Despite many previous studies on the life history of the squid Loligo forbesi, the roles of internal and external factors in growth and maturation have not
previously been investigated in detail. The present study takes advantage of
the availability of statistical techniques, namely generalised additive
models, which permit simultaneous evaluation of the effects of multiple
explanatory variables while avoiding the need to assume linear
relationships. This has the further advantage that the size of body parts
can be entered directly into the models rather than expressed as indices
(e.g., gonado-somatic index). The present analysis is based on measurements
taken from monthly market samples during 1989-1991 and aims to infer
patterns of reproductive and somatic investment though comparison of large
numbers of individuals at different (post recruit) life-cycle stages.
Results indicate that, once the effect of body size is removed, gonad weight
in both sexes is affected by month and digestive gland weight, consistent
with seasonal triggering of maturation, and with energy for gonad growth
being derived from food. There is also evidence of a negative relationship
between somatic and ovary growth in females, possibly indicating
remobilisation of somatic tissue to grow the ovary. In males, relationships
between variables tended to have more complex forms, probably related to the
existence of two or more growth patterns leading to different sizes at
maturity. As found in previous work, maturation begins around 1-2 months
earlier in males, suggesting that sensitivity to external triggers is
controlled by a sex-dependent internal factor.