Guidelines for reducing porpoise mortality in tuna purse seining

More than a decade has passed since the passage of the Marine Mammal Protection Act of 1972. During that time the U.S. tuna purse seine neet reduced its incidental porpoise mortality rate more than 10-fold. This was made possible through the development of gear and techniques aimed at reducing the frequency of many low probability events that contribute to the kill. Porpoise are killed by becoming entangled or entrapped in folds and canopies of the net and suffocating. The configuration of the net, both before and during the backdown release procedure, is a major determinant of the number of porpoise killed. Speedboats can be used to tow on the corkllne to prevent net collapse and also to adjust the net configuration to reduce net canopies prior to backdown. Deepening a net can reduce the probability of porpoise being killed by prebackdown net collapse. The effects of environmental conditions and mechanical failures on net configuration can result in high porpoise mortality unless mitigated by skilled vessel maneuvers or prevented by the timely use of speedboats to adjust the net. The backdown procedure is the only means to effectively release captured porpoise from a purse seine. It is also the time during the set when most of the mortality occurs. The use of small mesh safety panels and aprons in the backdown areas of nets reduces porpoise entanglement, and Increases the probability of an effective release. The tie-down points on the net for preparing the backdown channel must be properly located in order to optimize porpoise release. A formula uses the stretched depth of the net to calculate one of these points, making it a simple matter to locate the other. Understanding the dynamics of the backdown procedure permits a thorough troubleshooting of performance, thus preventing the repetition of poorly executed backdowns and thereby reducing mortality. Porpoise that cannot be released must be rescued by hand. A rescuer in a rigidly inflated raft can rescue porpoise effectively at any time during a net set. Hand rescue can make the difference between above average kill and zero kill sets. In all circumstances, the skill and motivation of the captain and his crew are the final determinants in the prevention of incidental porpoise mortality in tuna seining. (PDF file contains 22 pages.)

Purse seining for small pelagic fish around Sri Lanka

An attempt has been made to study skipjack (Katsuwonus pelamis) live bait availability and other small pelagic fish, their seasonal variations with respect to distribution, species and size composition. Exploratory surveys made use of echo sounding and lookout during the day, and light attraction at night. Percentage composition of spp caught at each station is tabulated. Seasonal variations are discussed and monthly variations in some important groups are plotted. Size composition, especially for Sardinella spp, is considered. The availability of 'red bait' would not be adequate to support an extended pole and line fishery for skipjack. The daytime fishing methods were not considered to have been especially successful, and the choice of gear and method of capture is discussed. It is suggested that the present fishery could be improved by the adoption of ring nets by local fishermen in place of the present purse seines when catching bait.

Draft environmental impact statement : proposed amendments to regulations governing the taking of marine mammals associated with tuna purse seining operations.

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1979 Ecological study of fishes and the water quality characteristics of Florida Bay, Everglades National Park, Florida

Fish collections under varying ecological conditions were made by trawling and seining, monthly and quarterly in depths of <1 m to depths of 3 m of the Florida Bay portion of Everglades National Park, Florida. From May 1973 through September 1976, a total of 182,530 fishes representing 128 species and 50 families were taken at 27 stations. An additional 21 species were identified from sportfish-creel surveys and supplemental observations. Most of the species collected were juveniles of species that occur as adults in the Florida Bay creel census survey, or were small species that were seasonal residents. Marked temporal and spatial abundance of the catches was observed. The greatest numbers and biomass of the fishes occurred in the wet season (summer/fall), whereas lowest numbers and biomass appeared during the dry season (winter/spring) The greatest abundance and diversity of fishes was found in western Florida Bay followed by eastern and central Bay regions respectively. Overall, five species comprised 75% of the numerical total while eleven species made up 75% of the total biomass. Collections were dominated numerically by anchovies (Engraulidae), especially Anchoa mitchilli, in western Florida Bay. Mojarras (Gerridae), mostly silver jenny Eucinostomus gula, and porgies (Sparidae), especially pinfish Lagodon rhomboides, dominated numerically in central and eastern portions of the Bay, respectively. Except for salinity, other measured physico-chemical parameters (water temperature, pH, dissolved oxygen, and turbidity) showed no variation beyond ranges considered normal for shallow, tropical marine environments. Salinity varied from 0 to 66 ppt near the mainland. Nearshore hypersaline conditions (>45 ppt) persisted for nearly 2 years during the 1974 - 1975 severe drought period. Significant reductions in fish abundance/diversity were observed in relation to hypersaline conditions. Bay-wide macrobenthic communities were mapped (presence/absence) and were primarily comprised of turtle grass (Thalassia), shoalgrass [(Diplanthera = (Halodule)], and/or green algae Penicillus. Seasonal dieoff of seagrasses was observed in north-central Florida Bay. (PDF contains 107 pages)

