Gains resulting from planned mitigation or improvement projects cannot always be quantified for similar reasons. Cumulative losses of even one element of fish habitat can extend over long time periods. Losses of habitat elements such as large woody debris can have effects for 80 to 160 years. Fish react to their habitat in a variety of ways, and changes in habitat can induce changes in ecology, behavior, growth, reproduction, homeostasis, organ function, histology, cell integrity, and gene function. Extremely small amounts of toxicants in the habitat can have significant effects, which may be sublethal, but result in lost production.
Cumulative effects occur in altered growth, reproduction, tissue, and behavior.
Trophic levels can determine the nature of cumulative effects. The type of habitat can affect chemical accumulation and fish can internally alter elements provided by the habitat. Cumulative effects of small habitat modifications cannot be simply and easily written into a precise linear equation, due to mathematical limitations. All individual effects on fish habitat result in cumulative effects on global fisheries. Encourage full disclosure and assessment of potential cumulative impacts during project planning, including ecosystem modeling when necessary.