BREIWCK ET AL : ESTIMATED INITIAL POPULATION SIZE OF BOWHEAD WHALE 



TABLE 5— Estimated recovery times for Bering Sea bowhead whale stock. Recovery time is that calculated with the 

 parameters indicated, assuming zero kill. The relative increases in recovery time that occur with various levels of 

 constant kill are tabulated in the last six columns. 



'Stock goes to zero. 



much interpretation (Mitchell footnote 4), but at 

 least the extrapolations will approximate true 

 trends. 



The aboriginal catch data for some years may 

 represent only the minimum landed catch. The 

 pre-1960 aboriginal catch fluctuates from to 47 

 (1908) per annum, where presently known. From 

 1978 back to 1854 there are many years for which 

 no data were recorded or obtainable. Also, for 

 many years for which data are available, the num- 

 bers given may not represent the true total landed 

 catch. In our analysis, these unrecorded kills have 

 implications only for the data from 1908 or 1912, 

 near the end of the commercial pelagic fishery 

 when the aboriginal catch begin to represent the 

 majority of the total catch. However, during the 

 much earlier period of high commercial catches, 

 the aboriginal catch composed a small percentage 

 of the total ( 59c or less of the pelagic catch at its 

 highest). Thus any analysis of recovery patterns 

 dependent upon the post-1900 data is entirely de- 

 pendent upon the completeness of the aboriginal 

 catch. Since few contemporary written records 

 have been kept and continued library research 

 yields new figures for given years, the aboriginal 

 catch must be regarded as minimum and provi- 

 sional. 



Limitations of the Model 

 All models with published results previously 



used on whale populations have been applied to 

 odontocetes, balaenopterids, or eschrichtiids, but 

 not to balaenids. Because we are dealing with a 

 separate zoological family (much older than the 

 balaenopterids and apparently different in many 

 behavioral features), caution should be used when 

 applying balaenopterid vital parameter values, by 

 analogy, to the balaenid model. No other reason- 

 able estimates are available, however. 



Although the model (Equation 2) used to esti- 

 mate initial abundance is relatively simple, it does 

 account for fishing and natural mortality and re- 

 cruitment as a function of the time-lagged popula- 

 tion size. It is quite possible, though, given the 130 

 yr we are considering, that the natural mortality 

 rate has changed. Such a change, if it has oc- 

 curred, probably would have had a relatively small 

 effect on the initial stock estimates. We have also 

 not considered the effect of a differential sex ratio 

 in the large pelagic catches, which could have re- 

 sulted in the 1912 population consisting of (in the 

 worst possible cases) mostly males, mostly old 

 females of low fertility, or young animals of either 

 sex. 



Although Figure 2 shows a minimum popula- 

 tion size occurring around 1912, we have not calcu- 

 lated the minimum size the population might have 

 declined to, for the following reasons: assumptions 

 that the population was much smaller then land 

 has appreciably recovered) cannot be proven, and 

 represent only one alternative explanation of the 



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