That’s according to Charles Birkeland at the University of Hawaii in Honolulu and Paul Dayton at Scripps Institution of Oceanography in La Jolla, California, who have reviewed the effects of fishing on populations. Until recently it was thought that all eggs and larvae have the same odds of survival, regardless of their parents’ size. Now studies show that the biggest fish are the most valuable for maintaining the population.

For a start, a female’s fecundity often increases dramatically with size. A 60-centimetre red snapper, for example, produces more than 200 times as many eggs as females that are two-thirds her size.

What’s more, larvae from older and larger black rockfish are bigger, grow more than three times as fast and can survive without food for twice as long as larvae from younger females. And in some species, the young learn the route to spawning areas by following older individuals (Trends in Ecology & Evolution, DOI: 10.1016/j.tree.2005.03.015).

Taking the largest individuals also favours fish that grow slowly and stay small. This has been shown in the lab (żěè¶ĚĘÓƵ, 13 July 2002, p 21), but the effect is now evident in wild populations, including Pacific salmon and European whitefish in the Gulf of Finland.

In a separate study, Carrie Kappel at the Hopkins Marine Station at Stanford University in California examined the threats to marine species. Unsurprisingly, of 338 species listed as vulnerable to extinction on the World Conservation Union Red List or under the US Endangered Species Act, overfishing was by far the biggest danger (see Chart). Many other species are endangered because they are caught accidentally. “The biggest threat for half of the species at risk is by-catch,” says Kappel.

Kappel and Birkeland agree that the best way to prevent over-exploitation is to set up protected marine areas in which fishing is banned. While national parks cover 10 per cent of the planet’s land area, only about 0.1 per cent of the world’s oceans are protected.

The daughter, an 11-year-old western lowland gorilla called Ione, had neglected her first baby, which her keepers raised. So for several days after the birth of her second baby at San Diego Wild Animal Park, the keepers and primatologist Masayuki Nakamichi of Osaka University in Japan kept a close eye on her.

Initially, Ione simply left her baby on the ground in front of her 21-year-old mother, Alberta, who picked him up and handed him back. When Ione made no move to take the baby, Alberta moved closer pushing the newborn into his mother’s face until she took him. Variations on this sequence occurred several times in the first two days.

By the third and fourth day, Ione was holding the baby. Sometimes, Alberta would hold the baby’s arm, and Ione would hand him over, but when the baby nestled into its grandmother, Ione quickly took him back. With time, Alberta became less involved.

Nakamichi argues that Alberta’s actions were attempts to teach Ione appropriate maternal behaviour. “These behaviours are subtle. It takes an acute observer to spot them,” says James Moore of the University of California in San Diego.

Sadly Ione died when the baby was 10 months old, but another female gorilla successfully fostered the baby.

Journal reference: Primates (DOI: 10.1007/s10329-003-0061-9)

In the past two years, scientists have found that seamounts are home to an astonishing diversity of species, with 40 per cent endemic to each mountain. Thousands of new species have been discovered in recent years – 600 on just five seamounts.

With 30,000 seamounts estimated to be in the Pacific alone, a huge slice of biodiversity is at risk. “They are hot spots for the evolution of new species,” says Karen Stocks, an oceanographer with the University of California at San Diego.

Although many coastal seamounts have been fished for decades, the researchers are warning that faltering fish stocks mean fishing fleets are heading into deeper waters in search of new catches. The boats are increasingly targeting pristine oceanic seamounts, home to highly marketable species such as orange roughy, alfonsino and deep-water redfish.

Slow recovery

Trawlers are often the first to discover seamounts, which they target using sophisticated sonar equipment. But bottom-trawling nets can do immense damage within a year or two.

Studies in the Tasman Sea show that coral and crinoids, a group of suspension-feeding echinoderms, cover 90 per cent of pristine seamounts. Once fished by trawlers, that figure drops to 5 per cent, and the seamount loses half its biomass. And recovery is painfully slow.

Some seamounts in the north Pacific have still not bounced back 50 years after boats first trawled them, says John Dower, a fisheries oceanographer at the University of Victoria in British Columbia, Canada.

Stocks organised an international symposium in Oregon last week to gauge the growing threat from commercial fisheries. Delegates were told that fewer than 150 of the world’s seamounts had been studied in detail, and that maritime nations should cooperate to manage these habitats before it is too late.

Each year, roughly a fifth of Bangladesh is flooded, and climate change is forecast to exacerbate the problem as sea levels rise, monsoons become wetter and more intense cyclones lead to higher tidal surges.

To make things worse, heavier rainfall triggered by global warming will swamp Bangladesh’s riverbanks, a previously unforeseen effect, flooding between 20 and 40 per cent more land than today, says Monirul Qader Mirza, a Bangladeshi water resources expert now at the Adaptation and Impacts Research Group at the University of Toronto.

Bangladesh is flood-prone because it lies in the delta of three great rivers, the Ganges, Brahmaputra and Meghna, which together drain 175 million hectares. People can grow crops on land regularly fertilised by nutrient-laden silt from the rivers. But extreme floods cause considerable hardship and loss of life: in 1988 and 1998 over two-thirds of the country was under water at some point.

Most climate models predict up to 20 per cent more precipitation in South-East Asia if temperatures rise by 5 °C. But no one had investigated how Bangladesh’s three major rivers would cope, says Mirza.

Scary scenarios

His team collected data on the relationship between current precipitation levels and the resulting discharge of water by the three rivers. They then fed this data into a software program developed by the Danish Hydraulic Institute, which simulates how factors such as sediment and water quality affect the flow of water within river basins. Researchers at the Surface Water Modelling Centre in Dhaka helped calibrate the model to Bangladesh’s particular geography.

Mirza’s team then ran the program for four climate change scenarios, known as global circulation models. In each, the peak mean discharge for all three rivers increased as global temperatures rose by 2, 4 or 6 °C. If temperatures rose by just 2 °C, two of the models showed that the mean flow of the Meghna and Brahmaputra rivers would increase by 20 per cent.

If there is an increase in temperature of 6 °C, the maximum predicted by the International Panel on Climate Change, then the greater flow of water through Bangladesh’s three great rivers will inevitably lead to between 20 and 40 per cent more flooding.

There will also be a steep increase in deeply flooded land – that covered by more than 1.8 metres of water for nine months of the year. Of the 3.1 million hectares that floods each year, 42 per cent is already deeply flooded. That will climb to 55 per cent if temperatures rise by 6 °C.

The land available to grow rice, vegetables, lintel, onion and mustard crops will be significantly reduced, placing an intolerable pressure on farmers. Policy planners should begin working on adaptation measures now, Mirza says.

Journal reference: Climatic Change (vol 57, p 287)