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John Hampton - One of the best experts on this subject based on the ideXlab platform.
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vertical movements behavior and habitat of Bigeye Tuna thunnus obesus in the equatorial central pacific ocean
Fisheries Research, 2015Co-Authors: Daniel W Fuller, John Hampton, Kurt M Schaefer, Sylvain Caillot, Bruno Leroy, David ItanoAbstract:Abstract 8217 days of data downloaded from 47 archival tags, recovered from Bigeye Tuna ( Thunnus obesus ) 51–134 cm in length ( x ¯ = 86.9 c m ) , 0.87–3.44 years of age ( x ¯ = 1.89 years ) at liberty from 36 to 851 days ( x ¯ = 183 days ) in the equatorial central Pacific Ocean, are evaluated herein. Analyses of depth and temperature records resulted in the classification of three daily behavior types: characteristic, associative (associated with floating objects), and other. For three defined length classes, 54–79.9 cm, 80–99.9 cm, and 100–134 cm, when exhibiting characteristic behavior, the proportions of time and average durations of events were 45.3% ( x ¯ = 5.1 days ) , 62.6% ( x ¯ = 8.5 days ) , 79.2% ( x ¯ = 17.5 days ) , and the average daytime depths and temperatures were 284 m and 12.6 °C, 305 m and 12.7 °C, and 312 m and 12.1 °C, respectively. For the same three length classes, when exhibiting associative behavior, the proportions of time and average durations of events were 9.5% ( x ¯ = 1.9 days ) , 4.8% ( x ¯ = 1.9 days ) , and 6.0% ( x ¯ = 1.8 days ) , and the average daytime depths and temperatures were 101 m and 23.2 °C, 105 m and 23.1 °C, and 74 m and 22.3 °C, respectively. There is a significant positive correlation between the proportion of time fish exhibits characteristic behavior and fish length, and significant negative correlations between the proportion of time Bigeye Tuna exhibit associative and other behavior with fish length. Behavior and habitat preferences of Bigeye Tuna should be considered for standardizing catch-per-unit of effort (CPUE) data from both longline and purse-seine fisheries targeting tropical Tunas in the Pacific, in an effort to provide more reliable estimates of relative abundance.
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movements dispersion and mixing of Bigeye Tuna thunnus obesus tagged and released in the equatorial central pacific ocean with conventional and archival tags
Fisheries Research, 2015Co-Authors: Kurt M Schaefer, John Hampton, Daniel W Fuller, Sylvain Caillot, Bruno Leroy, David ItanoAbstract:Abstract A total of 31,242 Bigeye Tuna was captured, tagged, and released, 30,793 with dart tags (DTs) and 449 with geolocating archival tags (ATs), in the equatorial central Pacific Ocean along the 140° W, 155° W, 170° W, and 180° meridians, during 2008 through 2012, of which 10,029 (32.1%) of the DTs and 74 (16.5%) of the ATs were returned. A subset of high-confidence filtered DT data was retained for 5807 fish at liberty for 30 d or more, for evaluating linear displacements from release to recapture positions. For the filtered DT data, days at liberty ranged from 30 to 1701 d (median = 187 d). Linear displacements ranged from 1 to 5372 nautical miles (M) (median = 936 M), with 71% eastward and 29% westward, and 95% within 3614 M of their release positions. The data indicate significant differences in the linear displacements by release locations, days at liberty, and fish length at release. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process 48 AT data sets from Bigeye Tuna at liberty for 30 d or longer, to obtain most probable tracks, improved estimates of geographic positions, and movement parameters. The 95% volume contours surrounding the position estimates, along the most probable tracks from Bigeye Tuna releases along the 140° W, 155° W, 170° W, and 180° meridians show substantial overlap. For the pooled AT data sets, the median parameter estimates from the UKFsst model for errors in longitude ( σ x ) and latitude ( σ y ) were 0.52° and 1.75°, for directed eastward and northward movements ( u and v ) were −2.01 M/d and −1.41 M/d, and for dispersive movement ( D ) was 496.7 M 2 /d. The linear displacements and most probable tracks obtained from these tagging data demonstrate constrained latitudinal dispersion, some regional fidelity, some extensive eastward longitudinal dispersion, and substantial mixing of Bigeye Tuna between release longitudes. The amount of mixing of Bigeye Tuna among these release areas in the equatorial central Pacific Ocean, with those in adjacent areas of the equatorial eastern and western Pacific Ocean, is dependent on distances between areas, with, in general, the greatest mixing occurring between the areas that are closest to one another.
