Understanding the patterns of recruitment and migration in a commercial loliginid squid population (Doryteuthis gahi) using statolith microchemistry

The Patagonian long-finned squid has a complex population structure, an annual life cycle, a weak stock-recruitment relationship and a high inter-annual variability in abundance, making stock assessment difficult. The effects of extrinsic factors such as temperature can often have a profound effect on stock size, distribution, timing of recruitment and size-at-maturity. Squid to the north and south of the ‘Loligo box’ were initially considered as separate cohorts due to significant differences in size and timing of recruitment. With no genetic differences evident, it has been suggested that food availability or temperature are responsible for this significant disparity in size. It may be that these squid are derived from different shallow-water spawning sites and that environmental conditions in one spawning area have resulted in accelerated growth during early life when growth is exponential. Understanding why these two groups are different is important for the definition of management units. At present, modified DeLury depletion models are calculated separately for north and south sub-areas of the ‘Loligo box’, dissecting the fishing zone into two at latitude 52°S.

The best way to determine why there are differences between these two groups of squid is to compare their migratory routes. Statoliths are calcified structures functioning in a similar way to our inner ear. Each day material is laid down around the statolith, resulting in daily growth rings that can be counted to obtain the total post-hatching age in days. When material is deposited around the statolith, elements are also incorporated into the statolith microstructure. Daily uptakes of certain elements are thought to reflect the environmental conditions in the squid’s surroundings at the time of incorporation. Statoliths can therefore be considered as ‘black boxes’, recording the conditions an individual has experienced throughout its lifetime, with daily precision. This study aims to quantify trace element concentrations using laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS). Individual ablation craters, ablated in a transect from the nucleus to the rostrum edge, can then be aged to produce high-resolution elemental chronologies. These can be used to compare temporal variation between squid from the north and south of the ‘loligo box’.

       Scientists

          Alexander Arkhipkin

          Jessica Jones

This research aligns with objectives #3 and #6. Specifically in objective #3 it states that the biology, ecology and life cycles of the main commercial species will be investigated with a targeted outcome of revealing population structure by fine chemical methods which are aligned with the aims of this research.