The research surrounding bycatch of endangered, threatened, and protected (ETP) species of marine megafauna highlights significant challenges regarding the unintentional capture of these species during fishing activities. Addressing the challenges around this topic requires a multifaceted approach, combining scientific inquiry with multiple stakeholder collaboration to develop effective mitigation strategies, being the fishing industry the key partner of such collaboration.
Innovative mitigation measures are being researched, yet the scope of bycatch challenges remains vast, with insufficient understanding among other things, of species-specific rates and demographic impacts. Notwithstanding, research on fisheries bycatch mitigation has highlighted various strategies and technologies aimed at reducing interactions with ETP species. These studies demonstrate the effectiveness of specific measures implemented in different fishery contexts and the ongoing need for innovation and a strong stakeholder engagement in bycatch management and mitigation. A very common consideration on studies around the subject relates to the need for context specific approaches.
What is new?
A new study recently released in Marine Policy by Acevedo-Iglesias et al., coauthored by scientist affiliated to academia, the fishing industry and national research institutions, including contributors from the H2020 REDUCE Project, evaluates the impact of two decades (2003-2022) of bycatch management measures on purse seine tuna fisheries in the Atlantic and the Indian Oceans (under ICCAT and IOTC Regional Fisheries Management Organisations, RFMOs) to assess whether these measures have improved the survival of ETP species and whether they have enabled a decrease in discards and increased retention for non-ETP species.
The study concentrates, specifically, on the Spanish-owned tuna purse seiner fleet and other vessels associated with the OPAGAC-AGAC[1] observer program. The study analyses bycatch trends and the fate of non-target species caught during fishing activities targeting tropical tuna species such as yellowfin tuna (YFT), skipjack tuna (SKJ), and bigeye tuna (BET). These fisheries are among some of the most important fisheries globally. The fishing methods addressed include sets on free-swimming schools (FSC) and schools associated with floating objects (FOBs).
The data for this research were primarily sourced from scientific observers under Spain’s National Data Collection Framework (DCF) and the OPAGAC-AGAC observer program. These programs, funded BY both the EU and OPAGAC-AGAC. provide comprehensive data on the fishing activities of Spanish-owned tuna purse seiners. Additionally, the Spanish fleet implemented a Code of Good Practices (CGP) in 2012, aimed at mitigating the impacts of the fishery on ETP species, making it a valuable case study for assessing the effectiveness of bycatch mitigation measures. The CGP involved increasing the observer coverage to 100% of the fishing activities by 2015, details on the fishing activities such as the location and the fishing sets, the fishing methods (FSC or FOBs), the amount of catch retained and discarded by species and the condition at release of the discarded animals.
What is the overall outcome for the Atlantic purse seine tuna fisheries on what it refers to ETPs bycatch?
For the Atlantic purse seine tuna fisheries, the study highlights significant improvements in the live release rates of ETP species due to the implementation of the CGP and various t-RFMO regulations. Overall outcomes include:
The majority of the bycatch (69%) in weight was for neritic and temperate tunas and most of those were retained. The group of other bony fish (with about 90 species) represents another 19% of the bycatch rate, most of it also retained. But what happened to ETP species?
- Sharks: This group represents about 8% of the bycatch in weight. Live release rates improved significantly after 2014 as a result of regulation implementation, with sharks achieving a 75% live release rate in recent years. Interactions show similar values for FOB and FSC.
- Billfish Species: represent 2,61% of the total bycatch weight. Most billfish bycatch was dead upon retrieval as these species normally arrive dead on deck. Retention rates initially increased but still dead discards rise up to 70% in the last years of the study period. It is noticed a decreasing trend on interactions with FSC sets in comparison with FOB.
- Mobulids and Rays represent only 1% of the bycatch weight. Since 2012 rays show an increase in live discards reaching an average of 93% in the last three years. Again, interaction values are similar between FSC and FOB.
- Marine Turtles: Nearly all marine turtles accidentally caught were released alive throughout the study period, with no significant changes observed, as live release rates were already near 100% before the CGP implementation.
- Cetaceans and Whale Sharks: Interactions with these species were rare, and nearly all were released alive. Interaction rates for cetaceans decreased significantly over time, with very few cases reported in recent years.
And what are the findings for the Indian Ocean data analysed?
For the Indian Ocean purse seine tuna fisheries, the study highlights the following findings regarding ETP species bycatch:
- Sharks: As well as in the Atlantic, represent the most abundant group of bycatch, among the ETPs, in weight (11,48%). There were observed significant improvements in live release rates after 2014, with live releases increasing to 42–70% in recent years. Bycatch rates for shark species were about 4 times higher in FOB than in FSC. Silky sharks accounted for over 90% of the total bycatch for sharks.
- Billfish species account for about 2% of the total bycatch weight. Most of the billfish species are already dead when brought on board. In the initial years, the majority of the catches were discarded (dead), contrasting with the beginning of the second observation period, where the majority of the bycatch of this group was retained. Higher rates of interaction probability occur on FOB.
- Rays and Mobulids account for 0,7% of the discarded weight in this area, with giant manta ray being the most predominant species. Live release rates improved significantly, with dead discards decreasing from over 60% in earlier years to around 21% after 2015. Improvements after 2015 are reported on both FSC and FOB.
- Marine Turtles: Nearly all marine turtles were released alive, with live release rates close to 100% in recent years. Interaction rates with turtles were higher in sets on floating objects (FOBs) compared to free-school sets
- Cetaceans and Whale Sharks: Interactions were rare. All observed cetaceans and most whale sharks were released alive, with only one whale shark released dead in 2016 and 2022. Interaction rates for these species were very low
What are the overall take-aways from this research?
The implementation of the Code of Good Practices (CGP) and t-RFMO regulations has led to significant improvements in live release rates for sharks and rays, while marine turtles and whale sharks already exhibited high survival rates. However, challenges remain, such as reducing post-release mortality and addressing the increasing discard rates for billfish species.
Additionally, the bycatch rates observed were generally lower in the Indian Ocean, as compared to the Atlantic. Another important consideration to highlight is that the findings from this study may differ from those for other fleets due to several factors such as the characteristics of the fishing areas and the operational differences among the fleets.
From a geographic perspective the study also provided some very relevant information on areas where purse seine bycatch rates are higher. Heatmaps reveal that bycatch interactions are higher for purse seine fisheries in coastal waters near Gabon, Angola, and Mauritania, in the Eastern tropical waters of the Atlantic Ocean, which show higher bycatch rates of sensitive species like cetaceans, whale sharks, sea turtles, sharks, and rays. In the Indian Ocean, while cetaceans and whale sharks do not show higher catch rates in any specific area, higher interaction probabilities for other groups appear in the northwest (10–20°N), with mobulids and rays widely distributed, especially north of Seychelles.
The scrutiny of ETPs bycatch data in this research demonstrates why it is so important to assess the bycatch issue on a case-by-case basis, with a context specific approach. This stresses also the need to conduct similar studies for other key fisheries, in particular gillnet and longline fisheries, which are known to have higher catch rates of ETP species, in order to be able to assess hotspots for ETP species and consider meaningful actions to mitigate those impacts.
[1] Producers’ Organisation of Large Freezer Tuna Vessels from Spain.
