world of fish migration

world of fish migration
The migration of fish is a complex and often little understood part of the biology of the marine world. Anglers are usually closely tuned into the way that fish migrate and turn up at a particular spot at a certain time of year.
The following article shares a few of my observations based on years of experience, and without doubt, things have changed in the last decade or so, with new species turning up in places they haven’t been seen before and the number and abundance of certain fish changing each year. The East Australian Current is a highway for migrating fish. It starts to wind its way south in September each year and reaches southern Queensland around late November before pushing south along the NSW coastline. It is a strong flow of warm water coming from the northern Great
Barrier Reef and carries an abundance of life.
Each year is a bit different. In a good season, we encounter juvenile black marlin in big numbers, yet in a poor season, we can see few or no fish. This juvenile marlin is spawned in late winter and spring and grow rapidly as they move down the Queensland coastline. Sometimes the current and the bait schools it carries can be well off the coast, and areas can miss out on good fishing as the fish continue to move on, bypassing some ports. The abundance of fish, however, is more related to how successful the spawning run was in the previous spring. Most adult black marlin spawn on the reef edges north of Cairns and the juveniles move inside the edge of the reef where they rapidly grow before moving south with the current. This movement of marlin fry is thought to be dependent on strong south-easterlies that push the juveniles inside the reef passages into warm shallow water. In general, if there is a good fishing season for big black marlin off Cairns there will generally be plenty of juveniles moving southwards a few months later. When the inshore currents run close to the coast a lot of juvenile marlins are caught very close to shore, and in some seasons large numbers of these fish are encountered in Hervey Bay, creating one of the most exciting inshore marlin fisheries in the world.
When this happens there can be spectacular fishing on the shallow flats where fish can at times be sight cast to. One angler I know caught a juvenile black marlin when he was targeting flathead!
As well as marlin, the East Australian Current carries a wide range of other pelagic species including dolphin fish, wahoo and tuna. Spanish and spotted mackerel tend to migrate south on the inner edge of this current and never stray too far offshore. Every year we see a marked difference in the numbers and species we catch as the current snakes its way south. We rarely see all of the more common species in abundance. Some years dolphin fish dominate, in other seasons there is plenty of destructive wahoo cruising the current edges. The inshore mackerel season can vary greatly from year to year. These fish tend to turn up at exactly the same spots each season. Spotted mackerel, in particular, seem to have an internal GPS that takes them to a particular reef, while nearby similar areas hold none of these fantastic fish.
For many species of fish, migration occurs in relation to breeding. Flathead is a good example of this. In my local area in late August large numbers of big female flathead, accompanied by swarms of smaller male fish, move into the mouths
of the estuary to spawn. Further south, similar migrations take place a few months later. At this time the female flathead is located near the spawning beds, which are generally made up of quite coarse sand. This granularity of sand allows the milt and roe to mix in the gaps between the sand grains, and these very important spots are extremely important to maintain flathead populations. At this time of year, all flathead in the estuary are extremely active and feed aggressively prior to the spawn. The interesting thing about the flathead population in my local region is how hard they are to find in the summer months when the water temperature gets hot and the northerlies start to blow hard. Most tagging data shows that f la thread tend to stay in one area for most of their lives, but the absence of fish in the summer months is quite perplexing. Some anglers believe they move out to sea and live in the surf line in summer, where they are often caught by anglers chasing other species. The spawning migration of sea mullet is quite fascinating. In preparation for spawning, these fish move out of the rivers and estuaries and form large schools and move offshore. While most of this fish travel along the beaches just past the surf line.