10 research outputs found
Vertical migration for horizontal transport while avoiding predators: I. A tidal/diel model
Spatial organization of schools of the SquidIllex illecebrosus
Illex illecebrosus squid appear to have a speciesâtypical and internally organized spatial arrangement of their groups. Squid maintained an average angle of 25° with respect to their nearest neighbour, and mostly had angular deviations between 5° and 20°. They maintained distances to nearest, second and third neighbours in a ratio of 1:1.5:2. The distances were strongly affected by group size (4, 20, or 38), with larger groups maintaining closer distances. Interindividual distances were not affected by two variables, dayânight and presence of a current in the large pool in which they were kept. The similarity of this organization to that of fish schools is discussed
Predatory strategies of squid (Illex illecebrosus) attacking small and large fish
Feeding strategies are different when adult Illex illecebrosus prey on large (trout) and small fish (mummichogs). Attacks on trout are characterized by (1) rotation as the squid changes from tailâfirst to headâfirst swimming; (2) an approach phase involving rapid acceleration towards the prey; (3) a tracking phase where the squid slowly follows the trout; (4) the capture phase. No tracking phase is present in attacks on mummichogs.
These differences in feeding strategies can be explained by performance limitations of the squid jet propulsion system. Headâfirst acceleration rates in Illex are low (max. = 12 m âą sâ2) and maneuverability poor compared to fish. A large fish could thus outâperform an attacking squid if forced into evasive action. The tracking phase is a type of oceanic stalking strategy designed to bring the squid into close proximity to larger fish. The behaviour is not necessary when attacking small fish due to their low swimming speeds
Costs of locomotion and vertic dynamics of cephalopods and fish
The world's oceans are threeâdimensional habitats that support high diversity and biomass. Because the densities of most of the constituents of life are greater than that of seawater, planktonic and pelagic organisms had to evolve a host of mechanisms to occupy the third dimension. Some microscopic organisms survive at the surface by dividing rapidly in vertically well mixed zones, but most organisms, small and large, have antisinking strategies and structures that maintain vertical position and mobility. All of these mechanisms have energetic costs, ranging from the âforegone metabolic benefitsâ and increased drag of storing highâenergy, lowâdensity lipids to direct energy consumption for dynamic lift. Defining the niches in the mesopelagic zone, understanding evolution, and applying such ecological concepts as optimal foraging require good estimates of these costs. The extreme cases above are reasonably well quantified in fishes, but the energetic costs of dynamic physiological mechanisms like swim bladders are not; nor are the costs of maintaining vertical position for the chief invertebrate competitors, the cephalopods. This article evaluates a matrix of buoyancy mechanisms in different circumstances, including vacuum systems and ammonium storage, based on new data on the metabolic cost of creating buoyancy in Sepia officinalis
(Table 3) Water temperature, salinity, pH and oxygen concentration in inner Frobisher Bay, Canada (July-September 2008/2009)
(Table 2) Stomach content of anadromous Arctic char (Salvelinus alpinus) sampled in inner Frobisher Bay, Canada
(Table 1) Body temperature and swimming depth of individual Arctic char (Salvelinus alpinus) tracked in intertidal and subtidal zones of inner Frobisher Bay, Canada (July-September 2008/2009)
Water chemistry, and body temperature, swimming depth and stomach contents of Arctic char (Salvelinus alpinus) in inner Frobisher Bay, Canada
The influence of salinity, temperature and prey availability on the marine migration of anadromous fishes was determined by describing the movements, habitat use and feeding behaviours of Arctic char (Salvelinus alpinus). The objectives were to determine whether char are restricted to the upper water column of the inter-/subtidal zones due to warmer temperatures. Twenty-seven char were tracked with acoustic temperature/pressure (depth) transmitters from June to September, 2008/2009, in inner Frobisher Bay, Canada. Most detections were in surface waters (0-3 m). Inter-/subtidal movements and consecutive repetitive dives (maximum 52.8 m) resulted in extreme body temperature shifts (-0.2-18.1 °C). Approximately half of intertidal and subtidal detections were between 9-13 °C and 1-3 °C, respectively. Stomach contents and deep diving suggested feeding in both inter-/subtidal zones. We suggest that char tolerate cold water at depth to capture prey in the subtidal zone, then seek warmer water to enhance feeding/digestion physiology