southern bluefin tuna surveys

​Social media as a tool to characterise and ‘bench-mark’ recreational fisheries

For the last four years I have been personally interested in pursuing the Southern bluefin tuna that appear and disappear off the local coastline where I live in Victoria. My local ports on the Barwon River and Queenscliff, along with many other towns all along the coast are key access points for thousands of keen recreational fishers just like me who spend their weekends ‘tuna watching’ and sometimes even catching!   One day when I was probably over-stimulated by social media feeds depicting tuna-champions battling with  mega-barrels – I simply thought, “Hmmm,… I wonder how much tuna would social-media report over a year?” And then, “How would that compare with the real-estimates of total tuna catch?”

I’m well-aware that what you see on Facebook and Instagram is a long way from what’s reality, but even so, my curiosity was aroused. Back in 2012, when I worked for a fisheries agency, I was part of a team that estimated the actual recreational catch of tuna in Victoria with boat-ramp surveys. That estimate for the 2011-season was  240 tonnes and in those days the fishery was really only off the western part of the coastline between March and July, peaking off Portland in April and May (Green et al. 2012). A broader National survey of retained catch for 2018 estimated that only 270 tonnes were harvested annually by anglers in five states, with Victorian anglers responsible for only 89 tonnes (Tracey et al. 2021). Again, the Vic survey component only focussed west of Apollo Bay. Fast forward to 2023 and it was clear to anyone that the fishery was now well established at least as far east as Wilsons Prom with so-called “Melbourne tuna” being caught by every-man (and woman)-and-his/her dog.

So, in August 2023, I started to note down the date, count and weight of Southern bluefin tuna in every Facebook and Instagram post that I could identify as being a “Victorian catch”. I spend way-too-much time on socials as it is, so my tally rapidly started to grow. I switched it over to a spreadsheet by the end of September and I kept it going all year. I have no idea how the algorithm works, but I saw a lot of tuna posts !

Clearly, what I had at the end of this process was NOT what anyone would regard as an estimate of total catch. The data I have collected is undoubtably less accurate, and more limited in many ways than would be obtained from a properly designed recreational fisheries survey.  I think, it’s interesting, nonetheless. I hope you do too. I prefer to think of this data as giving a rough, relative minimum estimate of catch, with some idea of catch size-composition and distribution across the year. Of course, the biggest unknown factor, or bias in this data is what real Fisheries Science likes to call ‘unreported catch’. In this case it’s entirely reasonable, and expected, that a large proportion of the tuna caught would not be posted on social media. I get that! Some people just aren’t Facebook or Instagram fans. Even among those who are social-media savvy, no doubt many choose not to publicise their catches. Even for those that did engage with social media, I may just not have seen their posts. I did have a few friends (“i.e., real live people”) scouting for me and sending me links to ones I may have missed. Some folks may even deliberately misdirect, by exaggerating quoted size or the timing of their captures, but I’m reasonably confident these would be minor issues.
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One of the inaccuracies I had to deal with was ‘weight’. For many of those larger fish, the weights were detailed in the accompanying text or was displayed in the video of the ‘weigh-in’. I used whole-weight where provided and added a small proportion to the cleaned-weight where necessary. For some large fish, and most of the posts about the smaller school size fish weight information was often lacking, so I used my personal and professional judgement to estimate these weights for individual fish (including comparing with posts where weight was described and weighing fish myself occasionally to check). I only counted fish I could see in the images provided (for instance a charter boat may claim to have “bagged out in the morning, and again in the arvo”, but I only included fish from the trip pictured. 

​Here are the results, warts-and-all…From August 2023 through until July 2024 in social media posts on Facebook and Instagram, I observed 1239 individual Southern bluefin tuna that were harvested (i.e., kept) and landed at Victorian ports.   The total estimated weight of these harvested fish was 38.7 tonnes. 

So, what does it tell us about the fishery in 2023-2024? Firstly, I was surprised at the size of the final total. With my estimate being over 40% of the most recent ‘proper estimate’ for Victoria that suggests to me that we really need a better idea of how big the catch now is to make-sure it’s being managed ok and determine how important it is to Victoria’s anglers. 

