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Delivering on Climate & Biodiversity Targets Through Better Fisheries Management:Questions and Answers

Delivering on Climate & Biodiversity Targets Through Better Fisheries Management


Questions and Answers

From Monday 22 March, 2021: Science webinar: Ending overfishing delivers for climate mitigation, adaptation, biodiversity and people

  • Q: This is a question I put to Rashid earlier: How can we create economic incentives so that fishers value future catch higher than current catch? 
  • Q: Is there any back of the envelope estimate for implications of that 1.5 GT aqueous emissions for reduction in atmospheric drawdown, or it is simply unknown at this point? 
  • Q: A new study showed that bottom trawling is causing significant amounts of carbon being released to the marine ecosystem, which otherwise would be stored in sediments thus contributing to the climate crisis. Calculations say that this effect is similar to the global airfare carbon release. In that sense it seems that regulation this type of fishing would be especially effective (and urgent). What is the take of the panelists on this?
  • William: I agree that protecting important carbon stock in the seabed sediment from releasing into the atmosphere will contribute to climate mitigation, and have the “co-” benefits of protecting seafloor biodiversity. Improved knowledge about seafloor biogeochemistry and ecology (especially in the deep ocean) would help.
  • Ivonne: I also agree, but I’ll consult some references and one of my colleagues more familiar with bottom trawl net gear, as I would think they have different impacts. Importantly here – gear modifications can be included (e.g. non pelagic trawl nets vs pelagic trawl nets)
  • Angela: I agree that more information is needed to be able to regulate effectively, as well as to understand how long the carbon remains in the water column and its effects on the physical pump (diffusion of CO2 into the ocean) and thus atmospheric CO2. The amount of carbon in sediments is not uniform (e.g. Smeaton et al. 2021), so trawlings effect on carbon released depends very much on the sediment of the trawled area. Managing trawling in areas with high sediment carbon could be especially effective in reducing carbon release from sediments to the water column. However, the emission of greenhouse gases to the atmosphere are the key drivers of climate change, so reducing the emissions from global air travel would be more effective in this regard than trawling regulations.


  • Q: What are the creative opportunities to use global focus   on climate issues to support work better fisheries management and vice versa? As a USAID project – SALT (, we are trying to get creative in thinking about how we can use data collected in seafood supply chains for traceability to feed back into producer country government systems to improve  fisheries management (stock assessments, MPA monitoring, etc.).  We are also looking at ROI which shows traceability leading to more efficient use of fuel – which has a carbon benefit too.  I suspect there are many good ideas here!
  • William: I agree. There are many possibilities for utilizing our data and knowledge to support this.


  • Q: While hake SSB increased 5-folded within 10 years from 2008-2019, how did related prey-species develop? 
  • Angela: Good question! We haven´t yet got there, but we plan to include ecosystem perturbation effects in the article, so hopefully can answer this!


  • Q: To what extent would excess C02 in the water column from bottom trawling negatively affect atmospheric CO2 absorption? 
  • Angela: Theoretically, if more CO2 is released to the water column it could reduce the rate of absorption of CO2 from the atmosphere through the physical pump (i.e. alter the concentration gradient). In addition, more dissolved CO2 in the water column contributes to ocean acidification. However, the actual impact of trawling on this is not well understood: for example, we don´t know for how long the carbon released by trawling remains in the water column. 


  • Q: Is there an estimate of whether total CO2 emissions will change if efficiency increases, but more fish are caught with increasing stocks? 
  • Angela: With regard to the hake fishery in the Northern Area, our preliminary results indicate that the total CO2 emissions increased due to more fishing opportunities with increasing stock (i.e. greater catches and more fishing activity than when the stock was depleted), even with the increased efficiency. 
  • Erica: Just to add on to Angela’s point: I am not aware of any global estimates, however, our preliminary work from the North Atlantic suggests that increasing hake populations support more fishing and therefore a higher footprint overall (despite potential gains in catch per unit effort). Now, one might imagine that if more low-carbon food becomes available in X location or from X industry, then less high-carbon food will be harvested in Y location/industry; on net, this might decrease carbon emissions associated with the food we eat. But this hypothetical scenario is just that, a hypothetical, and it raises all sorts of new and important questions related to “climate-friendly” fishing. Ultimately, this question hints at an important truth: while efficiency and emission intensity per kilogram of food is an important component of the seafood-carbon “story”, it’s certainly not the only one. The push to understand the effects of overfishing on ecological well being and carbon sequestration represents an active and burgeoning area of research, and one that I believe will be integral to our understanding of securing sustainable seafood in a world where emissions are increasing and time is of the essence.


From Tuesday 23 March, 2021: Delivering on Climate & Biodiversity Targets Through Better Fisheries Management

  • Q: Is it known how much the sequestered carbon impacts seafloor invertebrates like deep sea corals and sponges?
  • Q: @Emma Cavan If I understood correctly your focus on feces, carbon sink and storages in the ground. How far do you consider possible stock biomass increases as possible carbon storages?
  • Emma: Carbon ‘storage’ for the purpose of reducing the impacts of climate change needs to get carbon out of circulation, so buried in sediments or stored in the deep sea. Whilst living biomass prevents some carbon from re-exchanging with the atmosphere, it will only be stored for the life of the fish. So biomass does not result in long term carbon storage.


