04 · Sustainability
The page where we tell
you the bad news.
Most sustainability pages are a wall of logos. This one is a stock-status table, a list of claims we are not entitled to make, and the sources for every number we publish.
Stock status, species by species
Two of our four species have
no clean answer. Here they are.
Status is taken from the Indian Ocean Tuna Commission's Scientific Committee, the body that actually assesses these stocks. We do not grade our own homework.
| Species | Assessment | SB/SBMSY | F/FMSY | MSY | 2024 catch | Status |
|---|---|---|---|---|---|---|
| Yellowfin tuna | 2024 | 1.32 | 0.75 | 421,000 t | 489,742 t | Not overfished |
| Kingfish (narrow-barred Spanish mackerel) | 2023 | 0.98 | 1.07 | 161,000 t | 157,754 t | Overfished & overfishing |
| Dorado (mahi-mahi) | — | — | — | — | ~5,500 t | No assessment |
| Red snapper (Lutjanus spp.) | — | — | — | — | — | No assessment |
IOTC Scientific Committee stock status summary, 2025; yellowfin executive summary IOTC-2025-SC28-ES04. Dorado landings from FishSource stock page 1073, which records that the stock “has not been assessed at the regional level”. Last checked 21 September 2026.
On yellowfin, the honest version. Indian Ocean yellowfin was classified as overfished from 2015 until the 2024 assessment moved it into the green. That is good news, and we are not going to oversell it: the 2024 catch of 489,742 t exceeded the estimated maximum sustainable yield of 421,000 t by roughly 16%, and scientists reviewing the assessment have urged caution about remaining model uncertainty. A stock above BMSY that is being fished above its long-run sustainable yield is not a stock anyone should be relaxed about.
On kingfish, the part a competitor would bury. Narrow-barred Spanish mackerel is classified by IOTC as both overfished and subject to overfishing. We sell it. We sell it single-hook caught, fully traceable, and at a price that supports the fishers who catch it — but we do not describe it as sustainably stocked, because it is not. If you need a species with a clean stock assessment, buy the yellowfin and we will tell you so.
The claim ledger
What we cannot claim.
Every claim a seafood company might want to make, and whether we are actually entitled to make it. This list will get shorter as the evidence arrives. Until then it stays exactly as it is.
If a competitor makes any of the claims marked Not supported below, ask them for the same thing we would have to produce: the assessment, the observer data, or the audit.
“All our species are sustainably fished” Not supported
False on its face for our range. Kingfish is overfished and subject to overfishing per IOTC's 2023 assessment. Dorado and snapper have no regional assessment at all. Only yellowfin currently sits in the green, and with caveats. We will never make a blanket claim across the range.
“Our bycatch is 0.65%” Not supported
We quote 0.65% as the published figure for the Maldivian pole-and-line tuna fishery — the closest comparable gear with peer-reviewed observer coverage. It is not a measurement of our boats, our gear, or our waters. No equivalent published study exists for Western Indian Ocean handline. We have not yet run our own observer programme; when we do, the result gets published whatever it says.
“The Pemba Channel is an exceptionally productive upwelling zone” Not supported
A tempting line, and the only peer-reviewed measurement of it says the opposite. Localised upwelling along Pemba's western edge is real and confirmed, but the authors estimate it enhances local productivity by only about 20%. That is a modest enrichment, not a Benguela-scale system. Anyone describing these waters as extraordinarily productive on the basis of upwelling is overstating the published science.
Painter et al. (2021), Ocean & Coastal Management 200, art. 105462.
“Certified sustainable” Not supported
We hold no MSC, Friend of the Sea or Fair Trade certification today. We are not going to display a logo we have not earned, and we are not going to imply one with words like “certified-standard” or “equivalent to”. Note also that Friend of the Sea's own stock criteria — B ≥ BMSY and F ≤ FMSY — would currently exclude our kingfish.
“Guaranteed species identification on snapper” Qualified
We sell snapper to genus — Lutjanus spp. — not to species. “Red snapper” is one of the most substituted market names in the global trade. Species-level confirmation requires DNA testing, which we offer on request and are working to make routine. Until it is routine, we will not print a species name we cannot prove.
