Protected seabirds at risk of predators attracted by larger tuna farms

The increased predation by yellow-legged gulls on protected storm petrels and other smaller birds around Mellieha could be a consequence of relocation of tuna farms to just 4.8km from the Rdum tal-Madonna cliffs.

An environmental impact assessment for Azzopardi Fisheries’ plans to double the size of its tuna cages stated that seabird colonies off the Rdum tal-Madonna cliffs and eastern Comino could be affected by the new aquaculture zone.

The tuna pens were given a temporary relocation permit last year without any environmental impact study in 2017. Since then, Azzopardi Fisheries has applied for a permit to double tuna cages in the same area, claiming the tuna fish do not have sufficient space to grow at optimal size.

Biologist John J. Borg said in the EIA that the raw and unwashed fish food is attracting storm petrels closer to tuna pens, which in turn could also attract birds that prey on them. “The same food supply has attracted a constant presence of small fish around the pens which in-turn attract gulls and terns,” he said.

Tuna farmers want to double the size of their cages

BirdLife Malta has already raised the concern of the potentially increased vulnerability of storm petrels to seagulls.

But the EIA states that it is unclear whether gulls would actively hunt storm petrels aggregating around the tuna pens. “If these introduced opportunities result in an increase in the seagull population, this could directly and indirectly impact upon the breeding population of the other breeding seabirds through increased predation and competition for nesting sites,” the EIA warns.

The impact would be lessened if feeding regulations are enforced and the baitfish is washed before being fed to the tuna.

While adult storm petrels regularly fall prey to yellow-legged gulls on the isle of Filfla, no interactions between gulls and storm petrels have yet been noted near the tuna pens.

Since shearwaters and storm petrels are diving birds, they face the risk of entanglement in the fish farm nets, resulting in drowning. Borg has noted, however, that no such incidences have yet been reported.

Fish farms can be a source of marine debris such as plastics, which can cause death to seabirds by dehydration, blockage of the digestive tract, or toxins released in the intestines.

The EIA recommended minimising light and noise pollution which can impact on the bird colonies.

In the past entire seabird breeding colonies in Xlendi Bay, Hal-Far, Ghar Lapsi and Wied iz-Zurrieq were abandoned when electricity was introduced in the area.

To avert these impacts the EIA suggests a downscaling of activities at night, the setting up of a seabird monitoring programme, the monitoring of gull colonies and the training of staff “in appropriate bird handling and reporting”.