Inshore Fish Survey
Overview of annual Shetland trawl survey data (2011 - 2018): catch rates and size compositions of commercial demersal fish species in nearshore waters
Since 2011 the NAFC Marine Centre has undertaken an annual survey of fish in the inshore waters around Shetland, up to 12 nautical miles offshore, with the intention of providing an independent index of the relative abundance of commercially important and other fish species in the waters around Shetland. The survey also aims to determine the extent of inter-annual variability in the local distribution of commercially important species.
An overview of results from annual trawl surveys conducted by the NAFC Marine Centre from 2011 - 2018 of the coastal waters around the Shetland Islands is presented. The purpose of the surveys was to provide independent information on the distribution, relative abundance, and population structure of fish species in local waters. Key results from the available data are reported here with a focus on commercially important species. This report is intended for a general audience with information presented in a concise and non-technical format.
The annual fish surveys have been carried out using the 12 m MFV Atlantia II (LK 502) during August and September each year using a standardised survey trawl fitted with a small-mesh (20 mm) cod-end. The annual inshore fish survey involved hauls from 27 pre-defined locations within 12 nautical miles of Shetland. Since 2017, a concurrent shallow fish survey has also been undertaken with 25 hauls targeting potential nursery grounds around the coast of the Shetland Islands. Catch rate results were used to investigate the relative abundance of commercial species by considering catch per unit effort (CPUE). Length data were used to further interpret variations in population structure and recruitment.
Results are presented for the 12 most significant commercially important demersal species sampled throughout the surveys. Key findings include:
- Species-specific trends in relative abundance and inter-haul variability are shown by CPUE results with 2018 data indicating that catch rates were generally within the range of previous years.
- A record high number of lemon sole (Microstomus kitt) and haddock (Melanogrammus aeglefinus) was observed in the 2018 inshore survey data, while a slight decrease in relative abundance since 2017 is shown for most other species.
- Results from the shallow survey were considerably different from the inshore survey and suggest that shallow hauls were successfully targeting juvenile communities for some species.
- Catch rates and length data from both the inshore and shallow surveys show that 2018 has been an exceptional year for high numbers of small cod (Gadus morhua), whiting (Merlangius merlangus), and in particular, haddock.
- Trends over previous years indicate that the high abundances of young year-classes recorded for these species are likely to result in strong recruitment to the local commercial fishery.
Final points of this report include suggestions for further analysis and the recommendation that the annual inshore and shallow fish surveys are continued.
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