Feeding habits of skipjack tuna Katsuwonus pelamis and other tuna Thunnus spp. juveniles in the tropical western Pacific

ABSTRACT: The feeding habits of skipjack tuna Katsuwonus pelamis juveniles (8.5–66.8 mm standard length) were examined, collected from the tropical western Pacific in October to December 1994, and their habits were compared with those of the other tuna Thunnus spp. juveniles (9.8–55.3 mm standard length). The indices, frequency of occurrence of each food item in the total number of stomachs examined (% F ), percentage of number of each food item to the total number of all food items identified (% N ), percentage of wet weight of each food item to the total wet weight of all food items identified (% W ), and relative importance of each food item ( IRI ) were estimated in the north equatorial current (NEC) and the north equatorial countercurrent (NECC) areas. The most dominant prey item of skipjack juveniles in the two areas was fish larvae. Other major prey items in the NEC area were Euphausiacea, Amphipoda, and Copepoda; whereas those in the NECC area were Copepoda, Cephalopoda, Euphausiacea, and Amphipoda. In the other tuna juveniles, the IRI of fish larvae in the two areas was remarkably high. Other prey, Euphausiacea and Cephalopoda in the NEC area only and Cephalopoda in the NECC area, were also found. These results indicate that the skipjack juvenile is primarily a piscivorous feeder although they also depend on various other prey organisms, whereas the other tuna juveniles are stronger piscivorous feeders.     

中西太平洋鲣鱼丰度的时空分布及其与表温的关系

中西太平洋是全球金枪鱼围网的主要海域,鲣鱼(Katsuwonus pelamis)是金枪鱼围网的主要作业对象。本研究利用1983～2007年中西太平洋金枪鱼围网渔获物数据,结合海洋表层温度(SST)数据,分析中西太平洋鲣鱼资源丰度在时间序列和空间位置上的分布规律。研究表明,1983～2002年,各年平均CPUE在时间序列上呈一定的上升趋势,1983～2002年,平均SST在一定范围内上下波动,平均CPUE和平均SST无显著相关性;2003～2007年,平均CPUE和平均SST均呈较大幅度上升,两者呈显著相关。从空间位置分析,鲣鱼资源量集中出现在SST为28～30℃之间的海域,在5°N和10°S附近海域CPUE反映的总体资源量较高,而在0°和5°S的资源量较低。鲣鱼资源量较大区域分布在冷暖水团交汇处。     

The relationship between the skipjack tuna (Katsuwonus pelamis) fishery and seasonal temperature variability in the south-western Atlantic

The spatio‐temporal distribution of tuna fishing effort has been related to oceanographic circulation and features in several seas of the world. Understanding the relationship between environmental variables and fishery resource dynamics is important for management decisions and to improve fishery yields. The relationship between sea temperature variability and the pole‐and‐line skipjack tuna (Katsuwonus pelamis) fishery in the south‐western Atlantic Ocean was investigated in this work. Data from logbooks, satellite images (sea surface temperature), and oceanographic surveys were used in the analyses. Skipjack are caught in warm tropical waters of the Brazil Current (BC). The north–south displacement of fishing effort was strongly associated to seasonal variation of the surface temperature, which was coupled to the tropical BC flow. Oceanographic fronts from autumn to spring and a shallow thermocline in summer probably induces the aggregation of skipjack schools over the shelfbreak, favouring fishing operations. Hypotheses are proposed to explain the relationship between peaks of fishing events and the presence of topographic peculiarities of the shelfbreak.     

Habitat characteristics of skipjack tuna (Katsuwonus pelamis) in the western North Pacific: a remote sensing perspective

