Green Stuff: Eco-news and discoveries
Scientists reveal the effect of fishing on cod size and question turning crops into fuel.
Fishing causes cod to evolve differently
Early explorers described the cod along Newfoundland’s Grand Banks as more numerous than grains of sand. They told stories of catching fish with little more than baskets weighted with stones and lowered into the water.
But by the 1990s, decades of overfishing by modern fleets had taken its toll. Cod stocks on Georges Bank and the Grand Banks collapsed.
Scientists have a number of explanations for why, somewhat bafflingly, they have yet to recover. For example, a pulse of cold water from the north may have slowed cod’s reproductive success. Or changes in the balance of species may have made life more difficult for cod. But one of the more intriguing theories relates to how predation – in this case, fishing – becomes an evolutionary force itself.
Scientists have long noted that whenever Homo sapiens arrived, the first living things to disappear were the largest – mammoths and sloths in North and South America, for example. Modern scientists have observed that fishing applies a similar downward pressure on average fish size.
A new study on Icelandic cod in the journal PLoS ONE reveals how fishing pressure can alter body size and behavior in a given stock.
Certain genes determine whether cod prefer shallow or deep water, or an area in between. In Iceland, fishermen tend to focus on shallower waters. As one might predict, the scientists find that fish possessing shallow- water genes are in decline. The average size at which cod reach reproductive maturity is also diminishing by almost one centimeter yearly.
Scientists observed a similar shrinking body size just before Newfoundland’s cod collapse, so the authors warn that a collapse of Icelandic stocks is probably imminent. To prevent that from happening, they suggest establishing no-take marine reserves. Then, in a protected piece of ocean, natural selection of both deep- and shallow-water-loving fish can resume.
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Bioelectricity versus biofuels
In recent years, biofuels – fuel made from plant material – have received much attention because they seemed to offer solutions to two pressing problems: global warming and dependence on oil.
But upon closer scrutiny, biofuels appear less the panacea than initially hoped. After accounting for the fossil fuel burned in tractors or applied as fertilizer while cultivating biofuel crops, for example, are they really carbon neutral? And if they occupy land that might otherwise grow food or contain forests, do rising food costs and biodiversity loss overshadow their contribution to energy independence?
A study in the online edition of the journal Science raises these questions. The authors find that generating electricity by directly burning plant matter the same way coal-fired plants use coal, and then charging battery-powered cars with that electricity, could yield 80 percent more miles of transportation per acre of crop than ethanol fed into a combustion engine. The internal combustion engine isn’t as efficient as an electric motor, and using bioelectricity to power a car yields double the greenhouse-gas offsets compared with ethanol.