Scientific knowledge of biological processes potentially useful in fish stock predictions

Abstract

SUMMARY: Based on an extensive review of available knowledge, several sources of information have been identified as potentially useful in fish stock predictions. They refer to a variety of biological processes of importance for stock dynamics, e.g. growth, maturation and egg production as well as early and juvenile life stage survival and subsequent recruitment, for which examples are given. Environmental variables impacting these processes were derived, ranging from simple statistical exploratory analyses to complex process studies for various stocks in different sea areas. Causal relationships are understood to varying degrees and in several cases the identified variables may only be taken as proxies for processes not investigated in detail yet. Besides the explanatory power of relevant variables, their predictability and related predictive time frames are of major importance for a potential application in stock predictions. These criteria in particular may hamper implementation in the foreseeable future in several cases. However, the information may still be highly relevant for a) hindcasting stock developments that are so far not fully understood, b) defining stock projection scenarios for simulation of different fishery management strategies under varying environmental conditions and considering species interactions and c) elucidating areas of future research to further enhance our predictive capabilities.

Implications of climate change for the management of North Sea cod (Gadus morhua)

“…Stock assessment models should not be made more complex by including environmental covariates with the aim of improving predictions (e.g. Brander, 2003;Köster et al, 2003). The requirement is for simpler management procedures that meet management objectives and are robust to uncertainty about the true dynamics (Walters and Collie, 1988;Basson, 1999).…”

Systematic bias in estimates of reproductive potential of an Atlantic cod (Gadus morhua) stock: implications for stock–recruit theory and management

“…Incorporating a higher degree of biological information into fisheries management is therefore regarded as essential (Marteinsdottir and Begg 2002;Köster et al 2003;Berkeley et al 2004). This study illustrates that there are no technical impediments to incorporating alternative indices of reproductive potential into the framework of the precautionary approach (e.g., change points).…”

Year-to-year variation in larval fish assemblages of the Southern North Sea

“…Additionally, a prolonged drift phase may increase egg mortality (McGurk 1986). On the other hand, a moderate amount of dispersal is needed to explore new habitats or reach nursery grounds (Köster et al 2003;Van der Veer et al 1998. This seems to be achieved by a compensation of the decrease of the duration of the planktonic phase caused by warmer water and by the preference towards pelagic eggs with rising temperatures.…”

“…However, knowledge of the duration of the planktonic larval Wsh stages is essential to be able to implement these Wndings properly into recruitment models. For the design and interpretation of Wsh larvae surveys it is vitally important to match the period of larval occurrence in the plankton (Köster et al 2003;Wieland et al 2000), otherwise abundance will be underestimated and this will result in weak larval abundance-recruitment-relationships (Bradford 1992).…”