"To Hit et al.: A method to improve size estimates of Theragra chalcogramma and P/eurogrammus monopterygius 



505 



Table 1 (continued) 



Species and 

 structure code 



Category 



Distinctive external morphological features 



Atka mackerel 

 INTE 



HYPO 



ANGU 



QUAD 



DENT 



OTO 



G Like that of walleye pollock (WP) (except no point), with ridge, neck and notch clearly defined. 



F li Ridge present, but shows signs of wear. 2) Swan neck shows wear resulting in a "horseshoe" shape. 

 3 1 Notch shows only minor wear or chipping and does not prevent accurate measurement. 



P 1) Loss of characteristic ridge and neck with body worn (may contain holes). 2) Both neck and notch 

 show clear damage. 



G 1) Cone rounded and complete, tube complete, retains characteristic shape. 2) Minor nicks on cone 

 and tube may be present but do not impact total length measurement. 



F Cone worn, loss of rounded shape, and area 1 shows minor chipping or damage or tip of tube is broken 

 or clearly chipped. 



P 1) Cone body and area 1 show major wear, chips, and breaks. 2) Tube broken or absent entirely, 

 unable to measure length. 



G Like WP. additionally cap rounded and head shows only minor wear. 



F Like WP, additionally 1) cap worn with loss of shape. 2) Head worn, chipped, and often has holes, 

 3) Ridge on dorsal side above neck worn smooth. 



P Like WP. additionally 1 ) head shows major damage, wear, breaks, and holes, 2 ) Difficult to determine 

 side with confidence. 



G It Horns rounded and in good condition, with angle between horns clearly curvilinear. (Note: Horns 

 are of unequal size and shape and one side is more robust, rounded, and sloped.) 2 1 Evidence of ridge 

 and spike observable. 3) Definition of left and right sides is easily achievable. 



F 1) Horns have lost rounded definition and may be pointed or worn on one side, making distinction 

 between sides difficult. 2) Ridge and spike often only residual. 



P Like WP, additionally no distinction between horns easily achievable. 



G Like WP (except no hammerhead), additionally 1) head retains characteristic features, tooth sockets 

 present, 2) Ventral side of head a defined point. 



F Like WP, additionally 1) head eroded or chipped with tooth sockets noticeably worn, 2) Point on 

 ventral side of head eroded or chipped. 



P Like WP, additionally head eroded or flattened with point often heavily eroded or badly chipped, 

 accurate measurement unattainable. 



G 1 1 Rostrum not chipped or broken. 2 ) Sulcus clearly defined, as are anterior and posterior colliculums. 

 3 ) Scalloping on antirostrum and posterior end clearly distinguishable. 4 ) No obvious wear or chipping 

 with no obvious reduction in length (width). 5) Cristae of antirostrum forms a well-defined ridge. 



F 1) Rostrum shows some wear but remains unbroken and retains characteristic shape. 2 1 Sulcus 

 still has definition despite wear, shown as a uniform channel, anterior and posterior colliculums 

 indistinct. 3) Cristae and scalloping on antirostrum and posterior end worn smooth. 



P 1 ) Rostrum or posterior end broken or worn to such a degree that accurate measurement cannot be 

 obtained. 2) Sulcus difficult to distinguish or worn smooth. 3) Cristae and scalloping on antirostrum 

 and posterior end worn completely smooth. 4) Side cannot be easily obtained. 



Nevertheless, we recommend that a hands-on reference 

 collection be used. 



The procedure we recommend to estimate fish length 

 after classification involves excluding structures 

 considered heavily digested (condition category poor) 

 and applying specific condition-category DCFs (Ta- 

 ble 2) to the remaining structure prior to calculating 

 fish length from allometric regressions (see Tollit et 

 al., 2004, this issue). The exclusion of structures in 

 poor condition was necessary because of the large and 



variable size reduction observed in this category. Our 

 technique uses changes noted in the morphological 

 features of the structures themselves and is therefore 

 not specific to Steller sea lions. Because structures 

 are likely to erode in a predictable manner whatever 

 the species of the stomach they are held within, it 

 seems probable that they can also be classified into 

 a particular condition category for use with DCFs. 

 Consequently, our technique may be appropriate to 

 marine piscivore dietary studies where prey size needs 



