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Mackerel under the microscope NSW STH COAST
Steve Starling www.fishotopia.com
The online publication of an ABC News item on 14 June, 2021, marked the first time most of us had heard about a startling new assessment concerning
been updated. In other words, different modelling is now being used to come up with an estimate for the remaining biomass of mackerel. Apparently, this new methodology is still under peer review in scientific circles, and it remains to be seen if it ultimately passes muster. If
and even the underlying motivations of some of the scientists producing the figures. Like many others, I was sceptical about an apparent drop in east coast Spanish mackerel stocks from around 40% of the pre-1911 unfished biomass to just 17% in a few years.
Spanish or narrow-barred mackerel are an incredibly important species to recreational, charter boat and commercial fishers in Queensland and northern NSW. the depletion of Spanish mackerel stocks along the eastern seaboard of Australia. According to this news report, a meeting of the East Coast Spanish Mackerel Working Group in Brisbane earlier that same month had been presented with new stock assessments indicating that the biomass (total amount) of Spanish mackerel remaining in east coast waters had been reduced to just 17% of its unfished (pre-1911) levels. This is below the 20% trigger point at which a fishery is recommended to be completely shut down under the current Sustainable Fisheries Strategy. U n d e r s t a n d a b l y, this alarming news sent shock waves through the commercial and recreational fishing worlds, as well as the seafood industry and the wider public, especially in Queensland. How the hell had things become so bad so quickly? The new 17% figure was particularly puzzling in light of the fact that a 2018 stock assessment contained in a 2020 report from the Fisheries Research and Development Corporation (FRDC) had indicated a remaining east coast Spanish mackerel biomass of 30-50% (most likely around 40%), and listed the status of the fishery as ‘sustainable’. So, what had changed in just a few years? NEW MODELLING The short answer is that the actual methodology of the scientific process for assessing the stock has 38
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it does, east coast mackerel stocks are clearly in a very bad place indeed. Not surprisingly, many observers were quick to question the alarming new figures, arguing that there had actually been strong runs and good catches of Spanish mackerel off Queensland and Northern NSW across the past few seasons. This certainly didn’t look or feel like a fishery on its knees and potentially nearing the brink of catastrophic collapse. These same critics questioned the new stock assessment methodology
It didn’t sound credible to me. However, I decided to keep my scepticism in check and do a little more investigating. One source of information and advice I reached out to was a semiretired researcher and avid Queensland fisher who has his finger well and truly on the pulse of such things. Like myself and many others, he’d also been initially suspicious of the new figures, but they had prompted him to do some more digging. In the process, he’d unearthed
several earlier scientific and academic papers that rang serious alarm bells about a dramatic, but largely unseen, century-long decline in east coast Spanish mackerel stocks. He passed the links to these papers on to me. SMOKING GUNS That 2018 Queensland Government stock assessment quoted earlier (yes, the one that came up with the reassuring 30-50% remaining biomass figure) makes a good starting point for some further digging into this vexing issue. As the assessment states: “Australia’s east coast Spanish mackerel, Scomberomorus commerson, are large offshore pelagic fish. The species can live for up to 26 years, weigh in excess of 30kg and mature between 2-4 years of age. Based on current research, east coast Spanish mackerel form a single genetic stock in ocean waters between Cape York Peninsula and northern New South Wales.” The paper goes on to explain that: “During September to November each year, Spanish mackerel school to form one of the most notable and predictable spawning aggregations of fish on the Great Barrier Reef. The aggregation occurs in reef waters north of Townsville where Spanish mackerel gather to breed mostly over a two lunar month period. Research has identified that Spanish mackerel usually have strong reef fidelity during the spawning season.” In other words, we know that these fish return to specific reefs at specific times of year to spawn. In the language
Spanish mackerel don’t handle and release as well as many other species. To optimise their chances of survival, they should be quickly unhooked in the water.
Recent mackerel seasons have been pretty good, so why should we believe that these fish are in serious trouble? of the boffins, this makes them “obligate transient aggregators”. It also renders them extremely vulnerable to over-harvesting by both commercial and recreational fishers. Furthermore, the density and predictability of these spawning aggregations tends to mask even quite significant declines in their overall numbers, as it’s still possible to go to those reefs at those specific times and catch reasonable numbers of mackerel, even if you’re pulling these fish from a smaller and smaller total ‘pool’ of spawners. Their seasonal aggregation hides the decline in numbers — a phenomenon with obvious parallels to the relatively recent “crash” of snapper stocks in South Australia’s gulfs (and the subsequent shut-down of that fishery). DECLINING COMMERCIAL CATCHES It’s worth noting that commercial landings of Spanish mackerel in the Queensland east coast fishery peaked at more than 1,000 tonnes per annum in the mid to late 1970s, with a second, slightly smaller series of peaks in the late 1990s and early 2000s. Commercial fishing effort for the species (numbers of
boats and boat days fished) hit its high point in 1998. In February, 2003 an ‘investment warning’ was issued by the Queensland Government, effectively discouraging further expansion of the industry, and commercial catch quota procedures were implemented in 2004, with an annual commercial limit of 619.5 tonnes put in place (this has since been reduced to a little over 570 tonnes). Commercial effort has declined significantly in subsequent years, and annual catches remain well below the quota limit, averaging around 300 tonnes per year since 2004. The annual commercial catch in northern NSW waters fluctuates considerably from year to year, but has reportedly never exceeded 52 tonnes. Across this same period, recreational and charter boat effort and catches have ramped up significantly. (It’s worth noting in passing that until 1990 ‘recreational’ fishers were still allowed to sell some of their catch in Queensland.) A rec’ possession limit of 10 Spanish mackerel over a minimum length of 75cm was introduced in Queensland in 1993,
