Limitations on locomotor performance in squid

An empirical equation relating O2 consumption (power input) to pressure production during jet-propelled swimming in the squid (Illex illecebrosus) is compared with hydrodynamic estimates of the pressure-flow power output also calculated from pressure data. Resulting estimates of efficiency and stress indicate that the circularly arranged obliquely striated muscles in squid mantle produce maximum tensions about half those of vertebrate cross-striated muscle, that "anaerobic" fibers contribute to aerobic swimming, and that peak pressure production requires an instantaneous power output higher than is thought possible for muscle. Radial muscles probably contribute additional energy via elastic storage in circular collagen fibers. Although higher rates of aerobic power consumption are only found in terrestrial animals at much higher temperatures, the constraint on squid performance is circulation, not ventilation. Anaerobic power consumption is also among the highest ever measured, but the division of labor between "aerobic" and "anaerobic" fibers suggests a system designed to optimize the limited capacity of the circulation

The forces acting on swimming squid

1. Analysis of cine films and intramantle pressure records for squid Loligo opalescens Berry swimming in a tunnel respirometer provided estimates of all the forces acting in the horizontal and vertical planes for swimming speeds from 0.1 to 0.5 ms−1. 2. Different speeds used different gaits; fin thrust was only important below 0.2 ms−1, ‘anaerobic’ circular muscles were recruited only at supracritical speeds, and hyperinflation caused by contraction of the radial muscle was not seen in steady swimming. 3. The extent, rate and frequency of contraction of the obliquely striated circular muscles varied little with speed, and jet thrust was matched to speed primarily by active pressure control through adjustments in the size of the funnel orifice. 4. Hydrodynamic lift production to compensate for negative buoyancy during enforced horizontal swimming in the tunnel required 30–90% of the total force over the speed range studied and appears less efficient than direct use of jet thrust. This suggests a new rationale for ‘climb-and-glide’ swimming which reduces previous estimates of the gross cost of transport for squid under natural conditions by at least 35%, with no loss of speed. 5. The cost of accelerating water into the mantle of a squid moving at high speed appears to have been underestimated in previous studies. A simulation of a series of escape jets predicts a maximum speed of 8 body lengths s−1 (1.4ms−1), reached after only two jets, because of the high deceleration during refilling

Properties of IIlex illecebrosus Egg Masses Potentially Influencing larval Oceanographic Distribution

Visual observations and video-tape records of the spawning of captive IIlex illecebrosus show that this species can produce gelatinous egg masses 50 cm or larger in diameter while swimming in open water. Measurements of the density of the eggs and the changes in water density which are necessary to lift egg masses indicate that the masses have densities about 0.005% greater than the water used to make the gel, whereas the eggs are more than 5% denser than typical seawater. The gel thus appears to function as a buoyancy mechanism which prevents eggs from sinking. Measurements of rates of temperature equilibration between egg masses and the surrounding water indicate that complete density equilibration requires many days under most conditions. If spawning occurs pelagically, common oceanographic situations where density increases with depth, due either to decreasing temperature (e.g. North Atlantic Central Water) or increasing salinity (e.g. the Gulf Stream), could allow the egg masses to be suspended in the mesopelagic zone. Such a mechanism, which could retain pelagically-spawned eggs of IIlex and other oegopsids, particularly ommastrephids, in a zone where temperatures are adequate to allow embryonic development, helps to explain why there are so few records of ommastrephid eggs in nature

Respiration and Swimming Performance of Short-finned Squid (Illex illecebrosus)

Intramantle pressure transducers allowed the monitoring of respiration and swimming performance of cannulated and freeswimming squid (IIlex illecebrosus). Jet pressure and oxygen consumption of individual squid were measured simultaneously in a tunnel respirometer at various swimming speeds. The rate of oxygen consumption increased logarithmically with swimming speed up to critical speeds of 70-90 cm/sec (about two body lengths per second). Oxygen consumption values for a400 g squid at 15° C were the highest that have been recorded for marine poikilotherms at this size and temperature: 313 ml/kg/hr for standard metabolism and 1,047 ml/kg/hr for active metabolism at maximum speed. A 40-cm squid (total length) uses about six times more energy per unit distance than a sockeye salmon of similar length at 15° C. The rate of oxygen consumption increased linearly with average jet pressure generated in the mantle cavity and the relationship was highly correlated for speeds of 0.15 0.80cm/sec. The results from telemetric monitoring of jet pressure generated by a free-swimming squid in a 15-m pool and the oxygen-pressure relationship show great promise for studying the activity and bioenergetics of squid in nature

The Respiratory Metalbolism and Swimming Performance of the Squid, Illex illecebrosus

Pressure transducers, measuring intra-mantle pressure allowed monitoring of total P-V work associated with swimming and respiration in cannulated and free-swimming squid (Illex illecebrosus)

Evaluation of Male Reproductive Features as Maturity Indices for Short-finned Squid (IIlex illecebrosus)

Various aspects of maturation in male IIlex illecebrosus were examined in an attempt to find evidence for a more realistic maturity scale than that currently in use. Simple indices, based on morphology of the hectocotylized arm, failed to provide satisfactory relationships, but the observed variation in hectocotylus measurements may provide useful insights into the population ecology of the species. The earlier maturation of males than females and the observed premature release of spermatophores cast doubt on the usefulness of spermatophore counts as the basis for developing a reliable maturity scale for male I. illecebrosus. Preliminary examination of spermatophores and spermatozoa with lighl and scanning electron microscopes have so far failed to reveal any difference between material from early and late "mature" males

The Locomotion and Energetics of Hatchling Squid, Illex illecebrosus

Although never seen in nature, gelatinous egg masses up to 1 m in diameter containing 10,000 to 100,000 eggs have been produced in captivity by female Illex illecebrosus swimming in mid-water in the 15 m diameter Aquatron pool. When incubated at temperatures between 13 and 26°C these masses produced viable hatchlings whose behaviours were observed and recorded. The hatchlings sink at 5 mm s-1, swim vertically at speeds up to 26 mm s-1, hover and avoid both the surface and the bottom. Metabolie rates estimated from rates of yolk utilization and calculated values for swimming costs were used to predict " critical periods'' or survival times for unfed hatchlings in various temperature and activity regimes. Theseare discussed in relation to the hypothesized role of the Gulf Stream in distribution of the hatchlings of this commercially important but still poorly understood squid species. Potential benefits from vertical migration are suggested and a comparison with Loligo opalescens made

Validation and Application of an Ageing Technique for Short-finned Squid (IIlex illecebrosus)

A technique has been developed which simplifies the ageing of short-finned squid (IIlex illecebrosus) through microstructural examination of the statotiths. The spatial pattern of growth increments was studied with the use of light and scanning electron microscopy. Daily growth increments in statoliths were validated by employing chemical "time" markers (strontium and tetracycline) and laboratory-reared animals of known age. Increment formation continued through periods of food deprivation and minimal temperature fluctuations