TY - BOOK
T1 - Pelagic fish in the Dutch coastal zone : Phase 1 of Monitoring, Research, Nature Enhancement, Species Protection (MONS)
AU - Couperus, Bram M.
AU - Volwater, Joey
AU - Maris, Ties
AU - Sakinan, Serdar
AU - van Walraven, Lodewijk
AU - van Hal, Ralf
N1 - Project number: 4316100315
PY - 2024
Y1 - 2024
N2 - Project "Monitoring Pelagic Fish Phase 1" is part of the Monitoring, Research, Nature Enhancement, Species Protection (MONS) program, established according to agreements within the North Sea Agreement. The project began in early 2023 and consisted of the following components: - Acoustic survey in the coastal zone in summer (June 2023) - Acoustic survey in the coastal zone in winter (January 2024) - Acoustic registrations during the regular ‘fisheries’ research survey IBTS Q1 - Surf zone monitoring in 2023, and complementary data of previous years (2020-2022) - Stationary acoustic monitoring The first four components have been completed, and the results are discussed in the following report. The last component has been postponed and will be reported separately. The objective is to enhance our knowledge about pelagic fish in Dutch waters, with a particular emphasis on understanding their spatial and temporal distribution. This is to assess the future availability of ‘pelagic fish food’ for top predators, particularly birds. Currently our understanding of pelagic fish in Dutch waters is limited, despite their crucial role as food for birds and marine mammals in the North Sea food web. Understanding food availability and its spatial variation requires multi-year research. This first year of the program provides a first snapshot. The broader scope is on the integration of these new data with previous national, and international regular monitoring in a larger area. This serves as a foundation for efficiently gathering relevant data in the future to increase our understanding of pelagic fish. Hydroacoustic surveys Two hydroacoustic surveys were conducted, one in summer 2023 and the other one in winter 2024, following zigzag transects from the Belgium to the German coast, covering a depth range from approximately 10 m water depth near the coast to 20 nmi (nautical miles) offshore. Multiple transducers with a wide range of frequencies were used, the 38 kHz data are used for further analyses resulting in a focus on pelagic fish with a swim bladder. For species composition, 36 fishing hauls were performed in summer, and 10 in the winter. In summer, the hauls were distributed in grid, in winter fishing occurred based on high acoustic signals on the echogram. Both stratifications provided sufficient information to differentiate the acoustic signals to species level. The method used in winter is preferred as it required less effort and prevented fishing in areas without or with low concentrations of fish, unlike the grid system. Both surveys indicate a patchy distribution of pelagic fish, with more pelagic fish found closer to the coast than at the offshore parts of the transects. The summer survey recorded a higher number of fish than the winter survey, with sprat being the dominant species. Herring was sparsely observed, mainly in the shallowest hauls near the coast, indicating a distribution closer to the shore. This is consistent with surf zone monitoring and previous work in shallower areas. Anchovy and sardine were only found in the summer survey indicating seasonal patterns. Due to the similarity in design and methods, it was possible to compare the MONS survey with the regular acoustic survey in the North Sea (HERAS). The MONS survey in summer revealed higher densities compared to HERAS, where the density of the acoustic transects and the extent closer to the shore were important factors since patchiness increased in the nearshore zone. To extend the winter survey, acoustic data were recorded during the first quarter International Bottom Trawl Survey (IBTS Q1). The current added value of the IBTS acoustics was very limited. Improvements are possible, but these require slight adjustments to the IBTS design which might impact on the primary objective of the IBTS, which is only possible when there is spare time, or additional time needs to be funded. Surf zone monitoring Surf zone monitoring conducted in IJmuiden was carried out by volunteers for several years prior to MONS. For MONS, sampling took place on ten days between April and October 2023. Although the gear (2m beam trawl) is designed for catching flatfish, various pelagic species were caught. The surf zone monitoring also can provide insight in the occurrence, timing, and growth of some pelagic species that utilise this zone at least part of the year, adding to the findings of the acoustic surveys. Along the beach, herring and sandeel were caught almost every monitoring day, with a similar pattern observed in previous years (2020-2022). The herring was found as larvae at the beginning of the season and showed growth to approximately 8 cm by the end of the season. The sandeel remained about 6-9 cm throughout the entire period. Sprat was caught sporadically, like previous years, indicating that sprat avoid the surf zone. Juvenile golden grey mullet and sea bass were mainly caught in the shallow channels from August onwards. Anchovies were also caught in August/September. Conclusion This study offers important insight in the food availability of the breeding bird colonies and wintering seabirds. Catches provide length and weight data of potential prey species for marine birds. For clupeids – mainly sprat - this study offers a detailed snapshot of species composition and density distribution in a crucial feeding habitat for birds. Consistent data gathering over multiple years is essential to monitor this habitat. Spatial patchiness of species is evident in the data, but temporal variability is also crucial in such studies. Consistent time series data are necessary for informing management decisions aimed at preserving marine birds in the region.
