Swimming mechanics and behavior of the shallow-water brief squid Lolliguncula brevis
Ian K. Bartol1,*,
Mark R. Patterson2 and
Roger Mann2
1 Department of Organismic Biology, Ecology, and Evolution, 621 Charles E. Young Drive South, University of California, Los Angeles, CA 90095-1606, USA and
2 School of Marine Science, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062-1346, USA
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Fig. 1. Mantle (Man), arm and funnel (Fun) angles of attack for Lolliguncula brevis swimming at various speeds. Results for squid swimming in a tail-first orientation are displayed in A, C, E and G, whereas those for squid swimming in an arms-first orientation are shown in B, D, F and H. Data from four size classes are included in the figure. Squid 1.0–2.9 cm in dorsal mantle length (DML) are depicted in A and B, squid 3.0–4.9 cm in DML are depicted in C and D, squid 5.0–6.9 cm in DML are depicted in E and F and squid 7.0–8.9 cm in DML are depicted in G and H. When a significant linear relationship between angle of attack and speed was detected, regression lines were plotted, and regression equations, r2 values and P values were included to the right of graphs. When significant relationships were not detected, the data points were simply connected with lines and no regression information was included. All error bars represent ± 1 S.E.M. (N=3).
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Fig. 2. Video frames of a 4.4 cm dorsal mantle length Lolliguncula brevis swimming tail-first at 3 and 24 cm s–1 (upper frames) and arms-first at 3 and 12 cm s–1 (lower frames). Mantle and arm angles of attack decrease with increasing swimming speed for both swimming orientations. Angle of attack differences are less pronounced for arms-first swimming because a more restricted velocity range is considered (L. brevis only swims arms-first at low to intermediate speeds). Note that the trailing body section, whether the arms during tail-first swimming or the mantle during arms-first swimming, is often positioned at higher angles of attack than the leading body section.
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Fig. 3. Arm and mantle angles of attack, vertical fin motion (relative to the point where the fin connects to the mantle), mantle diameter, changes in linear velocity (relative to free-stream flow) and acceleration for a 4.4 cm dorsal mantle length (DML) Lolliguncula brevis swimming tail-first at 6 cm s–1 against a current in a flume. In total, 60 frames were analyzed to generate the traces.
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Fig. 4. Mantle contractions frequency and fin-beat frequency for Lolliguncula brevis swimming against a steady current in a flume over a range of speeds in both tail-first and arms-first orientations. Data from four size classes are depicted: 1.0–2.9 cm, 3.0–4.9 cm, 5.0–6.9 cm and 7.0–8.9 cm dorsal mantle length (DML). When significant linear relationships were detected, regression lines were plotted, and regression equations, r2 values and P values were included underneath graphs. All error bars represent ±1 S.E.M. (N=3).
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Fig. 5. Mantle diameter, funnel diameter and vertical fin motion (relative to the point where the fin connects to the mantle) of a Lolliguncula brevis (7.3 cm in dorsal mantle length, DML) swimming (A) tail-first and (B) arms-first at 9 cm s–1 against a steady flow in a flume. For each swimming orientation, 60 frames were analyzed to generate the traces.
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Fig. 6. Mantle expansion and vertical fin motion (absolute vertical distance between maximum upstroke and downstroke) plotted over a range of swimming speeds for Lolliguncula brevis swimming in both tail-first and arms-first orientations. Data from four size classes are depicted: 1.0–2.9 cm, 3.0–4.9 cm, 5.0–6.9 cm and 7.0–8.9 cm dorsal mantle length (DML). When significant linear relationships were detected, regression lines were plotted, and regression equations, r2 values and P values were included underneath graphs. All error bars represent ± 1 S.E.M. (N=3).
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Fig. 7. Polar diagrams of drag (CD) and lift (CL) coefficients calculated from squid models (with fins) oriented tail-first and arms-first relative to the free-stream flow. The various symbols, which are described in the figure, represent the angles of attack of the mantle. Degree markings within the figures represent angles of attack of the arms. Only mantle/arm angle combinations observed during swimming trials of brief squid are represented. At each mantle angle, the arm angle providing the highest lift-to-drag ratio is denoted in bold type and the ratio is provided in parentheses next to the angle.
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Fig. 8. Added mass coefficients (CA) for Lolliguncula brevis swimming in tail-first and arms-first orientations at various angles of attack. Mantle angles (degrees) are plotted on the x-axes and arm angles are denoted using symbols. Only mantle/arm angle combinations observed during swimming trials of L. brevis are represented. Polynomial regressions were performed when more than four data points were available, and these results are displayed next to the graphs.
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Fig. 9. Vertical and horizontal forces acting on a 4.4 cm Lolliguncula brevis swimming tail-first at 6 cm s–1. In the vertical forces graph, negative values represent forces acting towards the flume floor (i.e. buoyant weight), whereas in the horizontal forces graph negative values represent forces acting in the direction of free-stream flow (e.g. drag). Since there was some net altitude change over the 2 s video sequence, the height of L. brevis above the flume floor is displayed next to the vertical forces graph. There was no net horizontal change over the video sequence. Fin thrust contributions are not included in the figure.
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Fig. 10. Vertical and horizontal forces acting on a 4.4 cm Lolliguncula brevis swimming tail-first at 15 cm s–1. In the vertical forces graph, negative values represent forces acting towards the flume floor (i.e. buoyant weight), whereas in the horizontal forces graph negative values represent forces acting in the direction of the free-stream flow (e.g. drag). Since there was some net altitude change over the 2 s video sequence, the height of L. brevis above the flume floor is displayed next to the vertical forces graph. There was no net horizontal change over the video sequence. Fin thrust contributions are not included in the figure.
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© The Company of Biologists Ltd 2001
