バショウカジキの音響捕食
Jul 24, 2023Scientific Reports volume 13、記事番号: 13820 (2023) この記事を引用
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バショウカジキが海面近くの渦の中でトビウオの群れを囲い込むために旋回すると、反対側に配置された 70 度のセクターに限定された円弧状の表面波の小さなパッチが一貫して分散しているように見えますが、なぜでしょうか? 魚の動きが突然止まると、囲い込まれた群れが圧縮され、尾部の推進渦が遠心渦の回転から解放された圧力に触れ、破壊し、放射して音響単極子を形成することがモデル化されています。 表面波パッチは放射球の一部です。 バショウカジキとトビウオの反対側に配置された湾曲した体は、モノポールの周りに凹面音響鏡として機能し、その間に反響する鐘形のマントを作り出し、トビウオの耳骨と膀胱を振動させて方向感覚を失わせます。 テーブルにしっかりと置かれた水の入ったカップは、純粋な放射状モードの同様の振動を引き起こします。 バショウカジキは、風による垂直面での水中でのトロイダル運動が無視できる深さで群れの周りを旋回するため、トビウオは上空の追い風の方向を感知できず、泳いで正しい方向に浮上して滑空する能力が制限されます。 。 実験により、トビウオの尾部の剛性は素早い弾道脱出には低すぎることが確認されており、これも求められていません。
光合成により、熱帯海洋の上層には生命体と捕食者と被食者の相互作用が豊富にあります (「方法」セクションで定義)。 アッテンボロー 1 の鮮明なビデオ写真 (および https://drive.google.com/file/d/1gn-uabapyDTq7DYlEkmlRuEBC7ExYxA2/view?usp=drive_link) で撮影されたバショウカジキとトビウオの捕食者と被食者の相互作用では、タイムスタンプ m :s 0:45−0:51 (「方法」セクション) では、見落としやすい高度に組織化された小さな表面波パケットが自由表面に現れ、コヒーレンスを維持しながら放射状に分散します。 波束はどこから来て、なぜ形成されるのでしょうか? さらに、自由表面近くでは、海は半無限です。 では、バショウカジキはどのようにして約100匹のトビウオを囲い込み、滑空するため、あるいは深海への逃亡を独力で阻止するのでしょうか? (2 匹目のバショウカジキが加わることもありますが、その後になります)。 バショウカジキは囲い込むことに驚くほど成功しているのに、同じように積極的に追跡しているにもかかわらず、トビウオをほとんど捕まえることができないのはなぜでしょうか? 後者は、バショウカジキが三次消費者、つまり頂点捕食者であるのに対し、トビウオは二次消費者であるため、より驚くべきことです。 理論的な相互作用モデルは、波のパッチがどのように形成されるのか、そしてなぜ最初は囲い込みが成功するのかを説明しますが、その後、異常な位相分岐の不安定性により獲物の魚が逃げてしまう理由を説明しています。
この相互作用の重要な背景は、バショウカジキが最初に長さスケールとして 1 m を確立するのに対し、トビウオの長さスケールは 0.1 m であり、巡航速度がそれに関係する体長であるということです。 この相互作用の最も注目すべき側面は、群れのトポロジーにあり、群れが圧縮されて「点」に漸近的に崩壊する瞬間が突然現れ、トビウオの群れは互いに平行に泳ぐのではなく、仮想の空間に集団で泳ぎます。まるでシンクの流れのように、口を大きく開けてパニックを起こしているようだ。 物理的には、相互作用のスケールは 1 m \(\rightarrow\) 0.1 m から減少します。 恐怖と関係のある学校教育は進化と同じくらい奥が深いのに、何がそのような基本的な本能を無効にしたのでしょうか? トポロジカルな不安定性とそれに伴う恐怖の引き金は、最終的にトビウオの脳に作用して耐え難い痛みを引き起こす音響インパルスによって引き起こされるかのようにモデル化されています。 渦回転の運動エネルギーはバショウカジキによって突然停止され、凹面音響鏡として機能する反対側に配置されたバショウカジキとトビウオの群れの間で反響する圧力インパルスが発生します。 オイラー波およびライトヒルノイズ方程式は、理論を音響事象の自由表面波フットプリントと比較するために使用されます。 渦破壊モデルは、衝撃の圧力と時間スケールを推定するために与えられます。
0\) and for flying fish \(z > 0\) or \(z < 0\); the sailfish remains in the swimplane thereby increasing the separation. The flying fish cruising returns where \(z > 0\) or \(z < 0\). The interaction then is about reduction of swim velocity and separation−a frictional process. The concave sail fish and flying fish bodies cloak (wrap around) the space of vorticity and acoustics. (c): shaded area is laboratory disk measurements, left line is laminar, right line is turbulent and the curved line is transitional./p>> I_x\) in the sailfish, but \(I_x \approx I_y\) in the flying fish allowing the former to camber easily in the horizontal plane while the latter can apply torsion. One-to-one pursuit shows torsional escape by a corralled flying fish below the swim-plane1. The sailfish then is a planar swimmer while the flying fish is a three-dimensional swimmer. Because the smaller flying fish swim in schools, it is easier to corral them in the horizontal plane. Assume \(\pi d = 2L\), where d is the minimum packing diameter of the school and L is the length of the sailfish. For L = 1 m, \(d =\) 0.64 m. If \(d=20 b\), \(b =\) 3 cm, which is reasonable, that is 10 flying fish are stacked side by side. We get \(10^2\) fish in the school which is approximately as observed1. Alternatively, for a 50 kg sailfish, the equivalent flying fish mass is 0.50 kg which is reasonable. Approximately, the packed flying fish school equates to a sailfish./p>>1\) in the winglets. The wide winglet portfolio means that the sailfish reduces \(C_{di}\) at all speeds. Methods gives the properties of the axial locations of the two primary winglets \(W_1\) and \(W_2\), where the streamlines and circulation gradients change sign in order to improve stability. In Fig. 2d–f, the winglets are deployed then merged back as the camber \(\rightarrow\) 0, and \(U \rightarrow 0\). The sequence is similar to bald eagle landing./p>> | \Gamma _f |\) resulting in \(\Delta r_f (t) \rightarrow 