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shifting from marine reserves to maritime zoning for conservation of pacific Bigeye Tuna thunnus obesus
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: John R Sibert, Patrick Lehodey, Inna Senina, John HamptonAbstract:Over 50% of the total Bigeye Tuna (BET) landed in the Western Central Pacific Ocean is caught incidentally in the purse seine fishery and sold for canning at prices less than US$2/kg. The remainder is landed in longline fisheries directed at BET and sold as fresh or frozen Tuna at prices greater than US$10/kg. The combined fishing mortality by all gears will soon reduce the BET biomass in the Pacific Ocean to less than that capable of producing maximum sustainable yield. Closure of the high-seas enclaves in 2009 was hailed as a conservation measure, but was not scientifically evaluated before implementation and appears to have had no beneficial effect on the BET stock. A spatially explicit age-structured ecosystem model, SEAPODYM, is used to simulate alternative area-based fishery management policies to conserve Bigeye Tuna in the Western Central Pacific Ocean. Closing the high-seas enclaves to purse seine fishing has negligible effect on the BET biomass. Fishery management policies that control mortality on both juveniles and adults, through prohibition of fish aggregation devices in the purse seine fishery and restrictions on longline fishing in spawning areas, are the most efficient conservation policies. Large-scale benefits from Bigeye conservation measures will become apparent only in the 2030s, assuming timely implementation and minimal effects of climate change.
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preliminary forecasts of pacific Bigeye Tuna population trends under the a2 ipcc scenario
Progress in Oceanography, 2010Co-Authors: Patrick Lehodey, John R Sibert, Inna Senina, Laurent Bopp, Beatriz Calmettes, John Hampton, Raghu MurtuguddeAbstract:An improved version of the spatial ecosystem and population dynamics model SEAPODYM was used to investigate the potential impacts of global warming on Tuna populations. The model included an enhanced definition of habitat indices, movements, and accessibility of Tuna predators to different vertically migrant and non-migrant micronekton functional groups. The simulations covered the Pacific basin (model domain) at a 2 � 2 geographic resolution. The structure of the model allows an evaluation from multiple data sources, and parameterization can be optimized by adjoint techniques and maximum likelihood using fishing data. A first such optimized parameterization was obtained for Bigeye Tuna (Thunnus obesus) in the Pacific Ocean using historical catch data for the last 50 years and a hindcast from a coupled physical– biogeochemical model driven by the NCEP atmospheric reanalysis. The parameterization provided very plausible biological parameter values and a good fit to fishing data from the different fisheries, both within and outside the time period used for optimization. We then employed this model to forecast the future of Bigeye Tuna populations in the Pacific Ocean. The simulation was driven by the physical–biogeochemical fields predicted from a global marine biogeochemistry – climate simulation. This global simulation was performed with the IPSL climate model version 4 (IPSL–CM4) coupled to the oceanic biogeochemical model PISCES and forced by atmospheric CO2, from historical records over 1860–2000, and under the SRES A2 IPCC scenario for the 21st century (i.e. atmospheric CO2 concentration reaching 850 ppm in the year 2100). Potential future changes in distribution and abundance under the IPCC scenario are presented but without taking into account any fishing effort. The simulation showed an improvement in Bigeye Tuna spawning habitat both in subtropical latitudes and in the eastern tropical Pacific (ETP) where the surface temperature becomes optimal for Bigeye Tuna spawning. The adult feeding habitat also improved in the ETP due to the increase of dissolved oxygen concentration in the sub-surface allowing adults to access deeper forage. Conversely, in the Western Central Pacific the temperature becomes too warm for Bigeye Tuna spawning. The decrease in spawning is compensated by an increase of larvae biomass in subtropical regions. However, natural mortality of older stages increased due to lower habitat values (too warm surface temperatures, decreasing oxygen concentration in the sub-surface and less food). This increased mortality and the displacement of surviving fish to the eastern region led to stable then declining adult biomass at the end of the century.
