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All of these methods attempt to provide the necessary data for appli- 

 cation in highly sophisticated models. Many methods require extensive 

 laboratory work, which is usually carried out on shore. All of the many 

 models utilized are based upon the assumptions outlined earlier; assumptions 

 that hopefully restrict the distortions that are likely to arise from se- 

 lected observation of a highly variable ecosystem. The complexities of the 

 marine ecosystem drive creation of highly complex models; some of the com- 

 plexities are summarized in the next section. In addition, fishing activity- 

 its technology, management, and historical pattern of development — adds 

 further complexities to assessments, which also are discussed both on the 

 following pages and in detail in Part II, "The Georges Bank Groundfishery 

 Example." Before considering existing stock assessment capabilities and 

 needs (Part III), it is important to recognize that the greatest need by 

 far is achieving understanding of the system this science seeks to assess, 

 both natural and human. 



