Bycatch of Cetaceans from Dutch Fishing Vessels, a long Described problem in Irish waters. 

Martyna Frankowska | ORCA SciComm Team. • 20 March 2020

By-catch of cetaceans (whales, dolphins, porpoises), are a common problem all over the world. By-catch are the unwanted fish and other marine creatures trapped by commercial fishing nets during fishing operations for commercially valuable species. This occurs because these nets trap everything larger than the net's mesh. This often includes sharks, seabirds, marine turtles and cetaceans.

Harbour porpoise by-caught in fishing net. Photo source: WDC, U.K.

The numbers of cetaceans accidentally caught by Dutch fishing vessels between 1989 and 1994 in Irish waters was studied extensively. Although at first, it was difficult at first to persuade these vessels to cooperate and record the amount of by-catch of cetaceans, by 1994, 12/12 Dutch fishing vessels agreed to cooperate. Each vessel was equipped with a poster with clear illustrations of numerous cetacean species and information about the project.

Atlantic white sided dolphin on Faroese dock. Source: fodderforthinking Wordpress.

(A total of 61 dolphin stomachs were analysed to see which fish species were the most commonly consumed. The by-caught individuals examined included 47 Atlantic white-sided dolphins ( Lagenorhynchus acutus ), 11 short-beaked common dolphins ( Delphinus delphis ), 2 bottlenose dolphins ( Tursiops truncatus ) and 1 white-beaked dolphin ( Lagenorhynchus albirostris ). Sieves were used to separate hard prey remains, (e.g. otoliths), of fish from the dolphin stomachs. These remains were then carefully examined. The results showed that 44 white-sided dolphins had intact or partly digested fish in their stomachs most of which consisted of mackerel. Horse mackerel remains were mainly found in stomachs of common and bottlenose dolphins but not at all in white-sided dolphins. Silvery pout (which is a mesopelagic species) were most frequently found in stomachs of white-sided dolphins.

So, why was it that mainly white-sided dolphins that were captured most often? It is believed that Atlantic white-sided dolphins migrate from deeper oceanic water to more shallow water (about 200m) when mackerel arrive on their migration.


So, why is it that mainly white-sided dolphins were being captured most often? It is believed that Atlantic white-sided dolphins migrate from deeper oceanic water to more shallow water (about 200m) when mackerel arrive on their migration.


Strandings of Atlantic white-sided dolphins are less frequent in recent years along the Irish coasts. This can possibly be due to the quantity of by-catch caused by the fishing industry which greatly reduced their numbers in Irish waters or changes in distribution as a result of climate change.



Reference :

Couprus, A.S.,(1997). Interactions between Dutch midwater trawl and Atlantic white-sided dolphins ( Lagenorhynchus acutus ) on the southwest of Ireland. Journal of North Atlantic Fisheries Science . 22, 209 - 218.

© Ocean Research & Conservation Ireland (ORCireland) and www.orcireland.ie , est. 2017. If you like our blogs on the latest news in marine science and would like to support our work, visit www.orcireland.ie to become a member, to volunteer or to make a donation today.

SHARE THIS ARTICLE

by ORCA SciComm Team 5 September 2022
Bird Flu is a serious threat to Irish Gannet Colonies. ORCA SCI-COMM TEAM | 04 September 2022 ORCA Ireland are deeply concerned about the severe epidemic of bird flu of the H5N1 strain, which is highly pathogenic in cases of pelagic seabirds and has now hit seabirds in Irish waters. According to top scientists at the University College Cork (UCC), avian influenza has now reached Irish Gannet colonies. Recent reports from Irish scientists and members of the public have indicated a huge increase in the numbers of dead northern gannets off the Irish coasts. These increases in seabird deaths may be linked to the Highly Pathogenic Avian Influenza (H5N1).
by ORCA SciComm Team 14 July 2022
PCB Pollution Threatens Global Killer whale ( Orcinus orca ) Populations. ORCA SciComm Team | 14th July 2022 Global killer whale population are predicted to collapse due to pollution with polychlorinated biphenyls (PCBs). A scientific report which used individual-based models combined with globally available data on PCB concentrations found that PCB-mediated effects on reproduction and immune function threaten the longterm viability of >50% of the world’s killer whale populations.
by ORCA SciComm Team 29 April 2022
Russian Navy Trained Dolphins Deployed in Crimea ORCA SciComm Team | 29th April 2022 Russian Navy Trained Dolphins may have been deployed in Crimea, with two sea pens having been spotted at one of their bases in satellite imagery since the start of the Ukraine invasion in February, according to the US Naval Institute.
by Danielle Brennan | Communications Officer 15 March 2022
FEMALE KILLER WHALES FACE GREATER IMPACT FROM NOISE POLLUTION Danielle Brennan | Communications Officer | 15th March 2022
by ORCA SciComm Team 1 March 2022
A solitary common dolphin can speak porpoise language! ORCA SciComm Team | 1st of March 2022 A new paper published in “ Bioacoustics - The International Journal of animal sound and its Recording ” has detailed how a solitary common dolphin in Scotland has learned to speak porpoise language!
by ORCA SciComm Team 4 February 2022
Iceland to end whaling in 2024 with drop in demand for whale meat. ORCA SciComm Team | 4th February 2022 Iceland have announced an end to commercial whale hunts in 2024, after a government minister commented there was "little justification for the practice". Whaling in Iceland is no longer profitable, due to a decrease in the consumption of whale meat and since Japan re-commenced whaling operations after a three decade hiatus in 2019.
by ORCA SciComm Team 25 January 2022
RUSSIAN MILITARY TESTS THREATEN WHALES IN IRISH WATERS ORCA SciComm Team | 25th of January 2022
by ORCA SciComm Team 11 December 2021
Shell Oil & Gas Seismic Surveys Threaten Whales off South Africa ORCA SCI-COMM TEAM | 11th of December 2021 Across the globe there is public outrage due to the planned seismic surveys to search for oil and gas deposits off South Africa's Wild Coast by energy company Shell. Environmental NGO's, Human Rights Organisations and local fishing communities are trying to stop the seismic surveys through litigation, due to the harmful impact seismic surveys can have on marine wildlife. South Africa is home to 37 species of whales and dolphins, but these anthropogenic activities threaten the survival of wild whales off Africa's south coast. Let's dive deeper to investigate what seismic surveys are and how they can harm whales!
by ORCA SciComm Team 9 December 2021
How to Create a Sustainable Wardrobe! ORCA SciComm Team - 9th December '21 The idea of creating a sustainable or ethical wardrobe from scratch is, without a doubt a challenging task. You may not be able to wear the brands you are used to, limiting your choices in terms of trends, not to mention having to spend a little more than you would normally. All of these are valid concerns, but creating a sustainable wardrobe isn't as hard as you may think. Read on to find out tips and tricks to help you transition from a "fast fashion" foe to a "slow fashion" soul sista!
by ORCA SciComm Team 4 December 2021
Russian “Whale Jail” finally Abolished. ORCA SciComm Team | 3rd of December 2021 The incommodious confined pens in Russia’s infamous “Whale Jail” have finally been abolished to ensure marine mammals will not be held in these captive facilities in the future!
Show More