I was interested to read your take on the likelihood of decreased bag limits and such in South East Queensland and, in particular, for snapper (Qld Fishing Monthly Vol 22. No.2. Dec 2008 "From the Editors Desk"). My take is a little different to yours and I will attempt to clarify my main dissentions. My comments in the following relate only to snapper in SE Qld waters with probable implications for Northern NSW waters also:
• Long-term sustainability of a fish species
There are many thoughts on what proportion of the spawning stock need to survive to maintain long-term sustainable fish stocks (long-term = >100 years; for example: Leaving your children’s children some chance of catching a fish).
There are numerous estimates in Fisheries Research Journals that suggest that somewhere between 30-40% of the virgin biomass (untouched resource) spawning stock need to survive annually, except for extremely long lived species, in order to ensure long term sustainability. Some may argue that snapper in SE Qld are a different species\life history\habitat availability and so on and require a much lower percentage survival, but I suggest they would be on dangerous ground.
• Concept of virgin biomass
The concept of virgin biomass is admittedly a slippery concept, but in the case of snapper stocks in SE Qld, the earliest reports and stock estimates we can rely on are the published works of the likes of Wellsby who fished both inshore Moreton Bay and Offshore, at least between Caloundra and the Tweed, in the late 1800s and early 1900s.
But what can these reports tell us? That snapper were at least seemingly more common in those days than now? If so, then we need a way of testing these conclusions.
The only way to test the veracity of these claims is to duplicate the exact conditions of the ‘Wellsby’ reported catches of, for example, 500+ squire (1-6kg) around Flat Rock in an afternoons fishing.
In order to be scientifically controlled, one would also need to duplicate the gear of the day, the exact season, and even the weather, if possible. Duplicating such an experiment presents problems and relies critically on season, time of day, bait, tackle and weather.
It is my guess that if you took a team of anglers to those locations with no mod-cons (no GPS, sounder, radar, etc) in daylight hours to duplicate the feat, their catch rate would be zero snapper for the afternoon.
• What can this tell us?
Taking aside the anecdotal reports of Wellsby catching 500-800+ fish a day, let’s use a conservative estimate of catching 100 squire (1kg+) a day back in 1900. Using the amazing technology/gear we have today to catch a 100 squire at Flat Rock (ignoring bag limits and zoning) would be quite a feat. Therefore, using gear from the 1900s to catch today’s squire I would estimate a total catch rate of 10 fish per day. So, 100 Wellsby squire/10 modern squire = 10% of surviving virgin biomass.
In reality, the true figure is more likely to be less than 1% of virgin biomass. This conflicts dramatically with the 30-40% suggested by research.
• But that’s just Flat Rock, what about other areas?
The same scenario is played out up and down the SE Qld Coast. Produce any catch records for snapper from a fishing club dating back to the 1900s and attempt to reproduce those catch rates using the same gear\bait\season\time.
It is my guess that similar ratios of existing virgin biomass will be revealed. And I am fairly sure that that ratio will be less than 1% of virgin biomass.
• Why is this massive decline not been noticed\recorded by anglers?
There are many studies that have examined just that question. The answer lies in the generational acceptance of what we are born into, as being the ‘baseline’ for our mental measurements of how things are changing. So each generation only gauges against what they grew up with.
Every generation has said the same damn thing, "Fishing has gone bad since I was little!" In fact, Wellsby mentions his father as saying something akin to "the fishing in the Brisbane River is stuffed" in the late 1800's compared to his childhood!
• What about those who say they catch more snapper in Moreton Bay today than ever?
This is all about the ‘Effort Creep’ syndrome. As new technology is more available, the home ranges\feeding times\precise locations and such, allows more anglers to catch fish that would never have been subjected to fishing pressure.
I have a good mate who swears he catches more snapper now in Moreton Bay than ever before and, from his catch rates, he infers that snapper stocks are in good health. He uses plastics in daytime. My answer to test his theory is to revert back to the standard rig of using bait in daylight hours and see what you catch. Plastics work really well but you are just rounding up the last few fish using technology. More ‘Effort Creep’. It’s rounding up the ‘last few spawners’.
There are many cases in the literature where commercial fish stocks have held up under increasing pressure. For example, for the Atlantic cod catch rates actually increased each year as the species approached crash point. The cod distribution had contracted to an ever-decreasing area due to ever-increasing levels of exploitation, plus more efficient technology to detect\catch them. Of course the stock collapsed years ago and hasn’t shown any real ability to recover. One might be wondering whether a similar contraction is\has occurred in snapper stocks in SE Qld.
• Other examples of Effort Creep
Advances in technology can lead to massive changes in the ability of fishers to find and catch species. For example, the introduction of GPS into the Northern Prawn Fishery has conservatively estimated to make the trawling fleet 11% more effective at finding and catching banana prawns in the Gulf of Carpentaria.
Generally, banana prawns congregate in similar offshore regions each year, due to the combined effects of the timing and levels of rainfall, along with other parameters. Swapping of GPS discs between Skippers of past historical locations where banana prawn schools were caught effectively brought the level of efficiency of the any newcomer Skipper up to just below that of the old timers, in only a year or two. That equals ‘Effort Creep’.
The exact same process has occurred with the introduction of GPS\sounders\speedboats and such in the SE Qld offshore snapper fishery. The introduction and swapping of GPS discs allowed the learner Skippers to quickly arrive at the most likely locations\timings where congregations of snapper occur.
• So what does all this mean?
I have been around for a while on this planet and I am absolutely certain that catch rates of snapper have massively declined from when I was a lad. Are the stocks in strife? It would take a real gambler to bet that snapper stocks in SE Qld are healthy.
If you disagree with existing research estimates of the proportion of spawners (long-term) required to ensure sustainability, and discounted that value to even 10%, I suspect you would struggle to prove the case "that the populations of snapper in SE Qld are not presently under major stress".
If you can't, then the alternatives seem to be reductions in bag limits. – Don HealesReads: 4991