Climate, and Ecological Effects on Pacific Halibut Size-at-age: Cumulative effects of size-selective fishing on size-at-age in the Gulf of Alaska and Bering Sea

• Main Author: Martell, Steve
• Format: Dataset
• Language: English
• Published: Axiom Data Science 2020
• Subjects: Bering Sea; Gulf of Alaska; Pacific; Sullivan; Alaska
• Online Access: https://dx.doi.org/10.24431/rw1k453; https://search.dataone.org/#view/10.24431/rw1k453

We developed an age- and size-structured equilibrium model using the software package R to examine the long-term relationship between fishing mortality and size-at-age of Pacific halibut. We limited our study to International Pacific Halibut Commission (IPHC) regulatory areas in the Gulf of Alaska (2B, 2C, 3A, and 3B), because these areas provide the greatest contrast in terms of historical fishing mortality and changes in size-at-age. Primary inputs to the equilibrium model included sex and area-specific von Bertalanffy growth parameters that were estimated externally using fisheries-independent observations of halibut length-at-age collected by the IPHC collected from 1980 to 1989, when halibut size-at-age was at its peak. This growth curve, which defines mean size-at-age and variability in size-at-age, was used to generate a series of “growth-type groups,” or groups within a cohort that differ in growth and relative abundance. Additional model inputs included parameters associated with maturity, natural mortality, length-weight allometry, and recruitment Model results were evaluated in terms of changes in mean size-at-age with fishing mortality under equilibrium conditions. Model outputs used for Sullivan (2016) include a data frame of predicted weight-at-age under varying equilibrium fishing mortalities, size limits, and discard mortality rates. This model was coded in the statistical software program R version 3.2.5 (R Core Team 2016). Model results are stored as a dataframe within R but could be exported as a csv or text file.