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Fishery Bulletin 102(2) 



fishing mortality. At lower natural mortalities, a 

 change in fishing mortality has a greater effect on 

 escapement. At m =0.1 and /'= 0.35 i? e ,, malI is 50%. 

 Doubling the fishing morality to 0.7 R etnm would 

 be 33%, producing a loss of 17% in escapement 

 (Fig. 11A). Increasing the rate of daily egg deposi- 

 tion (v) from our preferred value of 0.25 to 0.65 also 

 diminishes the effect of fishing mortality on escape- 

 ment but the effect of fishing on egg escapement is 

 most marked at the low natural mortality of m = 

 0.1 and is relatively minor when natural mortality 

 reaches /?; = 0.4. Thus, uncertainties regarding the 

 true initial values of egg deposition seem relatively 

 unimportant at these high mortality rates. It is 

 important to remember that in this discussion that 

 we are discussing daily mortality rates that last 

 only a few days or weeks of the life of a semelparous 

 animal; hence the rates are very high and resemble 

 the typical daily mortality rates of small pelagic fish 

 eggs (Alheit, 1993) that also exist for short periods. 



Cost effective methods for monitoring fecundity If 

 egg escapement were adopted as a monitoring and 

 management tool for the market squid fishery, a 

 cost-effective method for monitoring fecundity of 

 L. opalescens would be needed. A direct estima- 

 tion of the standing stock of oocytes in an ovary by using 

 a microscope and video system (as preformed in this 

 study) is too time consuming for routine monitoring of the 

 fishery because it takes about 4 hours per specimen. 



Our first approach for an indirect estimator was to 

 use the measurements routinely taken by CDF&G staff 

 who sample the catch. These measurements were dorsal 

 mantle length, mantle condition index, and an oviduct 

 classification system for approximating the numbers of 

 ova. To estimate the oocyte standing stock (E Y ) of the 

 catch females, using only length and mantle condition, we 

 fitted a nonlinear model to the data for all squid classed 



Elapsed time (/, days) 



Figure 10 



The cumulative egg release curve (solid line) and the density func- 

 tion of longevity on the spawning grounds of adult females I dashed 

 line) of Loligo opalescens for a total mortality rate (z) of 0.45 and 

 a egg release rate (v) of 0.25. The plotted solid circle represents 

 mean egg deposition estimated by the model as a proportion of the 

 potential fecundity and model estimate of the mean duration of 

 the spawning period. 



as mature (spawning individuals and pre-ovulatory) in our 

 1998 research survey data set. This yielded the equation 



£ v = 220.453e ll - 99C + - 0079il , (17) 



where L = dorsal mantle length; and 

 C = mantle condition index. 



Equation 17 for E Y explains only 33% of the variability 

 within the survey data set (n=90) and therefore is rather 

 imprecise. Using this model we estimated E Y to average 

 about 2221 oocytes in the ovaries of the mature females 



0.0 



0.2 



0.4 



0.6 



1.0 



Fishing mortality (I) 



Figure 11 



The egg escapement rate, R, , ( Eq. 12) of L. opalescens as a function of various daily natural adult mortality rates (in ), daily egg 

 deposition rates (rO, and daily fishing mortality rates if). In each panel, the solid circle indicates the /'value for preferred values: 

 2 = 0.45 and v = 0.25. 



