Lukim yu bihain is an informal good-bye in Tok Pisin, a Bislamic language spoken in Papua New Guinea (PNG) – the place where this blog post starts. More specificaly, we start on the island of New Britain, which is part of the Bismark Archipelago – a group of islands off the northeastern coast of PNG.

I ask you to consider that while the relationships between people and the sea, or the ‘social life’ of the sea, has been rather extensively studied in the South Pacific, the social lives of rivers have not been given as much attention. As Torgersen (2018) posits, given the importance that rivers hold for society, it makes sense to ask whether rivers in the Pacific are equally as interesting and complex as the sea (Wagner and Jacka 2018). Given my time living and working in Australia and other parts of the Pacific, I say YES, both in terms of those rivers being interesting and complex, and to riverine social lives being overlooked.

In 2019, I started back to work in the South Pacific, with colleagues and communities in New Britain, to identify and explore questions about riverine fishes as well as local dependencies and cultures linked with these species and rivers. I thought I’d take the opportunity through this blog series to highlight some of the fishes that live in New Britain rivers that share a fascinating form of migration with others across the Pacific.

Remarkable and colourful fishes inhabit the rivers of New Britain and other islands across the Pacific. These islands are colonised by fish species from the Gobiidae family, and others, whose life cycle is adapted to the oligotrophic (that means low dissolved nutrients, sparse algae growth, and high oxygen content) and seasonally variable hydrology of local rivers. Some of these inhabitants are featured in the short video below – I hope they inspire interest!

Now, the theme of our running series is migration, and the fishes dwelling in island rivers across PNG and the Pacific do not fail to deliver! While many of these fish species are tiny (picture finger length on average) they pack a migratory punch!

Many of the fish species adapted to the river conditions present across much of the Bismarck Archipelago undertake a form of migration called amphidromy, which means that they spawn in rivers, their larvae drift to sea where they eat and grow, and individuals return to rivers as juveniles to grow and then reproduce in those rivers as adults!

For those who are new to migratory life cycles, and amphidromy, I made a handy graphic (below) to put this a bit more in perspective.

In New Britain and PNG, the greatest number of these amphidromous fish species are likely belong to the sub-family Sicydiinae. The fish species in Sicydiinae have a sucker formed by the fusion of their two pelvic fins (often situated between the mouth and gills on the fish’s underside; see below), and this adaptation allows them to rapidly access high reaches of rivers where large boulders and waterfalls prohibit access by other species. Some of these waterfalls can be hundreds of meters high (see below).

There’s no challenge too big for these members of team tiny fish! They use those fused pelvic fins to scramble 100s of metres up waterfalls to find the world’s best mate!

If waterfall scaling isn’t impressive enough for you, juveniles of these amphidromous fishes drift dozens of kilometres downstream to sea where they can spend weeks floating along, feeding and growing before finding their way back to rivers! Nemo’s got nothing on these fishes ability to find their way ‘home’.

That brings me full circle back to the title of this post, and why I started it with, Lukim yu bihain. That is because these amphidromous members of team tiny fish are adapted to ‘saying’ good-bye to persist in the dynamic rivers and coastal systems that dominate Pacific island nations. Their tiny size, the focus on the social lives of the sea, and these species adaptation to say good-bye to the rivers and sea throughout their life cycle is part of why we know so little about them.

My interest in these amphidromous fishes started during my doctoral training in northern Australia where previously undocumented species of Gobiidae started being sampled by scientists in the fast-flowing coastal waters. Having held so many of these fishes in my hands, and watched them dart across river bottoms, I can’t help but continue to be inspired them. I look forward to continued work with communities in New Britain about these remarkable fishes and the rivers (and sea) that they depend on!

Thank you for reading! Our next migratory species post is in two weeks!

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