Three Numbers That Make The Case For Shrimp Welfare
Rethink Priorities has been exploring whether farmed shrimp suffer and how to estimate the scale of their negative experiences, so that advocates can better understand their experiences relative to other farmed species.
Animal advocates often have to prioritize how to allocate resources to different species. The number of animals raised per year can act as a first-pass proxy for the species most in need of help. Our estimates suggest that approximately 440 billion farmed shrimp are slaughtered for human consumption annually. This is more than any other farmed taxa, save for insects. This alone paints an almost incomprehensible picture of an urgent need to take a closer look at shrimp welfare, but until recently, very little attention has been given to these animals. This may be because it is hard to appreciate the scale of the issues or for other reasons.
Perhaps shrimp have good lives on farms? A deep dive into the scientific and industry literature gives some clues about the conditions they are raised in and the kind of experiences they may have. We identified 18 potential welfare threats farmed shrimp may face, from poor environmental conditions and health to behavioral restriction. As we learned more about their lives on farms, three numbers stood out as important reasons to help farmed shrimp: the scale of shrimp farming, the mortality rates, and the level of pain they experience.
Note: The terms ‘shrimp’ and ‘prawn’ are often used interchangeably. The two terms do not reliably track any phylogenetic differences between species. Here, we use only the term “shrimp”, covering both shrimp and prawns. Note that members of the family Artemiidae are commonly referred to as “brine shrimp” but are not decapods, so they are not included in our estimations here.
Around 230 Billion Shrimp Are Alive On Farms At Any One Time
If we are to understand not just the scale of shrimp production but the scale of shrimp suffering we must look beyond slaughter statistics. Slaughter figures miss important aspects like the length of time shrimp spend on farms and the individuals who die before reaching slaughter age. A step in the right direction is to look at the number of individuals alive on farms at any given moment. This metric better indicates the time shrimp spend on farms and how much opportunity there is for suffering at any given moment.
We found that around 230 billion shrimp are alive on farms at any given moment – more than any other farmed taxa. This means that more shrimp could be experiencing welfare challenges at any moment than farmed insects, despite more insects being raised each year.
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The shrimp farming industry has continued to grow since we analyzed the 2020 data (see the graph below). In particular, shrimp farms are getting more intensive over time, meaning they use higher stocking densities and raise increasingly larger numbers of shrimp.
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We used data for 2020 from the Food and Agricultural Organisation of the United Nations about the tonnes of shrimp produced, which we then converted to numbers of individuals. This conversion required estimations of shrimp body size, which varies drastically between species and between individuals of the same species. There is therefore some uncertainty around our estimation — we think there is a 90% chance that the number is between 150 billion and 370 billion shrimp alive on farms at any time.
Two things are implied by the large number of farmed shrimp alive at any time:
the farming cycle is relatively long for shrimp, providing ample opportunity for negative experiences, and
the pre-slaughter mortality rates could be high.
We next looked to quantify the latter.
Half Of Shrimp Die Before Reaching Slaughter Age
We estimated the pre-slaughter mortality rate of the three most farmed shrimp taxa, Penaeus vannamei, Penaeus monodon, and Macrobrachium shrimp, at all life stages. Here’s what we found:
Mortality rates (%)Mean number of individual shrimp dying in lifestage*P. vannameiP. monodonMacrobrachiumP. vannameiP. monodonMacrobrachiumLarval16 [9; 25]25 [19; 3]54 [38; 74]97B14B97BPostlarval16 [9; 24]25 [19; 31]18 [9; 34]82B10B15BJuvenile–subadult17 [4; 48]43 [3; 97]49 [38; 62]77B14B34BCumulative41 [27; 65]68 [44; 98]81 [71; 90]255B38B146B
*B = billion
It was typical to see pre-slaughter mortality rate estimates from the literature and industry sources of around 50%. That equates to about 1.2 billion shrimp deaths per day.
Such high cumulative mortality rates show that the scale of shrimp farming is even higher than originally suggested – though ~440 billion shrimp are slaughtered each year, a mortality rate of 50% means nearly double this are raised on farms annually.