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application of a habitat based model to estimate effective longline fishing effort and relative abundance of pacific Bigeye Tuna thunnus obesus
Fisheries Oceanography, 2002Co-Authors: Keith A Bigelow, John Hampton, Naozumi MiyabeAbstract:A new habitat-based model is developed to improve estimates of relative abundance of Pacific Bigeye Tuna (Thunnus obesus). The model provides estimates of ‘effective’ longline effort and therefore better estimates of catch-per-unit-of-effort (CPUE) by incorporating information on the variation in longline fishing depth and depth of Bigeye Tuna preferred habitat. The essential elements in the model are: (1) estimation of the depth distribution of the longline gear, using information on gear configuration and ocean currents; (2) estimation of the depth distribution of Bigeye Tuna, based on habitat preference and oceanographic data; (3) estimation of effective longline effort, using finescale Japanese longline fishery data; and (4) aggregation of catch and effective effort over appropriate spatial zones to produce revised time series of CPUE. Model results indicate that effective effort has increased in both the western and central Pacific Ocean (WCPO) and eastern Pacific Ocean (EPO). In the WCPO, effective effort increased by 43% from the late 1960s to the late 1980s due primarily to the increased effectiveness of effort (deeper longline sets) rather than to increased nominal effort. Over the same period, effective effort increased 250% in the EPO due primarily to increased nominal effort. Nominal and standardized CPUE indices in the EPO show similar trends ‐ a decline during the 1960s, a period of stability in the 1970s, high values during 1985‐1986 and a decline thereafter. In the WCPO, nominal CPUE is stable over the time-series; however, standardized CPUE has declined by � 50%. If estimates of standardized CPUE accurately reflect relative abundance, then we have documented substantial reductions of Bigeye Tuna abundance for some regions in the Pacific Ocean. A decline in standardized CPUE in the subtropical gyres concurrent with stability in equatorial areas may represent a contraction in the range of the population resulting from a decline in population abundance. The sensitivity of the results to the habitat (temperature and oxygen) assumptions was tested using Monte Carlo simulations.
Richard W Brill - One of the best experts on this subject based on the ideXlab platform.
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transectional heat transfer in thermoregulating Bigeye Tuna thunnus obesus a 2d heat flux model
The Journal of Experimental Biology, 2009Co-Authors: Jess Boye, Richard W Brill, Michael K Musyl, Hans MalteAbstract:SUMMARY We developed a 2D heat flux model to elucidate routes and rates of heat transfer within Bigeye Tuna Thunnus obesus Lowe 1839 in both steady-state and time-dependent settings. In modeling the former situation, we adjusted the efficiencies of heat conservation in the red and the white muscle so as to make the output of the model agree as closely as possible with observed cross-sectional isotherms. In modeling the latter situation, we applied the heat exchanger efficiencies from the steady-state model to predict the distribution of temperature and heat fluxes in Bigeye Tuna during their extensive daily vertical excursions. The simulations yielded a close match to the data recorded in free-swimming fish and strongly point to the importance of the heat-producing and heat-conserving properties of the white muscle. The best correspondence between model output and observed data was obtained when the countercurrent heat exchangers in the blood flow pathways to the red and white muscle retained 99% and 96% (respectively) of the heat produced in these tissues. Our model confirms that the ability of Bigeye Tuna to maintain elevated muscle temperatures during their extensive daily vertical movements depends on their ability to rapidly modulate heating and cooling rates. This study shows that the differential cooling and heating rates could be fully accounted for by a mechanism where blood flow to the swimming muscles is either exclusively through the heat exchangers or completely shunted around them, depending on the ambient temperature relative to the body temperature. Our results therefore strongly suggest that such a mechanism is involved in the extensive physiological thermoregulatory abilities of endothermic Bigeye Tuna.
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temperature sensitivity of cardiac function in pelagic fishes with different vertical mobilities yellowfin Tuna thunnus albacares Bigeye Tuna thunnus obesus mahimahi coryphaena hippurus and swordfish xiphias gladius
Physiological and Biochemical Zoology, 2009Co-Authors: Gina L J Galli, Holly A Shiels, Richard W BrillAbstract:Abstract We measured the temperature sensitivity, adrenergic sensitivity, and dependence on sarcoplasmic reticulum (SR) Ca2+ of ventricular muscle from pelagic fishes with different vertical mobility patterns: Bigeye Tuna (Thunnus obesus), yellowfin Tuna (Thunnus albacares), and mahimahi (Coryphaena hippurus) and a single specimen from swordfish (Xiphias gladius). Ventricular muscle from the Bigeye Tuna and mahimahi exhibited a biphasic response to an acute decrease in temperature (from 26° to 7°C); twitch force and kinetic parameters initially increased and then declined. The magnitude of this response was larger in the Bigeye Tuna than in the mahimahi. Under steady state conditions at 26°C, inhibition of SR Ca2+ release and reuptake with ryanodine and thapsigargin decreased twitch force and kinetic parameters, respectively, in the Bigeye Tuna only. However, the initial inotropy associated with decreasing temperature was abolished by SR inhibition in both the Bigeye Tuna and the mahimahi. Application of ...
