Fish Data - NFAs vs Netted Areas

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The only known scientific assessments of net free areas - either before and after implementation or comparing neighbouring areas.
These are examples of the most significant differences.

Lake Macquarie: combined shore-based and boat - % increase in number and size from '99 to 2004.

.................................................. ............individuals............. kilograms
trumpeter whiting ...................................... 119%.................... 138%
dusky flathead.......................................... .. 119% ................... 232%
tailor............................................ ............. 205%.................... 539%
sand whiting ............................................. 158% .................... 169%
silver trevally ............................................ 250%......................528%

Lake Illawarra: boat only - % increase in number and size.

yellowfin bream ........................................ 112%...................... 69%
sand whiting........................................... .. 834%.................... 1058%
sand mullet ............................................. 199%...................... 424%
blue swimmer crab ................................... 610%.................... 1118%
black bream............................................. 431%...................... 445%

note: a 100% increase means there is double the number from '99.


3 pairs of estuaries between Cairns & Bowen - Lay et al 2002. One estuary of each pair open to nets & the other open only to recs (5yrs).
Fish number taken in survey nets from each and % difference.

.................................................. .......open ............ closed............ difference
barramundi ....................................... 430 .............. 1227.............. 285%
requiem shark...................................... 33................ 133.............. 403%
tarpons .............................................. 83................ 125.............. 150%
mullets ........................................... 1113 .............. 1597............. 143%
milkfish.......................................... .... 13.................. 25.............. 192%
trevally.......................................... ... 193 ............... 521.............. 270%
grunters.......................................... .. 263................ 406 ............. 154%
threadfins ......................................... 257 ............... 612.............. 238%
barracudas........................................ . 16 ................. 32 .............. 200%

note: barramundi taken in closed systems were on average 8% larger (3.5cm) than those taken in open systems. Similar with other species.

I put Hinchinbrook Channel commercial catch data charts on the "one mullet net" thread, which tell a magnificent story about what happens when you have net free areas and a reduction in commercial effort (nets). But I can't call it a scientific assessment because I built the charts from FQ catch data.
The attachment below is a chart of NSW commercial catch data built by a scientist which shows how little effect rec fishing havens had on the commercial harvest, though it may be that without RFHs, the data could, or would eventually be, worse.

The untold story:

Critical ... and I mean really critical .... to all of this is the increased size of fish that net free areas clearly produce according to the above data and which would be expected and has been shown to be the case with MPAs. Larger fish produce vastly more and stronger/healthier larvae than smaller fish. They are more 'fecund'. This is especially important when there is 'harvest stress' on a species which makes fish much less fecund. So not only do we have fish that are more fecund in the system as well as more of them and smaller fish, they are not less fecund because they have safe refuges from nets. The difference between the 2 scenarios is huge. The spillover effect of these larvae and adult fish can only be significant and can be expected to be the reason why commercial harvests do not suffer under a management program that includes NFAs.
I did a rough estimate of egg production by the increased number and size of fish in the closed vs open research in NQ and it would be in the order of at least 25 times more eggs, and perhaps as high as 100 times. And these eggs produce stronger/healthier larvae that are more likely to survive and grow into larger/stronger/healthier adults.