In vivo total nitrogen and total phosphorous digestibility in Atlantic Bluefin Tuna (Thunnus thynnus thynnus Linnaeus, 1758) under industrially intensive fattening conditions in Southeast Spain Mediterranean coastal waters

Atlantic Bluefin Tuna (hereafter referred to as tuna) fattening has been developed quite a lot in south‐eastern Spanish Mediterranean coastal waters, but previous information about nutrition and environmental impact is scarce. Total nitrogen and total phosphorous digestibility was investigated in tuna under routine operation fattening conditions as a first step to know nutrient utilization and to provide tools for estimation of waste output. Tunas were fed ad libitum once a day with a mixture of mackerel, herring, pilchard and gilt‐sardine. Body weight of sampled tuna ranged between 150 and 350 kg. Faeces were collected by dissection of the distal intestine after slaughtering and directly with a manual sieve by scuba divers into the sea cages. Endogenous inert marker was acid insoluble ash. Apparent digestibility coefficient (ADC) for total‐N was lower when faeces were collected by dissection of the intestine (DI: 658.2 g kg^?1) than when by direct collection (DC: 937.4 g kg^?1). Total‐P ADC was lower when faeces were directly collected (DC: 481.4 g kg^?1) than when collected by intestine dissection (DI: 661.9 g kg^?1). The nitrogen digestibility in tuna was as high as in other carnivorous fish, while low phosphorous digestibility, as in many fishes, could be related with phosphorous excess in diet. DC results seem to be more consistent and appropriate for waste output estimation. Results demonstrate the need for a more accurate nutritional evaluation and development of formulated artificial diets.     

Bluefin tuna (Thunnus thynnus) distribution in relation to sea surface temperature fronts in the Gulf of Maine (1994–96)

Fishery‐linked aerial surveys for bluefin tuna (Thunnus thynnus) were conducted in the Gulf of Maine (GOM) from July through October, 1994–96. Each year, from 507 to 890 surface schools were detected and their locations examined in relation to oceanographic conditions. Correlations between bluefin tuna presence and environmental variables were explored for sea surface temperature (SST), distance to a SST front, frontal density (relative density of all SST fronts seen in a given 1 km area for 2 weeks prior to each tuna sighting), and bottom depth and slope. Mean SST associated with bluefin schools was 18.1°C (±2.8). Schools were located at a mean distance of 19.7 km (±19.6) from SST fronts, and in water masses with an average frontal density of 28.2 m km^?2 (±35.7). Mean bottom depth of detected schools was 139.0 m (±70.3), and mean bottom slope was 0.7% rise (±0.7). A binomial generalized linear model fit to these variables indicated that bluefin are seen closer to fronts than locations in which no tuna were seen. Using simple and partial Mantel tests, we investigated the spatial correlation between bluefin tuna presence and the environmental variables, controlling for spatial autocorrelation. For each day that schools were sighted, we performed 24 Mantel tests, on a combination of response and predictor variables. The spatial relationship between bluefin tuna and SST fronts was inconsistent. Our analysis identified significant spatial structure in the bluefin school locations that had no significant correlation with any of the measured environmental features, suggesting that other untested features, such as prey density, may be important predictors of bluefin distribution in the GOM.     

Inclusion of prey data improves prediction of bluefin tuna (Thunnus thynnus) distribution

We examined the distribution of Atlantic bluefin tuna ( Thunnus thynnus ) in the Gulf of Maine, Northwest Atlantic Ocean, from 17 to 23 August 1995, in relation to physical and biological parameters. Specifically, we fit a binomial GLM to the bluefin tuna presence–absence data and predictor variables that include: sea surface temperature (SST), ocean depth, distance to an SST front, time-lagged density of SST fronts, and an interpolated surface of Atlantic herring ( Clupea harengus ) density. In addition, we use simple and partial Mantel tests to examine whether bluefin tuna presence–absence data are significantly associated with these predictors, once spatial autocorrelation is accounted for. Results suggest that the distribution of bluefin tuna significantly correlated with herring density ( z  =   3.525, P  =   0.000424), and that inclusion of biological variables results in a more parsimonious model. Mantel tests results indicate that bluefin tuna abundance is significantly correlated with herring density after the effect of spatial structure is removed (Mantel r  =   0.043, P  <   0.019).     

