Allometry measurements fromin situvideo recordings can determine the size and swimming speeds of juvenile and adult squidLoligo opalescens(Cephalopoda: Myopsida)

Abstract

Juvenile and adult Loligo opalescens Berry were video taped in Monterey Bay with the remotely operated vehicle (ROV) Ventana, captured with an otter trawl in Santa Monica Bay, California, and adults were taken from the Monterey Bay fishery. Behavioral observations were made over a 13 h period of video sequences. Allometry measurements were made on 157 squids ranging in size from 12 to 151 mm mantle length (ML). In addition to ML we measured the morphometric characters of fin length (FL), fin width (FW), mantle width (MW), eye diameter (ED), head width (HW), funnel aperture diameter (FA), fourth arm length (AL) and tentacle length (TL). Loligo opalescens changes shape with ontogeny due to negative allometric growth of ED, HW, TL, MW, FA and positive allometric growth of AL, FL and fin area. The allometry measurements were used to determine the size of juvenile squids video-taped in open water. A linear regression can predict dorsal ML in mm from a dimensionless ratio of ML upon ED (r2=0.857, P<0.001). Sizes and velocities of video-taped animals were estimated from 26 video sequences ranging from <1.0 to 8 s. The average velocity for squids ranging from 12-116 mm ML was 0.21 m s(-1) and the maximum velocity was 1.60 m s(-1) (116 mm ML). Allometric measurements can provide scale for 2-dimensional images in order to estimate size, velocity and age of animals.