AB - Project "Monitoring Pelagic Fish Phase 1" is part of the Monitoring, Research, Nature Enhancement, Species Protection (MONS) program, established according to agreements within the North Sea Agreement. The project began in early 2023 and consisted of the following components: - Acoustic survey in the coastal zone in summer (June 2023) - Acoustic survey in the coastal zone in winter (January 2024) - Acoustic registrations during the regular ‘fisheries’ research survey IBTS Q1 - Surf zone monitoring in 2023, and complementary data of previous years (2020-2022) - Stationary acoustic monitoring The first four components have been completed, and the results are discussed in the following report. The last component has been postponed and will be reported separately. The objective is to enhance our knowledge about pelagic fish in Dutch waters, with a particular emphasis on understanding their spatial and temporal distribution. This is to assess the future availability of ‘pelagic fish food’ for top predators, particularly birds. Currently our understanding of pelagic fish in Dutch waters is limited, despite their crucial role as food for birds and marine mammals in the North Sea food web. Understanding food availability and its spatial variation requires multi-year research. This first year of the program provides a first snapshot. The broader scope is on the integration of these new data with previous national, and international regular monitoring in a larger area. This serves as a foundation for efficiently gathering relevant data in the future to increase our understanding of pelagic fish. Hydroacoustic surveys Two hydroacoustic surveys were conducted, one in summer 2023 and the other one in winter 2024, following zigzag transects from the Belgium to the German coast, covering a depth range from approximately 10 m water depth near the coast to 20 nmi (nautical miles) offshore. Multiple transducers with a wide range of frequencies were used, the 38 kHz data are used for further analyses resulting in a focus on pelagic fish with a swim bladder. For species composition, 36 fishing hauls were performed in summer, and 10 in the winter. In summer, the hauls were distributed in grid, in winter fishing occurred based on high acoustic signals on the echogram. Both stratifications provided sufficient information to differentiate the acoustic signals to species level. The method used in winter is preferred as it required less effort and prevented fishing in areas without or with low concentrations of fish, unlike the grid system. Both surveys indicate a patchy distribution of pelagic fish, with more pelagic fish found closer to the coast than at the offshore parts of the transects. The summer survey recorded a higher number of fish than the winter survey, with sprat being the dominant species. Herring was sparsely observed, mainly in the shallowest hauls near the coast, indicating a distribution closer to the shore. This is consistent with surf zone monitoring and previous work in shallower areas. Anchovy and sardine were only found in the summer survey indicating seasonal patterns. Due to the similarity in design and methods, it was possible to compare the MONS survey with the regular acoustic survey in the North Sea (HERAS). The MONS survey in summer revealed higher densities compared to HERAS, where the density of the acoustic transects and the extent closer to the shore were important factors since patchiness increased in the nearshore zone. To extend the winter survey, acoustic data were recorded during the first quarter International Bottom Trawl Survey (IBTS Q1). The current added value of the IBTS acoustics was very limited. Improvements are possible, but these require slight adjustments to the IBTS design which might impact on the primary objective of the IBTS, which is only possible when there is spare time, or additional time needs to be funded. Surf zone monitoring Surf zone monitoring conducted in IJmuiden was carried out by volunteers for several years prior to MONS. For MONS, sampling took place on ten days between April and October 2023. Although the gear (2m beam trawl) is designed for catching flatfish, various pelagic species were caught. The surf zone monitoring also can provide insight in the occurrence, timing, and growth of some pelagic species that utilise this zone at least part of the year, adding to the findings of the acoustic surveys. Along the beach, herring and sandeel were caught almost every monitoring day, with a similar pattern observed in previous years (2020-2022). The herring was found as larvae at the beginning of the season and showed growth to approximately 8 cm by the end of the season. The sandeel remained about 6-9 cm throughout the entire period. Sprat was caught sporadically, like previous years, indicating that sprat avoid the surf zone. Juvenile golden grey mullet and sea bass were mainly caught in the shallow channels from August onwards. Anchovies were also caught in August/September. Conclusion This study offers important insight in the food availability of the breeding bird colonies and wintering seabirds. Catches provide length and weight data of potential prey species for marine birds. For clupeids – mainly sprat - this study offers a detailed snapshot of species composition and density distribution in a crucial feeding habitat for birds. Consistent data gathering over multiple years is essential to monitor this habitat. Spatial patchiness of species is evident in the data, but temporal variability is also crucial in such studies. Consistent time series data are necessary for informing management decisions aimed at preserving marine birds in the region.
UR - https://edepot.wur.nl/679233
U2 - 10.18174/679233
DO - 10.18174/679233
M3 - Report
T3 - Wageningen Marine Research report
BT - Pelagic fish in the Dutch coastal zone : Phase 1 of Monitoring, Research, Nature Enhancement, Species Protection (MONS)
PB - Wageningen Marine Research
CY - IJmuiden
ER -