Hello @LewisBollard and @MichaelStJules thank you for your replies. Some answers to your considerations: 

1. If replacement to aquiculture is a logic, you can state the same to fight against land animal production, as this will all concentrate consumption on aquatic animals as people do not even know which fish is caught or farmed. Certainly this will mean more lives killed/ in suffering, the same way? Shall we stop talking about transitioning away from land animals? Certainly not. 
2. You mention the unlikeliness of promoting a ban on fishing. Although there will always be traditional communities depending on fishing to thrive, from these we should never impose a ban, it is certainly true by facts that: a. aquiculture is not replacing fishing, just increasing fish consumption, as you can see in popular stats from Our world in Data; b. for fishing, you need to consider deaths of fish and crustaceans which are significantly smaller than the fish farmed, a few examples are: krill x farmed shrimp, salmon x anchovies, etc. No wonder fished animals increase number of lives killed in the order of magnitude of 10x (but represents only 1/2 of the current tonnage yearly). Are we ok to ignore this huge elephant in the room? 
3. The thinking that fishing is increasing fish populations is certain on short term, but not true long term. A high spike on prey fish means less of their prey, subsequently, therefore diminishing their populations over time. There are a few studies on the effect of removing a predator from their ecosystem resulting not on increase of fish populations or biodiversity, but in fact, the opposite happening: less biodiversity, lower populations, ecosystem collapse. This can be easily noticed in scenarios before and after implementing a Marine Protected Area - I can share a few studies if this helps, let me know. 
4. This ask is also not impossible or far fetched: we had already moved great heaps when it coms to our culture of hunting land animals. In Brazil for example 100% of native land animals are protected towards hunting. However at see, all animals can be legally caught and die as 'bycatch'. Why not move also towards aquatic wild lives? It is massively possible to end industrial fishing: we have gone great lenghts with the international ban to the hunting of marine mammals and the hunting of sea turtles. We are starting to do the same for sharks and rays. It is only a matter of time that our dissonance between hunting wildlife on land and at sea will be fixed and we can notice how this significantly affects their welfare overall (certainly the welfare which is not ambiguous at all, of shortening their lives and killing large quantities of animals in an extreme cruel way (btw all industrial fishing techniques are extremely negative towards welfare - so if you agree on lowering the impact on fishing welfare, surely a ban on industrial fishing must be on the cards). 
5. Also, going beyond animal welfare and animal rights: when we talk about removing wildlife in this great quantity as I mentioned before, we are also talking about ecossystemic service of the ocean for the balance of the planet and all living beings on Earth. We are already seeing a global catastrophe happening on front of our very own eyes, and if we consider that the ocean provides at least 50% of the oxygen on Earth, and it is responsible for the historical of 85% in the atmosphere today, also considering the ocean absorbs 90% of the excess heat from CO2 emissions and is responsible for 25% of the cabon sink, it is our largest ally on the fight against climate change. However it needs a balanced ecosystem for it to keep performing its role. Fishing alone, especially illegal and industrial, already had depleted more than 70% of species (which are being overfished or are on the verge of collapse), it destroys 50x more land annually than deforestation.
6. For me it raises an important reflection: doing all we are doing for farmed land and aquatic animals, many people will also consider going to fished animals for their animal protein intake. Is this incentive a wise one to stimulate? 
7. Aquaculture also uses fished animals to feed their animals: therefore bans that lower fishing efforts can also make aquiculture less interesting to be pursued?
8. Finally, considering all of the above, shouldn't we refrain from stimulating consumption of wild animals completely? For their welfare, but also for our planet? Ignoring this issue for me certainly shows a huge area of neglect and efficiency gap, IMO.

Not clear Michael what you mean y saying 'making fishing more sustainable = more fishing, can you elaborate? (Remembering I mention here to ban industrial fishing, not increasing its welfare, which for me is an oxymoron).

Happy to evolve this conversation further with you both. Thanks!

