Earlier this year, a research team from Spain released a surprising new estimate of mesopelagic fish biomass that is 10 times greater than previous estimates. This new study raises the total estimated biomass of mesopelagic fish from 1 billion tons to 10 billion tons, accounting for 95% of all fish biomass. The news media ran with dozens of variations on the “plenty of fish in the sea” trope, suggesting that the global fisheries may be more abundant and reversing the doom-and-gloom message of fisheries decline.
This is not correct.
The fish in question are small, mid-water species like myctophids and cyclothones, fish that are incredibly important for ocean ecosystems, but commercially non-viable. The reason they were missed in previous studies is that these small, agile fish avoid nets; This new study uses SONAR and other acoustic tools to measure biomass. So while there is a huge, untapped fish stock in the mid-water world, it is not a commercial fishery.
Let’s put things in perspective.
The lower boundary estimate from these acoustic estimates places mesopelagic fishes at 95% of total fish biomass and 10 billion tons. Using the numbers from this study, that leaves 510 million tons of fish in the rest of the ocean, including almost all of the world’s commercial fisheries. In 2012, commercial fish catches weighed in at 90 million tons, down from the 96 million tons caught several years earlier, but still nearly one-fifth of the total available fish biomass. While there may be more total fish in the sea, we are still pulling out a massive proportion of the relatively few commercially viable fisheries.
To add even more context, while commercial fishery biomass is less than 510 million tons according to this study (that figure includes numerous non-commercial fish as well), the gross vehicle tonnage of the world’s shipping fleet tips the scale at 1.4 billion tons. Which means that our ships outweigh our fisheries by a factor of 3.
The correct comparison is shipping tonnage to shipping, fishing tonnage to fishing.
I agree that those numbers would be interesting, too. Unfortunately, it’s much harder to find the total vessel tonnage of the world fishing fleet. Those numbers aren’t tracked like shipping vessels are. I also tried to find recreational and naval vessel weights, to no avail.
Given the generally low productivity of mesopelagic fish and long time to reach sexual maturity, the biomass of the fish in the sea may not be that relevant to the potential yield and overfishing standards for these populations. A variety of factors are utilized in fisheries population dynamics models that support management regulations (assuming that we develop a sustainable management scheme for international waters and national exclusive economic zones that includes both fishing mortality from harvesting and natural mortality changes from environmental factors).