Fish swims to the same nest each year just like migrating birds

Gaël Modrak/age fotostock/Superstock

By Vera Novais

Species: Shanny (Lipophrys pholis)

Habitat: Rocky intertidal areas along the east Atlantic coast, from the UK down to Mauritania

The ocean is a big place, but one small fish finds its way back to the same nest to tend to its eggs year after year.

This behaviour is reminiscent of migratory birds such as white storks or swallows. But unlike them, the fish does not migrate over long distances. Instead, it disappears for months on end from its rocky shore breeding sites along the western coasts of Europe and North Africa, travelling offshore to feed.

“The most interesting thing is that they get back to the same nest or to a very close one,” says Paulo Esteves Jorge at the University of Lisbon in Portugal. “It’s surprising to see in a non-migratory species standard behaviours of a migratory one.”

Male shannies (Lipophrys pholis) – which care for the eggs – were already known to return to their nests if they were artificially removed during their breeding season, from October to April. “Males show a great fidelity to the nest, being able to quickly return to it in the same year if they were taken away,” says Jorge.

The fresh finding that they return each year has emerged after the team tracked 211 of the fish over a three-year period using tiny electronic tags. “We believe that other similar species will have the same behavioural pattern,” says Jorge.

The team also conducted experiments in which they removed four fish from their nests and placed them more than 100 metres away, finding that half of them returned within two months.

Returning to breeding sites, much like sea turtles do, requires homing abilities, including well-developed navigation skills and an aptitude for keeping track of your position.

Finding the way home

Paulo Jorge says it’s not yet clear how shannies find their way back, and they may use scent, visual landmarks or other cues. They are normally found in intertidal zones, which are submerged at high tide and exposed to air at low tide. They emerge from rock pools or from underneath damp stones and seaweed at high tide to forage over the shore.

“Many species of intertidal rock-pool fish have excellent homing capabilities backed up by fantastic spatial learning,” says Culum Brown at Macquarie University in Sydney, Australia. “This paper extends this work by tracking fish over a three-year time frame, far longer than previous efforts.”

So why do these fish do it?

Nesting seems to be energetically demanding for shannies, with some of them taking a gap year before returning to their nest – perhaps because they can’t feed as much while nesting.

Returning to well-known nests might be advantageous, saving the shannies energy on finding a new nesting location and meaning they know better where to find food and avoid predators while tending eggs.

Now, the team wants to know what makes a nest so special for a given male fish and how many females visit each nest to lay their eggs.

The researchers also still wonder why these animals only stay in the breeding area for a month during the breeding season – whether, for example, it is too energetically demanding to stay longer, or whether they have another nest to visit elsewhere.

Journal reference: Journal of Fish Biology, DOI: 10.1111/jfb.13171

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