Bigelow Age and growth of Onychoteuthis boreahjaponica 



15 



Figure 1 



Location of stations in the North Pacific sampled for Onychoteuthis boreahjaponica: Western North Pacific 1990 

 (open circles), central North Pacific 1990 (closed circles), central North Pacific 1991 (closed triangles), and east- 

 ern North Pacific 1990 (open squares). 



Periodicity of increment deposition Three sub- 

 adult squid caught by jig or trawl in the central 

 North Pacific were placed for two hours in 20 L of 

 seawater containing 250 mg/L oxytetracycline hy- 

 drochloride (OTC). After OTC exposure, squid were 

 maintained in a 20-L tank with flowthrough sea- 

 water under ambient photoperiod and temperature 

 conditions. Freshly captured live saury (Cololabis 

 saira) were introduced as prey, but no feeding was 

 noted or observed. Squids survived up to 61.5 hours 

 in captivity. Statoliths were prepared as above and 

 illuminated with ultraviolet (Fig. 4) and natural 

 light. Under fluorescent light, an ocular marker was 

 aligned with the inner edge of the OTC band. The 

 statolith was then examined under natural light, 

 but increments peripheral to the band were difficult 

 to count. Therefore, to determine the periodicity of 

 increment deposition, statolith growth following 

 OTC exposure was related to the average increment 

 width prior to exposure. The distance from the in- 

 ner edge of the OTC band to the statolith perimeter 

 was divided by the mean width of increments prior 

 to the OTC band. Three estimates of statolith 

 growth after OTC exposure were made, and the 



average increment width calculated for 15 incre- 

 ments prior to the OTC band. 



Statistical procedures 



Mantle length-weight relationships Mantle 

 length-weight regressions were fit to the data by 

 using the model 



WT(g) = a*ML(mm) b (D 



Separate ML-weight equations were developed for 

 both sexes, and a single equation was used for squid 

 of unknown sex (<60 mm ML). 



Fitting of size-at-age data Researchers have used 

 a variety of different models to describe cephalopod 

 growth (e.g., linear, logistic, von Bertalanffy), al- 

 though the rationale for using a given model is usu- 

 ally not stated. Schnute ( 1981 ) proposed a flexible four- 

 parameter model to describe growth which includes 

 most growth models historically used in fisheries re- 

 search as special cases. The model takes the form 



Y(t): 



V, +(Vi 



v ): 



1-e-""-' 1 ' 



-.j U,-r, ) 



l/i 



(2) 



