Age and growth of thread herring Opisthonema libertate, in the southern gulf of California

Abstract

To fit a growth model to Opisthonema libertate, the most common thread herring in a small pelagic fishery in the southern Gulf of California, size data of commercial landings and age were generated from sagittal otoliths assessed during three different years, 2005, 2008 and 2015, representing Neutral, La Niña and El Niño environmental conditions, respectively. A multimodel select approach on five special submodels of generalized Schnute model, including one, equivalent to the Von Bertalanffy model, were used. A total of 573 otoliths were analyzed; 219 from Neutral, 149 from El Niño and 205 from The Niña events. An opaque zone of otoliths formed in winter-spring when chlorophyll a (Chl-a) concentrations were at a maximum. However, a hyaline zone of otoliths formed during the summer of the reproductive period. Schnute submodel 1 was the best model selected in all three environmental conditions, but submodel 3 was the best on pooled data. Length of thread herring aged 0.5 years old in the El Niño year was lower than other environmental-years analyzed. A possible compensatory effect on growth with age was observed in the data because environmental conditions affected the growth of 0.5-year-old thread herring, as was evident in size variance in this age group under all three conditions, but variance decreased in the older age groups. Thus, a multimodel average of Schnute submodels 1 and 3 could be used to describe the growth of O. libertate in the southern Gulf of California.