Oceanographic perspectives on: 1) size and maturity at age in fishes and 2) the biomass spectrum in the Northumberland Strait

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This proposal has two foci representing two oceanographic themes that my lab has been pursuing for well over a decade. The first (1) focuses on the growing-degree-day metric (GDD - the thermal integral) and its ability to diagnose size and maturity changes in fish that result from size-selective fishing. The second (2) focuses on zooplankton biomass spectrum models that can explain variation in the ecological functioning of regional oceans.******1) We have shown that ~92% of length-at-age (LaA) variation in fish can be explained by the GDD metric among many fish species in both the wild and in controlled studies and others have since confirmed the utility of the metric among other species. We have also demonstrated that deviations from the expected LaA-GDD relation can be used to diagnose size-selective fishing effects on exploited fish stocks that include reduced size-at-age and earlier maturation. These effects have negative consequences on recruitment potential due to reduced fecundity and reduced egg and larval quality. Others have also shown that this may have genetic consequences that place new demands on sustainable fishery management. Working with a PhD student, we will use the GDD metric to diagnose size-selective fishing effects across a range of exploited marine stocks in the north Atlantic, and do so in collaboration with researchers in Norway. For those stocks that depart from expectation, we will examine the anomalies under the hypothesis that they are most easily explained by size-selective fishing. We will then address the consequences on recruitment expectations in relation to sustainable fisheries management.***2) Zooplankton are the trophic link between phytoplankton and fish production. The zooplankton biomass size spectrum can be used to quantify the structure and function of zooplankton communities because it reveals processes not readily apparent using conventional taxonomic approaches. Variations among spectra can be used to estimate the time and space transfer of energy from primary production through the zooplankton community to the fish community. Working with an MSc student, we will focus on the zooplankton component via time and space variation in the biomass spectrum and its association with variation in water mass structure. As our test case, we will rely on optical plankton counter and in situ net sample data coincident with conductivity, temperature and depth data collected in the Northumberland Strait. The spectrum - a species-independent measure of the Strait ecosystem - will help us in determining the energy transfer and transport in time and space. These data and analyses will also be used to contribute to a global study involving several researchers and institutions around the world where the focus is on using the size spectrum as an innovative method for estimating zooplankton growth, predation and production as food for fish and as well as improving ecosystem models.***********