An abundance of toothfish in the Ross Sea?

Perhaps you’ve heard the news – NIWA’s recent toothfish survey in the southern Ross Sea has found “high densities” of young fish, leading many news agencies to suggest the population is not at risk.  But they are leaving out some key details.

First off, we commend NIWA’s attempt to find out more about Ross Sea toothfish.  As of now, most of what we know is based on fisheries dependent data. This is limited to the months they fish (usually Jan-Mar) and the places and depths they fish (usually 1,000m or more). We really know so little – scientists nor fishers have ever found a larval or toothfish egg, in fact they’ve seldom caught any fish smaller than 40cm.We still don’t know exactly when and where they spawn – though we think it is in the seamounts to the North – a prime fishing area.

To say that there are plenty of Ross Sea toothfish, based on this survey, is a farce.  We actually have no accurate baseline for comparison – we don’t really know how many toothfish were in the Ross Sea before the fishery began in the mid-1990s.  New Zealand scientists only began assessing the stocks in 2005, already 8 years into the fishery.  Moreover stock assessments are based on tag-recapture data, put into a model with lots of untested assumptions – a flaw that the New Zealand Ministry of Fisheries has received a lot of flack for.  Moreover, tag-recapture models tend to favor small fish (which better survive the tagging process). This can skew the model, potentially overestimating stock size.

As Stu Hanchet, the NIWA lead scientist on the cruise stated, “a single survey tells us very little.”  Over the course of the next 5-6 years, if they continue the survey every year, which targets only subadult fish, they might know more about the status of the Ross Sea stock. Of course by the time we know with certainty that overfishing is occurring, it is usually too late to reverse the trend, particularly for deep-sea fishes. Evidence of this is the orange roughy, a fish and fisheries management blunder well known to New Zealanders.

Antarctic toothfish in McMurdo Sound (photo by Rob Robbins)

Antarctic toothfish in McMurdo Sound (photo by Rob Robbins)

Deep-sea fish, like toothfish are long-lived, late to mature and grow slowly – all traits that make them incredibly vulnerable to overfishing. Many fisheries scientists would argue that deep-sea fishes cannot be fished sustainably, ever. And we certainly don’t  know enough about toothfish to fish them sustainably. Nor do we know how the reduction in toothfish, the top piscine predator in the Ross Sea, is impacting the greater Ross Sea ecosystem. By NIWA’s own data, confirmed by other sources, the large fish are already disappearing. The fishery, now fifteen years strong, has been conjectured (by the model) to have reduced the spawning stock biomass (just the proportion of fish that spawn) by at least 20%.  Those fish, hatched before the fishery began, are gone from the ecosystem.

Regardless of these good intentions in managing the toothfish fishery, removing these fish from the Ross Sea is changing the ecosystem, which up until now has been the least altered large marine ecosystem in the world. The Ross Sea is the Last Ocean. Is it not worth leaving just this one place untouched for the sake of science and future generations?

Emperor Penguin and Ice Breaker (Photo by John B Weller)

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