Recruitment of Atlantic cod to Newfoundland coastal waters at daily and seasonal scales

Ings, Danny William (2005) Recruitment of Atlantic cod to Newfoundland coastal waters at daily and seasonal scales. Masters thesis, Memorial University of Newfoundland.

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Abstract

Recruitment of marine fish is influenced by abiotic and biotic processes operating at many spatial and temporal scales. Recruitment level was thought to be set during the larval stages but recent evidence suggests that year-class strength can be modified during the early juvenile stages. Annual recruitment has received much attention but variation at finer temporal scales may affect biological processes that influence year-class success. I tested the hypothesis that timing of recruitment of fish from the plankton to nearshore benthic areas is determined by water mass movements. I also tested whether seasonal recruitment of fish to near shore bottom habitats was associated with prey availability and growth rates of post-recruited fish. Seining was conducted daily at one location during 2002 and biweekly at 12 sites during 1998-2002 to monitor fish densities and arrival times nearshore. I found that daily recruitment of Atlantic cod (Gadus morhua ), Greenland cod (Gadus ogac) and hake (Urophycis tenuis) to sites on the northeast coast of Newfoundland was associated with onshore winds following upwelling. Results were consistent with larval transport onshore during downwelling. Recruitment of Atlantic cod, Greenland cod and hake to the nearshore was not associated with tidal stage. The phenology of Atlantic cod recruitment to near shore benthic habitats appears simple but seasonal growth rates are more complex. During July to November of2000 to 2002, the monthly pattern of abundance of newly-recruited Atlantic cod near shore was similar to seasonal patterns of zooplankton abundance that I observed near shore. Seasonal zooplankton abundances near shore were similar to those previously reported offshore . Newly-recruited Atlantic cod were relatively abundant during September and October of 2000-2002. During these months, growth rates of post-recruited fish were also relatively high. However, I found growth rates of post-recruitment fish were comparatively high twice annually with highest growth occurring during June and October. During both of these months water temperatures were near optimum for growth and the ratio of Atlantic cod abundance to zooplankton abundance near shore was similar. Abundance of newlyrecruited Atlantic cod near shore was relatively high during May of 2002 when growth rates offish were low, contrary to prediction. Monthly abundance of newly-recruited Atlantic cod near shore was more closely associated with the amount of zooplankton that fish could utilize at observed water temperatures rather than total abundance of zooplankton. At daily scales, recruitment of Atlantic cod near shore was found to be determined by physical processes but both abiotic and biotic processes were important at seasonal scales.

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