782 



Fishery Bulletin 97(4), 1999 



150 -I 



g 100 



75 - 



50 



25 



Bluefish consumption 

 Landings 



400 



mi 



- 200 2 



boreal iong-fmned butlert'ish menhaden 



Figure 4 



Estimated biomass < in thousands of metric tons ( t ) I of boreal squid, 

 long-finned squid, butterfish. and Atlantic menhaden consumed 

 by the U.S. east coast bluefish population (open histogram rep- 

 resents consumption by average bluefish biomass from 1982 to 

 1995, error bar represents range for consumption by a minimum 

 to maximum bluefish population size) and harvested by east coast 

 fisheries (closed histogram represents average harvest from 1984 

 to 1992, error bar represents range for harvest from minimum to 

 maximum I. 



mated the annual Q/B of bar jack, Caranx ruber, and 

 the dolphin Coryphaena hippuriis at 10.6 and 8.5, 

 respectively. Secondly, the estimate of Q/B with labo- 

 ratory-measured daily rations (age 0—2 yr fish) and 

 1995 VPA bluefish biomass data gave us an estimate 

 of Q/B of 10.8. This value was only slightly higher 

 than the estimate from Pauly's (1986) model. This 

 difference is likely a result of extrapolating C,„^,^ data 

 from Hartman and Brandt {1995a) to larger fish. 

 Assuming consumption rates of these larger fish were 

 overestimated, values of 2.0 to 3.0 kgAkg  d)  100 were 

 substituted for fish ages 4-9-I-. From this a Q/B value 

 of 6.6 was estimated. This value is more similar to 

 the Pauly model Q/B estimate of 7.7. Future esti- 

 mates of bluefish population consumption should 

 include laboratory or field estimates of feeding rates 

 of older bluefish. 



The Q/B estimate based on the 1995 VPA (10.8) 

 incorporates the age structure existing at that time 

 (recruitment not constant in the population), whereas 

 the estimate from Pauly's (1986) model (7.7) assumes 

 constant recruitment. Age structure may also con- 

 tribute to the differences between the two Q/B esti- 

 mates. For the 1995 bluefish stock, recent years of 

 low recruitment have led to peak biomass in the older 

 age classes (NEFSC*). These older, more abundant 

 age classes consume a higher biomass of prey than 

 younger age classes. In 1995, age-6 fish consumed 

 more prey biomass than any other age class. This 



A Simulated 



boreal long-finned butterfish menhaden 



Figure 5 



Daily consumption (not temperature corrected; t) of 

 boreal squid, long-finned squid, butterfish, and At- 

 lantic menhaden by the U.S. east coast bluefish 

 population based on simulated (A) and 1995 (B) data 

 ( see text for calculation methods ). Consumption was 

 estimated from pooled diet indices (open histogram) 

 and indices which were partitioned by age or size 

 (closed histogram). 



strong age class resulted from a relatively large re- 

 cruitment in 1989. If recruitment and mortality are 

 constant, our analyses predict that absolute prey 

 consumption will peak at about age 2 ( Fig. ID ). That 

 consumption rate tends to peak in the earlier age 

 classes has also been found in other species (Stewart 

 and Binkowski, 1986; Yafiez-Arancibia et al., 1993). 

 Bluefish ingest larger and a greater diversity of 

 prey and include more resource species in their diet 

 (e.g. butterfish, squid, Atlantic herring, and several 

 groundfish species), with increasing body size (Buckel 

 et al., 1999b; Morris'). When coupled with temporal 

 shifts in the biomass age structure of bluefish, such 

 ontogenetic changes in diet have important implica- 

 tions for impact on prey populations. For example, 

 bluefish recruitment was relatively high from 1982 

 through 1984. In 1984, peak absolute consumption 

 of prey occurred between age 2 and 3 compared with 

 age 6 in 1995. In 1984, the biomass consumption of 

 age-0 through age-3 fish was 40% of the entire 