“Sashimi grade” / “super-frozen” Qualified
Neither term has a legal definition in the EU or the US. We use “sashimi grade” as trade shorthand for our Grade 1 specification, which is written out on the products page. We do not use “super-frozen” at all today: our store holds at −30 °C, and the −40 °C core and −45 °C hold that the term implies belong to the facility we are building. When we reach those temperatures we will state them; until then judge us on the number we actually hold, not the word.
“Handline caught, single hook, no nets” Supported
Gear type is written on the landing sheet for every fish, against its lot number. This is a process claim about our own operation, which we can evidence directly. Troll line is recorded as troll, not folded into “handline”.
“Blast frozen to −40 °C core, held at −45 °C” Not yet
This is the specification of the facility we are building, not a description of today. Today we freeze and hold at −30 °C — well below the −18 °C legal floor, and above the −45 °C threshold in the research we cite on the blast-freezing page. When the tunnel controller logs a curve per lot, this line moves to Supported and the lot record shows the measured core temperature. Until then it stays here.
“Traceable to the vessel and the skipper” Qualified
Vessel and registration, skipper, landing site, date and whole weight are written on the landing sheet for every fish and carried on its lot number. That is a real record and we can show it. What we cannot show yet is a catch position or catch time from an instrument, or a temperature from a logger — those come with the vessel tracker and the facility. Read this claim as “traceable to the vessel and the skipper, by our own written record”, and no further.
Why only four
Pelagic, not reef.
That is the argument.
Pemba’s pressure is on the coral reef: the fish that live on it, breed on it and keep it clean. The species we sell live in the open water of the channel, and that choice is the most defensible sustainability decision we make.
Reef fish are site-attached, slow to grow and late to breed. Many gather to spawn in the same place each year, where a net or a spear gun can take a generation in an afternoon. The grazers and invertebrate-eaters among them keep algae and sea urchins off the coral; remove them and the reef itself starts to change. Yellowfin, dorado and kingfish are none of those things: fast-growing, migratory, passing through, and assessed as whole-ocean stocks by the IOTC — which is also why we can publish an honest status for each of them.
The exception we admit. Snapper is a reef-associated genus. We take it by handline on the outer shelf slope, in small numbers, and it stays on the list because buyers ask for it — not because it belongs with the other three. It is the one we would drop first if the numbers said so.
Sold as “sustainable”
What the word means on a
local price list.
Wholesale lists in Tanzania routinely describe the species below as sustainable. Open each one for what it is, what it does on the reef, how it is caught here, and what the evidence actually supports — and, at the end of each, why we give it the verdict we do.
Grouperchewa · Epinephelus spp.Reef predator; slow-growing, late-maturing, spawns in aggregationsNot supported
What it is
A family of large reef predators — brown-marbled, camouflage, malabar and potato groupers among them. Most live past twenty years, grow slowly and mature late, and many change sex from female to male as they grow, so the biggest fish in a population are its males.
Its place in the reef
Groupers sit at the top of the reef food web, keeping mid-sized fish and octopus in check; where they are fished out, the balance below them shifts. The larger species gather to spawn at the same sites on the same moons each year, which puts a whole year’s breeding stock within reach in a few nights.
How it is caught here
Speared, trapped and handlined on Pemba’s reefs, and netted when they aggregate. Spear guns are prohibited under the 2010 Act and remain in use: inside the conservation area a fifth of surveyed fishers reported using prohibited gear.
What the evidence says
No stock assessment exists for Zanzibar’s groupers. The brown-marbled and camouflage groupers are assessed Vulnerable by the IUCN across their range, thirteen of the fourteen threatened grouper species aggregate to spawn, and brown-marbled grouper aggregations are documented on the East African coast.
Why “Not supported”. A long-lived, late-maturing, sex-changing predator with no assessment, taken with prohibited gear at its own spawning sites, cannot be called sustainable by anyone. It can only be called available.
Emperorchangu · Lethrinus spp.The everyday shallow-reef fish; nursery in the mangroves, adult on the seagrassNot supported
What it is
The emperors — pink ear, spangled, thumbprint and others — are the workhorse fish of Zanzibar’s shallow reefs and seagrass beds and the commonest fish on a local plate. Juveniles shelter in mangroves and turbid shallows and move out onto seagrass and reef as they grow.