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Bigeye Tuna behavior and physiology their relevance to stock assessments and fishery biology
Collective Volume of Scientific Papers; 57(2) pp 142-161 (2005), 2005Co-Authors: Richard W Brill, K A Bigelow, Michael K Musyl, Kerstin A Fritsches, Eric J WarrantAbstract:Bigeye Tuna (Thunnus obesus) have distinctive depth distributions and vertical movement patterns. They remain in the uniformed temperature surface layer at night and can descend to greater than 500 m depth at dawn. They thus mirror the vertical migrations of the small nektonic organisms of the deep sound scattering layer and extensively exploit these as a food resource. At their maximum depths, Bigeye Tuna frequently experience prolonged exposure to ambient temperatures (.5 EC) that are up to 20EC colder than surface layer temperature, and oxygen concentrations less than 1.5 ml O2 l-1. In contrast, skipjack Tuna (Katsuwonus pelamis) and yellowfin Tuna (T. albacares) generally limit their forays to depths where water temperatures are no more than 8EC below surface layer temperatures, and ambient oxygen levels are above 3.5 ml O2 l-1. Understanding the vertical movements and depth distribution of Bigeye Tuna, as well as the physiological abilities/tolerances and oceanographic conditions controlling them, has been shown key for improving longline catch-per-unit effort analysis and long-term populations assessments in the Pacific. Similar work is needed in the Atlantic. (Less)
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Bigeye Tuna thunnus obesus behaviour and phisiology and their relevance to stock assessments and fishery biology
Second World Meeting on Bigeye Tuna, 2005Co-Authors: Richard W Brill, Michael K Musyl, Kerstin A Fritsches, K A Bigalow, Eric J WarrantAbstract:SUMMARY Bigeye Tuna (Thunnus obesus) have distinctive depth distributions and vertical movement patterns. They remain in the uniformed temperature surface layer at night and can descend to greater than 500 m depth at dawn. They thus mirror the vertical migrations of the small nektonic organisms of the deep sound scattering layer and extensively exploit these as a food resource. At their maximum depths, Bigeye Tuna frequently experience prolonged exposure to ambient temperatures (.5 EC) that are up to 20EC colder than surface layer temperature, and oxygen concentrations less than 1.5 ml O2 l -1 . In contrast, skipjack Tuna (Katsuwonus pelamis) and yellowfin Tuna (T. albacares) generally limit their forays to depths where water temperatures are no more than 8EC below surface layer temperatures, and ambient oxygen levels are above 3.5 ml O2 l -1 . Understanding the vertical movements and depth distribution of Bigeye Tuna, as well as the physiological abilities/tolerances and oceanographic conditions controlling them, has been shown key for improving longline catch-per-unit effort analysis and long-term populations assessments in the Pacific. Similar work is needed in the Atlantic. RESUME
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blood oxygen binding characteristics of Bigeye Tuna thunnus obesus a high energy demand teleost that is tolerant of low ambient oxygen
Marine Biology, 2000Co-Authors: T E Lowe, Richard W Brill, K L CousinsAbstract:We found blood from Bigeye Tuna (Thunnus obesus) to have a significantly higher O2 affinity than blood from other Tunas. Its P50 (partial pressure of oxygen, PO2 required to reach 50% saturation) was 1.6 to 2.0 kPa (12 to 15 mmHg) when equilibrated with 0.5% CO2. Previous studies employing similar methodologies found blood from yellowfin Tuna (T. albacares), skipjack Tuna (Katsuwonus pelamis), and kawakawa (Euthynnus affinis) to have a P50 of 2.8 to 3.1 kPa (21 to 23 mmHg). These observations suggest that Bigeye Tuna are more tolerant of low ambient oxygen than other Tuna species, and support similar conclusions derived from laboratory whole-animal studies, depth-of-capture data, and directly-recorded vertical movements of fish in the open ocean. We also found the O2 affinity of Bigeye Tuna blood to be essentially unaffected by a 10 C° open-system temperature change (as is the blood of all Tuna species studied to date). The O2 affinity of Bigeye Tuna blood was, however, more affected by a 10 C° closed-system temperature change than the blood of any Tuna species yet examined. In other words, Bigeye Tuna blood displayed a significantly enhanced Bohr effect (change in log P50 per unit change in plasma pH at P50) when subjected to the inevitable changes in partial pressure of carbon dioxide (PCO2) and plasma pH that accompany closed-system temperature shifts, than when subjected to changes in plasma pH accomplished by changing PCO2 alone. In vivo, the resultant large decrease in O2 affinity (i.e. the increase in P50) that occurs as the blood of Bigeye Tuna is warmed during its passage through the vascular counter-current heat exchangers ensures adequate rates of O2 off-loading in the swimming muscles of this high-energy-demand teleost.