Skipjack tuna habitat in the western North Pacific was studied from satellite remotely sensed environment and catch data, using generalized additive models and geographic information systems. Weekly resolved remotely sensed sea surface temperature, surface chlorophyll, sea surface height anomalies and eddy kinetic energy data were used for the year 2004. Fifteen generalized additive models were constructed with skipjack catch per unit effort as a response variable, and sea surface temperature, sea surface height anomalies and eddy kinetic energy as model covariates to assess the effect of environment on catch per unit effort (skipjack tuna abundance). Model selection was based on significance of model terms, reduction in Akaike’s Information Criterion, and increase in cumulative deviance explained. The model selected was used to predict skipjack tuna catch per unit effort using monthly resolved environmental data for assessing model performance and to visualize the basin scale distribution of skipjack tuna habitat. Predicted values were validated using a linear model. Based on the four‐parameter model, skipjack tuna habitat selection was significantly (P < 0.01) influenced by sea surface temperatures ranging from 20.5 to 26°C, relatively oligotrophic waters (surface chlorophyll 0.08–0.18, 0.22–0.27 and 0.3–0.37 mg m^?3), zero to positive anomalies (surface height anomalies 0–50 cm), and low to moderate eddy kinetic energy (0–200 and 700–2500 cm² s^–2). Predicted catch per unit effort showed a trend consistent with the north–south migration of skipjack tuna. Validation of predicted catch per unit effort with that observed, pooled monthly, was significant (P < 0.01, r² = 0.64). Sea surface temperature explained the highest deviance in generalized additive models and was therefore considered the best habitat predictor.     

Daily growth increment formation and its lunar periodicity in otoliths of the myctophid fish Myctophum asperum (Pisces: Myctophidae)

ABSTRACT: The surface-migratory myctophid fish, Myctophum asperum , of the western North Pacific was found to have daily growth increments of its sagittal otolith, which also exhibited lunar periodicity in the deposition of increments. Daily deposition of the otolith increments was verified because the width of the marginal increment increased during the night and early morning between 20.00 h and 08.00 h and its growth stopped during the day. An autocorrelation analysis of the increment widths, which were measured consecutively in 11 specimens covering 33 synodic months, also showed a lunar periodicity in increment deposition. The mean increment widths during five days around the time of a full moon were significantly narrower than those around a new moon in 18 of the 33 full moon cases ( P < 0.01: Student's t -test) and, on average, tended to be narrow in 29 cases. The cause of this tendency is thought to be slower growth caused by staying in deeper and colder habitat due to the suppression of diel vertical migration and/or lower food availability resulting from the possible dispersion of zooplankton during the full moon period.     

Operational oceanography applied to skipjack tuna (Katsuwonus pelamis) habitat monitoring and fishing in south‐western Atlantic

Skipjack tuna (Katsuwonus pelamis) ranks third among marine resources that sustain global fisheries. This study delimits the spatiotemporal habitat of the species in the south‐western Atlantic Ocean, based on operational oceanography. We used generalized additive models (GAMs) and catch data from six pole‐and‐line fishing vessels operating during 2014 and 2015 fishing seasons to assess the effect of environmental variables on catch. We also analysed Modis sensor images of sea surface temperature (SST) and surface chlorophyll‐α concentration (SCC) to describe fishing ground characteristics in time and space. Catch was positively related to thermocline depth (24–45 m), SST (22–24.5°C), SCC (0.08–0.14 mg/m³) and salinity (34.9–35.8). Through SST images, we identified that thermal fronts were the main surface feature associated with a higher probability to find skipjack. Also, we state that skipjack fishery is tightly related to shelf break because bottom topography drives the position of fronts in this area. Ocean colour fronts and plankton enrichment were important proxies, accessible through SCC, used to delineate skipjack fishing grounds. Catch per unit effort (CPUE) was higher towards summer (median 14 t/fishing day) due to the oceanographic characteristics of the southern region. High productivity in this sector of the Brazilian coast defines the main skipjack feeding areas and, as a consequence, the greatest abundance and availability for fishing.     

Comparison of the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna associated with drifting FADs in the equatorial central Pacific Ocean

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.     

Production of protein hydrolysates from skipjack tuna (Katsuwonus pelamis) viscera as feeding attractants for Asian seabass (Lates calcarifer)

Skipjack tuna viscera hydrolysate (TVH) was produced by enzymatic hydrolysis using alcalase. A study of the effect of time and enzyme concentration was performed and formed the basis for preparing TVH with the desired degree of hydrolysis (DH). An enzyme to substrate ratio of 5 g kg⁻¹ (TVH A1) and 16.4 g kg⁻¹ (TVH A2) at pH 8.0 with a temperature of 50 °C, and hydrolysis time of 60 min were found to be optimal conditions to obtain hydrolysis of 42.9% and 62.9%, respectively. Both TVH A1 and TVH A2 were analysed for chemical and amino acid composition and peptide size. The effectiveness of TVH at different DH as feeding attractants was estimated in a feeding trial at different inclusion levels. Ten experimental diets , including a fish meal‐based reference diet, were fed to Asian seabass for 28 days. Fish fed the diet supplemented with 30 g kg⁻¹ of TVH A2, and the reference diet showed the highest feed intake (P < 0.05). The growth performance of fish fed diets supplemented with TVH was slightly higher than those of fish fed the control diet, but the reference group showed a significantly higher growth rate (P < 0.05). These findings suggest that the supplementation of feed with TVH that has been processed under suitable conditions can improve feed palatability and growth performance when utilizing alternative protein sources in Asian seabass diets.     

