252 



Fishery Bulletin 100(2) 



Table 2 (continud) 



well with growth estimated by differences in mean values 

 at the entrance and exit of the estuary. 



Further evidence that residence in the San Francisco 

 Estuary was not beneficial to juvenile salmon was their 

 decline in condition (/i-factor) while migrating through the 

 estuary. But, along with faster growth, condition improved 

 markedly in juveniles in coastal waters. Changes in /iTcan 

 be due to several causes, including stomach fullness and 

 metabolic state. In an associated study of contaminants, 

 the weight of stomach contents was measured at the same 

 locations and dates as the ones described here. Stomach 

 contents were 0.5% ±0.1% of body weight in fish with food 

 in their stomachs at both the entrance and exit of the estu- 

 ary (MacFarlane, unpubl. data). Further, a greater propor- 

 tion of fish contained food at the estuary exit, where K 

 was the lowest. Thus, differences in stomach fullness were 

 not the cause of lower condition. Changes in metabolic 

 equilibria, reflected in altered body composition of protein 

 and lipids, can change body density, as shown by Brett 

 et al. (1969) for juvenile sockeye salmon iOncorhynchiis 

 nerka) and thus affect condition. In juveniles in the San 

 Francisco Estuary, body protein and total lipid concen- 

 trations were similar at all sampling locations, so chang- 



es in body density were unlikely contributors to reduced 

 condition. However, metabolic costs of smoltification can 

 cause changes in length - weight relationships. During 

 the transformation, salmon can become more slender due 

 to depleted energy resei-ves (Hoar, 1988), especially TAG 

 (Henderson and Tocher, 1987). It is possible that decreased 

 lipid and protein content, and not changes in relative con- 

 centrations, caused by catabolism for seawater adaptation, 

 resulted in juveniles leaving the estuary at a lower weight 

 for a given length than when they first entered. However, 

 in a study conducted in 1999, gill Na*, K+-ATPase activ- 

 ity, an indicator of seawater adaptation, was greater in ju- 

 venile Chinook salmon caught at the entrance to the estu- 

 ary (km 68) compared with that of those sampled within 

 the rivers leading into the estuary, but was not increased 

 further in those collected at locations within the San Fran- 

 cisco Estuary.'- This suggests that adaptation was largely 

 completed by the time of estuary entrance and may not be 

 the primary contributor to the body lower condition offish 



Alonzo, J. J., and R. B, MacFarlane. 1999. Unpubl. data. 

 Santa Cruz Laboratory, Southwest Fish. Sci. Ctr NMFS, NOAA. 

 110 Shaffer Road, Santa Cruz, CA 95060. 



