Plankton effect on forage fish production in the Northwest Atlantic

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Depleted marine ecosystems are numerous and represent tremendous unrealized fisheries productivity in the World Ocean. In the Northwest Atlantic, multiple Atlantic cod stocks have still not recovered despite twenty years of fishing moratoria. Coincident with the collapse of cod and other groundfish in coastal Newfoundland waters during the early 1990s, populations of capelin, a small forage fish that traditionally contributed 50-60% of adult cod diet, also rapidly declined and stabilized at low levels. This continued lack of forage fish production, considered an important factor preventing the recovery of groundfish populations, is anomalous in comparison to the dynamics of other sub-Arctic seas. As for most marine fish, recruitment of capelin depends on the survival of their larvae and juveniles. Survival rates during early life are largely determined by the co-occurrence of emerging larvae and their zooplankton prey. In Newfoundland coastal waters, long-term zooplankton data revealed that the decline of capelin coincided with reduced abundance of dominant copepod species. My research program aims at understanding larval feeding ecology to test the hypothesis of a "plankton effect" maintaining early survival and recruitment of capelin at low levels, thereby limiting groundfish recovery. Specific objectives include: (1) quantifying life history shifts in diet of young capelin and characterizing the effects of interannual fluctuations in the availability of preferred prey; (2) determining the functional response relationships linking prey availability, feeding success and growth of larvae; (3) assessing the abundance and distribution of juvenile survivors using fisheries acoustics, and (4) modeling larval growth to predict survival in a wide range of environmental conditions. Since capelin play a key role in transferring energy to large vertebrate predators such as Atlantic cod and may limit the recovery of groundfish populations, this study on the links between secondary production and larval survival will fill a key knowledge gap by quantifying the mechanisms influencing the current low productivity of some of the most socially and economically important fisheries grounds in Canada. The numerical models that will be developed will help forecast the response of these important marine ecosystems to future trends in climate, and will thereby inform industry, managers and policy makers about the primary factors driving biological production and fisheries yield in Northwest Atlantic food webs.