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First published online November 5, 2004
Journal of Experimental Biology 207, 4195-4203 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01276

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Allometry measurements from in situ video recordings can determine the size and swimming speeds of juvenile and adult squid Loligo opalescens (Cephalopoda: Myopsida)

Louis D. Zeidberg

Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039-9644, USA

View larger version (19K): [in a new window]   Fig. 1. Dorsal view of Loligo opalescens (40 mm ML), ventral view of 12 mm ML inset to left. Dimensions of each body part measured for allometry analysis: dorsal mantle length (ML), fin length (FL), funnel aperture (FA), fourth arm length (AL), tentacle length (TL), diameter of the eye (ED), fin width (FW), mantle width (MW) and head width (HW).

View larger version (15K): [in a new window]   Fig. 2. Date and dorsal mantle length ML of each Loligo opalescens squid captured with the otter trawl in Santa Monica Bay from March 1998 to February 2002. The missing size range (55–85 mm ML) in all 5 years is shaded grey. One to two cohorts exist in each year; fishing for spawning adults occurs near this area from October to May.

View larger version (14K): [in a new window]   Fig. 3. Loligo opalescens chromatic displays observed in juveniles but not in adults. (A) Double chevron; (B) white stripe.

View larger version (21K): [in a new window]   Fig. 4. Jet-and-sink behavior for a squid with an estimated mantle length of 18.55 mm for a 3.5 s video sequence [movie 3, jet_sink; available at supplementary material; video footage ©2000 MBARI]. (A) The vertical position of the mantle tip within the frame (y coordinate of pixel). (B) The velocity of the squid in each frame. (C) Mantle diameter (mm). In B and C, pixels are converted to m s–1 and mm via the allometry regression of Fig. 7A. Increases in velocity and vertical position corresponds to mantle contractions (arrows), with the greatest increase in vertical position and velocity, and the smallest mantle diameter, at time 1.4 s.

View larger version (16K): [in a new window]   Fig. 5. The fins of Loligo opalescens are triangular; surface area (SA) of both fins=2(0.5 x fin width x fin length at the base). The surface area of both fins provides lift that increases exponentially with the dorsal mantle length ML of the developing squid. y=2.361x–2.214; r2=0.957, P<0.0001, N=136. The slope of the linear regression line is 2.361, demonstrating positive allometry, i.e. slope is significantly different than 2.

View larger version (19K): [in a new window]   Fig. 6. Log diameter of funnel aperture (FA) versus log dorsal mantle length (ML). y=–1.053+0.803x; r2=0.758, F-test P<0.0001. Because the coefficient of the logML in the equation is <1, there is negative allometry of the funnel aperture with development; it is largest relative to the ML in the smallest squids.

View larger version (22K): [in a new window]   Fig. 7. Loligo opalescens. (A) Linear regression of dorsal mantle length (ML) from a ratio of ML upon eye diameter (ED). y=–85.285+18.205x; r2=0.857, P<0.001, N=157. (B) Total length, the sum of the dorsal mantle length, the head length and the fourth arm length, can be estimated from the mantle length by the linear regression y=–4.0244+1.6227x; r2=0.978, P<0.001, N=157.