An examination of fluctuations in the “concentration index” of purse seiners and baitboats in the fishery for tropical tunas in the Eastern Pacific, 1951-1961

ENGLISH: In the eastern Pacific Ocean nearly all of the commercial catches of yellowfin tuna (Thunnus albacares) and skipjack (Katsuwonus pelamis) are taken by two types of vessels, baitboats, which use pole and line in conjunction with live-bait, and purse-seiners. From its inception until very recently (1959), this fishery was dominated by baitboats. This method of fishing has been described by Godsil (1938) and Shimada and Schaefer (1956). From 1951 through 1958 baitboats caught between 66.4 and 90.8 per cent of the yellowfin and between 87.2 and 95.3 per cent of the skipjack landed by the California-based fleet. These vessels fished for tuna throughout the year and covered virtually all of the area from southern California to northern Chile. The purse-seine fishery for tunas developed out of the round-haul net fisheries for California sardines and other species. Scofield (1951) gives a detailed description of the development of gear and fishing methods. Prior to 1959 many of the seiners engaged in other fisheries during the fall and early winter months and consequently most of the fishing effort for tuna occurred in the period February-August. The vessels were quite small, averaging approximately 120 tons carrying capacity (Broadhead and Marshall, 1960), in comparison to the baitboats, of which the most numerous size-class was 201-300 tons. The seiners were naturally more restricted in range than the baitboats and most of their effort was restricted to the northern grounds. During the period 1959-61 most of the large baitboats were converted for purse-seining and the existing seiner fleet was modernized. These developments increased the range of the seiner fleet and resulted in a wider and more nearly even spatial and temporal distribution of effort. By the early part of 1961, the purse-seine fleet approximated the level of the preconversion baitboat fleet in amount of effort applied and area covered. The changes in the purse-seine fishery and the fishing methods employed in the modernized fleet are described by Orange and Broadhead (1959), Broadhead and Marshall (1960), McNeely (1961) and Broadhead (1962). The change in the relative importance of the two gears is illustrated by the decline in the proportion of the total logged tonnage landed by California-based baitboats, in comparison to the proportion landed by seiners. In 1959 baitboats landed 49.5 per cent of the yellowfin and 87.8 per cent of the skipjack. In 1960 these percentages were 22.9 and 74.7 respectively and in 1961 the decline continued to 12.6 per cent of the yellowfin and 30.0 per cent of the skipjack (Schaefer, 1962). In previous Bulletins of this Commission (Griffiths, 1960; Calkins, 1961) the baitboat catch and effort statistics were used to compute two indices of population density and an index of concentration of fishing effort and the fluctuations of these indices were analyzed in some detail. Due to the change in the relative importance of the two gears it is appropriate to extend this investigation to include the purse-seine data. The objectives of this paper are to compute two indices of population density and an index of concentration of fishing effort and to examine the fluctuations in these indices before and after the changes in the fishery. A further objective is to compare the purse-seine indices with those of the baitboats for the same time periods. SPANISH: En el Océano Pacífico Oriental casi todas las capturas comerciales del atún aleta amarilla (Thunnus albacares) y del barrilete (Katsuwonus pelamis) son efectuadas por dos tipos de barcos, los barcos de carnada que emplean la caña