0\) -an irreversible, topological and unstable singularity forms whence at least five fish turn simultaneously inward toward a point ("Methods" section)1. To disturb the equilibrium to induce a topological instability, the sailfish suddenly starts swimming in the counter direction nullifying the induced oscillations in order to still the water. There is evidence that the sailfish motion then is opposite to the school1. The instability is modeled as a one dimensional pitchfork instability given by \(Dz = \theta _b z - z^3\)33. The steady state solutions for \(\theta _b < 0\) and \(\theta _b > 0\) are shown in Fig. 1b where the corralling singularity is located at \(\theta _b, z = 0\). Post-bifurcation, two stable branches are possible. In the lower branch, most of the fish restore the school to swim below the swimplane in the diffuser (Fig. 1). In the upper branch, a few individual fish swim up to the nozzle, breaching the interface in order to glide (Fig. 1)./p>> \rho _a\)) interface of \(\nabla \rho\) under the gravitational acceleration g (Fig. 4). Receiving little resistance, water penetrates the air. As circulations \(+\Gamma , -\Gamma\) deposit sequentially at the inflection points along the interface length, a single mode interface of wave number \(k=2\pi /\lambda\) is formed. The single mode amplitude first grows linearly with time through symmetric crests and troughs. This mode is followed by the growth of multiple modes and nonlinearities when asymmetric crowns and spikes form. The tip of the spike rolls up into a crown. Small scale disturbances appear on the interface, developing into a chaotic regime19,39. In Fig. 4, there are nonuniformities in the spacing and the heights of the spikes meaning that extraneous perturbations contributing to nonlinearities are also growing. Hence, while the stabilizing forces remain the same, the destabilizing inertia forces are higher compared to when the most organized crowns and spikes first form at \(We=\) 20019. The destabilizing force drops during taxiing after emergence, that is when the sailfish threat recedes ("Methods" section)1./p> We > 800\)19 and is similar to in the ocean ("Methods" section). That the emergence is at a shallow angle of 19\(^{\circ }\) and a ballistic 90\(^{\circ }\) exit is not undertaken for a faster escape means the thrust is 0.03 N and not 0.981 N for a 100 g flying fish (60A hardness and not 95A or 75D−Fig. 4A). Moreover, a taxiing (Fig. 4C) is not avoided for quicker gliding. The flying fish is not in a tearing hurry to escape−a surprise. But, then the sailfish does not chase the prey after the topology is fully bifurcated (Fig. 1b). The flying fish motion becomes even more friction limited swimming up breaching the interface at a shallow angle./p> We > 800\) in Fig. 4B vs. \(200< We < 600\) in Fig. 4C) is definitely different (video time stamps in "Methods" section), which indicates the presence of multistability in the hydrodynamics, tail rigidiy EI and the olivo-cerebellar control of the flying fish tail oscillation18. The inertia force and disorganization are reduced while taxiing on the ocean surface than when emerging because the distance from the sailfish threat has increased. The multistability is not random, but chaotically controlled, depending on the threat perception./p>110\) Hz. The bones between the bladder and ears, the mechanical links, vibrate. The wave interference may cause a sudden bending of the polarized cilia in the fish ear, which are used for direction sensing, disorienting the flying fish36. Theoretically, the resonant frequency of a fish increases with depth. Models of reflection of resonant frequencies from fish show that for a given frequency, the target strength is greater for the side aspect than for the dorsal aspect. Further, the target strength increases with the size of the fish. That is, the ability of the sailfish in reflecting