东海条石鲷仔鱼耳石日轮与生长的关系

2009年4月15日-5月5日在浙江省舟山水产研究所条石鲷(Oplegnathus fasciatus)人工繁殖期间,逐日选择胚胎和仔鱼样本,连续解剖观察发育后期胚胎和前期仔鱼,光镜观察仔鱼矢耳石和微耳石的形态、日轮数,测定其直径,研究条石鲷的耳石日轮和生长。结果表明,受精后约26h,条石鲷胚胎听囊内出现1对矢耳石和1对微耳石;仔鱼孵出第2天形成第1个轮纹,之后每天形成1轮,孵化后天数(N)和矢耳石日轮数(D)的关系为N=D+1;在第8天左右,矢耳石上出现第2条明显的标记轮,为初次摄食轮。仔鱼耳石长径(rs,μm)与鱼体体长(L,mm)呈线性相关,其关系式为rs=18.146L-44.436;矢耳石长径rs与微耳石长径rl之间存在线性相关,其关系式为rs=0.6125rl+1.9882。根据结果确认,矢耳石轮纹可作为条石鲷仔鱼日龄的判别依据。     

ENSO现象对中西太平洋鲣鱼围网渔场的影响分析

ENSO(El Nin^-o Southern Oscillation)是引起全球气候变化的最强烈的海-气相互作用现象,对世界渔业生产具有重要影响。本文研究表明：ENSO现象对中西太平洋鲣鱼围网渔场的空间分布有显著影响,厄尔尼诺发生时,单位捕捞努力量渔获量经度重心随着暖池的东扩而东移,拉尼娜发生时则随着暖池向西收缩而西移。同时,Nifio 3．4区海表温度与单位捕捞努力量渔获量经度重心有显著相关关系,可将Nifio 3．4区海表温度作为预报、预测中西太平洋鲣鱼围网渔场位置的一个重要指标。     

A study of delayed capture mortality syndrome in skipjack tuna, Katsuwonus pelamis (1).

Abstract. This study was initiated to determine the cause(s) of delayed mortality in newly captured skipjack tuna, Katsuwonus pelamis (L.), being held at the National Marine Fisheries Service Kewalo Research Facility. Sixty-four per cent of 244 skipjack tuna delivered to the facility died, usually on the second or third day after capture. The capture history, morphological data, serum chemistry (21 standard parameters), haematology, and histological samples of major organs, were obtained from 30 fish sampled at sea immediately after capture, or after approximately 4, 9, 24, 48 or 500+ h in captivity. The cause(s) of death in these fish could not be attributed to anoxia, disseminated intravascular coagulation, lactic acidosis, capture myopathy or infection. Post-capture haemodilution is hypothesized as a major factor of delayed capture mortality syndrome in skipjack tuna.     

Relationships among yellowfin and skipjack tuna, their prey-fish and plankton in the tropical western Indian Ocean

Stomach contents of yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tuna caught by trolling and purse seining in the tropical western Indian Ocean, together with those of the prey-fish found in their stomachs, have been analysed. Epipelagic fish are the main prey of these tunas, whereas no vertically migrating fish, which inhabit subsurface layers at night, have been found in their stomachs. These tunas are thus considered day-feeders. Purse-seine-caught tunas, which belong to large schools, have a much higher number of prey-fish in their stomachs than tunas caught by trolling on small schools. Similarly, prey-fish from purse-seine tunas have a much higher number of plank-tonic prey in their stomachs than those from troll-caught tunas. Therefore, these tunas adopt a wandering strategy in small schools when food resources are scarce and form large schools when they are abundant. The planktonic organisms found in the stomachs of prey-fish are described by taxa and sizes; they represent the fraction of the planktonic biomass actually supporting the stock of tuna. Size ratios between the three links tuna-prey-fish-plankton are very high, suggesting that these tunas benefit from a short food chain which is probably efficient from the energetic point of view.     