Its place in the reef
Emperors eat crabs, shellfish and sea urchins on the reef flat and seagrass. That matters: where the fish that eat urchins are removed, urchin numbers climb and they strip seagrass and scrape living coral. The everyday fish is part of the reef’s maintenance crew.
How it is caught here
Basket traps, gillnets and dragnets in the shallows — gear that also takes juveniles by the thousand. Dragnets and beach seines are prohibited and still worked, across the very nursery habitats the fish depend on.
What the evidence says
No assessment for Zanzibar waters. Length-based work in Chwaka Bay found two emperor species harvested beyond the maximum sustainable level, with more than 80% of the catch juveniles. Inside PECCA, nine in ten fishers who saw their catch change over five years saw it fall.
Why “Not supported”. A fishery taking mostly juveniles, beyond its sustainable rate, with prohibited gear, on the reef the word is meant to protect. The adjective does all the work; the evidence does none.
SnapperLutjanus spp.Reef-associated mesopredator — the genus we sell tooQualified
What it is
Snappers are mid-sized reef predators. Several are long-lived — the two-spot red snapper can pass fifty years — and some gather to spawn. “Red snapper” on a Tanzanian menu covers several species, which is why we sell to genus and offer DNA confirmation rather than a species name we cannot prove.
Its place in the reef
Mid-level predators of fish and crustaceans on the reef slope. Long-lived and slow to replace: a population stripped of its big old fish loses a disproportionate share of its egg production.
How it is caught here
Handline on the outer shelf slope in our case; traps and nets on the shallow reef in most others. The gear, not the name, decides what else dies.
What the evidence says
No regional stock assessment exists for Western Indian Ocean snappers. That caveat applies to ours exactly as it applies to anyone else’s, and we say so here rather than let the handline settle it.
Why “Qualified”. Qualified for everyone, including us. Handline on the slope is the least damaging way to take a snapper; it does not make an unassessed reef species sustainable, and we do not say it does.
Bluefish, sole, flathead, amberjacktrade namesReef and lagoon demersals sold under names that map to no speciesNo evidence
What it is
“Blue fish” maps to no single species. Sole is a flatfish of the sandy lagoon floor; “crocodile fish” is a flathead, an ambush predator lying on rubble beside the reef; amberjack is a fast predator of the reef edge. None has a published biology for Zanzibar’s waters, let alone an assessment.
Its place in the reef
Different roles, one common thread: each is part of the reef and lagoon community, and none is monitored. Sole and flathead are taken from the seagrass and sand that nurse everything else; amberjack is an apex predator along the drop-off.
How it is caught here
Dragnets and beach seines over the seagrass for sole; spear and net for flathead; spear, handline and net for amberjack. Seine and dragnet gear takes the habitat along with the fish.
What the evidence says
No assessment for any of them, and a trade name on the invoice that cannot be traced to a species. A sustainability claim needs, at minimum, a species and a count; these have neither.
Why “No evidence”. You cannot substantiate a claim about a fish nobody has identified, let alone counted.
Barracudamzia · Sphyraena spp.Open-water predator; fast-growing, mostly net-caughtNo evidence
What it is
Fast-growing predators of the reef edge and open water. The great barracuda matures within a few years and lives around a decade and a half; on biology alone it is one of the more resilient fish on this list.
Its place in the reef
A roving apex predator over the reef and along the channel. Large individuals in some regions carry ciguatera risk — a food-safety point, not a sustainability one.
How it is caught here
Trolled and handlined by some boats, netted by many more. A gillnet set for barracuda takes whatever else swims into it.
What the evidence says
No assessment in the Western Indian Ocean. The biology is forgiving; the gear usually is not, and the invoice does not say which was used.
Why “No evidence”. The fish could be sustainable; the claim cannot be checked. Ask how it was caught before accepting the word.
