Effect of egg size on the growth rate and survival of wild walleye pollock Gadus chalcogrammus larvae

Abstract

To clarify the survival process of walleye pollock larvae of the Japan Pacific stock in relation to the individual egg size, we estimated the original relative egg diameter from the diameter of the hatch check formed on larval sagittal otoliths. Significant positive correlations were obtained between egg diameter and embryonic body length, yolk sac volume, and lapillar otolith diameter in 3-year groups (2013-2015 year classes) collected with a plankton net in Funka Bay. Embryos before hatching were without a check; however, checks were observed on all larval otoliths just after hatching. The check diameters showed significant positive regressions to age at collection (days after hatching) in 2014 and 2015 year classes, however not in the 2013 year class. Diameters of eggs collected with a ring net in Funka Bay gradually increased from 2013 to 2015 year classes. During the 2013-2015 spawning seasons, the proportion of adult females of the 2007 and 2009 year classes, which had relatively high abundances, gradually increased to higher proportions with age (43%, 57%, and <73%, respectively), indicating that the mechanism by which the eggs gradually became larger. The low water temperature experienced by the spawners ca. 2 months earlier, advancement in spawner age, and increase of repeat spawners (at least twice in their life time) would contribute to the increase in egg size and growth and survival rate of walleye pollock larvae.

Momma's larvae: Maternal oceanographic experience and larval size influence early survival of rockfishes

“…In addition, Robidas (2022) demonstrated that northern anchovy ( Engraulis mordax ) survival and age‐adjusted morphological traits were positively correlated with otolith core width‐at‐hatch. Similarly, the oceanographic conditions adult walleye pollock ( Gadus chalcogrammus ) experience off the coast of Japan influence the quality of eggs and larvae produced and contribute to their early growth and survival (Kajiwara et al, 2022). The fact that fishes with very different adult life history characteristics (benthic versus pelagic, long‐lived versus short‐lived) that were collected in multiple oceans (Pacific and Atlantic) show the same pattern reveals a promising relationship between otolith core width‐at‐extrusion and survival suggests that the size of larvae at hatch/extrusion may play an important role in early survival during a life stage characterized by high mortality (Houde, 1987).…”