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Dissertation zugänglich unter
Understanding the spatiotemporal recruitment dynamics of commercially important fish species in the North Sea
Zeitliche und räumliche Variabilität der Rekrutierung von kommerziell genutzten Fischarten in der Nordsee
Dokument 1.pdf (9.001 KB)
Fische , Rekrutierung , Nordsee , Fischerei , Modellierung , Meereskunde
42.94 , 38.90
Peck, Myron A. (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
Nearly 75% of marine fish stocks are overexploited and management based on sound science is needed to promote stock recovery and sustainability. Understanding recruitment, the number of fish entering the fishable stock every year, is key to sustainable management strategies. This thesis addressed the need for investigation of the spatial and temporal variability of the processes driving recruitment variability of commercially important fish species in the North Sea. In Chapter 4, a solid basis for analyses of the spatial and temporal variability of North Sea hydrography was produced. A physical-statistical model (Adjusted Hydrography Optimal Interpolation, AHOI) was developed to produce gridded hydrography based on available oceanographic observations. The AHOI was applied to produce high-resolution (0.2° x 0.2°) monthly maps of temperature and salinity in the North Sea for the period between 1948 and 2013. The accuracy of 0.3 °C for temperature and 0.1 for salinity maps was assessed. The AHOI dataset was made freely available for the scientific community to promote its use in ecosystem-related studies.
In Chapter 5, the AHOI maps were used to explore how the environment influences the biomass and reproduction of nine commercially important fish species in the North Sea. The stocks examined were: Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus), European sprat (Sprattus sprattus), European plaice (Pleuronectes platessa), haddock (Melanogrammus aeglefinus), Norway Pout (Trisopterus esmarkii), whiting (Merlangius merlangus), common sole (Solea solea), and saithe (Pollachius virens). Spatially-explicit cross-correlation analysis revealed a positive correlation between water temperature in the north-western North Sea and herring spawning stock biomass, and a negative correlation between temperature in the southern North Sea and the pre-recruitment survival index of sole. A positive correlation was found between water salinity and the spawning stock biomass and recruitment of sprat. Moreover, the results of Chapter 5 confirmed known relationships between recruitment of cod and plaice with water temperature. Plaice recruitment was found to correlate with temperature in the southern North Sea, whereas the strongest correlation between log-transformed cod recruitment and water temperature was found in the north-western North Sea, in the region of the Atlantic Water inflow. These findings pointed out the importance of the Atlantic Inflow for the recruitment dynamics of North Sea cod. A novel statistical method of incorporation of environmental covariates into stock-recruitment models used in fishery management was proposed using an example of North Sea cod.
Starvation and predation during cod early-life stages (ELSs) have been previously suggested to be the main regulators of cod recruitment in the North Sea. It was tested in Chapter 6 whether temperature-induced changes in the consumption rate of the main predators on cod ELSs can cause the observed relationships between recruitment and temperature. A biophysical model was developed to study the interplay between temperature-dependent growth and mortality rates of cod ELSs. It was demonstrated that cod early-life stages profit from warmer ambient temperatures only if the ratio between the temperature coefficients for the rate of growth and the rate of predator consumption exceeds 1. The findings of Chapter 6, even though being obtained only for North Sea cod, contributed to the “growth-survival” paradigm, one of the main hypotheses of the fish early-life stages biology.
In Chapter 7, the biophysical model was further developed to study other factors controlling the strength of predation mortality of cod ELSs in the North Sea. A spatially-explicit predator consumption was included in the mortality term based on the observed abundance, diet and distribution of the predators listed above. The model results showed that including realistic predation in the biophysical model altered substantially not only the spatial pattern of cod ELS survival but also the mean survival and its temporal variability. The sensitivity experiments showed that the variability of the spatiotemporal overlap between cod ELSs and their predators is an important driver of the inter-annual variability of the survival of cod ELSs in the North Sea.
Developing a biophysical model with realistic predator fields was an important step towards understanding how variability in predation mortality of ELSs may control the stock dynamics of Atlantic cod in the North Sea. The tools and concepts developed here are readily transferable to other data-rich systems and stocks. The results of this thesis will form a useful contribution to the scientific advice for cod fishery management and marine spatial planning in the North Sea.