Assessing changes in age and size at maturation in collapsing populations of Atlantic cod (Gadus morhua)

Abstract

By estimating probabilistic reaction norms for age and size at maturation, we show that maturation schedules of Atlantic cod (Gadus morhua) off Labrador and Newfoundland shifted toward earlier ages and smaller sizes during the late 1980s and early 1990s, when these populations underwent a severe collapse in biomass and subsequently were closed for directed commercial fishing. We also demonstrate that this trend towards maturation at younger ages and smaller sizes is halted and even shows signs of reversal during the closure of the fisheries. In addition, our analysis reveals that males tend to mature earlier and at a smaller size than females and that maturation age and size decrease with increasing latitude. Importantly, the maturation reaction norms presented here are robust to variation in survival and growth (through phenotypic plasticity) and are thus strongly indicative of rapid evolutionary changes in cod maturation as well as of spatial and sex-specific genetic variation. We therefore suggest that maturation reaction norms can provide helpful reference points for managing harvested populations with evolving life histories.Résumé : L'estimation de normes probabilistes de réaction pour l'âge et la taille à la maturation nous permet de démontrer que les calendriers de maturation de la morue franche (Gadus morhua) au large du Labrador et de TerreNeuve ont glissé vers des âges plus précoces et des tailles plus basses au cours de la fin des années 1980 et du début des années 1990; à ce moment, ces populations ont connu un effondrement important de leur biomasse, après quoi il y a eu interdiction de la pêche commerciale ciblée. Nous démontrons aussi que la tendance vers une maturation à des âges plus précoces et à des tailles plus petites s'est arrêtée et a même montré des signes de retour en arrière durant la période d'interdiction de la pêche. De plus, notre analyse démontre que les mâles tendent à atteindre la maturité plus jeunes et plus petits que les femelles et que l'âge et la taille à la maturation décroissent en fonction de l'augmentation de la latitude. Il est important de noter que les normes de réaction de maturation que nous présentons sont robustes vis-à-vis la variation de la survie et de la croissance (via la plasticité phénotypique) et qu'elles indiquent ainsi fortement l'existence de changements évolutifs rapides dans la maturation des morues, ainsi que des variations génétiques en fonction de l'espace et du sexe. Nous croyons donc que les normes de réaction de la maturation peuvent fournir des points de référence utiles pour la gestion de populations exploitées à cycle biologique en cours de modification.[Traduit par la Rédaction] Olsen et al. 823

Physiological aging in the Icelandic population of the ocean quahog Arctica islandica

“…Such slow growth may be the trade-off for slower aging and stable or increased reproductive output in later life, as documented for fish (e.g. Atlantic cod, Olsen et al 2005; for a review see Pauly et al 2002) and for long-lived turtles (Congdon et al 2003). In both cases, older females increase reproductive output (egg production, clutch size or reproductive frequency) with age.…”

Fish condition in introduced tilapias of Ugandan crater lakes in relation to deforestation and fishing pressure

“…The effects of fishing on life history traits are well documented, especially for major commercial fish stocks (e.g. Ricker 1981;Grift et al 2002;Olsen et al 2004Olsen et al , 2005. It is often assumed that fishing-induced reductions in population density of target stock lead to increased yield because of reduction in intraspecific competition that releases populations from density-dependence resulting in faster growth and earlier maturation (Jennings and Kaiser 1998;Hall 1999;Law 2000;Rochet et al 2000).…”

Changes in size at maturity of European hake Atlantic populations in relation with stock structure and environmental regimes

“…However, although decreasing size at maturity still can be a density-dependence effect, it normally provides an indicator that a fish population is coming under stress from too high rates of exploitation (Trippel, 1995). Barot et al (2004) used reaction-norms to identify a downward shift in maturation at size in Georges Bank and Gulf of Maine stocks of Atlantic cod (Gadus morhua) supporting the hypothesis that an evolutionary trend, probably caused by high fishing mortalities, is partially responsible for the observed decrease in age and size at maturation in these cod stocks (Olsen et al, 2005). Regardless the causes of maturation variation, this population characteristic can have large effects on the reproductive output of a stock.…”