Sex-change rules, stock dynamics, and the performance of spawning-per-recruit measures in protogynous stocks

Predicting and under-standing the dynamics of a population requires knowledge of vital rates such as survival, growth, and reproduction. However, these variables are influenced by individual behavior, and when managing exploited populations, it is now generally realized that knowledge of a species’ behavior and life history strategies is required. However, predicting and understanding a response to novel conditions—such as increased fishing-induced mortality, changes in environmental conditions, or specific management strategies—also require knowing the endogenous or exogenous cues that induce phenotypic changes and knowing whether these behaviors and life history patterns are plastic. Although a wide variety of patterns of sex change have been observed in the wild, it is not known how the specific sex-change rule and cues that induce sex change affect stock dynamics. Using an individual based model, we examined the effect of the sex-change rule on the predicted stock dynamics, the effect of mating group size, and the performance of traditional spawning-per-recruit (SPR) measures in a protogynous stock. We considered four different patterns of sex change in which the probability of sex change is determined by 1) the absolute size of the individual, 2) the relative length of individuals at the mating site, 3) the frequency of smaller individuals at the mating site, and 4) expected reproductive success. All four pat-terns of sex change have distinct stock dynamics. Although each sex-change rule leads to the prediction that the stock will be sensitive to the size-selective fishing pattern and may crash if too many reproductive size classes are fished, the performance of traditional spawning-per-recruit measures, the fishing pattern that leads to the greatest yield, and the effect of mating group size all differ distinctly for the four sex-change rules. These results indicate that the management of individual species requires knowledge of whether sex change occurs, as well as an understanding of the endogenous or exogenous cues that induce sex change.

Estimating the population density of prawns by the use of catch per effort data from prawn trawlers at Chilaw

The penaeid prawns of Sri Lanka from estuaries and sea are an important commercial fishery resource. This resource has been exploited over the last century or more by local fishermen using indigenous fishing gear from locally sail-driven or oar-driven fishing crafts. In more recent times, the Fisheries Research Division of the Department of Fisheries undertook surveys of the seas and lagoons of Sri Lanka with a view to ascertain whether any unexploited resources of prawns existed. These publications deal with the species composition, biology, distribution and abundance in the lagoons and inshore waters of Sri Lanka.

Estimating age of spotted and spinner dolphins (Stenella attenuata and Stenella longirostris) from teeth

This paper is an account of preparation and examination techniques and criteria used to estimate age in decalcified and stained tooth thin sections from spinner and spotted dolphins. A dentinal growth layer group (GLG), composed of two thin light and two thicker dark-stained layers, is deposited annually. The GLG component layers are variably visible, but the "ideal" pattern and successive thinning of dentinal GLGs are used as a guide to determine GLG limits. Age-specific thicknesses of dentinal GLGs found in Hawaiian spinner dolphin teeth seem to be applicable to teeth of spotted dolphins and can be used as an aid in locating GLG boundaries. Cementa1 GLGs are composed of a dark-stained and alightly stained layer and usually are deposited at a rate of one per year, but may be deposited every other year or two or three times per year. Two slightly different methods of counting dentinal GLGs are presented, along with guidelines for determining whether dentinal or cementa1 GLG counts provide the best estimate of age for a specimen. (PDF contains 23 pages.)

Year class mortality, abundance and yield-per-recruit of yellowfin tuna in the eastern Pacific Ocean, 1954-1959

