Mackerel under the microscope

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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. 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 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,

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.

Understandably, 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 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 Recent mackerel seasons have been pretty good, so why should we believe that these fish are in serious trouble?

although an amendment to these rules the following year made provisions for anglers to retain twice that limit on an extended charter trip of more than 48 hours duration. In 2003, the recreational possession limit was reduced to three fish per person and that regulation remains in force today (with a total limit of six Spanish mackerel per boat, when there are two or more people on board). In NSW, rec’ fishers are allowed five Spaniards per day, and the minimum legal

Spanish or narrow-barred mackerel can live for up to 26 years and potentially exceed 40kg in weight. Predation of hooked and recently released fish by sharks is a constant and increasing problem that needs to be factored into the equation.

length is also 75cm.

Despite these reasonably strict catch limits, the total recreational and charter harvest is obviously significant. Some estimates put the current Queensland rec’ catch as high as 170 tonnes a year or more, although this is obviously difficult to measure accurately. However, there’s no denying that the amount and sophistication of rec’ and charter boat effort is considerably greater now than it was at the turn of the millennium. Nonetheless, the combined annual catch of commercial, recreational and charter fishers in Queensland and NSW would appear, at best current estimates, to be somewhere under 600 tonnes: around half of those record peaks seen in mid 1970s and late 1990s. Could one reason for this drop be a previously undetected decline in stocks? ELEPHANT

IN THE ROOM

Another important factor to consider in all of this is the occurrence of fishingrelated predation (primarily by sharks) on hooked and recently-released mackerel in all three sectors: commercial, recreational and charter.

While this fishingrelated predation has always been an issue, there’s very strong anecdotal evidence that the loss of mackerel (and other fish) to sharks has increased dramatically

across the past decade or so. This is likely to be related to increases/recoveries in the numbers of certain shark species (particularly some of the whalers) as a result of decreased commercial pressure on their populations, as well as ‘learned behaviour’ on the part of these predators, meaning that they’re aggregating on popular fishing grounds and actively targeting hooked fish by responding to triggers such as changes in the revs of motors and so on.

Loss of mackerel to fishing-related predation is difficult to measure, but is potentially significant and really needs to be considered as part of the overall ‘harvest’ or take by all sectors.

ALARM BELLS

It seems that the writing may have been on the wall for some time in terms of declining stocks of Spanish mackerel. In an abstract of their 2017 paper entitled “Historical spatial reconstruction of a spawning-aggregation fishery”3, authors Buckley, Thurstan, Tobin and Pandolfi came to the following alarming conclusions about the Spanish mackerel fishery on Queensland’s Great Barrier Reef:

“Data were compiled from historical newspaper archives, fisher knowledge, and contemporary fishery logbooks to reconstruct catch rates and exploitation trends from the inception of the [Spanish mackerel] fishery. Our fine-scale analysis of catch and effort data spanned 103 years (1911–2013) and revealed a spatial expansion of fishing effort. Effort shifted offshore at a rate of 9.4 [nautical miles per] decade, and 2.9 newly targeted FSAs [fishspawning aggregations] were reported [per] decade. Spatial expansion of effort masked the sequential exploitation, commercial extinction, and loss of 70% of exploited FSAs. After standardizing for improvements in technological innovations, average catch rates declined by 90.5% from 1934 to 2011 (from 119.4 to 11.41 fish [per] vessel [per] trip).”

Concealed within that rather dry, academic summation of this detailed scientific analysis are some truly sobering conclusions. Basically, the authors are stating that it’s only the ongoing and continued geographic expansion of the fishery (with fishers heading further and further offshore and finding new spawning aggregations) that has allowed reasonable catches to be maintained. In their wake, those fishers (commercial, recreational and charter) have left a string of former aggregation sites that have effectively been exploited to the point of “commercial extinction”. Clearly, this pattern can’t continue indefinitely. A day of reckoning must eventually come and, with standardised average catch rates having declined by more than 90% (at least according to these

researchers), surely that day of reckoning can’t be too far off?

Another scientific paper sums the situation up like this: “… the overall size and thus reproductive potential of the east coast [Spanish mackerel] stock has been significantly reduced… the analysis of commercial fishery data through the extensive history of the Spanish mackerel fishery clearly identifies a fishery in continual decline…”

That “continual decline” may have reduced the current biomass of Spanish mackerel off our east coast to 30-40% of its original, or to as little as 17%, depending upon whose model you prefer to believe. However, with even the more optimistic 2020 assessment stating that a “target reference point” of 60% by 2027 is required to “build and maintain” the fishery, it’s pretty clear that we are headed very much in the wrong direction… the only uncertainty is by how much. WHAT’S TO BE DONE?

Suggestions for safeguarding the future of our shared east coast Spanish mackerel stock and (hopefully) helping it to rebuild over time seem to run the full gamut from “she’s apples, steady as you go, there’s plenty of mackerel” to a complete shut-down of the fishery and a moratorium on the taking of Spanish mackerel by all sectors for at least several years (as was recently done with snapper throughout most South Australian waters).

Between those two extremes lie a multitude of possible measures and levers, such as spatial and temporal (place and time) closures, the creation of new sanctuary zones to protect identified spawning aggregations, reduced recreational bag limits, commercial licence buy-outs and so on. None of these possible tweaks to the status quo are likely to be universally popular. But, as American General George S. Patton famously said: “If everyone agrees, someone is not thinking.”

Perhaps the one thing we do need to agree on is that there is a problem, and that means something needs to be done… and soon!

This is an extract from a blog Starlo recently wrote about the controversy now surrounding the status of east coast stocks of Spanish mackerel.

The author with Spanish mackerel from northern waters.

SOURCES

Spanish mackerel stocks under threat from overfishing, government says by Tom Major, ABC Rural, 14 June 20121. Stock Assessment of Australian east coast Spanish mackerel compiled by M. F. O’Neill of Agri-Science Queensland, Department of Agriculture and Fisheries, J. Langstreth of Fisheries Queensland, Department of Agriculture and Fisheries and S. M. Buckley, The University of Queensland and J. Stewart, Department of Primary Industries, New South Wales. © State of Queensland, 2018. Historical spatial reconstruction of a spawning-aggregation fishery [Abstract] by S. M. Buckley, R. H. Thurstan, A. Tobin and J. M. Pandolfi. Conservation Biology, Wiley Online Library, Volume 31, Issue 6, December 2017. Utilising innovative technology to better understand Spanish mackerel spawning aggregations and the protection offered by marine protected areas by A. Tobin, M. Heupel, C. Simpfendorfer, J. Pandolfi, R. Thurstan & S. Buckley, FRDC Project No. 2010/007. April 2014