A Queensland icon
The Spanish mackerel (Scomberomorus commerson) (Figure 1) is a well-known, sought after fish in Queensland. If you’ve had fish n’ chips from a local fish shop in Queensland, chances are it was Spanish mackerel. It features on restaurant and takeaway menus across the state, and is a prized catch for recreational fishers. Biologically speaking, east coast Queensland Spanish mackerel are part of a single genetic stock stretching from Cape York to Newcastle (Buckworth et al., 2007). They are relatively long-lived species, living up to 26 years. However, they do begin to reproduce between 2 and 4 years of age, which is good news for fisheries sustainability as this makes them a relatively productive species. East coast Queensland Spanish mackerel aggregate in large numbers on specific reefs in north Queensland each spring to spawn (Tobin et al., 2014). In fact, the spawning aggregations of Spanish mackerel are some of the largest and one of the most predictable biological events on the Great Barrier Reef.
Figure 1. Spanish mackerel (Scomberomorous commerson)
The state of our Spanish mackerel
The Fish and Fisheries lab supports sustainable fishing, and recognises that fishing and fisheries are valuable and legitimate activities that are central to the supply of healthy local seafood. We recognise that fishing means livelihoods, lifestyles, enjoyment, and meaning for thousands of Queenslanders. Our mission statement reflects this position.
Unfortunately, the best available science clearly indicates that Spanish mackerel are in poor shape. The 2021 stock assessment shows that the east coast Spanish mackerel stock is between 14 and 27% of the original unfished biomass, with the most accurate estimate being around 17%. In-line with best scientific practice, the stock assessment was reviewed by an independent fisheries modelling expert, and it has also been endorsed by the Queensland fisheries independent scientific panel. And really, the fact that Spanish mackerel are in trouble has been noted for some time. The Outlook Report for the Great Barrier Reef noted concerns about fishing of spawning aggregations back in 2009 (see page 166), with specific concerns about Spanish mackerel in 2014. The 2012 stock assessment advised that the Queensland East coast Spanish mackerel stock could be approaching an ‘overfished’ state (Campbell et al., 2012). A scientific paper was published in 2013 highlighting concerns about targeting Spanish mackerel spawning aggregations (Tobin et al., 2013), and a 2014 report produced by former researchers from this lab states that ‘the extirpation of historically important spawning aggregations from reefs east of Cairns as well as a reduction in size and frequency of Townsville reef aggregation is particularly worrying’ (Tobin et al., 2014). In 2017, another scientific paper raised concerns about long-term historical declines published over the last 80 years (Buckley et al., 2017). The simple fact is that we’re now in a situation where Spanish mackerel stocks are a fraction of what they once were and something needs to be done. How did we get here?
Explaining hyperstability
One of the factors contributing to this situation is an effect called hyperstability. This is where fishers can still catch good numbers of fish even though the stock is declining. Hyperstability can happen when fishers are fishing on aggregations of fish. These aggregations are a phenomenon where fish predictably gather at certain sites in large numbers, and often at very predictable times. These aggregations may occur for the purpose of spawning, mating, or an annual feeding event.
In the case of east coast Queensland Spanish mackerel, fishers have been exploiting fish spawning aggregations for over 80 years (Sadovy and Domeier, 2005; Buckley et al 2017). When so many fish come together to spawn, it significantly increases their reproductive output and for many species, these aggregations are the main opportunity to reproduce. Whilst spawning aggregations make good biological sense, these aggregations also make fish extremely vulnerable to fishing.
When aggregating in such high numbers, the assembled individuals can be caught easily. Depletion of our Spanish mackerel stock has probably been occurring over decades, but hyperstability means that fishers’ catches remain relatively unchanged even while the population was being overfished. Essentially, hyperstability translates to stable catch-per-unit effort rates (CPUE - a commonly used indicator of fish abundance) that mask overfishing and an underlying population decline (Sadovy and Domeier, 2005) (Figure 2).
Figure 2. Hyperstability: as the stock is fished down over time, catch-per-unit-effort remains stable despite declines in population size.
Given that spawning aggregations are formed of mature adults, overfishing can also lead to a decline in egg production, thereby also reducing the reproductive potential of a stock which adds to the problem.
The effects of hyperstability have been seen many times around the world in both commercial and recreational fisheries [e.g. Erisman et al., 2011; Hughes et al., 2020; Maggs et al., 2016; Hamilton et al., 2016]. One of the best-documented cases is that of the Nassau grouper (Epinephelus striatus), which was once the most commonly landed fish in the Caribbean and tropical western Atlantic (Figure 3).