ENGLISH: One primary duty of the Inter-American Tropical Tuna Commission is to estimate the maximum sustainable catches of yellowfin tuna (Neothunnus macropterus) and skipjack (Katsuwonus pelamis), and to investigate and recommend proposals to maintain the stocks at levels which will permit these catches to be obtained. To do this, there is required some means of predicting yields relative to fishing intensity. . . The age composition of catch, and growth rate of yellowfin tuna for recent years have now been estimated (Hennemuth, 1961). In this paper, relative abundance at age of yellowfin tuna shall be estimated -and used, in turn, to estimate total mortality rate. Yield-per-recruit calculations, based on Beverton and Holt's (1957) simple equation, will be presented to compare present utilization with theoretical maxima under varying levels of fishing mortality and different ages at first capture. SPANISH: Uno de los principales deberes de la Comisión Interamericana del Atún Tropical es estimar las pescas máximas sostenibles de los atunes aleta amarilla (Neothunnus macropterus) y barrilete (Katsuwonus pelamis) , así como estudiar y recomendar proposiciones para mantener los stocks a niveles que permitan obtener estas pescas. Para lograr este propósito se requieren algunos medios que permitan predecir el rendimiento en relación con la intensidad de la pesca. . La composición de edades de la pesca y la tasa de crecimiento del atún aleta amarilla en años recientes han sido estimadas ahora (Hennemuth, 1961). En este trabajo, la abundancia relativa a una edad dada de esta especie será estimada y usada, a su vez, para estimar la tasa de mortalidad total. Los cálculos del rendimiento por recluta, basados en la ecuación simple de Beverton y Holt (1957), serán presentados para comparar la utilización actual con los máximos teóricos bajo valores variables de mortalidad por la pesca y a diferentes edades a la primera captura.

Distribution of catch-per-unit-of-effort and fishing effort for tuna in the Eastern Tropical Pacific Ocean by months of the year 1951-1960

ENGLISH: Comparison of physical and biological environmental factors affecting the aggregation of tunas with the success of fishing by the commercial fleets, requires that catch and effort data be examined in greater detail than has been presented in these publications. Consequently, the United States Bureau of Commercial Fisheries Biological Laboratory, San Diego, to serve the needs of its program of research on causes of variations in tuna abundance, made arrangements with the Tuna Commission to summarize these catch and effort data by month, by one-degree area, by fishing vessel size-class, for the years 1951-1960 for bait boats and 1953-1960 for purse-seiners. The present paper describes the techniques employed in summarizing these data by automatic data processing methods. It also presents the catch and effort information by months, by five-degree areas and certain combinations of five-degree areas for use by fishermen, industry personnel, and research agencies. Because of space limitations and other considerations, the one-degree tabulations are not included but are available at the Tuna Commission and Bureau laboratories. SPANISH: La comparación de los factores ambientales físicos y biológicos que afectan la agrupación del atún, con el éxito obtenido en la pesca por las flotas comerciales, requiere que los datos sobre la captura y el esfuerzo sean examinados con mayor detalle de lo que han sido presentados en estas publicaciones. En consecuencia, el Laboratorio Biológico del Buró de Pesquerías Comerciales de los Estados Unidos, situado en San Diego, a fin de llenar los requisitos de su programa de investigación sobre las causas de las variaciones en la abundancia del atún, hizo arreglos con la Comisión del Atún para sumarizar esos datos sobre la captura y el esfuerzo por meses, por áreas de un grado, por clases de tamaño de las embarcaciones de pesca durante los años 1951-1960 en lo que concierne a los barcos de carnada y durante el período 1953-1960 en lo que respecta a los barcos rederos. El presente trabajo describe la técnica empleada en la sumarización de dichos datos mediante métodos automáticos de manejo de datos. También se da aquí la información sobre la captura y el esfuerzo por meses, por áreas de cinco grados y ciertas combinaciones de áreas de cinco grados para el uso de los pescadores, del personal de la industria y de las oficinas de investigación. Por falta de espacio y otras razones, las tabulaciones de las áreas de un grado no han sido incluídos en este trabajo, pero están a la disposición de quien tenga interés en los laboratorios de la Comisión del Atún y del Buró.

Catch-per-unit-effort and biological parameters from the Massachusetts coastal lobster (Homarus americanus) resource: Description and trends

Acomprehensive description of the Massachusetts coastal lobster (Homarus americanus) resou,rce was obtained by sampling commercial catches coastwide at sea and at dealerships between 1981 and 1986. Acommercial lobster sea-sampling program, wherein six coastal regions were sampled monthly, with an areal and temporal data weighting design, was the primary source of data. An improved index of catch per trap haul/set-over-day was generated by modeling the relationship between catch and immersion time and standardizing effort. This 6-year time-series of mean annual catch rates tracked closely the landings trend for territorial waters. During the study period there was a gradual increase in indices of exploitation and total annual mortality which corresponded to a gradual decline in mean carapace length of marketable lobster. The frequency of culls escalated from 10.0% in 1981 to 20.9% in 1986, while the percentage of lobster found dead in traps was consistently less than 1%. The sex ratio (%F:%M) was significantly different from 50:50 and approximated a 60:40 relationship during the study period. Male and female weight-length relationships were significantly different. Females weighed more than males at smaller sizes and less than males at larger sizes. A north-south clinal trend was evident wherein lobster north of Cape Cod weighed less at length than those from regions south of Cape Cod. Functional size-maturity relationships were developed for female lobster by staging cement gland development. Proportions mature at size represent more realistic values than those obtained by analyses of percent of females ovigerous. Regional variation occurred in most of the parameters studied. Three lobster groups, differing in major population descriptors, are defined by our data.(PDF file contains 28 pages.)

