of oceanic pelagic fishes: Tunas, billfishes, and sharks, Miami, Florida, February 15-18,1982

Accurate and precise estimates of age and growth rates are essential parameters in understanding the population dynamics of fishes. Some of the more sophisticated stock assessment models, such as virtual population analysis, require age and growth information to partition catch data by age. Stock assessment efforts by regulatory agencies are usually directed at specific fisheries which are being heavily exploited and are suspected of being overfished. Interest in stock assessment of some of the oceanic pelagic fishes (tunas, billfishes, and sharks) has developed only over the last decade, during which exploitation has increased steadily in response to increases in worldwide demand for these resources. Traditionally, estimating the age of fishes has been done by enumerating growth bands on skeletal hardparts, through length frequency analysis, tag and recapture studies, and raising fish in enclosures. However, problems related to determining the age of some of the oceanic pelagic fishes are unique compared with other species. For example, sampling is difficult for these large, highly mobile fishes because of their size, extensive distributions throughout the world's oceans, and for some, such as the marlins, infrequent catches. In addition, movements of oceanic pelagic fishes often transect temperate as well as tropical oceans, making interpretation of growth bands on skeletal hardparts more difficult than with more sedentary temperate species. Many oceanic pelagics are also long-lived, attaining ages in excess of 30 yr, and more often than not, their life cycles do not lend themselves easily to artificial propagation and culture. These factors contribute to the difficulty of determining ages and are generally characteristic of this group-the tunas, billfishes, and sharks. Accordingly, the rapidly growing international concern in managing oceanic pelagic fishes, as well as unique difficulties in ageing these species, prompted us to hold this workshop. Our two major objectives for this workshop are to: I) Encourage the interchange of ideas on this subject, and 2) establish the "state of the art." A total of 65 scientists from 10 states in the continental United States and Hawaii, three provinces in Canada, France, Republic of Senegal, Spain, Mexico, Ivory Coast, and New South Wales (Australia) attended the workshop held at the Southeast Fisheries Center, Miami, Fla., 15-18 February 1982. Our first objective, encouraging the interchange of ideas, is well illustrated in the summaries of the Round Table Discussions and in the Glossary, which defines terms used in this volume. The majority of the workshop participants agreed that the lack of validation of age estimates and the means to accomplish the same are serious problems preventing advancements in assessing the age and growth of fishes, particularly oceanic pelagics. The alternatives relating to the validation problem were exhaustively reviewed during the Round Table Discussions and are a major highlight of this workshop. How well we accomplished our second objective, to establish the "state of the art" on age determination of oceanic pelagic fishes, will probably best be judged on the basis of these proceedings and whether future research efforts are directed at the problem areas we have identified. In order to produce high-quality papers, workshop participants served as referees for the manuscripts published in this volume. Several papers given orally at the workshop, and included in these proceedings, were summarized from full-length manuscripts, which have been submitted to or published in other scientific outlets-these papers are designated as SUMMARY PAPERS. In addition, the SUMMARY PAPER designation was also assigned to workshop papers that represented very preliminary or initial stages of research, cursory progress reports, papers that were data shy, or provide only brief reviews on general topics. Bilingual abstracts were included for all papers that required translation. We gratefully acknowledge the support of everyone involved in this workshop. Funding was provided by the Southeast Fisheries Center, and Jack C. Javech did the scientific illustrations appearing on the cover, between major sections, and in the Glossary. (PDF file contains 228 pages.)

Some aspects of the age and growth of the anchoveta, Cetengraulis mysticetus, in the Gulf of Panama

