Temporary Closures: concepts & considerations

The Temporary Closures module is designed to evaluate single-species or aggregate multi-species temporal closures. The Temporary Closures module relies on records of catch per fishing event to provide a frame of reference against which closure options can be contrasted. In using Temporary Closures, catch data must contain dates (see Data Repository). To evaluate closure options, the catch data must be presented as fishing records in the units of catch in numbers per trip, thus, enabling estimation of the effect of a closure against current (or historical) trip records. This way, catch data provides a frame of reference for existing temporal fishing practices, against which closure options (i.e., proposed changes to existing practices) can be evaluated.

After specifying a closure option in the control panel, the immediate effect is calculated as (short-term or immediate) percentage catch reduction. This calculation is made using a bootstrap analysis, which makes use of the degree of imprecision in the catch data to calculate an expected range (between a minimum and maximum) of percentage catch reduction. The bootstrap analysis makes the following assumptions in calculating the effects of a temporal closure. First, fishing events (fishers) occurring during the closure will cease to occur. Second, fisher behavior will not change because of the temporal closure, nor will the quantity of fishing effort that occurs at other times of the year, nor will the closure reduce nor enhance entry to the fishery nor shifts in effort other fisheries. Finally, the effect of the closure is immediate, meaning it does not account for its longer-term effects on the size of the fish stock; accordingly longer-term effects may differ as the fish population responds to regulatory changes applied to fishers.

The Temporal Closure module can be used to analyze single-species closure options (single level of grouping variable selected) or aggregate closure options (multiple levels of grouping variable selected). Importantly, Temporary Closures uses trip identifier, column one in the loaded data set, as a unique identifier of each fishing trip. Summation by unique identifier occurs in the Temporary Closures module prior to analysis and presentation of results to users. Thus, non-unique (repeat) identifiers are presented as the summation of catches reported in column two. This summation feature enables the use of a grouping variable to examine single-species or aggregate options. When multiple group levels are selected, these should correspond to shared trip identifiers, thus, summation by trip will result in aggregate total catch per trip for the selected set of species (or group levels). Analysis of total catch reduction follows this aggregation step.