y el anzuelo en conjunto con la carnada viva, y los barcos rederos. Desde su comienzo hasta hace poco tiempo (1959), esta pesquería estaba dominada por los barcos de carnada. El método de pesca usado por estos barcos ha sido descrito por Godsil (1938) y por Shimada y Schaefer (1956). De 1951 a 1958, los barcos de carnada pescaron entre el 66.4 y el 90.8 por ciento del atún aleta amarilla y entre el 87.2 y el 95.3 por ciento del barrilete descargados por la flota que tiene su base en California. Estos barcos pescaron atún durante todo el año y cubrieron virtualmente toda el área de California meridional hasta la parte norte de Chile. La pesquería del atún con redes de cerco se originó en las pesquerías de las sardinas de California y otras especies, con redes que se remolcaban circularmente. Scofield (1951) dá una descripción detallada del desarrollo de los métodos y del equipo de pesca. Antes de 1959 muchos de los rederos se dedicaban a otras pesquerías durante los meses del otoño y a principios del invierno y consecuentemente, la mayor parte del esfuerzo depesca para la producción del atún ocurría en el período febrero-agosto. Las embarcaciones eran bastante pequeñas, con un promedio de aproximadamente 120 toneladas de capacidad para el transporte (Broadhead y Marshall, 1960) en comparación con los barcos de carnada, de los cuales la clase de tamaño más numerosa era de 201 a 300 toneladas. Los rederos estaban naturalmente más restringidos en su radio de acción que los barcos de carnada y la mayor parte de su esfuerzo se limitaba a las localidades del norte. Durante el período 1959-61, la mayoría de los grandes barcos de carnada fueron convertidos al sistema de pesca con redes de cerco, y se modernizó la flota existente de los rederos. Estos cambios aumentaron el alcance de la flota de los barcos rederos dando como resultado una distribución más amplia y casi más uniforme del esfuerzo espaciado y temporal. En la primera parte del año 1961, la flota de rederos se aproximó al nivel de la preconversión de la flota de clipers, en la cantidad de esfuerzo aplicado y al área comprendida. Los cambios en la pesquería con red y los métodos de pesca empleados en la flota modernizada, han sido descritos por Orange y Broadhead (1959), Broadl1ead y Marshall (1960), McNeely (1961) y Broadhead (1962). El cambio en la importancia relativa de los dos sistemas de pesca está ilustrado por la declinación en la proporción del tonelaje total registrado, como descargado por los barcos de carnada que tienen su base en California, comparado con la proporción desembarcada por los barcos rederos. En 1959 los clipers descargaron el 49.5 por ciento del atún aleta amarilla y el 87.8 por ciento del barrilete. En 1960 estos porcentajes fueron del 22.9 y 74.7 respectivamente, y en 1961 continuó la reducción hasta el 12.6 por ciento del atún aleta amarilla y el 30.0 por ciento del barrilete (Schaefer, 1962). En Boletines anteriores de la Comisión (Griffiths, 1960; Calkins, 1961) las estadísticas de la pesca y el esfuerzo de los clipers se utilizaron para computar dos índices de la densidad de población y un índice de la concentración del esfuerzo de pesca, y se analizaron algo detalladamente las fluctuaciones de estos índices. Debido al cambio en la importancia relativa de los dos sistemas de pesca, es conveniente extender esta investigación para incluir los datos correspondientes a los barcos rederos. Los objetivos del presente estudio son de computar dos índices de la densidad de población y un índice de la concentración del esfuerzo de pesca, y examinar las fluctuaciones en estos índices, antes y después de los cambios en la pesquería. Otro objetivo es de comparar los índices de los barcos rederos, con aquellos de los clipers en los mismos períodos de tiempo.

