FISHERY BULLETIN: VOL. 84, NO. 1 



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1950 I960 



YEAR CLASS 



1970 



Figure 17— Relative recruitment strengths of jack mackerel year 

 classes in southern California. Virtual year-class strength is 

 measured by the sum of percentage contributions to seasonal land- 

 ings over the lifetime of the year class. The dashed line indicates 

 average strength (from MacCall and Stauffer 1983; Fig. 4). 



feeding (Theilacker 1980a), and 4) a growth rate of 

 0.37 mm/d for healthy sea-caught northern anchovy 

 (Methot and Kramer 1979). Although the number 

 of first-feeding larvae was low in O'Connell's data 

 (n = 23), I calculated a starvation-induced mortal- 

 ity rate of between 35 and 46%/d. Thus my calcula- 

 tions indicate that substantial numbers of northern 

 anchovy larvae as well as jack mackerel larvae are 

 dying at the time of first feeding. This loss rate for 

 northern anchovy is similar to estimated total mor- 

 tality rate at this stage, 39%/d (Lo in press; 1978 

 data), which suggests that starvation is the major 

 source of mortality at first feeding. This conclusion 

 for northern anchovy could not be drawn at the time 

 that O'Connell did his work because the data on net 

 shrinkage were not known. The average rates 

 estimated by O'Connell were much lower because he 

 combined larval size classes. 



Attempts to assess larval starvation in the sea 

 using morphological criteria are more common 

 (Shelbourne 1957; Honjo et al. 1959; Nakai et al. 

 1969; reviewed by May 1974; Ehrlich et al. 1976), but 

 they have seldom been successful, probably because 

 of the biases introduced by failure to correct ade- 

 quately for shrinkage (see next section). Recently 

 Devonald (1983) used a morphometric index with 

 shrinkage adjustments to assess jack mackerel 

 feeding regimes off California. She found good 

 correspondence between jack mackerel condition 

 and prey availability and concluded that feeding con- 

 ditions were better near islands than in the area 



between islands. Several of her samples and my 

 samples were taken concurrently (San Clemente and 

 Tanner Bank; Table 1), and I found that 92% of the 

 jack mackerel from the island habitat were healthy. 

 Thus, my results obtained using histological criteria 

 confirm Devonald's conclusion. 



Other techniques used in the past to assess food 

 availability include RNA/DNA (Buckley 1980), food 

 in gut (Rojas de Mendiola 1974; Ciechomski and 

 Weiss 1974; Arthur 1976; Ellertsen et al. 1981), and 

 otoliths. Of course otolith work is critical because 

 estimates of growth rates are essential for assess- 

 ment of mortality, but it is of no value for assessing 

 growth at the onset of feeding (Methot 1981). 



Arthur (1976) conducted the only other study on 

 the feeding of jack mackerel off the coast of Califor- 

 nia. He found, after examining the stomach contents 

 of 750 specimens from 65 offshore samples, that 60% 

 of the first-feeding jack mackerel and 10% of the 

 older larvae (7 mm) had empty stomachs. This obser- 

 vation lends additional credence to my histological 

 evaluation of jack mackerel collected offshore that 

 shows 59% of the first-feeding fish and 3% of the 

 older fish (>4 mm) were starving. 



I believe my estimates of jack mackerel mortality 

 due to starvation are conservative The assumptions 

 I made about the persistence of starvation and the 

 duration of growth were based on extensive 

 laboratory studies (Theilacker 1978, 1981). Because 

 the majority of jack mackerel were collected at sites 

 warmer (16.1°-16.6°C) than the culture temperature 

 (15°-15.5°C), the durations for growth and starvation 

 may be altered, but the final estimate of mortality 

 due to starvation is higher after the appropriate 

 changes to the durations are made Furthermore, if 

 net retention of robust fish is greater than reten- 

 tion of thin fish of the same length, starvation may 

 be underestimated. In addition, the selection of 

 unhealthy larvae by predators would also increase 

 the starvation estimate 



Previous evidence supporting the occurrence of 

 starving fish larvae in the ocean has been mainly cir- 

 cumstantial (reviewed by May 1974; Jones and Hall 

 1974; Lasker 1975). Evidence from this study and 

 O'Connell's (1980) study shows that starvation does 

 occur and that the young stages of jack mackerel and 

 northern anchovy are highly vulnerable 



Comparison of Morphological and 



Histological Criteria for 



Starvation Diagnosis 



The incidence of starvation based on mor- 



14 