  • Q: Thank you Dr Emma. Dr Cheung yesterday hinted at the importance of top predators for an increased carbon sink, where you show the other side of that (as they reduce biomass of forage fish, who are an important carbon). Can you elaborate a bit on both effects and what good management would look like from this integrated pov? Thank you.
  • William: This is an important question and needed more science to understand the balance between carbon sequestration by different groups of organisms in the food web when they are being fished. But we need to address multiple objectives: not only climate mitigation, but conservation of threatened marine life (many of them are top predators) and it often is more desirable to identify solutions to deliver multiple “co-” benefits across different objectives.
  • Angela: With regard to predators, various studies have shown that predators have a role in maintaining healthy coastal ecosystems by controlling populations further down the food chain (e.g. Norderhaug et al. 2020, Atwood et al. 2018). For good management, these interdependencies that are important for the function of the ecosystem need to be considered.
  • Emma: It is important to protect the top predators as they keep the whole food web in balance, including those low trophic forage fish and zooplankton that are important sinkers. Those with larger biomass (i.e. small animals) are likely to have greater direct impact on sinking carbon. Ultimately preserving the entire ecosystem is most desirable to protect long term carbon storage.


  • Q: I would love to have a fishing method C  indicator  – green – orange – red list , eg  large dredger mussel seed  fishing for relaying and re-dredging in aquaculture  – bright  red , line fishing green
  • Erica: I agree it could be very helpful, particularly from a management perspective, to have clear indicators for bivalve fisheries and aquaculture.


  • Q: Yes, please. I have one question to Emma. In the slide where you present discards that go to the very bottom of the ocean., what sort of evidence do you (or science) have concerning that sort of “pooh” does not get available for the carbon cycle in upper waters, or even at the bottom with bottom species?
  • Emma: It depends on the depth the discards get to and where in the ocean they are. If they are in shallow waters then as you say they may become part of the upper water carbon cycle and influence the local biogeochemistry, having a potential negative impact on the carbon sink. Any kind of human-made unnatural decay is not good for nutrient cycles and the carbon sink. But really we do not know how discards impact the carbon cycle at the moment.


  • Q: to Ibraim Issifu: Both anthropogenic stressors and the COVID-19 pandemic represent significant economic challenges to aquaculture and fisheries systems across the globe, threatening the supply chain of one of the most important sources of animal protein, with potential disproportionate impacts on vulnerable communities. What is your particular opinion about this issue?
  • Ibrahim: So far it appears COVID-19 does not infect aquatic species (as there is no evidence that the virus is transmitted to or affect the health of fish and marine invertebrates), but I agree that the cumulative impact of  anthropogenic stressors (climate change, overfishing, and chemical pollution) (and the public health crisis by the COVID-19 pandemic will impact negatively on fishing and aquaculture production, as well as each step of the fish supply chain, from processing, to transport, and wholesale and retail marketing. It is more likely that many fish-dependent communities, low-income food-deficit countries (LIFDCs) and Small Island Developing States (SIDS), where diets are heavily reliant on fish will be disproportionate impacted in the short and long terms, affecting the wellbeing of fishers. However, more data and science are needed to understand the cumulative impacts of these environmental stressors on the seafood supply chain. I am aware a recent paper by G. Sarà, et al (2021, attempted to address this big challenge.
  • There is also a key and interesting paper by Nathan Bennett and colleagues (Bennett et al. 2020; on COVID-19 and small-scale fisheries and coastal fishing communities.


  • Q: To Emma Cavan: Considering the stronger stratification over oceans and less vertical water mass exchange, how the vertical C sinking process will have a new pattern?
  • Emma: Yes this will change the C sinking process. Stratification will reduce nutrients coming to the surface, decreasing primary production and the amount of carbon available to sink in the first place. 


  • Q: How can we support policies that strengthen enforcement and implementation of existing policies and regulations? e.g. regularly reefers go dark when they reach West Africa and reduce the overfishing issues?
  • Thank you all. Q for Ibrahim, are you considering modeling climate change scenarios also by regions (based on FAO climate report for instance)? Thanks in advance!
  • Ibrahim: I’m considering conducting vulnerability assessment of fisheries to climate and non-climatic stressors and the scope of reduction and mitigation from fisheries management perspective in the European region.
  • Q: What about more shallow seas such as the Baltic – is the carbon sink as substantial there?
  • Q: @Emma – I am surprised that southeast Asia is not considered an area with high fishing and high carbon sink. Why is that so?
  • Emma: SE Asia is an area of high fishing, but because the water temperatures are relatively warm, in the algorithm we used to calculate the carbon sink they are not as high carbon sink as cooler waters. So they were not highlighted in my analysis.