Serum biochemical profiles of captive and wild northern bluefin tuna (Thunnus thynnus L. 1758) in the Eastern Mediterranean

Northern bluefin tuna (NBT) are a prominent marine pelagic fish species. There are few reference values for their blood chemistry and this is the first report to demonstrate blood biochemical values in the Eastern Mediterranean. The study was carried out with 60 captive (penned) and 60 wild NBTs from Ildir Bay (Izmir) and Antalya Bay in the Eastern Mediterranean, from winter to early summer 2003. The aim of this research was to determine the biochemical parameters of wild male/female and captive male/female NBTs. According to the present results, the blood biochemical values of the captive NBTs were significantly higher than those of wild NBTs ( P <0.05) except albumin, globulin, total protein and very low-density lipoprotein levels. Moreover, many of the biochemical parameters were detected at high levels in captive and wild male NBTs than those of the females. Especially, the values of glucose, lactate dehydrogenase, creatine phosphokinase, γ-glutamyl transferase, cholesterol, triglyceride, low-density lipoprotein, ferritin, transferrin and iron levels were significantly higher, although high-density lipoprotein values were significantly lower in wild and captive male samples than those of both groups of females ( P <0.05).     

Spatio‐temporal distribution of albacore (Thunnus alalunga) catches in the northeastern Atlantic: relationship with the thermal environment

When the spring seasonal warming starts, North Atlantic albacore (Thunnus alalunga) juveniles and pre‐adults perform a trophic migration to the northeastern Atlantic, to the Bay of Biscay and to the southeast of Ireland. During this migration, they are exploited by Spanish trolling and baitboat fleets. The present study analyzes the relationship between the albacore spatio‐temporal distribution and the thermal environment. For this approach, several analyses have been performed on a database including fishing logbooks and sea surface temperature (SST) images, covering the period between 1987 and 2003. SST values and the SST gradients at the catch locations have been statistically compared to broader surrounding areas to test whether the thermal environment determines the spatial distribution of albacore. General additive models (GAM) have been used also to evaluate the relative importance of environmental variables and fleet behaviour. The results obtained show that, although juvenile albacore catch locations are affected by fleet dynamics, there is a close spatial and temporal relationship with the seasonal evolution of a statistically significant preferential SST window (16–18°C). However, differences have been identified between the relationship of albacore with SST within the Bay of Biscay in July and August (higher temperature). Such differences are found also in the spatial distribution of the catch locations; these reflect clearly the presence of two groups, differentiated after the third week of the fishing campaign at the end of June. The analysis undertaken relating the distribution of North Atlantic albacore juveniles with thermal gradients did not provide any evidence of a relationship between these catch locations and the nearby occurrence of thermal gradients.     

Environmental influences on Atlantic bluefin tuna (Thunnus thynnus) catch per unit effort in the southern Gulf of St. Lawrence

The Atlantic bluefin tuna (Thunnus thynnus) population in the western Atlantic supports substantial commercial and recreational fisheries. Despite quota establishment and management under the auspices of the International Commission for the Conservation of Atlantic Tunas, only small increases in population growth have been estimated. In contrast to other western bluefin tuna fisheries indices, contemporary estimates of catch per unit effort (CPUE) in the southern Gulf of St. Lawrence have increased rapidly and are at record highs. This area is characterized by the Cold Intermediate Layer (CIL) that is defined by waters <3°C and located at depths of 30–40 m in September. We investigated the influence of several in situ environmental variables on the bluefin tuna fishery CPUE using delta‐lognormal modelling and relatively extensive and consistent oceanographic survey data, as well as dockside monitoring and mandatory logbook data associated with the fishery. Although there is considerable spatial and temporal variation of water mass characteristics, the amount of available habitat in the southern Gulf of St. Lawrence (assuming a > 3°C thermal ambit) for bluefin tuna has been increasing. The percentage of the water column occupied by the CIL was a significant environmental variable in the standardization of CPUE estimates. There was also a negative relationship between the spatial extents of the CIL and the fishery. Properties of the CIL account for variation in the bluefin tuna CPUE and may be a factor in determining the amount of available feeding habitat for bluefin tuna in the southern Gulf of St. Lawrence.     

