Recent studies into the effects of seismic energy on molluscs have demonstrated a number of cumulative and sub-lethal impacts that indicated impairment of immune systems, cellular damage and adverse changes in behaviour. In scallops, cumulative exposure to seismic energy resulted in increased rates of mortality after 120 days (R Day et al. (2017)). These findings are of critical importance to the pearling industry, which relies on the harvest and husbandry of pearl oysters in coastal shelf water . Pearl oyster crops are typically 2 years duration, so long term effects will have a chronic sub-lethal effect on pearl production. In addition, as the oysters were still not fully recovered at the day 180 sampling, there is concern that the long recovery time may result in a reduction of the reproductive output for up to one year. Energetically compromised oysters will have a reduced reproductive output, and a higher proportion of male oysters, as egg production is more energy intensive.

This would have major ramifications for recruitment into the wildstock pearl oyster fishery and the pearling industry it underpins.

To these ends it became apparent that a 4th sampling round was critical in order to provide a condition data from the oyster sample set after 360 days; so that the responses of the oysters to seismic treatment may be better understood after the completion of one year – bearing in mind that at different times of the year oysters do different things.

The overarching objective of this experiment is to measure the impact of seismic surveys on wild harvested pearl oysters in a way that provides information that is useful to stakeholders in the pearl production and oil and gas industries and to the managers of these resources. The uncertainty surrounding the long-term impacts of seismic surveys on the health of pearl oysters and their pearl production capacity is the key driver of this study.

Recently, the risks resulting from not accounting for variability in productivity have become translated into potential risks associated with environmentally driven trends in recruitment, particularly the risk created by ongoing declines in recruitment (and/or growth) driven by climate-change induced trends in water temperature, weather and current patterns.

A number of southeast Australia fish stocks have failed to 'recover' following substantial reductions in catch and effort, and a number of research projects have concluded that some of these have undergone an environmentally-driven reduction in productivity. A productivity shift has already been demonstrated for Eastern Jackass Morwong, with the stock-recruit relationship and reference points being adjusted to reflect this change. Ecosystem and climate-change modelling have predicted increasing likelihood of similar changes in productivity for a number of Australian fish stocks.

Current harvest strategies assume either equilibrium or some average B0, and associated target (B48) and limit (B20) reference points. Use of equilibrium B0-based reference points and harvest strategies do not correctly reflect the natural dynamics of stocks where productivity changes. This can lead to sub-optimal management, either over-utilising a reduced productivity stock or under-utilising an increased productivity stock. In contrast, reference points based on some proportion of naturally variable unfished biomass (Bunfished or dynamic B0) will fluctuate to follow environmentally-driven productivity changes. Dynamic reference points have been evaluated and adopted for a number of international fisheries.

The need to adapt stock assessment methods and harvest strategies to explicitly and justifiably account for shifts in productivity has been recognised by the AFMA Resource Assessment Group for the Southern and Eastern Scalefish and Shark Fishery (SESSF), not least as a result of clearly evident declines in biomass (Jackass Morwong, Redfish) or recruitment (Silver Warehou) that cannot be attributed to fishing under current productivity assumptions.