Seasonal closure and minimum legal size for barramundi in the Gulf ...

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greater equity between east coast and Gulf commercial fishers. Currently the closure in the Gulf ends just before the east coast in some years and just after it in others. Aligning the closure end dates would put both groups of fishers on an ‘equal footing’ in relation to marketing their early season product. In terms of proposing a set date to start the seasonal closure, as discussed previously the primary issue for consideration is the timing of the two-week spring school holiday. The benefit of certainty about the closure would apply regardless of the actual date that is set. The only set date simpler than any other would be the start of the month (i.e. 1 October), as this may be easier to recall. The two-week spring school holiday starts on a Saturday and is generally set to cover at least one week in September, and usually part of the first week in October. The closure ends on a Sunday, which is normally the first Sunday of October. It should be noted, however, that at the time of writing Education Queensland has only confirmed holiday dates until 2010. Both the timing of the seasonal closure and the timing of the holiday period therefore vary. The scheduled starting dates of the seasonal closure and the most likely dates of the school holidays are set out in Table 2. This table also shows the number of day’s impact on both the school holidays and the seasonal closure under three different scenarios: 1. Maintain the current variable closure. 2. Change the start date of the closure to 1 October. 3. Change the start date of the closure to 7 October. Table 2 Number of days impacted for the spring school holidays (SH) and the Gulf barramundi seasonal closure (SC) under three different scenarios Days impact if SC started as indicated: Leave SC as is Start SC 1 Oct Start SC 7 Oct SC start School holidays SH SC SH SC SH SC 25 Sept 2009 19 Sept – 4 Oct 1 -9 0 -3 -6 0 -12 30 Sept 2010 18 Sept – 3 Oct 1 -3 0 -2 -1 0 -7 4 Oct 2011 17 Sept – 2 Oct 2 0 0 -1 +3 0 -3 7 Oct 2012 22 Sept – 7 Oct 2 0 0 -6 +6 0 0 26 Sept 2013 21 Sept – 6 Oct 2 -10 0 -5 -5 0 -11 1 Oct 2014 20 Sept – 5 Oct 2 -4 0 -4 0 0 -6 4 Oct 2015 19 Sept – 4 Oct 2 0 0 -3 +3 0 -3 8 Oct 2016 17 Sept – 2 Oct 2 0 0 -1 +7 0 +1 28 Sept 2017 16 Sept – 1 Oct 2 -3 0 0 -3 0 -9 The impact on the school holidays shown in Table 2 relates to actual days during the holiday when barramundi fishing could not be undertaken. For this reason the figures in the SH column of the table are negative if the closure scenario would prevent fishing, or zero if it would not. The impact on the spawning closure, however, relates to potential spawning days lost or gained compared to the current variable closure, but only at the start of the 1 Approved 2 Likely but not yet approved Technical report prepared for the Gulf finfish review. Not government policy. 8
seasonal closure. For this reason the impact is shown as positive if the closure starts earlier under the scenario than it otherwise would have, or negative if it starts later under the scenario than it otherwise would have. It is worth noting that the impact on total potential spawning days would only be the same as the values shown in the SC column of Table 2 if the end date of a changed closure remained as it is under the current regime. Moving the end date to 1 February, however, would mean that in those years when there is a ‘loss’ of potential spawning days at the start of the seasonal closure, there would also generally be a ‘gain’ at the end. The current closure lasts 118 days. Moving the closure to start on 1 October and end on 1 February would cover 123 days. While such an increase in the closure of five days might theoretically affect the overall yield of the fishery, this was not tested due to limitations of the monthly based model; however, any marginal changes would, in reality, be undetectable anyway. Such a change would not completely remove the impact on the school holidays anyway, as there would still be a maximum of six days of holiday fishing lost in 2012. Moving the closure to start on 7 October and end on 1 February would cover 116 days—a decrease in the length of the seasonal closure by two days. Again, this scenario could not be tested under the model and any changes would be undetectable. A decrease of two days would not be significant in terms of the protection afforded to barramundi and other fish throughout the total length of the closure. The loss of early season potential barramundi spawning days represents the greatest possible impact from moving to a 7 October closure starting date, with a maximum loss of 11 days at the start of the 2013 seasonal closure compared to five under a 1 October starting date. There is no quantitative information available to assess the relative importance to fishery productivity of the lunar-based seasonal closure compared to one that is fixed in time. Pre-spawning fish are known to aggregate leading up to the new and full moon phases, therefore moving to a fixed date 11 days after the earliest starting date for the current closure would, at most, lose one potential night-time spawning moon a year. This would be unlikely to affect the productivity of southern Gulf barramundi, because spawning does not occur in that area until mid-November. The impact in the northern Gulf may be greater, as spawning is known to occur from early October. This may make barramundi more vulnerable to fishing as they aggregate leading up to the first night-time full or new moon tide in October. This means that it might be worth considering mitigating measures that apply to northern stocks of barramundi (and possibly other fish). One obvious approach would be to have an earlier seasonal closure in the north of the Gulf than in the south. Having two different closure periods, however, would be contrary to the aim of simplifying the current regime, as it would mean there would be three different seasonal closures in the state. It would also be likely to result in significant compliance difficulties, particularly on the boundary between the two closure areas. An alternative approach would be to introduce an area closure to a significant estuarine region in the north-western part of Cape York to protect aggregating barramundi and other actively reproducing species. Such a closure could prohibit all Technical report prepared for the Gulf finfish review. Not government policy. 9
Page 1 and 2: Seasonal closure and minimum legal
Page 3 and 4: Contents Contents 1 Purpose of the
Page 5 and 6: Summary The current minimum legal l
Page 7 and 8: Protection for spawning barramundi
Page 9: While the significance of this to m
Page 13 and 14: Modelling of impacts As discussed p
Page 15 and 16: Table 4 Definitions of symbols Nota
Page 17 and 18: Relative proportion 1 0.8 Commercia
Page 19 and 20: Discussion on analysis The analysis
Page 21 and 22: Appendix Model settings Table A1 Ba
Page 23 and 24: 12 10 log(ML/month) 8 6 4 2 0 2 4 6
Page 25 and 26: 0.5 0.4 Average spawning pattern Ea

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