Figure 3. Nassau grouper (Epinephelus striatus) (Image taken by Clark Anderson/Aquaimages, 2006, Image licensed under (CC BY-SA 2.5)) At their peak, Nassau grouper spawning aggregations hosted upwards of 100,000 individuals, with fish travelling as far as 260 km to aggregate. Fishery data from Cuba reported a peak catch of 1,800t in the 1960s. Following intense exploitation of these spawning aggregations, regional populations collapsed (Waterhouse et al., 2020). The same dynamics are at play here. Our Queensland east coast Spanish mackerel are swimming a long way and predictably gathering at specific reefs, making them highly vulnerable to fishing (Tobin et al., 2013), and declines have now occurred.
The good news is that with responsible management, the stock can recover. We are currently witnessing sustained recovery in Nassau grouper stocks following management decisions. The management package includes seasonal closures, bag limits, gear restrictions, and no-take zones (Waterhouse et al., 2020). It may be that a comprehensive package of measures is needed to recover species that experience targeting of their aggregations. For example, research on leerfish (Lichia amia) showed that just reducing bag limits and making the species a recreational-only species was not enough to halt the stock’s decline, and more measures including spatial and temporal closures and no-retention policies were needed (Maggs et al., 2016). Meanwhile, the Nassau grouper example shows that with a responsible management package, stocks can recover.
What is being proposed for Spanish mackerel
At the February 2022 Fisheries Working Group for Spanish mackerel, fisheries managers tabled several options to halt the decline and rebuild the stock (Figure 4). The options for consideration include a 12-week regional/seasonal closure during September-November for the northern sector, a 12-week regional/seasonal closure during January-May for the southern sector of the Queensland areas, and reduced catch limits. The closures would apply to anyone who targets Spanish mackerel during these times and would therefore affect both the recreational and commercial fishers. The intention of halting fishing during these periods is to protect Spanish mackerel aggregations, and to reduce fishing pressure and allow the stock to rebuild. Alongside the closures, it’s been proposed to reduce the total allowable commercial catch (TACC) limit by between 75-90%.
Figure 4. Proposed management options: the management measures proposed in the Spanish mackerel Working Group meeting held on 7-8th February 2022.
To address recreational harvests, options to be discussed include reducing in-possession limits from three mackerel to one mackerel per person, and for recreational vessels with two or more people on board, the limit of six fish would be reduced to two. Given that boat ramp and recreational survey data already report an average of just one Spanish mackerel across 70% of fishing trips where Spanish mackerel are caught (see communique), these changes ought to be considered in conjunction with the other management options proposed. Overall, the proposed options are similar to those used elsewhere for situations like the Nassau grouper. Other fisheries have introduced further measures. For example, the decline of snapper in South Australia has led to a package of management measures introduced in 2019 that includes a catch-tag system (‘no tag no fish’) as well as spatial and temporal closures.
As for Spanish mackerel, we do not know what the eventual package will look like, but substantial changes such as the options being discussed are going to be needed to rebuild the stock. If these measures are implemented effectively and in good time, it is predicted that the stock could rebuild to 40% of the unfished biomass in 7-14 years.
So, where to next?
There’s no beating around the bush, the proposed measures would hurt fishers and dependent businesses. If fully implemented, the ability for commercial and recreational fishers to target Spanish mackerel during the usual peak fishing season, and the amount of fish they can keep, would be significantly reduced. The commercial fishers whose livelihoods rely on Spanish mackerel are likely to be the most affected, and the stress and personal strain of impacts of changes like this are likely to be significant. These impacts on commercial fishers are becoming more and more well documented. Unfortunately, when a stock is at 17%, hard decisions have to be made. Fishing of spawning aggregations for any species is a risky business for long-term sustainability, and as documented in numerous other examples, it often doesn’t end well. Significantly reducing catch levels and closing fishing during specific periods are reasonable, necessary, and evidence-based steps that need to be taken to rebuild a fishery.
Additionally, the Spanish mackerel fishery is taking place within the Great Barrier Reef World Heritage Area, and inside a marine park. Having a stock decline to 17% runs contrary to the purpose and intent of these areas. While we believe that sustainable fishing is a legitimate activity in the Great Barrier Reef that provides food, enjoyment, culture, and livelihoods to Queenslanders – when fishing is happening in a World Heritage Area marine park, the expectations and scrutiny for sustainable management are high.
As it stands, the proposed management plans will need to be discussed further within the fishery working group, between the different management agencies, with commercial and recreational fishers, and the public. We don’t know where things are going to end up. However, as a Lab, we hope to see two things:
Commitment to make the hard decisions needed to rebuild the stock, i.e. implement a package of management actions based on those tabled at the Feb 2022 meeting. If managers in the Cayman Islands can take these steps to rebuild Nassau grouper, we can do it here, in our Great Barrier Reef. This will give us the chance to have healthy Spanish mackerel stocks for the future.