Yingqi Zhou - One of the best experts on this subject based on the ideXlab platform.
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Growth and mortality rates of Bigeye Tuna Thunnus obesus (Perciformes: Scombridae) in the central Atlantic Ocean.
Revista De Biologia Tropical, 2013Co-Authors: Liuxiong Xu, Yingqi Zhou, Xinjun ChenAbstract:Age and growth parameters were estimated for Bigeye Tuna Thunnus obesus Lowe, 1839 sampled from China longline fisheries in the central Atlantic Ocean from October 2002 to July 2003 and from August 2004 to March 2005. The von Bertalanffy growth parameters were estimated at L ∞ =217.9 cm fork length, k=0.23 year-1, and t 0 =-0.44 year. The total mortality rate (Z) was estimated to be from 0.82 to 1.02, the fishing mortality (F) and the natural mortality were 0.54 year-1 and 0.39 year-1, respectively. The exploitation ratio (E) was 0.35. This study provides the detailed estimates of growth and mortality rate for Bigeye Tuna in the central Atlantic Ocean, which can be used as biological input parameters in further stock evaluations in this region. However, age analysis, additional validation of the size composition and stock structure are needed for future studies. Rev. Biol. Trop. 57 (1-2): 79-88. Epub 2009 June 30.
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developing an integrated habitat index for Bigeye Tuna thunnus obesus in the indian ocean based on longline fisheries data
Fisheries Research, 2010Co-Authors: Liming Song, Yingqi ZhouAbstract:Abstract Two surveys were conducted in 2005 and 2006 aboard Chinese longliners in the Indian Ocean to evaluate how environmental variables might influence the spatial distributions of Bigeye Tuna, Thunnus obesus. Models were developed to estimate integrated habitat indices (IHI) for Bigeye Tuna at eight depth strata between 80 m and 400 m and to predict the spatial distributions of Bigeye Tuna in these depths. Catch rates and environmental variables (water temperature, salinity, chlorophyll-a, and dissolved oxygen) at these depth strata were obtained at 30 sampling stations in the survey, and the quantile regression method was used to develop the IHI models. This study suggests that the weighted average temperature, chlorophyll-a, and dissolved oxygen (when the dissolved oxygen was less than 0.85 mg L−1) had significant impacts on the spatial distribution of Bigeye Tuna. The IHI models developed in this study performed well in predicting catch rates with selected environmental variables. The key environmental parameters in the IHI models differed among the depth strata, suggesting impacts of the environmental variables on the Tuna distribution differed among different depth strata. This study provides an effective approach to identify optimal habitats for the Bigeye Tuna.
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reproductive biology of Bigeye Tuna thunnus obesus scombridae in the eastern and central tropical pacific ocean
Environmental Biology of Fishes, 2010Co-Authors: Liuxiong Xu, Yingqi ZhouAbstract:Understanding the reproductive potential of any species is of great importance for resource assessment and management. We studied the reproductive biology of Bigeye Tuna, Thunnus obesus, based on 1283 samples taken from the Chinese longline vessels in the eastern and central Tropical Pacific Ocean during February through November 2006. The female-male ratio was 1.0 : 1.5 and males were predominant in all length classes except for the length class of 166–170 cm (fork length). Males dominated in sizes larger than 171 cm, all specimens of 192 cm or larger were males. The main spawning period of Bigeye Tuna was between March and November. Gonadosomatic rates of males were larger than those of females. Statistically, female and male Bigeye Tuna had no significant reproductive seasonality. The observed minimum length at sexual maturity for female Bigeye Tuna was 94 cm. Length at 50% sexual maturity of female Bigeye Tuna was estimated at 107.8 cm, and maturation rate was 0.106 cm−1. The results derived in this study provide the information critical to our understanding of key life history parameters of Bigeye Tuna in tropic Pacific Ocean.