sound is higher than in an individual flying fish, but equals to the school. In shallow waters, the propagation loss due to fish populations is complex. The sailfish-flying fish interaction under consideration occurred in the early morning. It is unknown if the propagation loss increased or decreased when the acoustic predation occurred. However, in some populations there can be a drop during the early morning. The sailfish acoustic predation utilizes body concave mirroring, echo wave interference and precise spatial localization at the prey fish ear drums. The energy expense is lower than man-made noise. The dB level along the black lines in Fig. 3 may only be \(>85\) dB as in humans threshold, but applied suddenly to startle (the bladder does not burst out of the mouth)1. The pile driving guideline of 150 dB re 1 \(\upmu\)Pa (rms) amplitude is irrelevant41. Underwater ambient SPL is as follows. In air, the corn popping mean SPL is 85 dBA18,51. In a controlled 200–300 Hz impulse of amplitude 2 psims for 1 ms in a 9.1 m deep tank the peak SPL is 185.5 dB (re 20 \(\upmu\)Pa) in-water, equivalent to 5.44 psi, causes no human hearing loss at 1006 m away52. The ambient SPL is \(\le\) 70 dB, the quietest sea conditions at dawn. The ocean ambient SPL level near the free surface is \(\approx\)80 dB (Fig. 1)18 . In the UK, the ambient ocean noise is higher, \(\ge\) the survey vessel. It is painful to humans when the intensity is \(\ge\) 85 dB. The noise is unbearable at 120 dB (= disco noise; \(\ge\) trawler noise)15,51,53,54,55. Because the noise is not prolonged, the high dB levels along the bold black lines in Fig. 3a is only what will intensify the SPL in the ears of the flying fish. For the same reason, the energy input in the present example of predation should be lower than more commonly studied man-made noise13,15,36,55. Masking is the hearing threshold above the near free surface oceanic noise which is 70 dB at dawn. Median ocean noise levels ranged in UK measurements from 81.5 to 95.5 dB re 1 \(\upmu\)Pa for 0.33 octave bands from 63 to 500 Hz53, but deeper in the ocean away from the UK shores, the noise level is closer to \(\le\) 70 dB, also \(\approx\) 70 dB re 1 \(\upmu\)Pa due to baleen whales, toothed whales, bottlenose dolphins and killer whales55./p> 0\), the boundary layer has thinning effect; \(\partial \Gamma /\partial x > 0\); the streamlines near winglet-body junction are converging, that is, this is a line sink flow, if \(s, \delta\) are the surface distance and the boundary layer thickness, \(\partial \delta /\partial s < 0\). The rear half of the body and the sail has these opposed properties. The axial pressure gradient is \(\partial p/\partial x > 0\), that is adverse and decelerating; the boundary-layer is laminar, thick and prone to separation; the body axial curvature is concave on the pressure side and destabilizing and convex on the suction side and stabilizing; the axial gradient of the elliptic body cross sectional area A is \(\partial A/\partial x < 0\), the boat tail boundary-layer has thickening effect; \(\partial \Gamma /\partial x < 0\); the streamlines near the winglet-body junction are diverging, that is, this is a line source flow and \(\partial \delta /\partial s > 0\). Inflection in streamline is minimized. The streamlines follow the axial direction closely and not the spanwise direction. Circulation \(\Gamma\) is load whose moment about the center of pressure determines the roll, pitch and yaw control force and moment laws. The circulation is front-loaded (Fig. 2c). The sail is multiply split in the ’boat tail’ where \(\Gamma\) is declining./p> We > 600\), which reproduces the lower We of the flying fish tail strike on ocean surface during taxiing after emergence indicating multistability of We. The unstable We drops as the sailfish threat recedes./p>
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