The utility of length, age, liver condition, and body condition for predicting maturity and fecundity of female sablefish

Abstract

The objectives of this study were to determine if relative body condition and relative liver size (hepatosomatic index, HSI) could be utilized to predict maturity 6–8 months prior to spawning, when samples are readily available, and if these condition measures were related to fecundity. Female sablefish were sampled on four survey legs during a summer longline survey in July and August 2015 and during a winter survey in December 2015, which is 1–3 months prior to the spawning season in the Gulf of Alaska. The relative body condition and HSI of fish increased throughout the summer survey, reaching measurements similar to those observed during the winter. There were significant differences between immature and mature fish HSI and relative body condition and these differences increased throughout the summer, making these factors useful for predicting maturity on the last legs of the survey. On these later legs, models that utilized relative body condition and HSI, as well as length and age, to predict whether a fish was immature or would spawn produced maturity curves that best matched models based on histological maturity classifications. However, models without HSI may be the best choice for future work because liver weight is not regularly collected on annual surveys and on the last leg of the survey the addition of HSI to predicitive models did not improve maturity-at-age curves. Utilizing the winter data set, which is the time period when fecundity could be enumerated, fecundity was significantly related to relative condition and HSI. Increasing or decreasing these measures of condition by one standard deviation in a model of fecundity, which also included length, resulted in an estimated decrease in fecundity of 32% or an increase of 47% for an average size fish (78 cm). These results show the importance of incorporating fish condition into measures of population productivity.