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environmental preferences of Bigeye Tuna thunnus obesus in the indian ocean an application to a longline fishery
Environmental Biology of Fishes, 2009Co-Authors: Liming Song, Ji Zhou, Yingqi Zhou, Tom Nishida, Wenxin Jiang, Jiaqiao WangAbstract:A survey of the fishing grounds for Bigeye Tuna, Thunnus obesus, in the Indian Ocean was carried out for a better understanding of the environmental preferences of Bigeye Tuna in a longline fishery. Catch rates of Bigeye Tuna were analyzed with respect to the ranges of depth, temperature, salinity, chlorophyll-a, and dissolved oxygen. The optimum capture depth, water temperature, and dissolved oxygen range of Bigeye Tuna were identified as 240.0 m to 279.9 m, 12.0°C to 13.9°C, and 2.00 mg·L−1 to 2.99 mg·L−1, respectively, in the study area of Indian Ocean. Neither salinity nor chlorophyll-a had a detectable effect on the vertical distribution of the adult Bigeye Tuna. The dissolved oxygen is the principal factor limiting the vertical distribution of Bigeye Tuna.
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growth and mortality of Bigeye Tuna thunnus obesus scombridae in the eastern and central tropical pacific ocean
Environmental Biology of Fishes, 2009Co-Authors: Yingqi Zhou, Liuxiong XuAbstract:Biological parameters such as age, growth and age (or size) at maturity are vital for stock assessment and management. Aging is essential in yielding such information. However, limited aging studies have been conducted for large tropical pelagic species in the eastern and central tropical Pacific Ocean. The objective of this study is to conduct a length frequency analysis for estimating growth and mortality of Bigeye Tuna in the eastern and central tropical Pacific Ocean using samples from the Chinese longline fishery during February to November 2006. The von Bertalanffy growth parameters of asymptotic fork length L ∞ and growth coefficient k were estimated at L ∞ = 207.4 cm fork length, k = 0.23 year-1, and theoretical age at zero length t 0 = −0.40 year. The total mortality rate (Z) was estimated to be 0.60; the fishing mortality rate (F) and the natural mortality rate (M) were 0.25 year-1 and 0.35 year-1, respectively. The exploitation rate (E) was 0.16. This study provides the estimates of growth and mortality rate for Bigeye Tuna in the eastern and central tropical Pacific Ocean, which can be used as biological input parameters in further stock evaluations in this region. However, age analysis, further validation of the age composition and stock structure are needed for future studies.
Philippe Borsa - One of the best experts on this subject based on the ideXlab platform.
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nuclear and mitochondrial dna markers indicate unidirectional gene flow of indo pacific to atlantic Bigeye Tuna thunnus obesus populations and their admixture off southern africa
Marine Biology, 2005Co-Authors: Jeandominique Durand, Adeline Collet, Seinen Chow, Bruno Guinand, Philippe BorsaAbstract:A sharp genetic break separates Atlantic from Indo-Pacific Bigeye Tuna (Thunnus obesus) populations, as the frequencies of two major mitochondrial (mt) DNA types (α and β) found in this species are different across the tip of southern Africa. The level of nucleotide divergence between mtDNA types α and β is of the same order as that between reproductively isolated taxa. To further investigate the genetic structure of Bigeye Tuna over its distribution range and in the contact zone off southern Africa, Bigeye Tuna samples collected between 1992 and 2001 (including samples from a previous mtDNA survey) were characterized for four nuclear DNA loci and for mtDNA. Nuclear markers did not support the hypothesis that α and β mitochondria characterize sibling species. Significant allele-frequency differences at one intronic locus (GH2) and one microsatellite locus (µ208) were found between Atlantic and Indo-Pacific samples, although the level of nuclear genetic differentiation (Weir and Cockerham’s % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! Bigeye Tuna samples represent a simple mixture of individuals from Atlantic and Indian stocks that do not interbreed, with a higher contribution from Indian Ocean individuals (about 2/3 vs. 1/3).
David Itano - One of the best experts on this subject based on the ideXlab platform.
