On the Moroccan Mediterranean coast, hundreds of boats equipped with large nets, called purse seines, go out six days a week to fish for small pelagic fish (coastal or oceanic fish).
In the last two decades, seine fishing has become more difficult as bottlenose dolphins attack the catch and pierce the nets, which extend like a wall into the sea. These nets are expensive to repair, and dolphins are sometimes caught, injured or killed.
Economic loss as a result of dolphins’ interference with purse seiners is difficult to estimate. The Food and Agricultural Organisation has estimated up to 36% losses by fishers and between 9% and 19% per ship annually in Morocco. The agency, in conjunction with the General Fisheries Commission for the Mediterranean, is developing a protocol for better data collection.
In Morocco, aquatic mammals like dolphins and whales are protected by national and international legislation and the Agreement on the Conservation of Small Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (Accobams) ratification law of 1999.
But it’s hard to protect a population when there’s not much information about the threats it faces.
A major challenge faced by the Moroccan Mediterranean fisheries sector is the lack of quantitative data on the interactions between bottlenose dolphins and purse-seiners. Only a few Mediterranean studies contain sufficient information to evaluate both the number of dolphins caught by mistake and the so-called “depredation” – attacks on the fishing gear by the dolphins.
As a PhD researcher completing my research on bycatch of vulnerable species in the Moroccan Mediterranean Sea, I joined a team of other marine biologists to conduct a study in the Al Hoceima region.
Our study was carried out in 2020 in Al Hoceima Bay, some 150km east of the Strait of Gibraltar. Using on-board observers and questionnaires, we determined the mortality rate of bottlenose dolphins and the financial losses incurred by fishermen in repairing nets attacked by bottlenose dolphins.
Our goals were to assess this interaction and identify ways to reduce the conflict.
We found that on average, more than two dolphins were caught on each of 48 trips. The mean cost of repairing damage to the nets was US$179 per incident. Sometimes it cost up to US$1,000. These costs have made fishing less attractive in the region. The seiners have shifted their activity to other areas since the 2010s.
The dolphins
The bottlenose dolphins prey on the fish that the fishers catch and are attracted by the way the nets concentrate the fish in one place.
As a result, they sometimes get caught in the nets. This results in death or physical injury to dolphins.
Our research revealed that a total of 121 dolphins were captured in nets during 48 fishing trips (four trips per month throughout 2020). Eleven of the dolphins died. Each trip included one to three fishing operations, depending on the seine tear rate. The number of fishing operations observed was 94 in total.
The Mediterranean bottlenose dolphin subpopulation is still classified as “Least Concern” by the International Union for Conservation of Nature. However, there are concerns about the decline of bottlenose dolphins in the Mediterranean.
The fishers
The Moroccan fishermen who fish along the Mediterranean coast are frustrated by the negative impacts that dolphin behaviour has on their industry.
In terms of damage to fishing gear, we observed between 28 and 230 holes per net per incident. Some were large, but the majority were smaller than 35cm. The cost of repairing the holes in nets caused by these interactions was estimated at US$179.52 per repair, which is costly for the fishers. For large holes the repair took from 24 to 72 hours. While the large holes were repaired, the fishermen continued fishing by using their spare net. Repairs required the hiring of 3 to 11 net menders, depending on the size and number of holes.
In Moroccan Mediterranean ports, small pelagic fish fisheries provide the greatest socio-economic benefits for the fishing industry. For the port city of Al Hoceima, purse seining for small pelagic fish plays an important role in the local economy. It provides 315 direct and 100 indirect jobs. In 2020, Al Hoceima purse-seiners made a total of 315 fishing trips, harvesting just over 669 tonnes in total, compared to 5,123 tonnes in 2015. This shows the direct impact of these dolphin interactions on jobs and the drop in fishermen’s income.
What must be done about it
There is a need for further research into bottlenose dolphin behaviour and mitigation strategies. This should include the possibility of using acoustic devices that emit sound waves to discourage bottlenose dolphins from purse seines. Research into alternative fishing techniques will also be valuable.
There should also be a compensation scheme to design effective conservation strategies and to improve the ecological and economic sustainability of the purse-seine fishery.