Free-swimming Tuna Research Articles

Role of the caudal peduncle in a fish-inspired robotic model: how changing stiffness and angle of attack affects swimming performance

In fish, the tail is a key element of propulsive anatomy that contributes to thrust during swimming. Fish possess the ability to alter tail stiffness, surface area and conformation. Specifically, the region at the base of the tail, the caudal peduncle, is proposed to be a key location of fish stiffness modulation during locomotion. Most previous analyses have focused on the overall body or tail stiffness, and not on the effects of changing stiffness specifically at the base of the tail in fish and robotic models. We used both computational fluid dynamics analysis and experimental measurements of propulsive forces in physical models with different peduncle stiffnesses to analyze the effect of altering stiffness on the tail angle of attack and propulsive force and efficiency. By changing the motion program input to the tail, we were able to alter the phase relationship between the front and back tail sections between 0° and 330°. Computational simulations showed that power consumption was nearly minimized and thrust production was nearly maximized at the kinematic pattern where φ = 270°, the approximate phase lag observed in the experimental foils and in free swimming tuna. We observed reduced thrust and efficiency at high angles of attack, suggesting that the tail driven during these motion programs experiences stalling and loss of lift. However, there is no single peduncle stiffness that consistently maximizes performance, particularly in physical models. This result highlights the fact that the optimal caudal peduncle stiffness is highly context dependent. Therefore, incorporating the ability to control peduncle stiffness in future robotic models of fish propulsion promises to increase the ability of robots to approach the performance of fish.

Application of Feature Point Matching Technology to Identify Images of Free-Swimming Tuna Schools in a Purse Seine Fishery

Tuna fish school detection provides information on the fishing decisions of purse seine fleets. Here, we present a recognition system that included fish shoal image acquisition, point extraction, point matching, and data storage. Points are a crucial characteristic for images of free-swimming tuna schools, and point algorithm analysis and point matching were studied for their applications in fish shoal recognition. The feature points were obtained by using one of the best point algorithms (scale invariant feature transform, speeded up robust features, oriented fast and rotated brief). The k-nearest neighbors (KNN) algorithm uses ‘feature similarity’ to predict the values of new points, which means that new data points will be assigned a value based on how closely they match the points that exist in the database. Finally, we tested the model, and the experimental results show that the proposed method can accurately and effectively recognize tuna free-swimming schools.

Environmental characteristics associated with the presence of the Spinetail devil ray (Mobula mobular) in the eastern tropical Pacific.

In the eastern Pacific Ocean, the tropical tuna purse-seine fishery incidentally captures high numbers of five mobulid bycatch species; all of which are classified as mortalities by the Inter-American Tropical Tuna Commission due to uncertainties in post-release mortality rates. To date, the factors (operational or environmental) leading to the capture of these species by the fishery have not been well studied. Here, we developed Generalized Additive Models for fisheries observer data to analyze the relationships between the presence/absence of Mobula mobular bycatch and oceanographic conditions, the spatial and temporal variability in fishing location, and the set type (associated with dolphins, free-swimming tuna schools or floating objects). Our results suggest that chlorophyll concentration and sea surface height are the most important variables to describe the presence of M. mobular in conjunction with geographic location (latitude and longitude) and set type. Presence of the species was predicted in waters with chlorophyll concentrations between 0.5–1 mg·m-3 and with sea surface height values close to 0; which indicates direct relationships with productive upwelling systems. Seasonally, M. mobular was observed more frequently during December-January and August-September. We also found the highest probability of presence observed in School sets, followed by Dolphin sets. Three areas were observed as important hotspots: the area close to the coastal upwelling of northern Peru, the area west to Islands Colon Archipelago (Galapagos) and the area close to the Costa Rica Dome. This information is crucial to identify the mobulids habitat and hotspots that could be managed and protected under dynamic spatial management measures to reduce the mortality of mobulid rays in the eastern Pacific purse-seine fishery and, hence, ensure the sustainability of the populations of these iconic species.