Improving the Color Shelf Life of Farmed Southern Bluefin Tuna (Thunnus maccoyii) Flesh with Dietary Supplements of Vitamins E and C and Selenium

ABSTRACT

The use of dietary antioxidants to increase the shelf life of farmed southern bluefin tuna (SBT) flesh was examined over a 10-week period using either a standard pellet (Control) or high-vitamin pellet (HV) fortified with vitamin E, vitamin C, and selenium. Following harvest, muscle samples were taken and assessed for antioxidant content. Flesh color shelf life was assessed in muscle stored at 4°C for 8 days. Muscle vitamin levels were significantly higher in the HV group than the Control group for vitamin E (20.4 ± 1.74 vs 9.7 ± 0.89 mg/kg) and vitamin C (29.1 ± 4.36 vs 4.3 ± 0.41 mg.kg^–1), but selenium levels were not higher. Muscle samples from the HV group had a slower rate of browning than did those from the Control group, particularly over days 4 to 7 of storage. Results indicated that feeding a diet approximately 10 times higher in dietary antioxidants raised levels of vitamin E and vitamin C, but not selenium, in tuna flesh and increased the shelf life of tuna.     

Oceanographic changes and exploitation drive the spatio‐temporal dynamics of Atlantic bluefin tuna (Thunnus thynnus)

Atlantic bluefin tuna (ABFT) has always displayed spectacular changes in its spatial distribution, but the underlying mechanism of such variations still remains obscure. This study focuses on this challenging issue by scrutinizing the intriguing ‘Brazilian episode’ during which a large quantity of ABFT (a temperate species) was caught during the 1960s in the equatorial Atlantic. To investigate this event, we applied a niche model to an extensive data set of catch and environmental variables from 1960 to 2009. ABFT exhibited a remarkably large ecological niche, which matches well with our current knowledge of ABFT. Our results also depicted a high probability of ABFT occurrence in the South Atlantic and, more interestingly, favorable environmental conditions in the western equatorial Atlantic during the 1960s, but not later. ABFT could thus have migrated from their northern spawning grounds to the South Atlantic during the 1960s through the western equatorial Atlantic, playing the role of an ‘ecological bridge’. We argue that the rarity of ABFT in the southern Atlantic during the last four decades would result from the interaction of several processes, particularly oceanographic conditions, migratory behavior, density‐dependence, exploitation levels and population structure. Examination of the catch data further indicated that the fish caught in the equatorial Atlantic were from the western stock and we concluded that the lack of rebuilding of this stock could result from a regime shift due to the combination of oceanographic changes in the equatorial Atlantic and overfishing in the North Atlantic in the 1960s and 1970s.     

大西洋海域大眼金枪鱼年龄与生长的初步研究

根据2001年6~10月在大西洋海域金枪鱼延绳钓渔业中采集的89 ind大眼金枪鱼样本,对其叉长、体重进行测定,并以脊椎骨作为年龄鉴定材料。结果表明,叉长组成为85~186 cm,体重组成为11.5~132.5kg,年龄为2~6龄。体重与叉长关系式为W=4.5026×10-5×FL2.8200。利用一般Von Bertalanffy生长方程来拟合,叉长和体重生长方程为:FL=257.90×(1-e-0.1960(t+3.7919))2.5933,Wt=284.28×[(1-e-0.1960(t+3.7919))2.5933]2.8200。叉长和体重的生长拐点分别为1.07龄和5.75龄。     

Environmental preferences of longlining for yellowfin tuna (Thunnus albacares) in the tropical high seas of the Indian Ocean

