Does population size structure affect larval viability in marine fish? Insights into maternal investment using stable isotopes

One of the most pervasive effects of decade long overexploitation of marine fish is the truncation of size distributions in affected populations.

Today, many populations of commercially important species, such as Atlantic cod (Gadus morhua), consist of smaller individuals than just a few decades ago.

Concurrently, a general decline in recruitment has been observed with severe consequences for population growth and productivity.

These observations have led to the formulation of the Big Old Fat Fecund Females (BOFFF) hypothesis, which states that older, larger females contribute disproportionally more to the recruitment because of their increased mass-specific fecundity and production of more viable offspring.

The first part of the hypothesis has been tested and confirmed, while the considerably more challenging test of superior offspring survival is hindered by the inability to link individual offspring caught in the open sea to the size of the mother.

In the POPULAV project, I will use size-specific natural biochemical markers (stable isotopes) to link maternal size to larval viability.

Larvae are provisioned with the maternal isotopic signature via nutrient transfer from maternal gonads to the eggs/larvae; A promising, novel tool to provide a robust test of the BOFFF hypothesis.

The objectives are to (1) confirm the size-effect on maternal gonadal isotopic signature, (2) assess size-dependent stable isotope transfer in laboratory experiments, (3) assign wild-caught larvae to the size of its mother using stable isotope profiles, and (4) use a simple model to estimate the effect of population size truncation on larval viability.

Data obtained in POPULAV will advance our understanding of how size truncation affects larval viability and thereby recruitment.

This knowledge can support decision making and fisheries management, and place its coordinators and the EU at the forefront of international efforts for understanding the impacts of fishing on our marine resources.