464 



Fishery Bulletin 103(2) 



Table 2 



Independent variables included in the stepwise linear regression models used to estimate original bluefish fork length and total 

 length. 



Variables included in 

 forward stepwise regression model 



Variables included in 

 backward stepwise regression model 



Fork length 

 Total length 



PMXL, OPL, DN 

 PMXL, OPL, DN, CL 



PMXL, OPL, DN 

 PMXL, OPL, DN, CL 



Discussion 



This study revealed that measurements of five skull 

 bones can be used as accurate predictors of original 

 fork length and total length of bluefish. Although the 

 methods of other studies were incorporated in this study, 

 the information is the first of its kind for bluefish and 

 may serve as a tool for the future study of this species 

 in the North Atlantic. 



In recent years there has been growing concern over 

 the stability of the bluefish stock and an increased ef- 

 fort to gather information on the possible mechanisms 

 affecting bluefish abundance and distribution in the 

 western North Atlantic. 4 One of the proposed mecha- 



In 1997 Rutgers University and the NMFS organized a work- 

 shop to study the factors that could be contributing to the 

 depressed state of the bluefish stock. A similar concern was 

 expressed by Congress at this time, and the Rutgers and 

 NMFS workshop led to a request for proposals for bluefish- 

 related research in 1998, 1999, and 2000. 



nisms that could be adversely influencing the recovery 

 of bluefish is top-down pressure by a number of apex 

 predators in the North Atlantic. Although indiscrimi- 

 nant predation on bluefish may not be a significant 

 pressure on the stock, size selective predation can dra- 

 matically alter the structure of the prey community 

 (Mclntyre and Ward, 1986; Trippel and Beamish, 1987; 

 Sharf et. al., 1997). 



In order to study the consumption rates of key preda- 

 tors in an ecosystem it is necessary to gather informa- 

 tion on the sizes of the prey being consumed (Elliot and 

 Persson, 1978; Sharf et. al., 1998). However, it is often 

 difficult to estimate the original size of a prey item 

 from stomach content data because of the complications 

 caused by digestion. Erosion of the prey bones from 

 digestive juices can lead to measurement error or bias 

 when prey sizes are back-calculated from digested parts 

 (Sharf et al., 1998). Although bias from digestion is a 

 concern that should be addressed in studies, internal 

 bones and hard parts of fishes have been shown to be 

 excellent predictors of original prey size (Trippel and 



