Decadal changes in reproduction of walleye pollock (Theragra chalcogramma) off the Pacific coast of northern Japan

Abstract

We examined stock fecundity, abundance of eggs and larvae, and catch per haul of age 0 walleye pollock, Theragra chalcogramma, and considered the relationship between reproduction, recruitment and the ocean environment off the Pacific coast of northern Japan for the period between 1985 and 1996. To calculate stock fecundity, we estimated age at maturity and fecundity, and expanded estimates to the expected age composition of the population as estimated by Virtual Population Analysis. Eggs and larvae were collected by research cruises in the main spawning ground in and around Funka Bay. Catch in number of age 0 per haul were obtained from catch statistics. Annual stock fecundity decreased in the late 1980s, from 97 billion eggs in 1986 to 74 billion in 1990, and increased in the 1990s, to 137 billion in 1995. Abundance of eggs and larvae, and catch of age 0 per haul, were high in the late 1980s; however, they were low or intermediate in the 1990s. The steepness of the spawner recruitment relationship in the 1990s was different from the late 1980s, based on positive relationships between stock fecundity and catch of age 0 per haul in each decade. Sea surface temperature in the main spawning ground around Funka Bay was low in the late 1980s, but high in 1990s. We conclude that the decadal-scale change in the ocean environment around the main spawning ground between the 1980s and the 1990s caused a change in the reproduction and recruitment of walleye pollock.

Density-dependent, landscape, and climate effects on spawning distribution of walleye pollock Theragra chalcogramma

“…In the case of pollock, year-class abundance was initially thought to be due to the environmental conditions experienced by eggs and larvae (Megrey et al 1996, Hamatsu et al 2004. Recent evidence suggests that environmental conditions can also mediate the influence of density-dependent processes occurring between the pollock egg and juvenile stages, and predators and water temperature can continue to modify abundance well into the juvenile stage (Bailey 2000, Ciannelli et al 2004.…”

Elemental analysis of otoliths of walleye pollock: A trial to discriminate the local stocks around Hokkaido, Japan

“…On assumption (i), FAO 21 have reported that walleye pollock reaches the first maturation at 3–4 years of age, 30–38 cm TL. Hamatsu and Yabuki 14 reported that 47–73% of the 4‐year‐old walleye pollock were mature in the Doto area, and Hamatsu 22 also reported that in 1990–1996 in the Doto area, about 80% of walleye pollock are observed as mature at 4 years old. Thus, it is natural to assume that 4‐year‐old fish mature and migrate to their spawning grounds.…”

Life-history traits of walleye pollock, Theragra chalcogramma, in the northeastern Japan Sea during early to mid 1990s

“…In the present study, data collected in October were used for the analysis, as the spawning period extends from late November through late March in the northern Japan Sea population (Tsuji, 1990). For inter-population comparison, maturity parameters were taken from Stahl and Kruse (2008) in the two Bering Sea populations, Dorn et al (2010) in the Gulf of Alaska population and Hamatsu et al (2004) and Hamatsu and Yabuki (2007) in the Japan Pacific population. Identification of individual sexual maturity was based on the GSI in the Bering Sea populations, whereas the identification was based on the visual observation in the Gulf of Alaska population and the Japan Pacific population.…”

“…Length-fecundity relationships were taken from Hinckley (1987) in the Bering shelf population, Yanagimoto et al (2002) in the Bering basin population, Miller et al (1986) cited in Kendall and Nakatani (1992) in the Gulf of Alaska population, Hamatsu et al (2004) in the Japan Pacific population, and Zver'kova (1978) in the northern Japan Sea population. In the Bering basin population, remarkable changes in the length-fecundity relationship occurred with dramatic population declines between 1984 and 1999, but fecundity of spawners <450 mm did not change (Yanagimoto et al, 2002).…”