Marlinoften sold as “swordfish”Billfish taken by longline and gillnet; three of three stocks in troubleNot supported
What it is
Blue, black and striped marlin: large, fast oceanic predators that take years to mature, caught mostly as bycatch by industrial longliners and in artisanal gillnets. On a menu they are frequently sold as swordfish.
Its place in the reef
Not a reef species, but a top predator of the same channel our boats fish, and a case study in what happens to a slow-maturing fish under gear that cannot select.
How it is caught here
Longline and gillnet, industrial and artisanal. Neither can leave a marlin in the water once it is hooked or meshed.
What the evidence says
IOTC 2025: striped marlin is overfished and subject to overfishing and has been in a highly depleted state for more than a decade; blue marlin is overfished and subject to overfishing; black marlin is subject to overfishing, with agreed catch limits exceeded four years running.
Why “Not supported”. Every marlin stock in the Indian Ocean is in trouble by the assessment of the body that counts them. Selling it under another fish’s name completes the picture.
SwordfishXiphias gladiusBillfish; the Indian Ocean stock in the greenSupported
What it is
A deep-diving oceanic predator assessed as a single Indian Ocean stock by the IOTC. Swordfish grow fast for a billfish and mature relatively young.
Its place in the reef
Not a reef species. It matters here as the honest comparison: a pelagic with a real assessment and a green status.
How it is caught here
Longline, overwhelmingly. The stock is fine; the gear also takes sharks, turtles and marlin, which is the caveat a buyer should attach.
What the evidence says
IOTC: neither overfished nor subject to overfishing.
Why “Supported”. Supported on stock status. Make sure it is swordfish and not marlin on the plate, and ask about the longline’s other catch.
SailfishIstiophorus platypterusBillfish; not overfished, by an assessment that flags its own uncertaintyQualified
What it is
The fastest fish in the ocean, a mainstay of the artisanal gillnet catch along the East African coast and of sport fishing, where it is often released.
Its place in the reef
Not a reef species; a pelagic predator of the channel.
How it is caught here
Gillnet and longline commercially; rod and line in sport fisheries.
What the evidence says
IOTC 2025: not overfished and not subject to overfishing — with the assessment itself recording considerable uncertainty and carrying the previous year’s advice forward while the model is checked.
Why “Qualified”. Probably fine, by a model its own authors are still testing. Qualified is the honest word.
Lobsterkamba koche · Panulirus spp.Reef spiny lobster; slow to mature, sold by weight grade aloneNot supported as sold
What it is
Spiny lobsters of the reef — painted, ornate and scalloped species — live in crevices, take several years to reach breeding size and carry their eggs externally for weeks: the “berried” females that every well-run lobster fishery protects.
Its place in the reef
Night-time scavengers and predators of the reef floor, and prey for groupers and octopus. Long-lived and slow to replace.
How it is caught here
Divers at night, by hand and spear — sometimes on prohibited scuba — and in traps. Undersized animals and egg-bearing females are the easiest to take and the most damaging to lose.
What the evidence says
No stock assessment. Good practice everywhere is a minimum size and a ban on landing egg-bearing females; the price lists we see state a weight grade and nothing else, into a hotel market that pays whatever is asked.
Why “Not supported as sold”. Not supported as sold. A lobster can be caught responsibly; a price list that grades by weight and says nothing about size limits or berried females is not evidence that this one was.
Octopuspweza · Octopus cyaneaReef cephalopod; lives about a year; closures demonstrably workSupported, with closures
What it is
The day octopus lives twelve to fifteen months, grows astonishingly fast, breeds once and dies. Few marine animals recover from fishing as quickly.
Its place in the reef
A mesopredator of crabs and shellfish on the reef flat, and staple prey for groupers and eels. Gleaning it at low tide puts feet on live coral, which is the harvest’s real ecological cost.
How it is caught here
By hand and spear on the reef flats at low tide, by women and men gleaners and by divers — one of the most inclusive fisheries on the coast.
What the evidence says
Pemba’s temporary closures, run by Shehia Fisher Committees since 2015–16, have documented results: at Fundo Island a three-month closure was followed by a more than twenty-fold jump in typical daily landings and larger animals, and the model has spread through dozens of committees. Compliance varies between villages.
