Six of the world's rarest fish - PART TWO

In the first part of this article last week we described three of the world's rarest fish species, and found out that about the only thing they had in common with each other was that they were critically endangered. The reasons for their rarity were very different, and each had an exciting and very sad story to tell. In this concluding part, we shall be looking at another three critically endangered fish and discovering how and why they may not be around on this planet for much longer.

Speckled Hind (Epinephelus drummondhayi)

This is one of the most beautifully marked and brightly-coloured groupers caught off the southeastern United States. Like other epinepheline groupers, speckled hind are protogynous hermaphrodites, which means they begin life as females and as they mature they become males. Females reach sexual maturity around four to five years of age but then change sex and most of the larger, older fish are males. They inhabit warm, moderately deep waters in depths ranging from 150 to 300 feet, from North Carolina to Cuba, including Bermuda, the Bahamas and the Gulf of Mexico.

They have been food fish for centuries, but in recent years they have been classified as endangered. The main threat to them is classed as 'mortality as a result of fishing', and they have been designated as 'overfished' as defined by the Magnuson-Stevens Fisheries Act.

However, this bare statement doesn't cover the whole story. It is the peculiar sexual characteristics of the species that may also prove to be its downfall. The rise in popularity of trophy fishing means that the largest and showiest specimens - i.e. the males - are the most sought-after. Even though the commercial fishermen who catch these fish for food prefer to take the larger specimens. This has led to a dramatic inbalance of the sexes, and according to some experts there are very few of the males left. Despite their increasing rarity it is still not illegal to catch them although a strict quota of one fish per vessel per trip has been imposed. Whilst researching this article I was appalled to find more websites dealing with recipes on how to cook these fish than there were websites dealing with its conservation.

Southern bluefin tuna (Thunnus maccoyii)

This is another species whose very existence is threatened by overfishing. However, once again the vagaries of its own particular biology are operating against it. In 1937 an aerial fishing survey spotted over 60,000 entire shoals of these fish in one 20-mile strip of the Australian Bight. Each of these shoals contained anything up to 100,000 fish. The people who made this discovery were so excited that they immediately opened a commercial fish cannery. Now, less than 70 years later the species is listed as critically endangered and according to the IUCN is in imminent danger of complete collapse. How could this be? How could such an enormous population be wiped out in 70 short years?

The answer is in the enormous shoals that were originally reported. Like the American bison, which once thundered across the prairies in herds so large that they stretched as far as the eye could see, and like the now extinct passenger pigeon whose flocks - in the early and mid-19th century - was so large that trees would collapse under the weight of roosting birds, they live in a large social group and as soon as the numbers of the species go below a certain level it takes extremely careful husbandry - as in the case of the North American bison - to turn the species back from the brink of extinction. Thus, even though extremely large numbers of a certain species - like the southern bluefin tuna - may be perceived to exist, the species may indeed still be doomed.

A panel of independent scientists has said that even at current catch levels there is

'little chance that the SBT spawning stock will be rebuilt to the 1980 levels by 2020.'

This is the stated conservation aim of the Commission responsible for managing the fishery. The scientific report goes on to say that 'substantial quota reductions would be required to achieve that goal.'

Stock levels could continue to decline under current catch levels.

Devil's Hole Pupfish (Cyprinodon diabolis)

At the end of the Pleistocene Epoch, 10,000 to 20,000 years ago, the glaciers that covered much of North America receded for the last time. The southwestern portion of the continent, although untouched by glaciation except in some of the highest mountains, was much cooler than today and surface water was abundant. In the last 10,000 years, and the whole of North America - and indeed much of the rest of the world - has been undergoing a gradual drying-out process. Effectively, this means that species of aquatic animal that were once inhabitants of a large and complex river system are now living in small, isolated oases. As a result of this, speciation takes place to a remarkable degree. Charles Darwin was the first to discover how finch species on neighbouring islands in the Galapagos system evolved relatively quickly into new species. The same mechanism can be seen at work across the desert states of the USA where a number of different species of pupfish and killifish have evolved.

In the Death Valley system, for example,there are more than 20 populations of pupfish that have evolved into 10 distinct species or subspecies. Each species of pupfish has taken on a distinct shape and markings as well as a unique set of biological adaptations. Ancestral pupfish presumably inhabited shallow lake margins, marshes, and streams where environmental parameters (temperature, salinity, dissolved oxygen, etc.) fluctuated daily and seasonally. These pupfish were probably highly variable in character and were able to withstand wide environmental extremes. Today some Death Valley pupfish populations are isolated in extremely variable environments, like the Amargosa River and Salt Creek. Others are isolated in stable springs with constant temperature, such as Devils Hole, School Spring, and The Nature Conservancy's Big Spring.

Because each of these species is isolated from the others the gene pool has become specialised and - to a certain extent at least - impoverished. The most divergent pupfishes of the Death Valley System, are those isolated for the longest periods (more than 10,000 years). The Owens pupfish (Cyprinodon radiosus), found most distant from the centre of pupfish distribution, and Devils Hole pupfish (Cyprinodon diabolis); existing in a higher, inaccessible habitat; are two such examples. In contrast, Amargosa pupfish (Cyprinodon nevadensis) habitats have been intermittently connected, reducing the length of isolation to spans ranging from 400 to 5,000 years. Consequently the Amargosa pupfish has changed less than others, evolving into several subspecies but not into distinct species.

The Devils Hole pupfish lives in one deep-water pool at Ash Meadows National Wildlife Refuge. The pupfish was nearly exterminated in the 1970s when the level of the pool was drawn down by pumping from groundwater wells near Ash Meadows but for once the level of national outrage was directed at something worthwhile, water pumping was stopped and the species was saved - for the time being at least.

This is an example of a threatened creature in the very truest sense of the word. Although it is highly protected, and at the moment the conservation strategies for it seem to be succeeding, all that needs to happen is for there to be an unforeseen event beyond anybody's control and this tiny fish will be lost forever.

Perhaps this is something that as the dominant species on the planet we should remember. No species lasts for ever. We tend to use the term dinosaur to describe something that is outdated and unsuccessful. This is a complete misnomer. Dinosaurs were one of the most successful groups of animals ever to live on Earth. However, an unforeseen event - or to be more exact a concentration of unforeseen events - wiped them out. The same could very easily happened to us. Events on a cosmic scale are way beyond our control. However, many of the things that go on across the world, which are threatening many species, including our own, are the direct result of human foolishness. For the sake of the creatures with whom we share this planet, as well as for our own sakes, we should take heed of the warnings before it gets too late.