Post-recruit growth of the Patagonian squid Loligo gahi (d'Orbigny)

Samples of Loligo gahi (D'Orbigny) were collected from commercial fishing vessels in the Falkland Islands Interim Conservation and Management Zone (FICZ) between March and October 1987, and from the R/V Wieczno during a survey in August 1988. Samples were divided according to the two fishing seasons (February to July; August to October) and the samples from the scientific survey were pooled with those of the second commercial fishing season. L. gahi were aged using putative daily growth increments within the statoliths. There was indirect evidence that growth increments in the statolith were laid down at the rate of one per day. The maximum life span of the males was a little over 1 year and was approximately 1 year in females. Back-calculation ofthe month of hatching reveals the presence of two spawning groups within the FICZ population which give rise to the two fishing seasons. Growth rates were calculated for both sexes from both seasons. There was considerable individual variation in growth rate in squid from both seasons and there was more scatter in the data from first season samples taken from the commercial fishery alone. Log-linear growth models give the best fit to the data combining the fishery and scientific survey samples from the second season. Very low or apparent negative growth exhibited by squid sampled during the first season may be due to bias because the commercial fishery samples a narrow depth range. Migration of schools of squid of similar size through the narrow depth range in which the fishery operates probably yields samples that are size selected. Care should be taken in modelling squid growth where migratory effects may bias the data