Growth, maturation, and longevity of maturation cohorts of Norwegian spring-spawning herring

Abstract

In 1907, the Bergen Institute of Marine Research started regular sampling of scales and lengths from landings of mature Norwegian spring-spawning herring. The actual age of each fish when caught was recorded, and from the early 1920s also the age at which it spawned for the first time. The present analyses concern biological samples secured during the fishing seasons 1940–1964. Herring in this stock do not all reach maturity at the same age. A small proportion of any one year class matures at 3 years. The majority matures from the age of 4–7 years, and a small proportion of some year classes at 8 and even 9 years of age. Subsequent age composition and growth of each maturation cohort were followed throughout mature life after spawning for the first time. The maximum age was found to increase with age at maturation, rising to an asymptote of about 22 years. The von Bertalanffy parameter L∞ shows an increasing trend with age at maturation, while K decreases. There is no strict length threshold at maturation and the curve joining the length at which each maturation cohort reaches maturity is less steep than the growth curve itself over the range of maturation ages. The data suggest that fish in this stock spawn, on average, eight times during a period of their life history in which the mortality rate is independent of age. After these eight spawnings, at an age referred to in this paper as the hinge age, the mortality rate increases sharply. Thus, the adult life is divided into two phases, called here pre-senescent and senescent. The total mortality rates in the pre-senescent phase are relatively stable for all maturation cohorts 3–9, but there is some evidence of a trend towards higher mortality rates during the senescent phase for the youngest maturing fish. This trend is caused mainly by a reduced natural mortality in the fish that mature when older. These findings have interesting demographic implications. Additional mortality due to fishing will change the relative contribution of young and old maturation cohorts in the senescent phase, thus making it appear that natural mortality is dependent on the intensity of fishing. Consequently, for stock assessment, analysis on a cohort basis seems advisable.

Life history consequences of overexploitation to population recovery in Northwest Atlantic cod (Gadus morhua)

“…Distinguishing mortality prior to and following maturity acknowledges, and allows for the inclusion of, a survival cost of reproduction (Beverton et al 1994;Roff 2002). Survival from birth to age 3 was quantified from abundance estimates of northern cod (Lilly et al 2001) and from age-specific fecundities, as described below, such that survival from birth to age 3 in year t, l 3(t) , was assumed to be a function of the number, n, of 7-to 11-year-olds in year t -3 multiplied by the average fecundity of those individuals such that Survival from birth to age 3 estimated in this manner for the 1962 through the 1988 year-classes of northern cod was weakly density dependent (see Myers et al 1995) and averaged 1.13 × 10 -6 ± 1.11 × 10 -6 (±SD).…”

“…By examining prereproductive growth during periods of life history change, I am then able to evaluate the degree to which these changes can be explained solely as phenotypic responses to reductions in density. The influence of earlier maturity and smaller size at maturity on Atlantic cod population growth, and thus rate of recovery, is then assessed by a stochastic, age-structured life history model that allows survival costs of reproduction to increase with declining age at maturity (Beverton et al 1994) and incorporates reduced hatching success among first-time spawners (Trippel 1998). This use of a stochastic model builds upon work pioneered by Lewontin and Cohen (1969), and extended by Roff (1974), who modelled the effects of random fluctuations in population growth rate on expectations of population size and probabilities of extinction.…”

Climate change and condition of herring (Clupea harengus) explain long-term trends in extent of skipped reproduction

“…that first spawned in the 105 same year (e.g. Beverton et al 2004). We previously tested the assumption that after maturation, herring return annually to the spawning areas (Engelhard and Heino 2005).…”

“…Finally, Beverton et al (2004) provided evidence that after about 8 spawnings, Norwegian spring-spawning herring suffer increased mortality through senescence; reliable ageing of very old herring is 190 moreover problematic. We therefore excluded any combinations of maturation cohort and 8 or more post-maturation years (n p > 7,y ).…”

Population structure and persistence of Pacific herring following the Great Tohoku earthquake

“…Generation time (t) is the crucial parameter in estimating GL. In our case, t = 2.35, whereas t = 5.25 for Atlantic herring (Larsson et al 2010) that have much greater longevity (~22 years) and older ages at maturity (3-9 years) (Beverton et al 2004) than the Japanese local herring (~8 and 2 years) (Kobayashi 1993). Our data show that the age at maturity of the Japanese local herring was 2 years (Table S1), and no fish older than 4 years were collected over the last decade.…”