A model of between-haul variation in selectivity

The selectivity of the same fishing net can vary between hauls. Most selectivity models ignore this between-haul variation by pooling data over hauls. This approach is shown to result in misleadingly small parameter standard errors, which can lead to incorrect inferences about the differences between nets. A model is developed which incorporates between-haul variation and which provides realistic parameter standard errors. Methods of parameter estimation are described. The model is illustrated by a comparison of the selectivity of two nets.