fish caught east of the Sydney Harbour Bridge , how safe are they ??

[leonardgid]

26 minutes ago, Little_Flatty said:

That's definitely true but I will note that @leonardgid was originally asking about fish caught east of the bridge and did raise the point it would be nice to know levels of dioxins in fish in the greater Sydney area, on an ongoing basis.

Regardless of the advice, some people will eat fish west of the bridge - I've met many - but apart from pointing out the government advice (once and only once), I'll never argue with them as it's their life. From their point of view, I've chosen to miss out on many good feeds of fresh fish. That's my choice.

I'm no marine biologist, but I suspect it's actually very complex to accurately determine dioxin levels in the fish.

Firstly, fish might move around a lot and secondly, it might be a destructive process to sample them. You'd likely also need a very large sample size to get an accurate estimate, which is likely costly in terms of both resources and labour.

To me as a final year student in a masters of applied statistics, the sample sizes do appear to be very small. Small sample sizes are common in biological and medical studies, for budgetary and ethical reasons. Often there is no other option. For instance, if sampling dioxin levels in fish is a destructive process and we needed 1000 fish to get a decent estimate, then you could imagine the backlash from both the angling community - amongst others - about destroying 1000 fish in every location designated for the study. If it's not that, then there would be an uproar from both bureaucrats and the public about the cost of testing that many fish. As a result of those two things, small sample sizes are common.

Weird data points are also part of life. I've encountered them in just about every set of data I have ever touched, and it's often the interesting part of the job. There appears to be something off about the Clifton Gardens result, and it also seems interesting that as far up as Breakfast Point, the fish seem to have about 'normal' levels of dioxins. I have lots of questions on that front. Unfortunately, without larger samples or more sophisticated/time/labour-intensive (read: expensive) experiments, it will be difficult to know with any accuracy what true levels are. That's why we need experts, like scientists, doctors and statisticians, to help bridge the gap. Ultimately it would have been their insight that informed the 'west of the bridge' rule and we don't really have much else to go off unfortunately.

Agree with them or not, I suspect that the view of the government(s) that have led us is that they sleep well at night knowing that the commercial fleet is no longer fishing these waters. That's a lot of dioxins not being fed to the population without their knowledge.

For the rest of us recreational anglers, they put up some signs and leave it up to us. We have been advised, and we can make our own decisions with regard to own levels of fish consumption from the harbour.

very interesting read,  its good to hear from someone  that  knows/understands   statistics and is able to explain  it to all of us  once again thank you for your help with this    , 

[Mike Sydney]

It should be pointed out dioxins are high in fish generally, including supermarket bought, not just in Sydney harbour, and are present in many fatty foods we eat already. 

While the advice is don’t eat west of the bridge, the same study in 2006 suggested 1 mean portion every 2 months (as opposed to 2 a month east of the bridge). 

This table is from the food standards authority 2020 report. Want an extra fish a month? Cut out butter!

The dietary advise likely also presumes an average consumption of food including bought fish, so if you aren’t getting fish from the shops as well you might have more leeway (7g a day was the average consumption of fish of all sources).

A fish here and there isn’t going to kill you. Just avoid habitually eating from west of the bridge where the fish are 3 times more toxic than average.
 

[noelm]

Another kind of interesting side to this is, Prawn trawlers have not operated for years (because of the heavy metals present) yet fishing hasn't improved one bit, neither has the amount of Prawns, people were eating "Harbour Prawns" for decades with no known ill affects. I guess in a way, the harbour has never been cleaner (water wise) with much stricter laws on just dumping "waste" into the water like was pretty common practice years ago, it would be interesting if some kind of tests were done and recorded way back, then every 10 years or so just to compare how things have changed over the decades as far as toxins in fish goes.

[Welster]

It seems that after they stopped commercial fishing the governments interest in monitoring toxins stopped as well.     I remember the commercial fishery wash shut down abruptly.  I think it coincided with the Who revising the acceptable levels of toxins in seafood.

I do wonder if the imported seafood is subjected to the same standards and testing or if the importer signs it off. The certainly didn't prevent Whitespot diseased prawns coming in.

 

[noelm]

24 minutes ago, Welster said:

It seems that after they stopped commercial fishing the governments interest in monitoring toxins stopped as well.     I remember the commercial fishery wash shut down abruptly.  I think it coincided with the Who revising the acceptable levels of toxins in seafood.

I do wonder if the imported seafood is subjected to the same standards and testing or if the importer signs it off. The certainly didn't prevent Whitespot diseased prawns coming in.

 

Imported fish is a bit of a tricky thing, if it is "processed" that being cooked, frozen, packaged or similar, then it's up to the original company to ensure everything is OK (hence why white spot enters the country) Australian customs/quarantine do not check processed food goods.