ENGLISH: Length-frequency samples of anchovetas were collected from January 1956 to March 1963. The findings for the most part corroborate those of previous studies in regard to the general pattern of age and growth. Recent tag returns demonstrate that some of the fish survive at least to the beginning of their fourth year of life. In 1961 and 1962 the fish were considerably larger than in any previous year for which data are available. The annual variation in the size of the young of the year is apparently related to the amount of upwelling and the density of the population during the early months of the year. SPANISH: De enero de 1956 a marzo de 1963 se recolectaron muestras de las frecuencias de longitud de las anchovetas. Las investigaciones, en su mayor parte, corraboran los resultados de los estudios anteriores referentes a los patrones generales de la edad y el crecimiento. Recobros recientes de mareas demuestran que algunos de los peces sobreviven por lo menos hasta el comienzo de su cuarto año de vida. En 1961 y 1962 los peces fueron considerablemente más grandes que en cualquiera de los años anteriores de los que se tienen datos disponibles. La variación anual en el tamaño de los peces jóvenes del año está aparentemente relacionada con el volumen del afloramiento y la densidad de la población durante los primeros meses del año. (PDF contains 51 pages)

Population dynamics of the anchoveta, Cetengraulis mysticetus, in the Gulf of Panama, as determined by tagging experiments

ENGLISH: The anchoveta is the major constituent of the important bait and reduction fisheries of the Gulf of Panama. It is a short-lived species, the great majority of the catch consisting of fish in their first year of life. Fish for reduction are caught chiefly in the Isla Verde area, between Punta Chame and the entrance of the Panama Canal. In 1960 and 1961 anchovetas were tagged with metal internal tags and released in the major areas of occurrence of this species. The tags were recovered from the meal in the reduction plants with magnets. From the 53,380 fish tagged in 1960, 745 tags were returned during the 1960 season, 246 during the 1961 season, and 8 during the 1962 season. From the 113,202 tagged in 1961, 373 tags were returned during the 1961 season and 48 during the 1962 season. Complete catch statistics are available, and length-frequency and length-weight data were used to convert these from pounds to numbers of fish of each year class. The annual survival rate for the fish of the 1959 year class in the Isla Verde area was estimated to be 0.086 by the Chapman-Robson method, 0.102 by the year-class method, and 0.088 by the Jackson positive method. The first method is considered to give the best estimate. Six estimates of the population of fish of the 1959 year class in the Isla Verde area were obtained from the sample tag ratios of six experiments conducted in that area in 1960. The estimates differed due to the temporal decrease in the population, but the downward trend corresponded fairly well to what was expected from the total annual mortality rate. It was estimated that the population of 1959-year class fish was about 818 million on March 8, 1960, and about 70 million on March 8, 1961. As the population of anchovetas decreases during the season the effort increases sufficiently that the catch remains roughly constant. This is described as the "constant absolute catch" type fishery. Of the original population of fish in the Isla Verde area at the beginning of the 1960 season, about 11 per cent were caught and 81 per cent died of natural causes. Evaluation of growth and mortality data demonstrated that beginning the fishery for the youngest age group later than March 8 (the date it began in 1960) would reduce the yield per recruit, while increasing the fishing effort would greatly increase it. Further, it is believed unlikely that increases in the catch in the Isla Verde area alone would noticeably decrease the number of recruits to that area. Therefore there is no foreseeable need for regulation of the fishery. SPANISH: El principal constituyente de la importante pesquería para carnada y para reducción en el Golfo de Panamá es la anchoveta. Es una especie de vida corta cuya pesca, en su mayor parte, está constituida por peces que se encuentran en su primer año de vida. Para la industria de reducción los peces son capturados principalmente en el área de Isla Verde, entre Punta Chame y la entrada del Canal de Panamá. En 1960 y 1961 las anchovetas fueron marcadas con marcas metálicas internas y liberadas en las áreas más importantes en que se encuentra esta especie. Las marcas fueron recobradas de la harina en las plantas de reducción por medio de magnetos. De los 53,380 peces marcados en 1960, fueron devueltas 745 marcas durante la temporada pesquera de 1960, 246 durante la de 1961, y 8 durante la de 1962. De los 113,202 marcados en 1961, 373 marcas fueron devueltas durante la temporada pesquera de 1961 y 48 durante la de 1962. Se dispone de estadísticas completas de captura, y los datos de frecuencia-longitud y de longitud-peso fueron usados para convertir éstos de libras a números de peces de cada clase anual. La tasa anual de supervivencia correspondiente a la clase anual de 1959 en el área de Isla Verde estimó en 0.086 por medio del método Chapman-Robson; en 0.102 por método de la clase anual; y en 0.088 por el método positivo de Jackson. Se considera que el primer método dé la mejor estimación. Seis estimaciones de la población de peces de la clase anual 1959 en el área de Isla Verde fueron obtenidas según la proporción de marcas halladas en las muestras correspondientes a seis experimentos efectuados en aquella área en 1960. Las estimaciones variaron debido a la disminución temporal de la población, pero esta tendencia descendente correspondió bastante bien a lo que se esperaba según la tasa total de mortalidad anual. Se estimó que la población de peces de la clase anual de 1959 era de unos 818 millones el 8 de marzo de 1960, y aproximadamente de unos 70 millones el 8 de marzo de 1961. Conforme a que la población de anchovetas disminuye durante la temporada pesquera, el esfuerzo aumenta lo suficientemente como para que la pesca se mantenga más o menos constante. Este es el tipo de pesquería descrito como de "captura absoluta constante". De la población original de peces en el área de Isla Verde al comienzo de la temporada pesquera de 1960, cerca del 11 por ciento fue capturada y el 81 por ciento murió por causas naturales. La evaluación de los datos del crecimiento mortalidad demostraron que al comenzar la pesquería a explotar grupo de edad más joven en una fecha posterior al 8 de marzo (la fecha en que comenzó en 1960) se reduciría el rendimiento por recluta, mientras que al aumentar el esfuerzo de pesca lo aumentaría considerablemente. Más aún, se cree improbable que el aumento en la pesca en el área de Isla Verde de por sí disminuyera perceptiblemente el número de reclutas en esa área. En consecuencia no se prevé la necesidad de una reglamentación de la pesquería. (PDF contains 172 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.)