Size composition, growth and sexual maturity of bigeye tuna, Thunnus obesus (Lowe), from the Japanese long-line fishery in the Eastern Pacific Ocean

Size composition data of bigeye tuna taken from the eastern tropical Pacific Ocean by Japanese Prefectural experimental training vessels from 1958 to 1964 are examined. A gradient of increasing fish size from east to west is noted. Males increase in ratio over females for the entire range of lengths examined, and beyond 170 cm comprise more than 75 per cent of the total. The first semester of the year is important as a bigeye spawning season. A general relationship between sexual maturity and thermal structure of the water is discussed. At the end of their 12th quarter of life bigeye are about 114 cm long, by the 16th quarter, 137 cm and at the end of 20 quarters, about 153 cm. The long-line fishery in the eastern Pacific has had a marked effect on the size composition of the stocks of bigeye, but whether the fishing has driven the stocks below a point which could afford a maximum sustainable yield could not be determined. (PDF contains 55 pages.)

A study of populations of the anchoveta, Cetengraulis mysticetus, based on meristic characters

ENGLISH: This study was undertaken to determine whether meristic characters indicate that more than one major population of anchovetas occurs in the range of the species from Mexico to Peru. Interest in this species lies in the fact that it is the principal bait fish used to catch yellowfin and skipjack tunas in the Eastern Pacific. Specimens examined were from collections made by California tuna fishing vessels at six major baiting localities covering nearly the entire range of the species, namely, Almejas Bay on the outer coast of Baja California, Guaymas and Ahome Point in the Gulf of California, Gulf of Fonseca, Gulf of Panama, and Gulf of Guayaquil. Four meristic characters were selected for study: vertebrae, dorsal fin rays, anal fin rays, and gill rakers on the first gill arch. Vertebral counts, using X-ray film, were taken from a total of 1,500 fish, 250 each from each of the six localities. For the other characters, 125 anchovetas were examined from each locality for a total of 750, the counts being made with the aid of a binocular microscope. Specimens were between 80 and 165 mm. standard length. SPANISH: Este estudio ha sido hecho con el propósito de determinar si los caracteres numéricos de las anchovetas indican que existe más de una población de este pez en la zona en que se encuentra la especie, comprendida entre México y Perú. El interés en dicha especie radica en el hecho de que éste es el pez de carnada usado principalmente para la pesca de los atunes "aleta amarilla" y "barrilete" en el Pacífico Oriental. Los especímenes que han sido examinados, se tomaron de las muestras recogidas por los barcos atuneros de California en seis de las mejores localidades en que se pesca la anchoveta, las cuales comprenden casi toda la zona en donde se encuentra la especie, a saber, Bahía de Almejas en la costa exterior de Baja California, Guaymas y Punta Ahorne en el Golfo de California, el Golfo de Fonseca, el Golfo de Panamá y el Golfo de Guayaquil. Cuatro caracteres numéricos fueron escogidos para su estudio: los que presentan 1) las vértebras, 2) los radios de la aleta dorsal, 3) los radios de la aleta anal y 4) las branquispinas del primer arco branquial. Mediante el uso de películas con rayos X, se contaron las vértebras en un total de 1,500 peces, es decir, 250 de cada una de las seis mencionadas localidades. En relación con los otros caracteres, se examinaron 125 anchovetas de cada área, o sea, un total de 750 ejemplares, habiendo sido hecho el conteo por medio de un microscopio binocular. Los especímenes tenían un largo standard entre 80 y 165 milímetros. (PDF contains 24 pages.)

Nordseegarnelen: Sind Anzeichen für einen Bestandsrückgang erkennbar?