Measures of tuna abundance from purse-seine operations in the Eastern Pacific Ocean, adjusted for fleet-wide evolution of increased fishing power, 1960-1971

ENGLISH: The fishing power of the tuna purse-seine fleet of the eastern Pacific Ocean has increased since the early 1960's. Because the entire fleet seems to have adopted equipment and techniques to increase its efficiency in capturing tunas, traditional methods of adjusting catch rates to a reference vessel type of fixed efficiency to index tuna abundance from fishing success are inapplicable. Instead, a methodology for such adjustment based on a mathematical representation of purse seining activities is developed. Observed changes in efficiency in subprocesses of purse seining are then used to adjust catch rates when computing abundance histories for yellowfin and skipjack in large regions of the eastern Pacific Ocean. SPANISH: La eficacia de pesca de la flota de cerco atunera en el Océano Pacífico oriental ha aumentado desde el comienzo del decenio de 1960. Como toda la flota parece haber adoptado equipo y métodos para incrementar su eficaciaen capturar atunes, no se pueden aplicar los métodos tradicionales de ajustar los índices de captura a un tipo normalizado de barco (es decir de eficacia fija) para indicar la abundancia del atún según los resultados de pesca. En su lugar se ha desarrollado un método para realizar tal ajuste basado en una representación matemática de las actividades de las embarcaciones de cerco. Cuando se calcula la abundancia histórica del atún aleta amarilla y barrilete en grandes regiones del Océano Pacífico oriental, se usan entonces los cambios observados en la eficacia de los subprocesos cerqueros para ajustar los índices de captura. (PDF contains 120 pages.)

Report on estimating the size of dolphin schools, based on data obtained during a charter cruise of the M/V Gina Anne, October 11 -November 25, 1979

Estimates of dolphin school sizes made by observers and crew members aboard tuna seiners or by observers on ship or aerial surveys are important components of population estimates of dolphins which are involved in the yellowfin tuna fishery in the eastern Pacific. Differences in past estimates made from tuna seiners and research ships and aircraft have been noted by Brazier (1978). To compare various methods of estimating dolphin school sizes a research cruise was undertaken with the following major objectives: 1) compare estimates made by observers aboard a tuna seiner and in the ship's helicopter, from aerial photographs, and from counts made at the backdown channel, 2) compare estimates of observers who are told the count of the school size after making their estimate to the observer who is not aware of the count to determine if observers can learn to estimate more accurately, and 3) obtain movie and still photographs of dolphin schools of known size at various stages of chase, capture and release to be used for observer training. The secondary objectives of the cruise were to: 1) obtain life history specimens and data from any dolphins that were killed incidental to purse seining. These specimens and data were to be analyzed by the U.S. National Marine Fisheries Service ( NMFS ) , 2) record evasion tactics of dolphin schools by observing them from the helicopter while the seiner approached the school, 3) examine alternative methods for estimating the distance and bearing of schools where they were first sighted, 4) collect the Commission's standard cetacean sighting, set log and daily activity data and expendable bathythermograph data. (PDF contains 31 pages.)

Feeding ecology and population characteristics of Oreochromis niloticus (L.) and trophic interactions in the fish community of Nyanza Gulf, Lake Victoria, Kenya

Oreochromis niloticus (L.) were caught by beach seining, hook and line and trawling from Nyanza Gulf, lake Victoria (Kenya) in order to study their feeding ecology and population characteristics. Collected fish were weighed and TL measured immediately after capture. Fish were dissected and sexed. Stomach contents were removed and preserved in 4% buffered formalin for laboratory analysis. In the laboratory items were sorted into categories such as three quarters, half and quarter and awarded 20, 15 and 5 points respectively. Main food items for O. niloticus from November 1998 to March 1999 were insects, algae, fish and plant material. Increase in insects in the diet of O. niloticus might be attributed to the lake infestation by water hyacinth which harbours different species of insects

Nearshore fish resources and fisheries around Kigoma, eastern coast of Lake Tanganyika

The fish habitats along an inshore water stretch along the eastern/central coast of Lake Tanganyika are discussed and a quantitative analysis of the species composition, distribution and abundance of the littoral fishes within the area of study is presented. Seventy-one species of fish belonging to 48 genera and to 15 fish families were collected and identified during the study. The majority of species belonged to the Cichlidae family. Intensive beach seining for clupeids is suggested as one of the causes of low fish biomass in the area surveyed. The areas south of Kigoma appeared to contain more fish, with average catch rates of 11.7 kg/haul than those north of Kigoma where average catch rates of 7.6 kg/haul were recorded. Some suggestions for improved management of these resources are given.

