Reviews in Fish Biology and Fisheries

, Volume 17, Issue 2–3, pp 207–221 | Cite as

Effects of commercial fishing on the population structure of spawning southern calamary (Sepioteuthis australis)

Original Paper


This study explored population dynamics of Sepioteuthis australis on a fine temporal scale before, during, and after a 3-month commercial fishing closure on the summer inshore spawning grounds of Great Oyster Bay, Tasmania, Australia. An abrupt change in male size (mantle length) and population sex ratio after the re-opening of the commercial fishery suggests that fishing alters the population structure on the spawning beds from a ‘natural’ structure which is highly biased towards males, to a more even ratio of males to females. Although jigs are taking a representative sample of the squid population using the spawning beds at any one time, the fishery is apparently still effectively selective for males, potentially as a function of differential spawning movements of the two sexes. Increased fishing pressure over the past 5 years had been correlated with a change towards a highly male-biased sex ratio on the spawning beds; however the current study suggests that increased fishing pressure in recent years may not have reduced the proportion of females. Instead, the inter-annual change in sex ratio may reflect changes in the degree of protection from fishing, with progressively longer closures allowing time for more males to accumulate on the beds and therefore, for the proportion of males to increase (as opposed to a decrease of females). As fishing is selective for males, fishing throughout the spawning season could potentially modify the process of sexual selection and the mating behaviors of the individuals within the spawning population, highlighting the need for closures over this crucial period. Additionally, examinations and comparisons of squid population structure need to be interpreted in light of fishing pressure and broader movement patterns.


Sex ratio Commercial closure Fishing pressure Population structure Squid Spawning aggregation 



Grateful acknowledgement is made to Dr George Jackson (IASOS, UTAS) whose valuable suggestions greatly improved the manuscript. The authors thank staff at Tasmanian Aquaculture and Fisheries Institute Marine Research Laboratories, particularly Sean Tracey for assistance with data collection and analysis; and Dr Natalie Moltschaniwskyj and Graeme Ewing for their enthusiasm and support with field operations. We are indebted to all the commercial fishers who volunteered their assistance in the collection of specimens, in particular to Ian and Barbara Barrett. This research was supported by ARC (grant number LP0347556), DPIWE, the Tasmanian Recreational Fishery Trust, and the Tasmanian Commercial Calamary Fishers.


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  1. 1.Institute of Antarctic and Southern Ocean StudiesUniversity of TasmaniaTasmania, HobartAustralia
  2. 2.Tasmanian Aquaculture and Fisheries InstituteUniversity of TasmaniaTasmania, HobartAustralia

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