Recognition of the impact the proposed changes would have on people. Fishers, particularly those commercial fishers who have long caught Spanish mackerel and rely on it for their livelihood and retirement, would need help and support. If people decide that they have to leave the fishery and their livelihoods behind, they should get the assistance they need so that they can do so with dignity and respect.
It is in all our interests to make sure that we all do what is needed, and we hope that like the Nassau grouper, we will see the east coast Spanish mackerel stock rebuild and recover to the stage where it can be fished sustainably again – and preferably without targeting aggregations.
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Footnote 1: It has been suggested that management could include increasing the minimum Legal Size (currently 75 cm) to the length at which Spanish mackerel sexually matures (~ 90 cm). However, this measure was not supported by the Spanish mackerel working group as it appears that relatively few undersized mackerel are caught, and there are real concerns that post-release survival would probably be very low, which would make this change ineffective.
Footnote 2: significant reductions in Spanish mackerel fishing on the east coast would put a dent in supply, but this doesn’t mean that all Spanish mackerel would disappear from fish n’ chip shops. Other Spanish mackerel fisheries would be still be able to supply this iconic product. For example, some fish n chip shops source their mackerel from the Torres Straits where mackerel stocks are in better health. We also have the privilege of having other high quality, sustainable seafood options. For example, the 2020 stock assessment shows that Queensland East coast king threadfin populations are healthy. As we have said in previous blogs, if you’re buying seafood: know (1) what you’re eating; (2) how it was caught; and (3) where it came from.
References:
Buckley, S.M., Thurstan, R.H., Tobin, A., and Pandolfi, J.M. (2017) Historical spatial reconstruction of a spawning-aggregation fishery. Conservation Biology, 31(6), 1322-1332.
Buckworth, R. C., S. J. Newman, J. R. Ovenden, R. J. G. Lester, and G. R. McPherson (2007). The stock structure of northern and western Australian Spanish mackerel. Tech. rep. Dept. of Primary Industry, Fisheries and Mines.
Campbell, A.B., O’Neill, M.F., Staunton-Smith, J., Atfield, J.C. and Kirkwood, J. 2012, Stock assessment of the Australian East Coast Spanish mackerel (Scomberomorus commerson) fishery, Department of Agriculture, Fisheries and Forestry, Brisbane.
Erisman, B.E., Allen, L.G., Claisse, J.T., Pondella, D.J.I., Miller, E.F., Murray, J.H., and Walters, C.J. (2011) The illusion of plenty: hyperstability masks collapses in two recreational fisheries that target fish spawning aggregations. Canadian Journal of Fisheries and Aquatic Sciences 68(10), 1705-1716.
Hamilton, R.J., Almany, G.R., Stevens, D., Bode, M., Pita, J., Peterson, N.A., and Choat, J.H. (2016) Hyperstability masks declines in bumphead parrotfish (Bolbometopon muricatum) populations. Coral Reefs 35(3), 751-763.
Hughes, A.T., Hamilton, R.J., Choat, J.H., and Rhodes, K.L. (2020) Declining grouper spawning aggregations in Western Province, Solomon Islands, signal the need for a modified management approach. PLOS ONE 15(3), e0230485.
Maggs, J.Q., Mann, B.Q., Potts, W.M., and Dunlop, S.W. (2016) Traditional management strategies fail to arrest a decline in the catch-per-unit-effort of an iconic marine recreational fishery species with evidence of hyperstability. Fisheries Management and Ecology23 (3-4), 187-199.
Sadovy, Y., Domeier, M. (2005). Are aggregation-fisheries sustainable? Reef fish fisheries as a case study. Coral Reefs, 24, 254-262.
Tobin, A., Currey, L., and Simpfendorfer, C. (2013) Informing the vulnerability of species to spawning aggregation fishing using commercial catch data. Fisheries Research 143, 47-56.
Tobin, A., Heupel, M., Simpfendorfer, C., Buckley, S., Thurstan, R., and Pandolfi, J.M. (2014) 'Utilising innovative technology to better understand Spanish mackerel spawning aggregations and the protection offered by Marine Protected Areas.' (Centre for Sustainable Tropical Fisheries and Aquaculture, James Cook University: Townsville) 70pp
Waterhouse, L., Heppell, S.A., Pattengill-Semmens, C.V., McCoy, C., Bush, P., Johnson, B.C., Semmens, B.X. (2020). PNAS, 117(3), 1587-1595.