Worldwide, fisheries are on the decline due to problems in fishing practices. discuss at least three of these destructive practices, and explain the effect each is having on the marine environment

One is drift netting. These nets are indiscriminate and also catch, injure and kill fishes that are not intended to be caught. This, therefore, greatly affects the marine ecosystem. 

Second is over-fishing. This reduces the fish population to a point where they are unable to regenerate and hence predisposes/ condemning them to extinction   

Third is the destruction of marine ecosystem, deliberately, to clear an obstacle or pave the way for fishing lines. This damages the habits hence affecting the ecosystem from primary producers and up the food chain.

The number of big fish would increase

Explanation:

The amount of food for the big fish in the lake would increase, allowing the amount of big fish to increase until another factor (such as space or disease)  would stop that increase in population.