Death rates vary between species. In particular, up to 81% of Macrobrachium shrimp may die prematurely, while the rate is 41% for P. vannamei. Despite having the lowest mortality rate, since they are the most farmed species, most individual deaths are P. vannamei shrimp.
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Across species, most deaths happen in the larval stage. Some of these deaths may occur from an innately-mediated fragility of larval shrimp, as is often typical of species that have evolved to have a large number of offspring. Shrimp can spawn hundreds of thousands eggs at a time, resulting in the majority of them dying before adulthood. Farming environments would need to be tightly monitored and controlled to prevent this type of larval mortality.
Deaths in the other life stages may more likely result from common threats to welfare. For example, diseases and water quality issues seem prevalent in farming environments.
Given that animals can experience pain that does not cause mortality, pre-slaughter death rates only give us a minimum duration of adverse experiences. It is possible that shrimp experience prolonged suffering before their deaths. To understand the full extent of their negative welfare, we had to quantify both the lethal and sublethal pains they face.
Shrimp Likely Experience Hundreds Of Hours Of Pain From A Myriad Of Welfare Threats
We identified 18 issues that may threaten farmed shrimp welfare. We then estimated the duration, intensity, and prevalence of pain caused by each. We used the Welfare Footprint Project’s Pain-Track method to do so. This means pain intensity was measured in the categories ‘Excruciating’, ‘Disabling’, ‘Hurtful’, or ‘Annoying’. Annoying pain is aversive but generally doesn’t disrupt an animal’s daily life, while Excruciating pain is intolerable and usually represents imminent death.
Using this method, we found that the average farmed shrimp experiences an average of ~4,701 hours of pain during the main production stage, including several hours of severe (Disabling or Excruciating) pain.
It is important to clarify that we weighted the total hours of pain for each threat by their prevalence. For example, slaughter is weighted by the proportion of shrimp who survive to slaughter age and eyestalk ablation is weighted by the proportion of shrimp who are female broodstock. Additionally, welfare threats could happen simultaneously but are counted separately here.
The threats causing the longest duration of pain tend to have lower pain intensity. For example, high stocking density causes the most hours of pain to the average shrimp, but over three-quarters of the pain comes from the Annoying category. Conversely, ice-slurry slaughter and eyestalk ablation rank lower because they cause fewer hours of pain to fewer shrimp, but the pain they cause is higher intensity.
Even if the pain is prolonged, animals can still have positive experiences while enduring Annoying or Hurtful pain. Conversely, about 6 hours (0.13%) of the total pain caused to the average shrimp comes from the Disabling or Excruciating category. This means 6 hours of the average farmed shrimp life is inconsistent with any positive experiences.
Our uncertainty is vast, however. We think the total could be 4,701 hours of pain, but it could also be as low as 803 hours or as high as 7,403 hours. The culprit is a severe lack of welfare-focused information about farmed shrimp.
Despite the scale and myriad welfare issues they face, farmed shrimp have not yet been brought fully into the realm of animal welfare science and animal advocacy. Researchers in Brazil have just recently outlined the first welfare standards for shrimp, but a large gap in our understanding of shrimp biology and behavior remains.
There is a great opportunity and an urgent need to incorporate one of the most numerous farmed species into our efforts to help animals.
Takeaways
Our research suggests that the scale of shrimp farming is large, the welfare threats they may face are varied, and the pain they experience could be very prolonged.
Understanding the number of individuals alive at any time can provide more clues than slaughter statistics can about the time animals spend on farm, and how many die pre-slaughter
In the case of farmed shrimp, ~230 billion are alive at any moment, more than any other single taxa
Roughly 50% of farmed shrimp may die before even reaching slaughter age. This equates to 1.2 billion shrimp deaths per day.
The industry has only grown since these estimates were made, and farms are become more intensive over time
Farmed shrimp likely face a multitude of welfare issues at every stage of production, including high stocking densities, water quality issues, transport, harvest and slaughter, eyestalk ablation, and more.
Our estimates suggest the average farmed shrimp may experience around 4,701 hours of pain during the main production stage. Six of these hours are likely severe pain.
These pain estimates are quite uncertain, owing to a deficiency of welfare-focused shrimp research
The post Three Numbers That Make The Case For Shrimp Welfare appeared first on Faunalytics.
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