Catch and bycatch captured by tropical tuna purse-seine fishery in whale and whale shark associated sets: comparison with free school and FAD sets

In an ecosystem approach to fisheries management (EAFM) framework of the tuna purse-seine fishery, the assessment of target species, but also that of bycatch species, is essential. In the Atlantic and Indian oceans, purse-seine nets are sometimes set around tuna schools associated with whale sharks and baleen whales, although less frequently than around free-swimming tuna schools or those associated with fish aggregating devices (FAD). However, knowledge on the targeted catch and bycatch in these megafauna associated fishing sets is still relatively limited. Therefore, the aims of this study were to assess species and size composition of the target tuna species, as well as the diversity of bycatch species in whale and whale shark associated sets. Whale associated sets were found to be very similar to free school sets in terms of tuna catch (large yellowfin tuna), bycatch occurrence (presence in half the sets) and species assemblage (alpha and beta diversity). Whale shark associated sets were intermediate between FAD and free school sets, with tuna catch (skipjack and juvenile yellowfin) closer to FAD than to free school sets. However, the presence of large yellowfin, the bycatch composition (with almost no finfish, abundantly captured in FAD sets) and the species assemblage showed similarity with free school sets. This study highlights the need for an EAFM in the tuna purse-seine fishery by providing knowledge on pelagic multi-specific catches and bycatches.

The effect of environmental variables, gear design and operational parameters on sinking performance of tuna purse seine setting on free-swimming schools

There are three main types of tuna purse seine operations: setting on free-swimming schools, setting on fish aggregation devices, or setting on marine mammal associated schools. In this research, we measured sinking performance of 88 purse seine sets on free-swimming skipjack (Katsuwonus pelamis) schools in the western and central Pacific Ocean from October 2006 to May 2013. The sinking behavior of a purse seine is influenced by many factors (e.g. netting materials, sinker weight, length-height ratio, mesh size, purse line length, setting position, setting speed, current, wind, etc.), it may be difficult to quantify the effect these factors have on the sinking performance. A purse seine set is considered to have a better sinking performance if its purse line reaches a greater depth in a shorter time period, i.e., higher sinking speed and greater sinking depth. A generalized additive model (GAM) was used to analyze sinking depth and sinking speed under different sea conditions (current speed and direction at different layers), gear design (length-height ratio, towing line length and purse line length), and operational methods (shooting duration and setting speed). The results in this study showed that the sinking performance of a purse seine with a lower length-height ratio was better than a seine with a higher ratio, current speed at 120m depth was the most important environmental factor affecting sinking depth of the purse seine. Sinking depth was strongly associated with length-height ratio, shooting duration and purse line length. Sinking speed was related to length-height ratio, shooting duration, current speed at 60m, purse line length and towing line length. The sinking performance models obtained from this study can be used to predict sinking behavior in relation to operational and environmental conditions, which is essential for the success of tuna purse seine operation on free-swimming tuna schools.

人工集鱼装置对热带金枪鱼类摄食模式的影响研究进展

热带金枪鱼类具有聚集在漂浮物体周围的行为特性，形成的集群表现稳定，可捕性较高。以此特性，金枪鱼围网渔业研制并投放了大量的人工集鱼装置（Fish Aggregation Device，FAD）用于聚集并捕捞金枪鱼。然而，大规模出现的FAD会使某些海域海面漂浮物的密度迅速增加，从而在一定程度上人为地改变了金枪鱼的表层栖息环境，对金枪鱼种群具有一系列可能的潜在负面影响，摄食模式的改变就是其中之一。归纳并综合了近年来国内外关于FAD对金枪鱼类摄食模式影响的相关研究，从摄食行为、日摄食量、饵料种类与组成以及生态位宽度4个方面对比了随附于FAD的金枪鱼和自由状态下同类的不同，发现大多情况下FAD的存在会使金枪鱼的摄食模式发生一定的改变。最后，归纳了过往实验存在的不足，对今后研究的发展方向进行了展望。;Tropical tunas are a kind of highly migratory oceanic fishes whose food organisms in perched waters are relatively scarce and are distributed as patches. The tunas are obliged to swim quickly in response to dynamic changes of its prey because of hardly lasting aggregation of food organisms. Tropical tunas are inclined to form natural aggregations which are usually referred to as free swimming schools. In early days, however, the artisanal fisherman noted that the tropical tunas have the habit of gathering around natural floating objects such as logs, seaweed mats, branches and palm leaves, forming stable aggregations, termed as floating-objects-associated schools. They found that fishing was much efficient near these objects than in an open ocean. Tuna purse seine fisheries utilized this type of behavior to develop a great number of fish aggregation devices (FADs) for aggregating tuna and thus improve harvest efficiency. Two types of FADs are often used: drifting FADs (dFADs) and anchored FADs (aFADs). Since the first FAD deployments, FADs-based fishing technology had developed rapidly throughout the early 1990s, and FADs have been generally accepted as an effective mean to increase catch rates and reduce the energy consumption of purse seiners. The large-scale use of FADs, however, considerably increases the density of floating objects in some waters, and in turn, to some extent, artificially changes the surface habitat of the tuna. This may impose a series of potentially negative effects on tuna populations, such as changes in patterns of aggregation, feeding pattern and migratory movement and the decline of physical conditions for the population. Of those mentioned-above side effects, changes in the feeding pattern may have more profound impacts on fish populations as it exerts a direct effect on key life history processes, such as growth and reproduction. In the past 30 years, many studies have been conducted to evaluate whether and how FADs affect the feeding pattern. However, the results from these studies are still inconclusive and contradictory.<br> This review summarizes recent studies in regard to the tuna feeding patterns as influenced by FADs. We compare differences of feeding behavior, daily rations, the types of prey and ecological niche width between FAD-associated and free swimming tuna schools. It implies that, FADs tend to alter the large-scale migratory movements to some extents, but not the local and small-scale migratory movements. FADs may also influence the stomach contains and the rates of empty stomach. Thus, FADs, in most cases, do in fact change feeding pattern and behavior. This review also identifies shortcomings in previous studies in their research methods and contents, and accordingly proposes new research approaches, such as the use of underwater video camera to observe the feeding behavior of tunas directly, take advantage of remaining stomach contents to rebuild diet composition for the estimation of the daily rations. Stable isotope analysis (SIA) can also help improve our understanding of trophic ecology for tunas. We also include a discussion on possible future research direction in evaluating impacts of FADs on feeding behavior for tunas.

