visserijmortality

Visserijmortality, or fishing mortality, is the rate at which individuals in a fish population die as a result of fishing activities over a defined period, usually a year. It is a component of total mortality and is typically considered in contrast to natural mortality (M), which includes deaths from predation, disease, aging, and other non-human causes. The sum of fishing mortality and natural mortality gives total mortality (Z = F + M).

In stock assessment and fisheries management, visserijmortality is a key parameter used to describe how much fishing pressure a population experiences. Management aims to keep fishing mortality at sustainable levels, often defined relative to reference points such as FMSY (the fishing mortality that yields maximum sustainable biological yield). When F exceeds sustainable levels, the stock can decline; when F is too low, potential yields may be underutilized.

Estimating visserijmortality involves combining catch data, effort data, age or size structure, and information from surveys within stock assessment models. Methods include age-structured catch-at-age models, surplus production models, and integrated approaches that incorporate both fishery-dependent and fishery-independent data. Fishing mortality is also influenced by gear selectivity, regulatory measures, and changes in fishing practices, which can vary by stock, season, and region.

Understanding visserijmortality supports assessment of stock status, evaluation of management measures, and projection of future yields. It highlights the balance between harvesting opportunities and the long-term sustainability of fish populations.