By Shravan kumar sharma

CIFE,Mumbai

Top predators/Quaternary consumers 1. Sharks and rays

2. Sail fish

3. Tuna

4. Marlins

5. Bill fishes

6. Bonitoes etc.

Middle predators 1. Bigger croakers

2. Marine catfishes

3. Ribbon fishes

Lower/primary consumers 1. Sardines

2. Mackerel

3. Anchovies

According to FAO statistics, in 1997 China was the leading producer, importer and exporter of shark fins in the world

According to FAO 1998, south-east Asian region is the highest exporter, producer of shark fins.

Due to increase in new technologies like fish finding techniques, finding PFZ ---------over-exploitaion of resources occur.

Most of the world s fisheries are being fished at levels above their maximum sustainable yield and many regions are severely overfished.

In the late 1990s it was demonstrated that the mean trophic level of fisheries is declining, i.e. that global fisheries catches increasingly consist of smaller fish and invertebrates lower in the food web

This process, now known as fishing down marine food webs has become a major concern, as it means that fish stocks especially of large bodied fish are being overexploited and fisheries are not being sustainably managed. This severely threatens marine biodiversity.

The Marine Trophic Index (MTI) ------ investigate the impacts of fisheries on the world s marine ecosystems.

Fishing down effect has been demonstrated in various parts of the world such as Thailand, Canada, Greece, Iceland, etc.

S-E Asia Tuna catch from 1950-2000

Importance of top predators in a healthy ecosystems

As apex predators, sharks feed on the animals below them in the food web, helping to regulate and maintain the balance of marine ecosystems.

Apex predators not only affect population dynamics by consuming prey, but they also can control the spatial distribution of potential prey.

By preventing one species from monopolizing a limited resource, predators increase the species diversity of the ecosystem

Trawl fisheries are responsible for the largest by-catch numbers in coastal areas, while longlines capture the majority of sharks as by-catch on the high seas.

It is estimated that tens millions of sharks are caught as by-catch each year, which is nearly half of the total shark catch worldwide.

Additionally, they provide essential food sources for scavengers and remove the sick and weak from populations of prey species

1. Ghost fishing 2. By-catch 3. Overfishing 4. Oilspill

References

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