Detecting wild fish and zooplankton near fish farms during and after fallow periods in Southern Newfoundland

McTamney, Alexandria (2019) Detecting wild fish and zooplankton near fish farms during and after fallow periods in Southern Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

From November 2016 until September 2017, acoustic Doppler current profilers were deployed in two neighboring bays in Southern Newfoundland, East Bay and Cinq Island Bay. We set out to determine the in uences that aquaculture had on wild fish abundance in the ecosystem during fallow periods. Fallow periods describe the times when farms were not stocked with fish. It was hypothesized that during a time where a fish farm was newly inactive there would be a different abundance of wild fish nearby than during a time when the farm was active. In our study, both East Bay and Cinq Island Bay were fallow prior to November until June/July of the following year. After that time, fish farms were restocked with Atlantic Salmon. The acoustic Doppler current profilers were configured to collect data without the typical averaging of acoustic pings into ensemble averages. This processing allowed for the in- struments to act as fish detecting sonars. We calculated volume backscatter strength, fish counts, fish depths and target strengths of detected fish. Fish schools and diur- nal migration patterns occurred frequently and on some occasions, high backscatter intensities persisted for several hours. Depths of fish appeared to be similar during November, December, January, March and April. Summer months of June, July, Au- gust and September had opposing depth distributions. In Summer months, there were fish primarily at shallow depths and in Winter months fish were primarily at deeper depths. Summarizing the entirety of the time series resulted in depths distributions throughout the entire water column in East Bay suggesting that diel vertical migrat- ing species were commonly present. In contrast to this, Cinq Island Bay showed fish primarily at 50 meters, indicating that a different fish species frequented this area. Similar results from target strength distributions suggested two species or behaviors present in East Bay and one species present in Cinq Island Bay. Shifts of fish types or behaviors in East Bay occurred during the same time periods as the beginning of fish farm activity and also the start of the Summer season. Both bays displayed concurrent increased fish counts in January and May with a larger wild fish abun- dance in East Bay than in Cinq Island Bay. The amount of fish in both bays differed during and after fallow periods which coincided with seasonal changes. Because of this timing, distinguishing the effects of fallow periods from seasonal changes was not possible. This study demonstrates the value of using acoustic monitoring methods for collecting data from aquaculture sites. Altering future studies to include longer time series, simultaneous fish sampling and multiple acoustic Doppler current profil- ers in each bay could provide additional important data that may lead to concrete conclusions about aquaculture in uences on wild fish species.

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