A survey of yellowfin tuna, Thunnus albacares , fishing ground was carried out on board of the Chinese longliners from September 15 to December 12, 2005 in the tropical high seas of the Indian Ocean. The depth at which each yellowfin tuna was hooked was estimated using a stepwise regression analysis of theoretical hook depth and observed average hook depth measured using a temperature depth recorder. Water temperature, salinity, chlorophyll  a , dissolved oxygen and thermocline, which are important variables influencing yellowfin tuna habitats, were measured in the survey. Catch rates of yellowfin tuna were then analyzed with respect to depth, temperature, salinity, chlorophyll  a , dissolved oxygen and thermocline. We suggest that the optimum ranges of swimming depth, water temperature, chlorophyll  a and dissolved oxygen concentration for yellowfin tuna are 100.0–179.9 m, 15.0–17.9°C, 0.090–0.099  μ g L⁻¹, 2.50–2.99 mg L⁻¹, respectively; that salinity has less influence on the vertical distribution of adult yellowfin tuna; and that yellowfin tuna are mainly distributed within the thermocline in the high seas of the Indian Ocean. Our results match the yellowfin tuna's vulnerability to deep longline fishing gear well.     

渔获量不确定性对印度洋大眼金枪鱼资源评估的影响

大眼金枪鱼(Thunnus obesus)是最具经济价值的热带金枪鱼类,其资源状况一直是区域性金枪鱼渔业管理组织关注的重点。由于多种渔业作业、捕捞船队构成复杂,印度洋大眼金枪鱼的历史渔获量统计存在一定的偏差(Bias),但国际上近些年开展资源评估时都忽略了这一偏差。本研究根据1979~2015年的年渔获量、年龄结构渔获量及相对丰度指数数据,运用年龄结构资源评估模型(ASAP)对印度洋大眼金枪鱼资源进行评估,重点考查渔获量的不确定性(观测误差和统计偏差)对资源评估结果的影响。结果显示,印度洋大眼金枪鱼当前资源总体没有过度捕捞,但2015年初显示轻微的过度捕捞,通过对比基础模型与8个灵敏度分析模型的评估结果发现,渔获量观测误差(CV)的预设对资源开发状态的判断有一定的影响。当渔获量统计偏差调整量为15%时(即历史渔获量被低估了),评估结果与基础模型基本一致;统计偏差调整量为20%时,评估结果有过度捕捞的趋势。本研究结果表明,资源评估模型中渔获量观测误差的设定和历史渔获量统计偏差均会对评估结果产生影响,后者更为明显,因此,二者均不能忽略。     

热带中西太平洋大眼金枪鱼的繁殖生物学特性

利用漂流金枪鱼延绳钓作业方式,于2018年6月~2019年3月对热带中西太平洋海域(WCPO,2°03''S~11°17''S,163°14''E~173°35''E)的大眼金枪鱼(Thunnus obesus)进行了取样,对其中886尾进行了繁殖生物学测定。使用广义线性模型(GLM)和有序多元Logistic回归模型,结合圆形统计方法,分析个体叉长等生物因素、渔获水深和月度等时空因素对繁殖生物学参数的影响。结果表明: 雄性和雌性平均叉长分别为132.2(±19.1) cm和125.4(±16.8) cm;取样群体中,雌雄比为0.54(±0.74),且叉长与雌雄比具有负相关关系(r=0.323, P =0.003),叉长大于140 cm后,雄性占主导;GLM模型结果显示,性腺指数(GSI)与叉长之间存在显著的二次方关系(P<0.001),即个体GSI随着叉长增加,当雄性和雌性叉长分别达到130~140 cm和140~150 cm后GSI随叉长下降;基于圆形统计发现,月度对个体GSI具有显著影响,其中雄性GSI上半年较下半年高(正弦显著,P<0.001),而雌性GSI年末和年初高于年中(余弦显著,P=0.021);有序多元Logistic模型结果显示,性腺成熟度随叉长显著增加(P<0.001),雄性性腺成熟度在5~7月较高(余弦显著,P=0.004);此外,栖息水层对雄性个体的性腺成熟度具有显著的影响(正相关,P<0.001);雄性和雌性个体50%性成熟叉长分别为96.13(?1.24) cm和104.93(?2.60) cm。研究结果为更好地了解热带WCPO大眼金枪鱼的繁殖生物学特征、科学养护热带WCPO大眼金枪鱼资源提供参考。     