What is your take of the impact of fishing on animal welfare? When it comes to aquatic lives, why should we only focus on farmed aquatic life, not fishing? Why not prioritise work towards the ban of all fishing, esp. industrial fishing?

Some info: fishing alone is responsible for 90% of all lives killed per year for consumption, fishing is also destroying wild aquatic life habitats more than we destroy lands, and it also is affecting all wild lives that depend on them to survive: it is pretty much the largest ecocide in the world, and it is legalized. All this destruction for less than 2% of humanity's calories intake. Also, its current techniques to kill these animals are extremely cruel, long lasting, and in accumulation, it likely represents more suffering than in fish farms.

Important to note that by far most of the animals killed for human consumption are wild animals: they are the circa 8 trillion wild animals retrieved from their environments by the fishing industry (conservative scenario) x circa 1.5 trillion animals from aquaculture, and 70 billion animals coming from land production. Also, removing wild animals in large quantities from its environment has severe ripple effects to its environment and all other animals (and humans). Therefore focusing only on farmed animals as the most CE way to protect animals is the largest blindspot in this whole conversation. So if we talk about lives saved, you have a winner in WAW. If it is about improved lives, we should sum all the cruel hours of fishing processes (slowly dying from water pressure change, slowly dying from asphyxiation, slowly dying from pressing their bodies to other animals' bodies, etc) x all animals caught and then compare to farming. One other thing to consider is the suffering which comes from ecosystem destruction (ocean acidification, coral bleaching, depletion of preys, etc), all of which have a lot of pain as consequences. 

Thanks for your reply, Vasco - all clear and comprehensive. I'd only dispute the claim from How Wild-Caught Fishing Affects Wild-Animal Suffering: 'for example, catching big piscivorous fish may reduce zooplankton populations, while catching small zooplanktivorous fish may increase zooplankton populations.' - this does not consider the full balance of the trophic chain, and the fact that if you remove big piscivorous fish, you are in fact on the SHORT TERM increasing the population of zooplankton, however, this have many complex effects, one example: the decrease in the Caribbean shark population is met by an increase in its prey, the grouper fish. The expanding grouper population takes parrotfish, normally responsible for clearing coral of algae, in greater numbers. This could explain why algae now dominates many degraded reefs in the Caribbean. It also shows how the systematic elimination of one species—a key link in a complex web of relationships—can destabilize the entire ecosystem. When it comes to wild animals, no impact is so straightforward and isolated as we'd like to measure. This is my pet critic with EA, as the difficulty in measuring the clean direct impact of efforts in wildlife conservation can be hindering funds to these efforts, however, in the larger sense, the strategy to leave the ocean alone to rebalance its ecosystems is about saving all life on Earth - therefore the investment on ocean conservation has strong direct links to Existential Risk - ours and of all life on Earth. Perhaps this is a conversation to another topic/ thread...!! 

Hello Vasco, thank you a lot for your reply. Some food for thought (as I did not extend a full analysis of all being mentioned and shared): 

First, I'll respond to your second comment. As you can see in the numbers, fishing is responsible for more seabird deaths, but less death of mammals. But what I wanted to point out is that this is a more comparable number (and shows a group of animal can indeed suffer more by plastic than fishing or vice-versa) and it only reveals a part of the numbers, as I stated too in my response. As I said from the start: fishing is the single most cause of death in the ocean, if you include all fish, crustacea (if krills are included the numbers, the numbers of lives can be estimated to the quatrillions, as we fish 2.7 million tons of krill per year, and a krill's weight is 1 gram per average), though we shan't ignore the huge impact of plastic in the ocean, as the numbers shown can give higher impact to some of the groups of animals versus others.

Secondly, I read your reply from Michael St Jules, though affirming that 'microplastic ingestion rarely causes mortality in any organism' can't be farther from the truth. As an example from what we already debated, this is what led to the seabird numbers (as there are dozens of studies proving that plastic debris is their cause of death, as you had also pointed out). An example of study here: https://www.nature.com/articles/s41598-018-36585-9 .

