Ecosystem Assessment : Developing Environmental and Intrinsic Recruitment Indicators for Cod (Gadus morhua L.), Herring (Clupea harengus L.) and Sprat (Sprattus sprattus L.) in the Baltic and beyond
Marine ecosystems are facing difficult times as climate change and heavy exploitation lead to biodiversity loss, the need of advanced ecosystem services, and deliberate adjustments especially in the food production industry. Cod (Gadus morhua L.), as one of the most important species for human consu...
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky
2020
|
| Subjects: | |
| Online Access: | http://nbn-resolving.de/urn:nbn:de:gbv:18-106464 https://ediss.sub.uni-hamburg.de/handle/ediss/8486 |
| Summary: | Marine ecosystems are facing difficult times as climate change and heavy exploitation lead to biodiversity loss, the need of advanced ecosystem services, and deliberate adjustments especially in the food production industry. Cod (Gadus morhua L.), as one of the most important species for human consumption worldwide, is the focus of the presented study along with herring (Clupea harengus L.) and sprat (Sprattus sprattus L.) in the Baltic, as the species’ recruitment success oscillate according to environmental changes. The present study consists of three chapters that deal with the question of environmental and intrinsic indicators underlying recruitment success in marine fish species. Apart from Eastern Baltic (EB) (Chapter II) and Atlantic cod (Chapter IV), Baltic herring (Clupea harengus L.) and sprat (Sprattus sprattus L.) (Chapter III) were species examined in this study. The overall idea of the presented approach is to find, besides fishing pressure, key indicators per species, area and period of factors, that fundamentally affect recruitment success. In Chapters II and III, environmental indicators connected with recruitment success were obtained through a simple linear regression approach that can be applied in an easy and timesaving manner in other contexts. From these indicators, individual threshold values are derived by means of a 5-fold crossvalidation approach, that define the barrier between a “good” and “bad” recruitment environment for the analyzed species. As the response variable to recruitment success, the recruitment residuals (RecRes) gained from the recruitment – spawning stock biomass (SSB) relationship were used. By subtracting the threshold value of an environmental indicator, the degree of how “good” and how “bad” recruitment environment was in certain years was assessed. The standard deviation of the crossvalidation method serves as a range of uncertainty, where “good” and “bad” becomes neutral and hence gives more space for natural variability regarding recruitment success. In Chapter ... |
|---|