Biodiversity loss can be explained simply through one precept, however it is much more complicated than that, as Habitat loss, Pollution and Global Ocean Temperature rises are all causes and effects of the immediate environment. Overfishing seems to be at the forefront of biodiversity loss.
Overfishing is an important reason behind the population decline in the oceans, there is "increased pressure" from mankind and the global capitalist market that has seen the overfished stocks increase from 5 to 17 in 14 years (in Queensland alone). Barramundi and Australian Salmon a fish that is not greatly fished and is not really seen on the table is not overfished, however sole, halibut, redfish and anglerfish are being fished intermediately. The overfished species cause an indirect effect on the oceans causing a shift in the zooplankton and phytoplankton balance. This causes species that live in the tropics such as the Archer fish and the White breasted Blue Surgeonfish to see immediate effects on the insects and corals that they feed on. An increase in insects causes crop damage and subsequent farming costs. An increase in Corals can cause a myriad of changes to the environment of which I do not want to comment upon here. Overfishing causes population dynamic changes and subsequent environmental loss.
Dredging is wrecking the delicate balance of the ocean, especially of the coast of Queensland. This process causes the direct environment, especially the invertebrate community to suffer. Adapting to this tendency causes a shift to floating species such as the Naked Sea Butterfly which feeds on the Shelled Sea Butterfly, this carnivore has no exception but to kill, rather than feeding of the detrital matter on the continental shelf which could have been dredged. Hence more carnivore invertebrate's leave invertebrates to let the phytoplankton grow rapidly. The phytoplankton is then eaten by the small fish, such as pilchards and minnows to be eaten by the big fish. This change in diet effects the location of the fish and migration ensues.
Ultimately Overfishing will cause a shift in the balance and the process of fish location. This will ultimately leave the fish stocks reduced through trawling, dredging and long line fishing. The increase in fishing causes migration patterns of the fish to change the way in which the stocks are distributed. Migration is a natural process seen in Birds and Eels and now more recently in Bluefin Tuna.