Reproductive Ecology and Operational Sex Ratio of Worm Pipefish(<i>Nerophis lumbriciformis</i>) in Irish Waters

Abstract

Worm pipefish (Osteichthyes, Syngnathidae) are common members of the ichthyofaunal commu nity on rocky shores in western Europe. However, there has been little research into their biology and ecology. Male Nerophis lumbriciormis, like all syngnathids, brood eggs to hatching on a modified area on their abdomen. Worm pipefish are engaged in reproductive activity from January to October. During this period approximately two-thirds of the mature fish are capable of reproduction. Egg-beanrng males carry a mean of 49.5 eggs (SE + 1.4) in each brood. Male reproductive potential is dependent on the resources available to female pipefish for the generation of oocytes (clutch). While there was no significant difference in the median numbers in broods or clutches, the number of oocytes in female ovaries (55.17+ 1.77 (SE)) exceeds mean brood size. It is hypothesised that female pipefish are capable of mating with more than one male. The operational sex ratio (ratio of available males to females) from April to June is heavily biased towards female pipefish. Therefore, male pipefish become a reproductively-limiting resource for females during these months.