Growth, mortality and recruitment of Nile perch Lates niloticus (L. Centropomidae) in the Nyanza Gulf of Lake Victoria: an evaluation update

A reassessment of the estimates of growth, mortality and recruitment patterns of Nile Perch, Lates niloticus was made based on data from commercial landings collected during the Catch Assessment Survey Programme. Two sets of length frequency data, one each from beach seining and hook and line fisheries, were analyzed. Values of L8 = 169 and 230 (cm TL) and K= 0.18 yr-1 and 0.195 yr-1 were obtained. The total mortality estimates from the catch curve analysis were Z = 0.72 yr-1 and 0.94 yr-1, respectively, with a natural mortality M of about 0.35 for a mean environmental temperature of 27oC. The highest peak for recruitment was in November, December and January with a minor one in June, indicating recruitment of two cohorts per year. These results are discussed and compared to previously available information on L. niloticus in Lake Victoria.

Energy analysis of the ring seine operations, off Cochin, Kerala

Ring seines are lightly constructed purse seines adapted for operation in the traditional sector. Fish production and energy requirement in the ring seine operations, off Cochin, Kerala, India are discussed in this paper, based on data collected during 1997- 1998. The results reflect the Gross Energy Requirement (GER) situation that existed during 1997-1998. Mean catch per ring seiner per year worked out to be 211.9 t of which sardines (Sardinella spp.) constituted 44.3%, followed by Indian mackerel (Rastrelliger kanagurta) 29.7%, carangids 11.4%, penaeid prawns 2.2%, pomfrets 1.1% and miscellaneous fish 11.3%. Total energy inputs into the ring seine operations were estimated to be 1300.8 GJ. Output by way of fish production was determined to be 931.85 GJ. GER is the sum of all non-renewable energy resources consumed in making available a product or service and is a measure of intensity of non-renewable resource use. GER per tonne of fish landed by ring seiners was estimated to be 6.14. Among the operational inputs, kerosene constituted 73.4% of the GER, followed by petrol (12.7%), diesel (6.7%) and lubricating oil (2.4%). Fishing gear contributed 3.8%, engine 0.8% and fishing craft 0.3% of the GER. Energy ratio for ring seining was 0.72 and energy intensity 1.40.

Reproduction and recruitment of white mullet (Mugil curema) to a tropical lagoon (Margarita Island, Venezuela) as revealed by otolith microstructure

The reproductive activity and recruitment of white mullet (Mugil curema) was determined by observations of gonad development and coastal juvenile abundance from March 1992 to July 1993. Adults were collected from commercial catches at three sites in northeastern Venezuelan waters. Spawning time was determined from the observation of macroscopic gonadal stages. Coastal recruitment was determined from fish samples collected biweekly by seining in La Restinga Lagoon, Margarita Island, Venezuela. The examination of daily growth rings on the otoliths of coastal recruits was used to determine their birth date and estimate the period of successful spawning. Fish with mature gonads were present throughout the year but were less frequent between September and January when spawning individuals migrated offshore. In both years, juvenile recruitment to the lagoon was highest between March and June when high densities of 25–35 mm juveniles were observed. Back-calculated hatching-date frequency distributions revealed maximum levels of successful spawning in December–January that were significantly correlated with periods of enhanced upwelling. The relation between the timing of successful spawning and the intensity of coastal recruitment in white mullet was likely due to variations in food availability for first-feeding larvae as well as to variations in the duration of the transport of larvae shoreward as a result of varying current conditions associated with upwelling.

Gears and craft of Karwar: an overview

An account is given of the different types of gears and craft used to catch the pelagic and demersal fish in the inshore and estuary waters of Karwar, India. The main types of craft used during the fishing season September-May are: rampani boats, yendi boats, out-rigger boats, plank-built and dug-out canoes; important gears include: rampani, yendi, shore-seines, gill nets, boat seines, drift nets and hook and lines. Mechanized fishing, introduced during the sixties and seventies, included trawling and purse-seining. The types of gears used by the traditional fishermen depend on local conditions, seasons and distance covered from the shore. The major share to the total landings of fish in Karwar coast is brought mainly by the mechanized craft.