The early life history of the short-finned squid, Illex illecebrosus (Cephalopoda: Ommastrephidae), as reconstructed from the gladius structure.
Date
1994
Authors
Perez, Jose Angel Alverez.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
The annual populations of the short-finned squid, Illex illecebrosus, are spawned throughout the year south of Cape Hatteras (35$\sp\circ$S), and recruit in different places along the eastern coast of North America. The early life, a critical period for survival and recruitment, is spent in the meandering Gulf Stream/Slope Water front where offspring increase a hundred fold in length, change from a planktonic to a nektonic adult lifestyle and experience a decrease in environmental temperature of as much as 20$\sp\circ$C. Growth during this phase was reconstructed from periodic growth marks deposited on the gladius. The main objectives were to investigate the variability of juvenile growth in relation to life history events, oceanographic structure, geographic distribution and seasonal and interannual fluctuations of the environment. The juvenile/offshore growth phase was exponential. A change to linear growth occurred after the adult/onshore life-style was attained (GL $>$ 80-90 mm). During the juvenile life, a major change in body shape and a separation between two size-specific growth phases was associated with the transition from the macroplanktonic to micronektonic habitats (30-40 mm GL). Sexual growth differences occurred among subadults (GL $>$ 120 mm) prior to the onset of maturation. Juvenile growth conditions improved as squids moved from the Gulf Stream to colder and food-enriched Slope Waters. In these conditions metabolic costs decreased and more food became available. In the Slope Water off the Scotian Shelf, growth was enhanced shoreward and particularly in proximity to the shelf/slope front. The access to and retention of individuals in these favourable areas were related to processes of transport in the Gulf Stream and Slope Water. Growth conditions of juveniles were enhanced during spring probably as a consequence of the seasonal peak of biological production off Nova Scotia. Interannual variations of the environment here were not consistently detected in the gladius growth variability suggesting that patchy production plays a role in recruitment regulation. Southwards, near the spawning grounds, juvenile growth of Illex sp. was much slower contradicting laboratory studies indicating faster growth in tropical cephalopods due to positive effects of high temperatures. The results of this study emphasized the potential of the gladius technique for squid growth history reconstruction, and provided empirical evidence for hypothesized ecological processes acting during early life of Illex and other pelagic squids.
Thesis (Ph.D.)--Dalhousie University (Canada), 1994.
Thesis (Ph.D.)--Dalhousie University (Canada), 1994.
Keywords
Biology, Ecology., Biology, Oceanography., Biology, Zoology., Agriculture, Fisheries and Aquaculture.