How many trawl hauls, and how many fish from each haul are needed to obtain a given precision in the age structure estimate for Norwegian spring spawning herring? A bootstrap approach ...

• Main Author: Hjellvik, Vidar
• Format: Conference Object
• Language: unknown
• Published: ASC 2006 - Theme session I 2024
• Subjects: Fisheries and aquaculture; Technologies and data; Vestfjorden
• Online Access: https://dx.doi.org/10.17895/ices.pub.25258801; https://ices-library.figshare.com/articles/conference_contribution/How_many_trawl_hauls_and_how_many_fish_from_each_haul_are_needed_to_obtain_a_given_precision_in_the_age_structure_estimate_for_Norwegian_spring_spawning_herring_A_bootstrap_approach/25258801

No abstracts are to be cited without prior reference to the author.The Norwegian spring spawning herring is assessed each year from acoustic surveys. The age structure in the stock is estimated from trawl samples. Typically, about 10 trawl samples are taken per survey, and 100 fish from each sample are age measured. The uncertainty in the age structure estimate depends both on the number of trawl hauls and the number of fish for which the age is measured within each haul. The same is true for the length structure. Length is much easier to measure than age, and in the Vestfjorden survey in December 2002, more than 6000 fish distributed on 72 trawl samples were length measured, making possible the investigation undertaken in this paper, where the bootstrap is applied to estimate the number of hauls/fish needed to obtain a given precision in the length distribution. It is reasonable to believe that the precision in the age distribution will depend on the number of fish/hauls in the same way. The sampling ...