Estimates of the rates of mortality of yellowfin tuna in the Eastern Pacific Ocean derived from tagging experiments

ENGLISH: Tag release and return data for the Baja California and Gulf of Guayaquil areas were selected for this study because substantial numbers of returns resulted from these releases and because the effects of emigration are small in these areas. The returns of tags per unit of fishing effort for several experiments in each area were used to estimate the coefficients of total mortality and shedding. The coefficient of annual natural mortality was estimated to be less than 2.0, which is in agreement with a previous estimate of 0.8, but does not improve upon it. The estimates for the average coefficients of catchability are 2.02 X 10-3 for the Baja California area and 0.67 X 10-3 for the Gulf of Guayaquil area. SPANISH: Se seleccionaron para este estudio algunos da tos de liberación y retorno de marcas en las áreas de Baja California y el Golfo de Guayaquil debido a que cantidades substanciales de retornos resultaron de estas liberaciones y porque los efectos de migración son pequeños en estas áreas. Los retornos de marcas por unidad de esfuerzo de pesca de varios experimentos en cada área fueron empleados para estimar los coeficientes de mortalidad total y desprendimiento. Se estimó que el coeficiente de mortalidad natural anual fue inferior a 2.0, lo que está de acuerdo con una estimación anterior de 0.8, pero no la mejora. Las estimaciones de los coeficientes promedios de capturabilidad son 2.02 X 10-3 en el área de Baja California y 0.67 X 10-3 en el área del Golfo de Guayaquil. (PDF contains 58 pages.)

Marquages de Penaeus duorarum notialis en Côte d'Ivoire. 2 - Migrations et mortalités

Petersen disc tag marking experiments confirm the influence of animal size and marking time on the recapture rate. Westward migrations occur, probably following the Ivorian undercurrent. Catchability coefficients have been evaluated for the Grand-Bassam fishing ground and tentatively extrapolated to the other fishing areas. The extrapolated non weighted coefficient for the entire fishing areas is q=0.00069/fishing day for an area of 390 miles. The instantaneous coefficient of residual mortality X taken as a first and possibly slightly overestimated value of M the natural mortality, has been estimated at 0.155/month, strongly corroborating Berry's results (1967). This value is however much smaller than that given by earlier authors. It is suggested that q could have a higher value during the very first weeks of exploitation at sea, when the juveniles are concentrated near the lagoon outlets.