Landings of brown shrimp (Crangon crangon L.) for human consumption from the North Sea had reached a maximum in 2005. The German share was 16 485 tonnes, i. e. 44.2 %. However, German landings declined in 2006 and the question arose, whether effort reductions or a reduced stock caused this development. Logbook data, basis for the German fisheries statistics, have been analysed and revealed a first decline in LPUE (landings per unit effort) after a series of years with positive development.

Spawning of yellowfin tuna and the discrimination of subpopulations

ENGLISH: The spawning of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean was examined to ascertain the existence of separate subpopulations within this area. Investigations of biochemical genetics of yellowfin indicate that there are a number of genetically distinct groups in the eastern Pacific. In addition, yellowfin belong to two recruitment cohorts, X and Y, which are composed of a mixture of these genetically different groups. Spawning data were collected from 1956 through 1961 from the coastal fishing grounds, and from 1970 through 1973 from the offshore fishing areas. Temporal and spatial aspects of spawning of the fish of the two cohorts were analyzed to determine if yellowfin spawning behavior supports the existence of genetically separate subpopulations. Spawning condition was inferred from the maturity of the ovaries. It was found that the coastal fish of each cohort exhibit at least two spawning periods per year which vary in length and time of occurrence from year to year. Fish taken from the offshore fishing grounds did not exhibit this variable spawning pattern. Although samples were not available for all months, the data showed that each cohort has a spawning period of at least 7 months and may spawn year around. Samples from offshore areas also had much higher percentages of spawners than those from the coastal areas. Temporal differences in spawning are not maintaining the genetically separate groups found in the fishery, since fish of both recruitment cohorts spawn at the same time. Also, fish of both the X and Y cohorts spawned in all areas examined; however, these data are insufficient to determine whether spatial isolation of spawning groups is occurring within the areas. SPANISH: Se examinó el desove del atún aleta amarilla (Thunnus albacares) en el Océano Pacífico oriental para averiguar la existencia de subpoblaciones separadas en esta zona. La investigación genética bioquímica del aleta amarilla indica que existen varios grupos genéticamente distintos en el Pacífico oriental. Además, el aleta amarilla pertenece a dos cohortes de reclutamiento X e Y, formadas por una mezcla de estos grupos genéticamente diferentes. Los datos del desove fueron obtenidos de 1956 a 1961, en las regiones neríticas de pesca y desde 1970 a 1973, en las áreas oceánicas de pesca. Se analizaron los aspectos temporales y espaciales del desove de los peces de las dos cohortes, para determinar si el comportamiento reproductor del aleta amarilla, apoya la existencia de subpoblaciones genéticamente diferentes. Se derivó la condición del desove según la madurez de los ovarios. Se encontró que los peces costeros de cada cohorte exhibían por lo menos dos períodos anuales de desove que varían en duración y fecha de ocurrencia de un año a otro. Los peces capturados en las regiones oceánicas de pesca no exhibieron este patrón variable de desove. Aunque o se consiguieron muestras en todos los meses, los datos indican que cada cohorte tiene un período de desove por lo menos de 7 meses y puede que desoven durante todo el año. Las muestras de las regiones oceánicas tuvieron porcentajes mucho mayores de reproductores que los de las zonas neríticas. Las diferencias temporales en el desove no sirven para explicar la presencia de grupos genéticamente separados que se encuentran en la pesca, ya que los peces de ambas cohortes de reclutamiento desovan al mismo tiempo. Además, los peces de ambas cohortes (X e Y) desovan en todas las zonas examinadas; sin embargo, estos datos no son suficientes para determinar si el aislamiento de los grupos de desove ocurre en las zonas. (PDF contains 53 pages.)

