It's easy to talk about "declining fish stocks" in the abstract. It's harder, and more useful, to look at the actual numbers fisheries scientists use to track a stock's health: biomass as a percentage of its unfished level β what the population would be if no one had ever fished it. Below are four New Zealand species where that number has been measured for decades, each telling a slightly different version of the same story.
Snapper (SNA1) β the recovery story
Snapper in the Hauraki Gulf and Bay of Plenty (the SNA1 stock) is New Zealand's best-known fisheries recovery. By the early 1980s, heavy fishing pressure had driven the stock down to roughly 10β15% of its unfished biomass. The introduction of the Quota Management System in 1986 changed the trajectory: SNA1 has since rebuilt to somewhere in the 40β50% range, with a formal target of 40% of unfished biomass under the current SNA1 Management Plan.
Tarakihi (East Coast) β the stock still falling
Tarakihi tells the opposite story. The East Coast stock was estimated at around 17% of unfished biomass in 2017, and a 2018 assessment put it lower still, at 15.9% β meaning roughly 84% of the original tarakihi population had been removed from east coast waters. Modelling shows the stock has not been above 27% of unfished biomass since 1975, and has sat below 20% since the early 2000s. The current rebuild plan targets 35% of unfished biomass, but not until 2037.
Rock Lobster (Hauraki Gulf) β locally "functionally extinct"
Crayfish in the inner Hauraki Gulf show how a species can collapse locally even while broader regional numbers look healthier. Research at the Leigh and TΔwharanui marine reserves found legal-sized lobster biomass on fished reefs outside the reserves sitting at just 2β3% of the biomass found inside them; a comparable study at Hahei found fished reefs at around 7% of in-reserve biomass. By 2016, scientists were describing Hauraki Gulf crayfish as "functionally extinct" in the areas open to fishing β even as the wider CRA2 stock assessment (which spans a much larger area) has shown signs of recovery in recent years.
Orange Roughy β the cautionary tale
Orange roughy is the starkest example of how badly a deepwater fishery can go wrong when a slow-growing species (it can live to 120 years) is fished like a fast-growing one. New Zealand's Challenger Plateau stock collapsed to just 3% of its unfished biomass before catch limits were drastically cut, and three of the country's eight orange roughy fisheries had closed entirely by the end of the 1990s. A 2025 assessment found the fishery's largest stock close to collapse again, at an estimated 8β18% of unfished biomass β and modelling suggests that even if fishing stopped immediately, recovery to a safe level could take 33 to 74 years, possibly longer.
Current (or most recent) biomass as a percentage of unfished biomass, compared with each stock's official rebuild target where one exists. Rock lobster and orange roughy figures reflect the specific local studies and historic collapse cited above, not the full management-area stock assessment.
Why this matters for kelp
Snapper and rock lobster aren't just food fish β they're the predators that keep kina in check on Aotearoa's reefs. When their numbers collapse locally, as they have across much of the inner Hauraki Gulf, kina populations explode unchecked, graze kelp forests down to bare rock, and create the urchin barrens that Kelp Helpers exists to reverse. The decline in this chart isn't a separate problem from kelp loss β it's the cause of it. I've gone deeper on the rock lobster side of that story in Crayfish "Functionally Extinct".