page 03 1. (continued) Many marine organisms use external fertilisation. This process is slightly unusual in squid as male squid produce capsules of male gametes called spermatophores, which are transferred to the females during mating. One individual female squid can lay thousands of eggs. The researchers analysed squid caught by commercial fishing boats. Figures 3a and 3b show the relationship between mantle length of male squid and the length and number of spermatophores produced in mature male squid. Figure 3 0 10 20 30 mean spermatophore length (mm) Figure 3a 0 400 800 1200 number of spermatophores Figure 3b 100 200 300 400 mantle length (mm) mantle length (mm) 500 600 100 200 300 400 500 600 The sexual maturity of individual squid was estimated using a scale of 1–3, where stage 1 was the most immature, and stage 3 the most mature. Squid in stage 3 reproduce actively. Figure 4 shows the proportion of squid at each maturity stage, caught over the course of a year by commercial fishing boats. Figure 4 0 0·1 0·2 0·3 0·4 0·5 0·6 0·7 0·8 0·9 1·0 September October November December January February March April May June July August proportion of squid at each maturity stage stage 3 stage 2 stage 1 month squid maturity stage Key [END OF SUPPLEMENTARY SHEET] page 04 [BLANK PAGE] DO NOT WRITE ON THIS PAGE