基于声学映像的南海灯光罩网渔业中鲣的时空分布

基于灯光罩网和EY60科学探鱼仪采集鲣(Katsuwonus pelamis)的生物学数据与声学映像,通过分析后向体积散射强度Sv (dB)、平均目标强度TS (dB)及单位采样体积的平均鱼类数目(Nv)等信息,研究鲣的时空分布与现场目标强度变化.S13站位的鲣平均叉长(362.20±35.73) mm,S14站位的鲣...     

中西太平洋金枪鱼围网鲣鱼渔获量时空分布分析

中西太平洋的金枪鱼围网渔业目前的年产量约在100×104t左右,其中鲣鱼占有很重要的地位。本文通过对20世纪70年代以来围网捕获的鲣鱼渔获数据进行时间序列以及空间位置变化等时空分析,试图找出其变化规律以及趋势。结果表明,从20世纪70年代以来,随着渔船数的增加,中西太平洋的围网捕获的鲣鱼渔获量分布,从太平洋岛屿近海逐渐向太平洋热带中部海域扩展。渔获量经度重心随着中西太平洋金枪鱼围网渔业的发展有向东移动的趋势,70年代在128°E附近变化,80年代在144°E左右,90年代在153°E左右,近年在158°E左右变化。而鲣鱼渔获量纬度重心位于赤道区域,70年代在2°N附近,80年代在1°30′S左右,90年代在2°50′S左右,近年在2°55′S左右变化。经纬度5°×5°单个小区范围内10年内的最高总产量则从70年代的11×104t,增加到90年代超过了69×104t。渔获量空间分布除了随着渔业发展向外海向赤道以南扩展以外,还受南方涛动(ENSO)现象的明显影响,一般来说在相邻的数年中渔获量经度中心在厄尔尼诺年比较偏东,在拉尼娜年比较偏西。     

Predicting skipjack tuna forage distributions in the equatorial Pacific using a coupled dynamical bio-geochemical model

Skipjack tuna ( Katsuwonus pelamis ) contributes ≈70% of the total tuna catch in the Pacific Ocean. This species occurs in the upper mixed-layer throughout the equatorial region, but the largest catches are taken from the warmpool in the western equatorial Pacific. Analysis of catch and effort data for US purse seine fisheries in the western Pacific has demonstrated that one of the most successful fishing grounds is located in the vicinity of a convergence zone between the warm (>28–29°C) low-salinity water of the warmpool and the cold saline water of equatorial upwelling in the central Pacific (Lehodey et al ., 1997). This zone of convergence, identified by a well-marked salinity front and approximated by the 28.5°C isotherm, oscillates zonally over several thousands of km in correlation with the El Niño–Southern Oscillation. The present study focuses on the prediction of skipjack tuna forage that is expected to be a major factor in explaining the basin-scale distribution of the stock. It could also explain the close relation between displacements of skipjack tuna and the convergence zone on the eastern edge of the warmpool. A simple bio-geochemical model was coupled with a general circulation model, allowing reasonable predictions of new primary production in the equatorial Pacific from mid-1992 to mid-1995. The biological transfer of this production toward tuna forage was simply parameterized according to the food chain length and redistributed by the currents using the circulation model. Tuna forage accumulated in the convergence zone of the horizontal currents, which corresponds to the warmpool/equatorial upwelling boundary. Predicted forage maxima corresponded well with high catch rates.     

南海灯笼鱼加工优质鱼粉的关键工艺研究

根据2015年6-7月于南海北部陆坡海域采集的207尾粗鳞灯笼鱼(Myctophum asperum)样本,对其耳石形态特征及形态参数进行了初步分析。结果表明,粗鳞灯笼鱼耳石的耳石长(otolith length,L₁)、耳石宽(otolith width,L₂)、周长(otolith perimeter,P)和面积(otolith area,A)有明显的性别差异。耳石宽、耳石周长、耳石面积与体长呈对数函数关系(P < 0.05);耳石长与体长呈幂函数关系(P < 0.05);耳石长、耳石宽与体质量呈幂函数关系(P < 0.05);耳石周长、耳石面积与体质量呈对数函数关系(P < 0.05)。随着体长逐渐增大,耳石绝对尺寸逐渐增大,相对尺寸保持不变。耳石基叶(rostrum)长和翼叶(antirostrum)长存在线性关系。