Why “Supported, with closures”. Supported where the closures are respected. It is one of the few local sustainability claims with numbers behind it, and the closure that earned it belongs on the invoice.
Prawnsvannamei, black tigerFarmed, imported frozen; not a Zanzibar fisheryNot local
What it is
Whiteleg and black tiger shrimp are farmed in ponds in Asia and Latin America and arrive frozen. Whatever the farm’s certification, the animal has never seen the Western Indian Ocean.
Its place in the reef
None here. Shrimp farming’s footprint — mangrove clearance, feed and effluent — falls somewhere else; Tanzania’s own wild prawns come from mainland trawl fisheries with a bycatch problem of their own.
How it is caught here
Farmed. The “local” in “local and sustainable” is the first thing to fall away.
What the evidence says
Not a Zanzibar fishery at all.
Why “Not local”. A local sustainability claim attached to an import is not so much wrong as meaningless.
CalamarisquidShort-lived and resilient — and of unstated originUnknown origin
What it is
Squid live about a year and reproduce prolifically; as a group they bounce back from fishing faster than almost any fish. Most calamari sold here arrives frozen from abroad.
Its place in the reef
Small local squid are taken over seagrass and reef at night under lights; the imported product has no local footprint at all.
How it is caught here
Jigs and lift nets locally; trawl bycatch or industrial jigging elsewhere. The box rarely says which.
What the evidence says
Resilient biology, unknown provenance. A claim cannot be checked for a product whose origin is not stated.
Why “Unknown origin”. Could be the best thing on the list or trawl bycatch from another ocean. Until the origin is on the label, it is a shrug.
Nile perch, tilapiafreshwaterMainland lakes and farms; not marine, not from ZanzibarNot a Zanzibar fish
What it is
Nile perch was introduced to Lake Victoria in the 1950s and 60s and became one of the world’s largest freshwater fisheries — while the lake lost hundreds of its native cichlid species. Tilapia is farmed or lake-caught. Neither is marine.
Its place in the reef
None. The Lake Victoria story is about an introduced predator reshaping a lake, not about any reef.
How it is caught here
Gillnets and longlines on Lake Victoria under slot-size rules; ponds and cages for farmed tilapia.
What the evidence says
Lake Victoria’s Nile perch stock is managed, monitored and argued over; its sustainability is a real debate with real data. It is simply a different debate.
Why “Not a Zanzibar fish”. Not a Zanzibar fish and not a reef question. Listing it beside reef species under one “sustainable” banner is where the word stops meaning anything.
Norwegian salmonfarmed Atlantic salmonFarmed and air-freighted from the North AtlanticNot local
What it is
Farmed Atlantic salmon from Norwegian pens, flown some seven thousand kilometres to arrive fresh.
Its place in the reef
None. Its footprint — sea lice, escapes into wild rivers, feed drawn from other fisheries, and the flight — is real, and entirely elsewhere.
How it is caught here
Farmed.
What the evidence says
Norway regulates and reports on its salmon farms in detail. Nothing in that reporting concerns Tanzania’s reefs.
Why “Not local”. On a Tanzanian “sustainable seafood” list, an air-freighted farmed import is the tell that the word is decoration.
Species taken from wholesale price lists circulating in Tanzania in 2025–26; the sellers are not named because the point is the claim, not the company. Billfish status: IOTC Scientific Committee stock status summary, 2025. Groupers: IUCN Red List assessments of Epinephelus fuscoguttatus and E. polyphekadion; grouper aggregation records for East Africa. Emperors: length-based assessment of the Chwaka Bay multispecies fishery (2014 data). Fisher-reported declines and gear use inside PECCA: Rashid (2026), Frontiers in Marine Science. Octopus closures: Shehia Fisher Committees with Mwambao Coastal Community Network, Fundo Island results 2016 onward; compliance: Drury O’Neill (2024), People and Nature.
Gear matters more than adjectives
Why the method is
the argument.
You cannot fix a stock assessment from the deck of a boat. What you can control is what your gear kills that you did not intend to kill.
