This document discusses marine ecosystems and overfishing. It outlines the trophic levels in marine food webs, with top predators including sharks and tuna. Many fisheries are overexploited due to new technologies and fishing practices. This fishing down of food webs threatens biodiversity as it removes large predators and disrupt natural population controls. Bycatch from trawling and longlining is a major issue, with tens of millions of sharks caught annually. Ghost fishing from lost or abandoned gear also negatively impacts ecosystems.

1. By Shravan kumar sharma
CIFE,Mumbai

6. Top predators/Quaternary consumers
1. Sharks and rays
2. Sail fish
3. Tuna
4. Marlins
5. Bill fishes
6. Bonitoes etc.

7. Middle predators
1. Bigger croakers
2. Marine catfishes
3. Ribbon fishes

8. Lower/primary consumers
1. Sardines
2. Mackerel
3. Anchovies

9.  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.

10.  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.

11.  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.

13. S-E Asia Tuna catch from 1950-2000

14. 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

15.  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

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

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 www.fao.org