Research Document 2019/012

Relative strength of three cohorts (2015-17) of Atlantic Cod, from nearshore surveys of demersal age 0 and 1 juveniles in Newman Sound, Bonavista Bay

By Gregory, R.S., Dalley, K.L., Newton, B.H., Sargent, P.S, and E.L.L. Cooke

Abstract

We qualitatively assessed the relative strength of three cohorts (2015-17) of Atlantic Cod (Gadus morhua) based on abundance of demersal age 0 and 1 juveniles in Newman Sound, Bonavista Bay in summer and autumn of two years (2016-17) at nearshore sites (<10 m deep) using a seine net. Our assessment was based on comparisons with abundance of Atlantic Cod sampled at 6-12 sites, every 2 weeks from July until November, from 1995-2017 in Newman Sound, Bonavista Bay. Analysis of annual length frequency and abundance data indicated that age 0 Atlantic Cod settled in the nearshore in several distinct pulses, the first pulse arriving in early August in 2016 and mid-July in 2017, which was typical for this coastal location. Second and subsequent pulses followed the first by as much as two months later. The 2016 and 2017 cohorts were numerically strong, especially for the first recruitment pulse. The 2015 and 2016 cohorts remained strong as age 1 fish in 2016 and 2017 seasons. Age 0 and 1 abundances in Newman Sound in 2016 and 2017 suggests that all three of these cohorts will be moderate to strong, relative to other cohorts in the time series, but well below that of the large 2013 cohort, which remains the strongest cohort in the time series. Stronger than average abundances and lower than average age 0 mortality rates within season have been observed during each of the past three years (2015-17) compared to other years within our 22 years of monitoring. In addition, preliminary results of a companion study we conducted at eight additional coastal sites in both Trinity Bay and Notre Dame Bay in 2017, supported our long-held view that settlement pulse structure of Atlantic Cod in Newman Sound is typical of broad patterns by age 0 juvenile cod along the northeast Newfoundland coast from all three of these major bays.

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