Self-organized critical branching in systems that violate conservation laws

A non-conservative critical branching model is proposed to demonstrate that self-organized criticality (SOC) can occur in mean-field sandpiles that violate a conservation law. The critical state is characterized by avalanche sizes and lifetimes that obey an inverse power-law distribution with exponents τS = 3/2 and τT = 2, respectively. Criticality is achieved when the branching process is coupled to a background activity characterized by the spontaneous switching between refractoriness and quiescence among system components. The stationary state of the system is analysed mathematically and numerically, and is shown to exhibit a transition from a subcritical phase to a critical phase. SOC in sandpile models has been widely believed to occur only when grains are conserved during avalanches. However, such a conservation law is likely to be violated by open, non-equilibrium systems such as biological networks and socially interacting systems like animal groups. The model explores the role of dynamic synapses and synaptic plasticity in maintaining criticality of cortical networks. These brain networks have been found to display neuronal avalanches that obey a power-law distribution. The non-conservative model also emulates the main features of the size distributions of free-swimming tuna schools and red deer herds. Demonstrating criticality in self-organizing systems that violate conservation laws enhances the predictive ability of the theory of SOC in the arena of biocomplexity.

ALTERNATIVE FISHERIES AND THE PREDATION RATE OF YELLOWFIN TUNA IN THE EASTERN PACIFIC OCEAN

Apex predators in pelagic ecosystems may play key roles in determining food web structure and ecosystem dynamics. Commercial fisheries can thereby have large effects on pelagic ecosystems by selectively harvesting apex predators. We assessed the potential ecological consequences of fishing due to alternative harvest practices currently employed in the capture of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean (EPO). Specifically, we estimated the demand on the prey resources consumed by yellowfin tuna and how this demand is altered by three methods of purse seining and by long-lining. These fishing techniques are contrasted by stark differences in age selectivity; longline and purse seine sets on yellowfin associated with dolphins (“dolphin sets”) capture old fish, whereas purse seine sets on free-swimming tuna schools or floating objects (“dolphin-safe sets”) capture young yellowfin. Yellowfin tuna predation rates were estimated from a bioenergetics model coupled with a population model based on natural mortality estimates and age-specific vulnerabilities for each gear type. Maximum equilibrium fishery catch (measured in megagrams per year; 1 Mg = 1 metric ton) was lowest for dolphin-safe sets and highest for dolphin sets and longline fishing. Moreover, the present combined fishery yield could not be sustained by either of the dolphin-safe sets, but could be sustained with either dolphin sets or long-lining. The predation rate of the yellowfin population was highly sensitive to the magnitude and type of fishing mortality: yellowfin predation rate declined by ∼119 Mg per megagram of floating object set catch, 72 Mg per megagram of school fish set catch. In contrast, predation declined by only 34 Mg and 17 Mg per megagram of dolphin set and longline catch, respectively. When considering all fishing techniques simultaneously in proportion to the present fishery, we estimated that total yellowfin predation is presently only one-third the magnitude expected from an unfished population. This reduction in predation was unevenly distributed among prey items; the prey of large yellowfin experienced 80% less predation, whereas the prey of small yellowfin experienced only 50% less predation, compared to an unfished population. We conclude that fisheries can have large effects on trophic linkages in pelagic food webs even when fishing rates are sustainable, and that these ecological effects vary considerably for different types of fishing gear and fishing practices.

