Wallace, Alistair I. (2022) Patterns of neutral genetic diversity of Baltic Cod (Gadus morhua) over a period (1996 – 2015) of strong exploitation and environmental change. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 41 pp.

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Abstract

Eastern Baltic Cod (Gadus morhua) populations have been declining due to the deterioration of environmental conditions in Baltic Sea. The decrease in dissolved oxygen in Baltic basins due to increased nutrient pollution and the changes in salinity, combined with overfishing have led to a strong decline in Spawning Stock Biomass (SSB) of Eastern Baltic Cod as well as a possible decrease in recruitment. Under these conditions it is possible for the development of population bottlenecks, characterised by strong decreases in genetic diversity over a short period of time. This study used a timeseries data set samples between 1996 and 2015 in the Bornholm Basin and an ensemble of methods to measure neutral genetic diversity to assess the genetic diversity over that period, including multiple different estimates of effective population size (Ne) and allelic richness (AR), using 12 microsatellite markers, a minimum of 34 samples per year (total of 1394 samples) for 10 time points over 19 years. The results of the study show that there are no differences in neutral genetic diversity in the Bornholm Basin between 1996 and 2015, which contrasts with the strong decline of the Eastern Baltic Cod population over 3 decades. These findings, even when considering methodical limitations, show that Baltic cod in the Bornholm Basin does not decline over the duration of the timeseries. These findings corroborate older and contemporary studies that found stability in genetic diversity over time in Atlantic Cod populations, while other marine fish populations showed signs of genetic diversity loss during similarly stressful conditions in older and contemporary studies.

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