大西洋金枪鱼延绳钓渔场的地统计分析

使用地统计方法研究大西洋金枪鱼延绳钓渔场空间变异特征及时空分布,分析数据为1982―2010年日本大西洋大眼金枪鱼(Thunnus obesus)延绳钓渔捞数据。结果表明,大眼金枪鱼渔场分布具有较强的空间相关性,6月、10月和11月空间相关性显著(P<0.05),其他月份空间相关性极显著(P<0.01);指数模型能够较好地表达渔场的空间变异特征,其相关系数介于0.6~0.9之间,模型拟合较好;预测图表明大眼金枪鱼渔场变化呈现出两种轨迹,一种是大西洋中部与美洲近岸之间的循环变化,另一种是大西洋中部与非洲近岸之间的循环变化;预测结果验证表明,地统计能较好地对渔场空间分布进行预测,但是单位捕捞努力量渔获量(CPUE)预测值显著高于2009―2010年实测值,资源状况差异可能是引起本次研究预测值偏高的主要原因。     

Climate‐induced vulnerability of fisheries in the Coral Triangle: Skipjack Tuna thermal spawning habitats

We investigated projected changes in sea surface temperature (SST) and the associated impacts on spawning habitat for skipjack tuna (Katsuwonus pelamis) in the Coral Triangle region (CT). A multimodel aggregate of SST CMIP5 models for the CT region, based on a comprehensive skill validation assessment, was used to identify the five best performing of 36 models tested for inclusion in a regional multimodel ensemble. Monthly 1° SST multimodel aggregate projections for the CT region under RCP8.5 show that increases in SST, as high as 2.8°C (mean value), will likely occur by the end of this century. Using these estimates of SST change, we applied three parameterizations of skipjack tuna spawning temperatures to assess the potential for change in spawning habitat within the CT region. The three spawning temperature parameterizations were as follows: (a) a square‐wave function derived from catch data with boundaries at 26 and 30°C; (b) a symmetric Gaussian function derived from the SEAPODYM models; and (c) an asymmetric Gaussian function that modifies the SEAPODYM curve in (b) to include the results of relevant physiological experiments. All three parameterizations show similar geographic patterns, with the amount of favourable spawning habitat decreasing throughout the central, equatorial CT region and increasing at higher latitudes. However, the three parameterizations show marked differences in the modelled magnitude of change, with an asymmetric Gaussian function (ASGF) showing a regionwide average of 66.1% decline in favourable spawning habitat between 2015 and 2099. These projected changes in tuna spawning habitats are likely to have important consequences on local and regional fisheries management in the CT region.     

Are the long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) population related to environmental changes?

We tested whether synchronous, long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) trap catches, collected from the ancestral Mediterranean and Atlantic trap fishery, might be related to large‐scale environmental change. Nine time series of trap catches of more than 80 yr long were compared with long time series of three preselected environmental variables, i.e. the North Atlantic Oscillation (NAO), the Length of the Day Index (LOD, a proxy of the atmospheric circulation index) and the temperature. Spectral analyses of trap catches, LOD and temperature displayed similar spectra with peaks at low frequencies, whereas those of the NAO exhibited a broad band spectrum. Regression analyses and tests of correlation did not reveal any clear relationship between trap catches on the one hand and NAO and LOD on the other hand. In contrast, long‐term fluctuations in trap catches appear to be closely and negatively related to long‐term trends in temperature. Underlying processes that could explain such a relationship are discussed, with special focus on changes in migration patterns of the Atlantic bluefin tuna.