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vertical movements behavior and habitat of Bigeye Tuna thunnus obesus in the equatorial central pacific ocean
Fisheries Research, 2015Co-Authors: Daniel W Fuller, John Hampton, Kurt M Schaefer, Sylvain Caillot, Bruno Leroy, David ItanoAbstract:Abstract 8217 days of data downloaded from 47 archival tags, recovered from Bigeye Tuna ( Thunnus obesus ) 51–134 cm in length ( x ¯ = 86.9 c m ) , 0.87–3.44 years of age ( x ¯ = 1.89 years ) at liberty from 36 to 851 days ( x ¯ = 183 days ) in the equatorial central Pacific Ocean, are evaluated herein. Analyses of depth and temperature records resulted in the classification of three daily behavior types: characteristic, associative (associated with floating objects), and other. For three defined length classes, 54–79.9 cm, 80–99.9 cm, and 100–134 cm, when exhibiting characteristic behavior, the proportions of time and average durations of events were 45.3% ( x ¯ = 5.1 days ) , 62.6% ( x ¯ = 8.5 days ) , 79.2% ( x ¯ = 17.5 days ) , and the average daytime depths and temperatures were 284 m and 12.6 °C, 305 m and 12.7 °C, and 312 m and 12.1 °C, respectively. For the same three length classes, when exhibiting associative behavior, the proportions of time and average durations of events were 9.5% ( x ¯ = 1.9 days ) , 4.8% ( x ¯ = 1.9 days ) , and 6.0% ( x ¯ = 1.8 days ) , and the average daytime depths and temperatures were 101 m and 23.2 °C, 105 m and 23.1 °C, and 74 m and 22.3 °C, respectively. There is a significant positive correlation between the proportion of time fish exhibits characteristic behavior and fish length, and significant negative correlations between the proportion of time Bigeye Tuna exhibit associative and other behavior with fish length. Behavior and habitat preferences of Bigeye Tuna should be considered for standardizing catch-per-unit of effort (CPUE) data from both longline and purse-seine fisheries targeting tropical Tunas in the Pacific, in an effort to provide more reliable estimates of relative abundance.
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movements dispersion and mixing of Bigeye Tuna thunnus obesus tagged and released in the equatorial central pacific ocean with conventional and archival tags
Fisheries Research, 2015Co-Authors: Kurt M Schaefer, John Hampton, Daniel W Fuller, Sylvain Caillot, Bruno Leroy, David ItanoAbstract:Abstract A total of 31,242 Bigeye Tuna was captured, tagged, and released, 30,793 with dart tags (DTs) and 449 with geolocating archival tags (ATs), in the equatorial central Pacific Ocean along the 140° W, 155° W, 170° W, and 180° meridians, during 2008 through 2012, of which 10,029 (32.1%) of the DTs and 74 (16.5%) of the ATs were returned. A subset of high-confidence filtered DT data was retained for 5807 fish at liberty for 30 d or more, for evaluating linear displacements from release to recapture positions. For the filtered DT data, days at liberty ranged from 30 to 1701 d (median = 187 d). Linear displacements ranged from 1 to 5372 nautical miles (M) (median = 936 M), with 71% eastward and 29% westward, and 95% within 3614 M of their release positions. The data indicate significant differences in the linear displacements by release locations, days at liberty, and fish length at release. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process 48 AT data sets from Bigeye Tuna at liberty for 30 d or longer, to obtain most probable tracks, improved estimates of geographic positions, and movement parameters. The 95% volume contours surrounding the position estimates, along the most probable tracks from Bigeye Tuna releases along the 140° W, 155° W, 170° W, and 180° meridians show substantial overlap. For the pooled AT data sets, the median parameter estimates from the UKFsst model for errors in longitude ( σ x ) and latitude ( σ y ) were 0.52° and 1.75°, for directed eastward and northward movements ( u and v ) were −2.01 M/d and −1.41 M/d, and for dispersive movement ( D ) was 496.7 M 2 /d. The linear displacements and most probable tracks obtained from these tagging data demonstrate constrained latitudinal dispersion, some regional fidelity, some extensive eastward longitudinal dispersion, and substantial mixing of Bigeye Tuna between release longitudes. The amount of mixing of Bigeye Tuna among these release areas in the equatorial central Pacific Ocean, with those in adjacent areas of the equatorial eastern and western Pacific Ocean, is dependent on distances between areas, with, in general, the greatest mixing occurring between the areas that are closest to one another.