Space dimension and scaling in fish school-size distributions

A simple model of aggregation has been used, in its mean-field version, to explain the observed scaling property of tuna fish school-size distributions (Bonabeau E and Dagorn L 1995 Phys. Rev. E 51 5220). This model makes additional predictions when the dimension of the space in which the fish move is taken into account. In this letter, we identify two cases where the mean-field assumption, which was justified for free-swimming tuna fish, is no longer valid. In these two examples, scaling is also observed and the exponent is modified from the mean-field case in a way predicted by the model.

Tuna Metabolic Rates Estimated from Energy Losses during Starvation

Metabolic rates were calculated from energy losses over time in fasting, freeswimming tuna (30-50 cm fork length). Water content accurately predicted caloric density measured by bomb calorimetry. A subsample that accurately predicted water and energy content in whole tuna was found. The mean metabolic rate for Katsuwonus pelamis starved < 1 wk was 0.36 kJ·d⁻¹ · g⁻¹ wet mass. Tuna kept for longer periods had lower and less variable swimming speeds and metabolic rates. Mean rates for 1-2 wk of starvation were 0.22 kJ·d⁻¹· g⁻¹ for K. pelamis and 0.18 kJ·d⁻¹ · g⁻¹ for both Euthynnus affinis and Thunnus albacares. For >2 wk of starvation, the mean rates were 0.14 kJ·d⁻¹· g⁻¹ for K. pelamis and 0.12 kJ·d⁻¹ · g⁻¹ for both E. affinis and T. albacares. Our energy-loss estimates of metabolic rate covered the same range as K. pelamis respiration rates. Energy losses in fasting tuna were about twice as high as in fasting cold-bodied fish under equivalent conditions.

The Influence Of Blood Gas Properties On Gas Tensions And Ph Of Ventral And Dorsal Aortic Blood In Free-SwimmingTuna, Euthynnus Affinis

ABSTRACT We have developed a technique for capture, anaesthetization, instrumentation and release of tuna and have made the first determinations of blood gas values in dorsal and ventral aortae of free-swimming tuna. Dorsal aortic varied from 34·5 to 91·7 mmHg, and ranged from 3·7 to 7 mmHg. Dorsal aortic blood [pHa = 7·77 ± 0·04 (8), mean ± one S.E.M. (N)] was more alkaline than ventral aortic blood [pHv = 7·65 ± 0·02 (7)]. Warming dorsal aortic blood from 25 to 35 °C in a closed system caused and to rise and pH to fall. Oxygen-combining curves for whole blood were sigmoid [mean Hill’s number = 1·72 ± 0·05 (11), range 1·57–2·0] and P50 over the pH range found in free-swimming animals was 21 ±1·75 (8) mmHg. The CO2-induced Bohr coefficient (ΔlogP50/Δ pH) was –0·59 ± 0·046 (30). Unusual features of CO2-combining curves are attributed to a significant Root effect. Although these in vitro properties of tuna whole blood are at variance with other published data on tuna they nevertheless substantiate our determinations made in vivo.

Temperature Discrimination by Captive Free-Swimming Tuna, Euthynnus affinis

Captive kawakawa, Euthynnus affinis, were instrumentally conditioned to respond to an increase in temperature to determine discrimination abilities. Two fish yielded a discrimination threshold of 0.10 to 0.15 C. Thermal sensitivity of this high-seas pelagic fish is thus no more acute than that of inshore fishes and appears inadequate for direct sensing of weak horizontal temperature gradients at sea.

Some Aspects of Gas Exchange in Tuna*

ABSTRACT Some aspects of gas exchange in restrained skipjack tuna were analysed. The average rate at which water flowed over the gills was 2·8 1/min.kg. The concentration of oxygen in water entering and leaving the gills was measured and used to calculate oxygen uptake (692 mg/h.kg) and utilization (0·71). The drop in hydrostatic pressure as water flowed over the gills was 1·9 cm water and agrees favourably with theoretical predictions. The partial pressure of oxygen was measured in blood afferent and efferent to the gills and used to calculate effectiveness of oxygen removal from the water (90%) and the transfer factor for oxygen (0·12 ml/min.kg.mmHg). The average utilization measured in free-swimming tuna was 0·56. The extraordinary ability of tuna to efficiently extract oxygen from the water at high gill water flow rates is discussed.