Alarm at the Blue: Why Large Predators in the Balearic Sea Leave Almost No Traces

Alarm at the Blue: Why the Large Predators in the Balearic Sea Leave Almost No Traces

Key question: What does it mean for Mallorca if the large predatory fish have practically disappeared from coastal waters?

Late in the afternoon, when the sun bathes the Passeig Mallorca in warm light and fishers at the harbor check their nets, hardly anyone talks about sharks, even after incidents such as Dead Shark at Playa Can Pere Antoni: Bite Marks Raise Questions. Yet the news from the waters around Cabrera touches precisely that everyday life: a study using environmental DNA found virtually no genetic traces of large species such as mako, porbeagle, hammerheads or the great white shark in water samples from twelve sites around the uninhabited islands. In roughly 80 samples, researchers could detect only 13 species of sharks and rays; their share of the total DNA was small.

Those numbers sound dry, but they are a warning signal. Large predators play a role in the sea that you do not immediately see: they regulate stocks, influence migrations and shape food webs. If they are missing, the balance changes — often gradually, until it becomes noticeable at the coast, for example through increased numbers of smaller predators or altered fish communities, which fishers in Portixol or Cala d’Or will also feel.

The environmental DNA method is elegant: filter water, analyze tiny skin or mucus particles, identify species without having to catch animals. But the technique has limits. eDNA decomposes quickly; a non-detection does not necessarily mean 'extinct', but can mean: nobody was present in the days before sampling. Spatial coverage and sampling timing also strongly affect results. The study authors themselves point this out.

At the same time, one cannot draw a reassuring 'everything is fine' from the absence or very low detection. The combination of rare finds and the disappearance of genetic traces over years is a red line: these species are no longer regularly present in the habitats that once served as migration corridors and hunting grounds — including the so-called Émile-Baudot ridge, which fieldwork suggests should attract pelagic species but yielded hardly any traces.

What is missing from the public conversation? First of all, clarity about the drivers of this decline. Discussions often only produce buzzwords: tourism, overfishing, protected areas. What is missing are precise open data on bycatch rates, on large-scale fishing gear such as longlines in the region, and long-term observation series that combine eDNA with visual methods and catch statistics. Also little discussed is the underwater noise level from shipping or yacht anchor activity, which can disturb migratory species.

A small everyday image: early in the morning at the marina you see vendors selling prawns from their coolers, sport divers at the quay discuss a weak tuna run last week. No one brags about shark sightings, as recent finds illustrate: Dead shark on Palma's city beach: a sign of a bigger problem?. And apparently that is no coincidence.

Concrete proposals that go beyond good intentions:

1) Expand and network monitoring: collect eDNA regularly and seasonally, complemented by BRUVs (baited remote underwater video), telemetry tags and reporting systems for fishers. Only a combined picture shows whether species are passing through the sea or gone for good.

2) Strengthen protected zones along key structures: the Émile-Baudot ridge and neighboring seamounts should face reduced fishing pressure and be considered functional protected areas with no-take sections. Protection must be enforced — rules on paper do little without control, as dramatic images of an injured shark off the Paseo have shown in Dead Shark at the Paseo: A Wake-up Call for Better Coastal Protection in Palma.

3) Regulate fisheries and reduce bycatch: longlines and similar techniques must be adapted in sensitive corridors: seasonal closures, mandatory bycatch reduction measures, and compulsory reporting of bycatch. This requires dialogue with coastal fishers; bans without compensation lead to resistance.

4) Fund research, use tourist contributions: part of the income from port and tourism fees can flow into monitoring programs. Transparent funding pools provide continuity for datasets that are as important as road maps for managing the sea.

5) Involve citizens: divers, sailors and fishers can do citizen science: report sightings, take water samples, upload photos. Local engagement builds acceptance and provides additional data.

My conclusion: the blank spaces on the eDNA map are a warning sign, not a final verdict. But we should act as if the ecosystem is under pressure — because it clearly is. Anyone eating an ice cream at the harbor in Palma and hearing a boat engine should not rely solely on the comforting fact that encounters with great white sharks are unlikely. It is rather about what is no longer visible: the invisible chains of marine life that also shape our fishing grounds, beaches and ultimately everyday life in Mallorca. Without targeted measures the island will notice the consequences sooner or later — and then the options will be more expensive and harder than making a change now.