The catches were spread in two main “seasons”. August–November is clearly barrel season, with fewer fish caught, but average size up around that magic 100 kg-size (and over). Although there were barrels reported on social media in every month of the year. Barrel-mania peaked in September with over 100 fish for 10-tonnes!  There was a lull until January, when it kicked off again with bigger numbers of smaller fish, which we all know as schoolies. This year on social-media it seemed the average size schoolie was about 15 kg, but with a good smattering of fish up to 25 kg and beyond mixed among them. There were also more small fish this year, than I have personally seen before. I saw these jelly-beans around 2-5 kg free-jumping around the boat on several occasions. Over most of the ‘schoolie season’ I was seeing around 150-fish per month on socials, although this peaked at over 300 fish for almost 5-tonnes in February. By June, the schoolies were almost absent, although there was a brief spell this August when a few of each size were being taken. 

How does this compare with quantitative surveys? Well, if at least 38.7 tonnes was reported on Facebook and Instagram the real catch is obviously far greater than this. Was the catch higher than the 2018 estimate of 89-tonnes? Probably, as in 2018 the survey effectively assumed no fishery east of Apollo Bay. Based on information obtained for the earlier 2011-survey when it was largely true – even by 2018, this was probably an underestimate as the fishery had spread to at least off the Rip. Unfortunately, for my own social-media survey, I couldn’t accurately determine a “local port” for many of the observations, although it was apparent that many were spread across Victoria at least from the SA border to Westernport, with a few from Corner Inlet ports and as far east as Lakes Entrance. The social-media observed this year, together with my personal observations tells me that a huge proportion of the catch must have come from boats originating from the Barwon River and coming through the Rip from the Port Phillip Bay ports, and from Westernport. As you’d expect, the offshore recreational fishery is quite weather-dependant, and on low-swell, days over summer with light offshore breezes it was not uncommon to count 50-100 boats out between Torquay and The Rip.

If nothing else, I feel that this simple social-media survey highlights the questions that need to be answered in a better, more-accurate and quantitative way. It cost me nothing more than a few minutes of my time each day while scrolling through the media I look at anyway. But the recreational fishers of Victoria should have better information than this. It’s been 7-years since the last quantitative survey. I think most fishers would agree, that the  local fishery has boomed since then, but by how much?

Why do we need to know? Obviously, we all want to make sure the fishery is sustainable into the future. For SBT there are a lot of moving-parts to that question. The species is fished commercially and recreationally in multiple countries and Australian states. The global stock-assessment includes a quota for Australian recreational fishers of 5% of the Australian quota (commercial + recreational). Without any reliable estimates of what’s being caught  - how can recreational fisheries managers negotiate for a bigger quota? Now we can tick-along pretending that 89 tonnes is an accurate measure of the Victorian catch (well-under quota) but if we do, surely there is a risk that the recreational quota could be ‘shaped’ down to that figure. Recreational fishing surveys are expensive, but compared to the capital investment in this fishery, the cost is minute.  On a given day there are several Million-$ worth of boats and tackle bobbing around off the Victorian coast all chasing the Southern bluefin tuna.

Could a similar social-media survey be used to design a better quantitative survey? I think so, with a better idea of the scale and direction of some of the biases discussed above. If a social-media survey was paired-with (i.e., co-occurring) with the next fully-quantitative angler-survey estimate of SBT catch we would have some idea of the level of unreported-catch on social media, which would effectively calibrate this highly cost effective survey method so it could be used more frequently; perhaps even on an annual basis, to keep anglers and fishery managers informed of trends in catches. 

P.S. Note that this blog is a year-late. I didn’t continue the social-media survey into the 2024-2025 tuna season, as I got too distracted by fishing ! “Such is life”. On reflection, I feel its still worth publishing as we still don't have a current estimate of catch.
My gut feeling is that 2024-2025 was a less productive tuna season for Victoria. Please comment on this if you feel you can.