Estimation of the relative annual abundance of yellowfin tuna, Thunnus albacares, in the Eastern Pacific Ocean during 1970-1985

ENGLISH: Estimates of relative annual abundance of yellowfin tuna in the eastern Pacific Ocean during 1970-1985 are made using catch rates, measured as tons caught by purse seiners per hour of searching. Catch rates are standardized a weighted generalized linear model. The important standardizing factors are vessel speed, season-area, and whether the yellowfin were caught in association with dolphins, skipjack tuna, or floating objects. Observations are weighted to give equal areas equal weight and to give each unit of fishing effort equal weight within an area. The results indicate that catch per days fishing underestimates abundance during the late 1970's when the fishery shifted some of its effort from dolphin sets to floating object sets, and overestimates abundance when the fishery shifted back to dolphin sets in 1984 and 1985. SPANISH: Se estima la abundancia anual relativa del atún aleta amarilla en el Océano Pacífico oriental (OPO) durante 1970-1985 por medio de tasas de captura, calculadas como toneladas cortas capturadas por barcos cerqueros por hora de búsqueda. Se usa un modelo lineal ponderado generalizado para estandardizar las tasas de captura. Los factores importantes de estandardización son la velocidad del barco, temporada-área, y si se capturaron los aletas amarillas en asociación con delfines, barriletes, o objetos flotantes. Se ponderaron las observaciones para otorgar igual importancia a áreas iguales y a cada unidad de esfuerzo pesquero dentro de un área. Los resultados señalan que la captura por día de pesca estima por bajo la abundancia durante los últimos años de la década de los 70, en cual época la pesquería trasladó parte de su esfuerzo de lances sobre delfines a lances sobre objetos flotantes, y la sobreestima al volver la pesquería a lances sobre delfines en 1984 y 1985. (PDF contains 45 pages.)

Catches per unit of effort of bigeye tuna: a new analysis with regression trees and simulated annealing

ENGLISH: We analyzed catches per unit of effort (CPUE) from the Japanese longline fishery for bigeye tuna (Thunnus obesus) in the central and eastern Pacific Ocean (EPO) with regression tree methods. Regression trees have not previously been used to estimate time series of abundance indices fronl CPUE data. The "optimally sized" tree had 139 parameters; year, month, latitude, and longitude interacted to affect bigeye CPUE. The trend in tree-based abundance indices for the EPO was similar to trends estimated from a generalized linear model and fronl an empirical model that combines oceanographic data with information on the distribution of fish relative to environmental conditions. The regression tree was more parsimonious and would be easier to implement than the other two nl0dels, but the tree provided no information about the nlechanisms that caused bigeye CPUEs to vary in time and space. Bigeye CPUEs increased sharply during the mid-1980's and were more variable at the northern and southern edges of the fishing grounds. Both of these results can be explained by changes in actual abundance and changes in catchability. Results from a regression tree that was fitted to a subset of the data indicated that, in the EPO, bigeye are about equally catchable with regular and deep longlines. This is not consistent with observations that bigeye are more abundant at depth and indicates that classification by gear type (regular or deep longline) may not provide a good measure of capture depth. Asimulated annealing algorithm was used to summarize the tree-based results by partitioning the fishing grounds into regions where trends in bigeye CPUE were similar. Simulated annealing can be useful for designing spatial strata in future sampling programs. SPANISH: Analizamos la captura por unidad de esfuerzo (CPUE) de la pesquería palangrera japonesa de atún patudo (Thunnus obesus) en el Océano Pacifico oriental (OPO) y central con métodos de árbol de regresión. Hasta ahora no se han usado árboles de regresión para estimar series de tiempo de índices de abundancia a partir de datos de CPUE. EI árbol de "tamaño optimo" tuvo 139 parámetros; ano, mes, latitud, y longitud interactuaron para afectar la CPUE de patudo. La tendencia en los índices de abundancia basados en árboles para el OPO fue similar a las tendencias estimadas con un modelo lineal generalizado y con un modelo empírico que combina datos oceanográficos con información sobre la distribución de los peces en relación con las condiciones ambientales. EI árbol de regresión fue mas parsimonioso y seria mas fácil de utilizar que los dos otros modelos, pero no proporciono información sobre los mecanismos que causaron que las CPUE de patudo valiaran en el tiempo y en el espacio. Las CPUE de patudo aumentaron notablemente a mediados de los anos 80 y fueron mas variables en los extremos norte y sur de la zona de pesca. Estos dos resultados pueden ser explicados por cambios en la abundancia real y cambios en la capturabilidad. Los resultados de un arbal de regresión ajustado a un subconjunto de los datos indican que, en el OPO, el patudo es igualmente capturable con palangres regulares y profundos. Esto no es consistente con observaciones de que el patudo abunda mas a profundidad e indica que clasificación por tipo de arte (palangre regular 0 profundo) podría no ser una buena medida de la profundidad de captura. Se uso un algoritmo de templado simulado para resumir los resultados basados en el árbol clasificando las zonas de pesca en zonas con tendencias similares en la CPUE de patudo. El templado simulado podría ser útil para diseñar estratos espaciales en programas futuros de muestreo. (PDF contains 45 pages.)