Line gear takes one fish at a time. Unwanted fish come up alive and go back alive. There is no net wall, no bottom contact, no fish aggregating device drifting for months. Across the Indian Ocean as a whole, line gears already account for 43.2% of the yellowfin catch — this is the mainstream method here, not a boutique one.
IOTC yellowfin executive summary, 2025: catch by gear, 2020–24 mean.
The law we work under
Zanzibar Fisheries Act,
2010.
Explosives and poison
“A person shall not use or attempt to use any explosive, poison or other noxious substance for the purpose of killing, stunning or disabling fish.” Penalty: TZS 100,000–10,000,000 and/or three months to five years.
Prohibited gear
Beach seines, fishing weirs, spear guns and any electrical or diving device are prohibited. Penalty: TZS 100,000–5,000,000 and/or three months to three years.
Licensing and marking
Every fishing vessel in Zanzibar's internal waters, territorial sea and EEZ must be licensed, and licensed vessels must be marked in the prescribed manner.
Mesh size
Nets and traps below the prescribed minimum mesh size are prohibited. The Act cross-references subsidiary regulations for the actual figure — we do not publish a millimetre number we have not read in the regulation itself.
Live legislative change. A Fisheries Development Bill 2026 was before the Zanzibar Revolutionary Council on 14 September 2026, with some clauses reportedly withdrawn. We are tracking it. Until it is enacted and published, the 2010 Act as described above is what we operate under, and we will update this page when that changes rather than leaving a stale citation up.
Zanzibar Fisheries Act 2010, full text via FAOLEX. Bill status per The Citizen, 15 September 2026. Last reviewed 21 September 2026.
Methodology
How we handle
a number.
Five rules. They are the reason this site has fewer superlatives and more footnotes than the rest of the category.
1. Every figure carries its source and its date
If a number appears on this site without an organisation and a year underneath it, that is a defect and we want to know. Figures from our own operation are labelled as ours; figures from third parties are attributed to them.
2. We separate measured from analogous
A figure measured on our boats is stated as ours. A figure from a comparable fishery elsewhere is labelled as an analogue, with the fishery and gear named. We never let an analogue drift into being presented as our own result.
3. Provisional numbers are marked provisional, and can go down
Lot records are automated from the tunnel controller and the landing log. They are reconciled against the HACCP record and, for snapper, against DNA results. Until reconciliation, a record is marked provisional — and reconciliation sometimes moves a number the wrong way. That is what reconciliation is for.
4. Where sources disagree, we say so
The area of the Pemba Channel Conservation Area is published as 270 km², ~1,000 km², ~1,200 km² and ~1,600 km² by four different credible organisations, and the World Database on Protected Areas lists it as “not reported”. We therefore do not put a number on it. Zanzibar's 2023 catch is reported as 80,000 t in a ministerial statement and 62,000 t by an independent survey for 2022; we cite the survey and flag the discrepancy.
5. We publish what we could not verify
The claim ledger above is the public version of our internal “could not substantiate” list. Items move off it when evidence arrives, not when marketing needs them to.
Principal sources
IOTC Scientific Committee status summary 2025; yellowfin executive summary IOTC-2025-SC28-ES04; Tanzania national report IOTC-2024-SC27-NR27E.
Miller et al. (2017), “Bycatch in the Maldivian pole-and-line tuna fishery”, PLOS ONE 12(5): e0177391.
JICA, Information Collection Survey on the Fisheries Sector in Zanzibar, January 2024. Zanzibar Blue Economy Policy, 2020. Zanzibar National Plan of Action for Small-Scale Fisheries, 2023.
Rashid, R.J. (2026), Frontiers in Marine Science 13, DOI 10.3389/fmars.2026.1840767. Jones, Levine & Jiddawi (2019), Ocean & Coastal Management 178.
Painter et al. (2021), Ocean & Coastal Management 200, art. 105462.
Reg. (EC) 853/2004 Annex III §VIII; Codex STAN 36-1981; FDA Fish & Fishery Products Guidance ch. 5; FDA CPG 540.525 (rev. Nov 2024); Nakazawa, Okazaki et al. (2020), Int. J. Refrigeration 112.
Full citations with URLs are available on request and will be published as a downloadable reference pack. Page last reviewed 21 September 2026.