Shark decline confirmed by demographic model

Sharks are in decline due to overfishing75% of cut-the-fin-dump-the-dying-shark fishery is illegal. Many sharks also die as by-catch of conventional fishing. These sharks never reach the shore either – and their deaths are also not documented.

Still the used methods to quantify a feared global decline of shark populations – either catching or filming wild sharks – have been criticised as being “indices of abundance” rather than proof of the opposite, species under threat and witnessing decline, a group of researchers of James Cook University says.

They have therefore devised a statistical model that calculates age distribution and population sizes for different shark species based on for instance measured shark lengths and birth rates.

In their PLoS ONE publication the marine biologists state “consensus estimates of natural and total population growth across multiple models support the hypothesis that these species are declining rapidly due to fishing, in contrast to conclusions previously drawn from catch rate trends.”

Holocene: conservation – or extinction

“Moreover, quantitative projections of abundance differences on fished versus unfished reefs, based on the population growth rate estimates, are comparable to those found in previous studies using underwater visual surveys. These findings appear to justify management actions to substantially reduce the fishing mortality of reef sharks.”

So again, if it were to exist, conservation would be effective.

Shark overfishing decline vs conservation
Overfishing versus conservation: the difference between population decline and recovery for two species of reef sharks.

In reality though the protection of ocean biodiversity lags far behind nature conservation measures on land, and with pollution, climate change and ocean acidification each adding their weight to the stress of overfishing, it’s not just plants with leaves and animals with lungs, but also the oceans that seem on the brink of the Holocene Mass Extinction.

Anyway, what could help: don’t eat shark fin soup. Or if for some hard to understand reason really ‘culture forces you’ – show some respect, and eat the rest of the shark too. That would make better sense in face of the protein crisis.

© Rolf Schuttenhelm |

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