Research Document - 2016/081

Relative strength of the 2010, 2011 and 2012 year-classes, from nearshore surveys of demersal age 0 and 1 Atlantic cod in Newman Sound, Bonavista Bay

By R.S. Gregory, C. Morris, B. Newton, and P. Sargent

Abstract

We surveyed demersal age 0 and 1 year old Atlantic cod (Gadus morhua) in the nearshore (<10 m deep) during the past 17 seasons using a seine net, to conduct a qualitative assessment of the strength of these year-classes. Our assessment was based on comparisons with abundance of Atlantic cod sampled at 6‑13 sites, every two weeks from July until November, from 1995‑2012 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 recruitment pulses, the first pulse arriving in early July (2012) or early August (2010 and 2011). Second and subsequent pulses followed the first by as much as a month and a half later. Strong pulse structure throughout the sampling period typically has resulted in the production of a strong cohort as measured independently during other surveys. Interestingly, the 2010 cohort appeared to be weak as age 0 individuals, but apparently high survival resulted in higher than expected numbers of one year olds sampled in 2011. The age 0 abundance in Newman Sound in 2011 and 2012 suggests that these two cohorts will also be moderate to strong, relative to other cohorts in the 17-year long time series. The 2012 cohort was second strongest in the 17 year time series in terms of mean abundance per set, timing of settlement, and strength of its recruitment pulse structure. This pre-recruit survey data indicates that stronger than average year classes have been produced during each of the past 3 years, compared to our 17 years of monitoring data.

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