Is commercial harvesting of spawning aggregations sustainable?—The reproductive status of the squid Loligo bleekeri

As marine species that are harvested during spawning aggregation tend to be overfished, sufficient “reproductive escapement” is required to manage such overexploited populations. Because the reproductive value of short-lived organisms changes towards the end of their life span, information is required not only on the total amount harvested but also on the characteristics of the individuals caught. As spawning aggregations of the squid Loligo bleekeri are targeted by the commercial fishing industry, we analysed biological data of harvested squid to identify indicators of reproductive status. Females of this species had several sperm resources associated with alternative mating behaviours: in seminal receptacle near the mouth, around the seminal receptacle, and inside the opening of the oviduct, associated with alternative mating behaviours. However, only the mass of sperm on the oviduct was significantly related to oviduct weight (including ovulated eggs): oviduct weight was less when sperm mass was attached to the oviduct than when it was not, indicating that the female had paired with a consort male and had spawned before she was caught. Using this indicator to confirm a recent spawning event, we determined that only 22.9% of females spawned before they were harvested. Our results show that the commercial fishing industry mainly harvests squid that have not spawned and have high reproductive values. Further information on the movement and reproductive behaviour of squid is required to develop a management strategy for the coastal fishing industry that ensure sufficient reproductive escapement.