This program has collected data on the development and performance of the fishery, as well as biological data relevant to assessment of the impact of fishing on the exploited population.

The development and operation of the fishing and processing sectors of the fishery are described as are the development and implementation of jack mackerel management in Tasmania.

Biological data presented for jack mackerel include size structure of catch, length-weight relationships, catch age structure and reproductive development Estimates for the Von Bertalanffy parameters L∞, K and t0 are resented. Problems encountered estimating mortality rates are discussed and preliminary estimates given.

The bycatch species redbait, Emmelichthys nitidus, and blue mackerel, Scomber australasicus, make up approximately 5% of the landed catch. Some biological information on these two species is also presented.

The discovery of several adult Peruvian jack mackerel Trachurus murphyi raises questions as to the importance of this species, if any, in the fishery. These samples constitute the most westerly reports of this species distribution.

The importance of inter-annual variability in this fishery is discussed with reference to examples in the short history of the fishery.

The principal aims of this study were to evaluate whether the locally­ produced Whayman-Holdsworth trap provides an effective method for minimising Asterias amurensis infestations on shellfish farms, and to objectively assess the value of seastar traps when used in commercial applications.

In an initial fishdown experiment, the efficiency of seastar traps was assessed at sites with low/ moderate and high densities of seastars. Intensive trapping effort directed at the low site failed to control the seastar population within the trap field, even though 1160% of the original population held been removed during the 51 day period of study. Furthermore, analysis of trapping and length-frequency data showed that catch rate did not decline towards the centre of the array, and that the mean size of seastars collected from within the low density array increased. A. amurensis clearly immigrated rapidly and persistently into the trapping array, precluding attempts to control seastar numbers within the trap field.

The proportion of the initial array population removed by trapping at the high density site during the initial fishdown was approximately 53%, considerably lower than that recorded for the low density site. However, a significant decrease in seastar density occurred over the period of fishdown at this site. Analysis of catch data showed that catch rate did not decline towards the centre of the array, and that seastars predominantly immigrated from a north easterly direction. Trap collected length­frequency distributions showed a decline in mean size, indicating the initial stages of trapping impact on the population. Immigration at this site therefore appears to have been considerably less than at the low density site.

Although no strong soak time related catch trends were apparent, traps were generally saturated after 24 to 48 hours. Few animals were caught as bycatch during the fishdown, with the five main bycatch species consisting of three crabs, an introduced seastar and an ascidian.

Following the initial experiments an attempt was made to counteract rapid immigration rates by pulling and resetting traps over several consecutive days (sequential 24 hour soak times), thereby maximising the numbers of animals removed from each trapping array. Seastar densities in both the high and low density arrays did not change significantly over time: however, a reduction in mean size of seastars following intensive trapping occurred, presumably because the mean size of animals removed in traps was greater than that of immigrant individuals.

The scientific literature has generally accepted that abalone populations are characterised by low levels of settlement and recruitment (Tegner in press), that mortality is relatively low (Doi et al. 1977; Beinssen and Powell 1979; Sainsbury 1982; Shepherd et al. 1982; Fournier and Breen 1983) and uniform throughout life (Shepherd et al. 1982), and correspondingly that the natural productivity of these stocks is low (Tegner in press). In some studies it has been noted that one or more year classes are apparently missing (Forster et al. 1982; Sainsbury 1982) and this has led to the conclusion that abalone recruitment is relatively sporadic and irregular. It has been generally assumed that larval dispersal is relatively widespread (20-50km; Tegner & Butler 1985). No relationship had been observed between the abundance of breeding stock and the abundance of recruitment. On the basis of these observations and laboratory studies, together with genera lly held assumptions, it has been accepted that oceanographic and other environmental factors would be the major determinants of settlement and recruitment density (Fedorenko & Spout 1982; Tegner in press).

It was these widely held views which led to the original rationale for this project, which was to develop an index of settlement or recruitment abundance which could be used to predict broad scale trends in the future abundance of the fishable stock.

In addition, there was also no scientifically proven method of ageing abalone prior to this study, and it was generally accepted that the Australian species of abalone could not be aged. The FIRTA-funded review of Ward (1986) found that this was a major impediment of research into and assessment of abalone stocks in Australia.