Sussing out the cycle for our favourite fish
  |  First Published: March 2017

One of the outstanding features of this season is the massive horde of baitfish in the harbour. On some days, at some of the well-known fishing spots in the Middle and North harbours, sounder ‘blackouts’ have been common. A blackout is when your entire sounder screen is filled with baitfish – that is, the entire water column, from top to bottom. To give you an idea of the magnitude of some of these schools, we have seen blackouts in 60ft of water over the area of a quarter acre.

Baitfish were traditionally targeted by some of the harbour’s commercial fishers, particularly in North Harbour and Rose Bay. The fact that the pros no longer fish in the harbour would account for some of the extra baitfish we are currently experiencing. Overall, this year’s abundance is probably simply due to seasonal fluctuations. Baitfish biomass reacts very quickly to favourable conditions like increased nutrient loads and warm water. They are boom and bust fish.

If you spend a while fishing the harbour, you’ll soon become aware that it’s a pelagic paradise. In various combinations and quantities over the years you will see hordes of bonito, salmon, tailor, cowanyoung, yellowtail and kings feeding on the surface. They are just the common ones. We also get visits from Watsons leaping bonito, frigates, mack tuna, striped tuna, spotted mackerel and even the occasional northern bluefin.

You will see most of these feeding on the surface. That doesn’t mean that they don’t also feed deep where you can’t see them on occasions. Then there are all the other fish that are also partial to baitfish. School mulloway give them a hammering at times, as do flatties, bream, amberjack, samsonfish and a multitude of predatory bottom huggers. Sea birds and penguins also eat their share.

I can’t help wondering how many baitfish the harbour holds and how much all the predators combined must consume. A recent experiment conducted by honours student Chris Lawson in conjunction with Fisheries and SIMS gives some hint. Chris’ study run in Chowder Bay estimates that over 56,000 baby tailor come into Sydney Harbour every year and that they eat 77t of baitfish and prawns. In fact, they eat 10t of prawn alone, which is double the recorded commercial take when trawling was happening in the harbour.

Tailor, in my experience, are nowhere near as abundant in the harbour as they were 30 years ago. My theory, backed by some biologists, is that they have been out-competed and displaced by salmon primarily and kingfish to a lesser degree. Both species have seen a huge increase in mass since commercial restrictions were placed on them. So, if a relatively small mass of baby tailor is eating 77t of baitfish, could you imagine what the dramatically larger mass of salmon are chewing through? If that figure boggles the mind, then factor in all the other above mentioned species. I would think a guess of 1000t would fall short.

Chris’ experiment also got me thinking about the nature of marine studies in general, and please don’t interpret my comments as criticism of his study. The short term of many recent studies provides a snap shot of the current situation, which can be very useful for short-term management. I’ve seen recent studies by both qualified and unqualified (called citizen science) people, aimed at long-term management solutions that fall short of the mark.

Chris’ study may have given a very different result if conducted 30 years ago. In this case, the decrease in tailor numbers is probably due to another Fisheries management strategy aimed at boosting a competitive species. Other factors that dramatically affect a species’ abundance often don’t get considered. The El Niño and La Niña cycles have a huge impact on fish cycles and abundance. El Niño events can occur as often as every three years, but sometimes as rarely as every seven years. To see the full effects of the cycles on fish stocks, a study would need to run for at least 10 years and preferably longer.

Another major factor is nutrient loads, which have a bigger impact on some species than others. These can vary due to things like upwellings, floods and even something as obscure as a dust storm fertilizing the ocean with iron. As mentioned, baitfish are a classic example of a boom-bust fish, as are bonito. The impact of baitfish mass through the food chain should not be underestimated. Nutrient loads vary considerably over the decades and, once again, a two or three year study is too short to determine the long-term average of their impacts.

In my experience of 35 years on the harbour, bonito boom and bust in 3-4 year cycles. When they’re booming, they are in near plague proportions. When they bust, you can go two years without seeing one. Anything less than a 10-year study of harbour bonito will not give you an accurate indication of their long-term presence or impact.

Another example, without trying to come to any conclusions as to why, is the hairtail. I’d heard stories about hairtail in the harbour, in good numbers, from the old boys. Clifton Gardens and North Harbour were the hotspots. For the first 20 years of my guiding career, I never encountered a single hairtail in the harbour. Then, all of a sudden, in they came. We have now had five years of good, regular hairtail fishing. It would be easy to conclude, in the 20-year absence, that they had been ‘fished out’ – and many did. The same went for the ‘quiet’ years on bonito. If you want an accurate picture of harbour hairtail cycles, you might need an 80-year study.

The harbour fishing has improved considerably with kingfish, mulloway and hairtail being the main features. There are stacks of school mulloway, the best run in years, hanging around the reefs and structure in the lower reaches. Their preference if for fresh squid, particularly the heads and guts, but fillets of mullet or tailor will work too. They are best targeted around the turn of the tides, mainly the high and preferably around dawn and dusk. Spots worth a look are North Harbour, Bottle and Glass Point and VB Reef in Middle Harbour.

Kings have been in good numbers and, as with mulloway, fresh squid is their weakness. February to April is the peak time for them, especially if you are looking for decent kings. Just keep in mind that kings over a metre are quite common now, so make sure your tackle is up to speed.

Hairtail have been showing up all through the harbour. The hotspots are North Harbour, lower lane Cove River and Vaucluse Bay. They are being caught in broad daylight in water temperatures of 23°C, which is in stark contrast to the midnight mid-winter sessions usually associated with them. They are not too fussy on bait, as pillies, yellowtail fillets and strips of squid are doing the trick. Fish unweighted baits that sink slowly and use a bit of berley. They are also being taken on unweighted SP lures worked slowly through mid-depths.

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