DAILY NET EMIGRATION FROM A SPAWNING CONCENTRATION OF CHOKKA SQUID (LOLIGO-VULGARIS REYNAUDII DORBIGNY, 1845) IN KROMME BAY, SOUTH-AFRICA

The net emigration from a spawning concentration of the loliginid squi d, Loligo vulgaris reynaudii d'Orbigny, 1845, was investigated quantit atively using a combination of tagging and hydroacoustic techniques, m idwater trawling, purse seining and SCUBA diving. Aquarium experiments were used to supply additional information on tag loss and mortality from tagging. The number of squid in a concentration containing T lagg ed individuals was assessed hydroacoustically and then c squid were ca ught by means of a midwater trawl or purse seine. It was assumed that the t(n) tagged squids in these catches were the result of natural mor tality, tagging mortality and net stability of the concentration (the result of emigration and immigration) n days after tagging. The averag e net emigration was then calculated to be 0.2 per day for 7.5 days of observations. This result is a first attempt to solve the so-called ' 'Hilborn's problem'', i.e. the problem of how to measure the aggregati on dynamics of nektonic organisms in the sea (instead of modelling). ( C) 1998 International Council for the Exploration of the Sea.