Considering the incredible number of between 150 – 200 million sharks destroyed each year, we need to look at the natural biology of sharks to fully understand the potential threat of extinction to these species. Most sharks are slow growing, have late maturation and low fecundity and this is the shark’s downfall. They cannot replace their stocks to keep up with human exploitation, such as say, sardines can. Lets look at the Great White Shark.
The Great White Shark female takes approximately 15 years to become sexually mature, and the male about 8 years. At these ages the female will be around five meters long and the male around four meters long. The Great White Sharks’ fecundity is low, so the female may possibly only give birth to several litters of pups in a lifetime and these litters are relatively small, ranging from about seven to eleven pups in a litter. The white shark is just an example, and if you look at all species, you find some which give birth to only one pup and some such as the Sandbar shark which only become sexually mature at about 25 years old. So due to the shark’s inability to reproduce quickly, stock replacement is not occurring, and subsequently the populations of the world are fast diminishing. In fact they are being wiped out far quicker than most people realise, with many species critically endangered and some species literally on the brink of extinction.
The Great White Shark is now protected in South Africa, California, South Australia and Tasmania, and although this is only one of almost 400 species of shark, its protection is a step in the right direction. The Great White is a key stone species on this planet and its protection, subsequent media attention and high public profile allows us to use it as a battering ram to push for the protection of other shark species.
Many species of shark need protection, but unfortunately, the protection of species is not the end to the problem. If we ascertained the status of a specific species, and then implement regulation which stipulates that no sharks of that species may be caught, one may presume that the problem is solved and that species will thus recover in numbers. Although the protection of that species would be a start in the right direction, it would possibly not guarantee the survival of that species. We have to look further into the complexities of the problems facing sharks, which brings us to our next obstacle, which is probably just as serious as over exploitation.
This huge hurdle is Habitat Degradation. More than half of the earth’s human population live within about 100 km of an ocean, and subsequently this ever increasing population encroaches on the inshore marine environment. Coastal marine habitats are subsequently adversely affected and altered at relatively accelerated rates by the development of harbours, building of piers, inshore fishing fleets, weekend boat anglers, sewerage and industrial outlets.
The majority of shark species utilise these shore zones for at least some stage of their lives, and are subsequently directly affected by humans altering this habitat. Humans with modern technology and machinery can alter a complete ecological environment within days, weeks or months. Sharks unfortunately do not have the ability to adapt to these changes in their habitat, and therefore stocks are affected. Most shark species utilise the inshore zone for nursery purposes which obviously indicates that these areas need to be stable, so when these nurseries are disrupted by say, a decline in prey, the young sharks may start broadening their predatory range. With their once secure nursery hunting grounds destroyed, they now find themselves in less protected areas where they have to compete with larger sharks for prey which may not be suited for them. The young shark is now faced with a situation where he becomes potential prey to a larger shark, and he now also has to hunt for food which may be to large for him. As this young animals natural biology of low reproduction stipulates that he should have a high degree of survival in a stable environment, his species is now facing serious stock replacement problems as his chances of survival are drastically reduced in his new forced upon environment.
It is evident that the problems facing sharks are serious and complex and need to be addressed from several directions, and not simply from a regulation of total catch. If reproduction in species is not taking place, it is then futile to regulate a catch quota, as the species will never bridge the gap. We need to thus focus attention on all aspects affecting sharks, and regulate from those angles. Sharks do not have the ability to reproduce quickly, so we need to restrict catching of juvenile and mature female sharks. Sharks which are known to be currently threatened require a total fishing ban. We need to re-evaluate shark fisheries and current shark conservation and management programs. We need to take a serious look at the conservation of shark nursery areas, as it will not be sufficient to only protect the adult stocks. If we are not very careful, we will not only lose our shark stocks, we will lose entire ecological systems.