Temporal and spatial variation in reproductive investment of Atlantic cod Gadus morhua in the northern North Sea and Scottish west coast

Abstract

The recent decline in many fish stocks has been accompanied by marked changes in age at maturity. However, there is little information on whether other components of reproductive investment have changed and the relative roles of phenotypic plasticity or genetic selection in such change. This study explored how reproductive investment in cod Gadus morhua from different regions around Scotland has changed between a period of high (1969, 1970) and low (2002, 2003) spawning-stock size. Maturity ogives indicated that inshore North Sea cod now mature at a smaller size and younger age than they did around 1970. The relationship between potential fecundity and size indicated that cod in the inshore region are now more fecund than 30 yr ago. Cod from the inshore region of the North Sea now have a higher fecundity at a given size and age than cod from the offshore region and the west of Scotland. There was no such spatial trend around 1970. Similarly, whilst the relative fecundity of cod in recent times is positively correlated with age, no such relationship was evident in 1969 and 1970. Nutritional influences on maturity and fecundity, particularly liver condition, were also evident from the recent study. However, the temporal and spatial differences in fecundity-size relationships were not consistent with a change in growth conditions, as there has been a significant decrease in body condition in recent times. Our findings regarding the temporal change in reproductive investment in the inshore North Sea region appear consistent with genotypic changes in life-history traits predicted to arise from intense periods of size-selective mortality.

Reproductive Characteristics of <i>Leuciscus vorax</i> (Heckel, 1843) from Al-Huwaiza Marshes Southern Iraq

“…However, there is compatible with our finding in the present work in general trends and with the previous studies on represented species (Al-Selah et al, 2010;Oymak et al, 2011;Al-Selah et al, 2012;Duman and Gul, 2013). Although the variance in absolute and relative fecundity between individuals of the same population in the year, appeardivers reproductive strategy for different species and stocks, which has been attributed to relation of influential factors to modify potential fecundity (Yoneda and Wright, 2004;Thorsen et al, 2006).…”

Spatial and temporal trends in condition of Atlantic cod Gadus morhua on the Icelandic shelf

“…In Atlantic cod Gadus morhua, condition is related to fecundity, fertilisation success, egg size, larval quality and viability, atresia and the probability of skipped spawning (e.g. Kjesbu et al 1991, Marteinsdóttir & Steinarsson 1998, Rakitin et al 1999, Rideout et al 2000, Marteinsdóttir & Begg 2002, Rose & O'Driscoll 2002, Yoneda & Wright 2004, 2005a. However, other studies (e.g.…”

Temporal trends in age and size at maturation of four North Sea gadid species: cod, haddock, whiting and Norway pout

“…Unfortunately, we could not include such an index in our analyses because individual weights were not available. This may have resulted in underestimating the downward temporal trend in cod PMRNs, since body condition has significantly decreased in recent years (Yoneda & Wright 2004). It is worth noting, however, that our analyses included the influence of food (prey) abundance, which is one of the main drivers of body condition.…”

“…Since cod, female whiting and haddock PMRNs have varied, demography and growth-dependent plasticity cannot fully explain temporal changes in their maturity ogives: changes in maturation propensity due to growth-independent plasticity in response to environmental conditions and/or fisheries-induced evolution in maturation are likely to have also played a role. Negative temporal trends in PMRN midpoints have already been observed for inshore haddock along the Scottish coast (Wright et al 2011a, but see Devine & Heino 2011) as well as for other cod stocks (Heino et al 2002b, Olsen et al 2004, 2005, Yoneda & Wright 2004, Pardoe et al 2009 Table 2. Regression coefficients and their standard errors (SE) for cod L p50 at age 3, haddock L p50 at age 2 and whiting L p50 at age 2, obtained from transforming back to the original set of axes the principal component regression coefficients and their SEs.…”