Biometric comparison of the anchoveta, Cetengraulis mysticetus (Gunther), from ten localities of the Eastern Tropical Pacific Ocean

ENGLISH: It is important to the Inter-American Tropical Tuna Commission to know whether the anchoveta (Cetengraulis mysticetus), the principal tuna bait species in the Eastern Tropical Pacific Ocean, is composed of one or several populations. Earlier research indicated that, on the basis of significant differences in certain meristic counts, populations of this species in six of the major baiting localities between Mexico and Peru, should provisionally be considered as separate stocks. Since that time, additional collections of anchovetas have been obtained from these and other intervening localities. Purpose of the present study was to confirm the results of the earlier work, and to determine whether the differences in the meristic counts persisted from year to year, as well as to examine certain morphometric characters of the fish from these areas, and to learn whether the populations from the other localities are also separate entities. SPANISH: La Comisión Interamericana del Atún Tropical está interesada en saber si la anchoveta (Ceteugrautís mvsticetus}, la principal especie usada como cebo para la pesca del atún en el Océano Pacífico Oriental Tropical, está compuesta de una o de varias poblaciones. Investigaciones previas indicaron que, a base de diferencias significativas encontradas en ciertos caracteres numéricos, las poblaciones de esta especie en seis de las principales localidades entre México y Perú, podían ser consideradas provisionalmente como pertenecientes a "stocks'' separados. Desde entonces se han venido haciendo recolecciones adicionales de anchovetas en éstas y otras localidades intermedias. El propósito del presente trabajo ha sido confirmar los resultados obtenidos previamente, y determinar si las diferencias en los caracteres numéricos han persistido de un año a otro, así como examinar ciertos caracteres morfométricos en los peces de estas áreas, y resolver si las poblaciones de las nuevas localidades muestreadas son también entidades diferentes. (PDF contains 76 pages.)

Aktuelle Informationen zum Hering in der Ostsee im Hinblick auf deutsche Fischereiinteressen

Germany is planning to construct a new herring factory on the Island of Rügen. This factory will need about 50 000 t of herring per year. For the German fishery this would mean to increase the past 10w 1andings of less than 15 000 t per year to a level which had a1ready been reached by the GDR before the reunification. News of less herring in the Baltic and a decline of German landings in 1998 compared to the years before have led to discussions whether the planned increase in landings could be reached and kept in the future. Information is given in view of German fishery interests about: • the actual assessed herring stock units and the corresponding recent stock development in the Baltic Sea • the Total Allowable Catch (TAC) values for the western and central Baltic Sea in 1998 and in 1999 • the German landings during spring of the years 1993 to 1998 in the Greifswalder Bodden, main German fishery ground in the Baltic Sea

Investigation of nematode Eustrongylides larvae infections in mudfish Clarias gariepinus and C. anguillaris from Bida floodplain of Nigeria

This is the first report and record of the determination whether mudfish Clarias were infected with the larvae of the nematode Eustrongylides. Also, documented the assessment of the socio-economic perceptions of three groups of fisher folks on the economy of infected mudfish Clarias fishing activities. Fifty-six (67.5%) of 83 mudfish Clarias caught by artisanal fisher folks were examined for the presence of the larvae of the nematode Eustrongylides. All the 8 sampled fishing localities in Bida floodplain of Nigeria had a mean intensity and abundance of at least 3 and 1 worm per fish per site, respectively. Two hundred and one (96.2%) of 209 worms recovered were from the musculatures at different depths resulting in undulations on the skin surfaces as grub-like presentations. The three groups of fisher folks assessed encountered economic losses from nematode infected mudfish Clarias which attract much debates or rejections during marketing due to its aesthetically displeasing appearance, faster deterioration, higher fragility in smoked form coupled with poorer taste compared to the wholesome ones. Infected female mudfish Clarias had higher worm burden than the males, for each fishing locality