For fish, the influence of plastic and microplastic causing deaths can be seen in some rare studies, some here:

An interesting study with Rainbow Trouts, is that when fish is exposed to MP and a virus, the chances of dying from the virus goes from 20% than up to 80%! Study here: https://www.sciencedirect.com/science/article/abs/pii/S004896972208295X?via%3Dihub

https://iopscience.iop.org/article/10.1088/1755-1315/631/1/012006/pdf#:~:text=The%20microplastics%20can%20have%20a,oxidative%20damage%20and%20abnormal%20behavior. - This brings an analysis of the plankton Daphinia magna you also shared a study from, showing the death effects of a 0,001 millimetre of plastic (microplastics are debris of 0,5mm or less, so this fits the size with a lot to spare) on their death rate (page 5).

Important to note that these types of research pose a difficulty, as death because of microplastic ingestion takes a while to study and is not realistic to be done in labs/ aquaria. There are more studies on marine mammals, turtles and seabirds in their natural habitat as these are examined more commonly by WW environmental agencies when reaching the surface/ ashore (and thus the numbers can be better extrapolated) than fish, frankly revealing the massive speciesism in the marine biology/ environmental studies arena. Also, important to note that these studies we both brought above focus on microplastic, and not cover the ingestion of larger plastic litter by fish, which we know can be the cause of deaths by entanglement, filled stomach (starvation) and choking. In short, there is a clear lack of study on fish deaths by consumption of plastic debris in general.

Another fact to point out on the fishing x plastics debate is that if we immediately stop fishing, the alleviation of the impact on marine life will be immediate, and complete. If we stop using plastics today, we would still have to manage the millions of tons of plastic we had already produced, and that are still in the environment. A study shows that if we stop using virgin plastic right now, in 2050 the amount of microplastics in the ocean will more than double by 2050, coming from the existing plastic pollution: https://www.researchgate.net/publication/358446217_Impacts_of_plastic_pollution_in_the_oceans_on_marine_species_biodiversity_and_ecosystems

I am roughly aware of Brian Tomasik's numbers on fishing as I work to fight against it myself. 

Just to be dead clear, I still am in complete alignment with you regarding the impact of fishing x plastics for the ocean's ecosystem, as a fighter for the end of fishing myself. I just wanted to shed a light on why not to de-prioritise the efforts on fighting plastic pollution for the protection of the ocean.

Thanks for sharing and for the debate.

First of all, I am very sorry if this was cited on the comments before, I did not have time to read all of it. I'd like to share some views on this: I completely agree that fishing is way more impactful for the ocean than plastic nowadays! However, it is not in the same proportion it's been shared here in this logic above. The main reason why is that it only calculates the death of birds and marine mammals killed by plastic x fish caught by the fishing industry. They left fish (also other animals such as corals, cephalopods, turtles, etc.) that die from plastic aside on the measurement of deaths by plastic per year, and used fish and other comercialised marine life (a group of species much more abundant in termos of biomass than birds and seabirds) to calculate impact of fishing. There is no data on sea mammals or birds on fishing impact , no data of fish for plastic impact. It is apples compared to oranges, this calculation has a huge flaw! If we want to compare 'like for like' (knowing there is no study on the impact of plastic on the death of fishes yet done, due to the low conservationists' interest in this), I then bring a comparison of deaths of sea mammals and sea birds from plastic pollution x fishing (as they also die in hoards because of bycatch!). There is the study that says that 300,000 mammals and that 320,000 seabirds are killed per year by fishing alone. This brings a much more comparative number, and it does show that plastic certainly impacts in a similar way or more (as per your numbers above, it kills around 1,000,000 birds/ 100,000 marine mammals). So yeah, as this more just comparison indicates: fighting plastic, as well as fighting commercial fishing, is ESSENTIAL to protect marine lives. 

Let me know our thoughts on this. Best, 

Nathalie Gil

President of Sea Shepherd Brazil