25/06/2026
Article written by Barry Wareham – June 2026
I can’t believe how long it has taken me to figure this out!
I have spent my entire life on and around the beaches and estuaries of our eastern seaboard and during this time I witnessed what I assumed to be larval crabs entering different streams and rivers. I just assumed it was probably our very tasty mangrove (or mud crab). I didn’t see it that often, probably ten or twelve times, but I had absolutely no idea as to exactly what was happening.
I really enjoy fishing with ultra-light tackle and artificial lures whenever the opportunity arises and am very familiar with when and where one of my favourite estuarine species, the perch (or river bream), spawns. This year I did a lot of this type of fishing as the sea was often too rough for anything else. At the beginning of this season, I very quickly noticed something really strange. We have often caught other predatory species whilst fishing for the perch, such as kob, kingfish, springer, flatheads, etc. At times there were lots of perch in a really rough sea at the river mouth and they were viciously attacking one of my favourite lures, the Rapala Countdown in a 3.5 and 5.5 cm size. Not only perch, but suddenly stone bream, blacktail and very small spotted pompano, were also in the mix. It wasn’t just the fact that it was a stone bream eating a Rapala that baffled me, but also that the fish were also in extremely shallow, turbulent water. To add to this, we should have been catching ripe running male perch, with the very odd female that had come down to release her eggs into the sea, but we were catching equal amounts of males vs females. Surely all the females were not down at the mouth spawning at the same time.
The next strange thing that I witnessed was an apparent spawning taking place on the wrong tide and in the wrong place. There were big swirls and little swirls, all over on the water surface and on the one occasion, my son Blayne and I actually watched this progress up the river. I was completely baffled and started doing some research, which didn’t help. Nothing was making sense! Then one morning again in a big sea and a strong surge, I noticed the same spawning type swirls happening on a very shallow bank next to the river mouth. At times the bank was high and dry and with the next surge, it would be covered in about a foot of water and there would be swirls all over, big ones and little ones. It definitely looked more like feeding behaviour and not spawning. On this particular occasion, the blacktail were very aggressively eating the Rapala in a channel about three metres wide and a metre deep of fresh water that was coming out of the river. What was going on?
The next day everything fell into place. Early in the morning in the dark it was very quiet, but as it got lighter the swirls started and became more and more abundant. The fish were absolutely wild. All of a sudden somebody turned the switch off! The swirls continued, but I could not get another bite, no matter what lure or technique I tried. I hadn’t noticed, but now that I did, I was amazed. The swash zone and sand was covered in tiny little crabs, all trying to make their way up the river. What a relief! Problem solved 😊 I used my phone camera to zoom in on an individual crab on the wet sand and only when I got home and looked at the pictures, did I see a completely transparent larval fish in the picture near the crab.
In the beginning, there were only small numbers of these little crabs and there was obviously a lot of fish there to eat them. Competition must have been quite fierce and any smaller fish were aggressively chased away, hence all the strange catches on the Rapala. As the quantity of food increased, there was suddenly no need to worry about competition and it got to a point where the fish were full of the tiny crabs. I had on a number of occasions in the past picked up these tiny little crabs, squashed them as hard as possible between my thumb and forefinger, rolled them around, put them down on the sand and watched them scuttle off on their way! Unbelievably tough.
This first wave of crabs must have lasted a good ten days and at its peak there was often a band of crabs fifteen metres long by a metre wide by 10cm deep making their way up the wet sand on the side of the river, swimming where they could, but walking where the current was too strong. I have since witnessed three of these waves of crabs over a period of three months. I also saw a few reports of these crabs being seen by the odd observant person, as far north as Sodwana and as far south as Uvongo. I took the time to go and investigate every single little fresh water stream or source in close vicinity of Salt Rock and was amazed to find them at every single one. At Westbrook, there is an outfall pipe at the lifesavers’ hut, forming a little stream down to the beach. These crabs were making their way up the stream to the rocks and cement, climbing up and into the pipe. The flow was strong inside the pipe and I filmed a video of them on both sides of the flow making their way up the pipe – fascinating!
This is an event of immense significance in nature.
I spent a lot of time chatting to friends in the scientific community and doing some research myself. The freshwater or river swimming crab (Varuna Litterata), lives in almost every freshwater river/estuary on the eastern seaboard of Africa, right up around India, down to Indonesia and parts of Australia. At some stage the female crabs release their fertile eggs into the ocean. Whether fertilisation takes place in the river or out in the ocean, is not clear, but these eggs (40,000 to 50,000 per female), hatch into the first stage of their lives (Zoea). These are tiny little planktonic creatures. They feed and grow, probably malting many times (nobody seems to know how long they do or can maintain this form).
At some stage, they are big enough and ready to metamorphosize into the second stage of their lives, which are the little crabs that we are witnessing. These are known as megalope. Between mid-April and the end of June, they emerge from the ocean and into our estuary and freshwater systems. They are about as big as a lentil, quite transparent with some freckles, but seem to have the ability to change colour somewhat, quite quickly. Their fairly obvious eyes are placed at the front and sides of their head. They are very good swimmers, but are also very able to walk. It seems that their activities are restricted to the day time and that they key into freshwater sources on the coast.
I have never seen them at our larger river mouths and estuaries as it seems that they are able to get in and up the river without having to walk up the sides of a fast-flowing small stream or river. They swim wherever they can, but walk on the sides where the flow is too strong. They have been recorded in the fish ladders alongside weirs in the Tugela river above Mandeni. Nobody seems to know how long they are at liberty in the ocean before making this upstream migration. It does seem that some batches of the megalope are bigger or smaller than others, so it could be that some have grown and malted more than others, because they have spent more time in the marine environment.
Once they have reached the area that they are happy with in the river or estuary, they then go through metamorphosis once again to become a proper juvenile swimming crab. In this last stage of their life they live in little burrows in the mud or river bank, or under branches, etc, and grow to become adults. Not clear again on how long it takes for them to reach sexual maturity and then whether they actually return after having spawned in the sea.
When you see the magnitude of this, you will be blown away and to think that it happens at every single little stream, river and outfall pipe on our coast, is truly an event of immense proportions. I have included some pictures and videos from this year’s event.
