Macy et al.; Metabolic rate of Brevoortia tyrannus 



291 



Metabolic budget 



R 



No n feed 



^Std 

 D 



"Swim 



creased drag of the filtration ap- 

 paratus, and the metabohc cost 

 of processing the food (specific 

 dynamic action [SDA]). SDA 

 could not be distinguished from 

 total metabolism during feeding 

 (Durbinetal., 1981) because food 

 is processed very rapidly as was 

 shown by the fact that 50% of ni- 

 trogen was excreted 1.4 h after 

 ingestion (Durbin and Durbin. 

 1981) and by the lack of a post- 

 feeding respiration peak. The high 

 cost of filter feeding in the menha- 

 den provides an interesting con- 

 trast with a sedentary, ambush 

 predator such as the Northern 

 pike, where the energy required for 

 prey capture is relatively small and 

 where most of the cost of feeding 

 is associated with SDA during an extended postfeeding 

 period of digestion (Lucas et al.. 1991). 



The bioenergetics of feeding differ between filter 

 feeders, such as menhaden, and particulate feeders 

 that consume zooplankton by individual capture. 

 Prey consumption increases linearly with prey con- 

 centration and predator swimming speed for filter 

 feeders but increases hyperbolically (Durbin, 1979) 

 for particulate feeders because of the limitations of 

 handling time. The energy cost is higher for filter 

 feeding than for particulate feeding. Both feeding 

 modes are energetically more expensive than rou- 

 tine swimming (James and Probyn, 1989). The opti- 

 mal swimming patterns in relation to food concen- 

 tration and foraging time therefore differ between 

 filter and particulate feeders (Ware, 1975; Durbin 

 and Durbin, 1983). Many planktivorous fishes switch 

 between filter and particulate feeding, according to 

 the size and concentration of prey in the water (north- 

 ern anchovy: Leong and O'Connell, 1969; O'Connell, 

 1972; Hunter and Dorr, 1982; cape anchovy: James 

 and Probyn, 1989; pilchard: van der Lingen, 1994; 

 Pacific mackerel: O'Connell and Zweifel, 1972; At- 

 lantic herring: Gibson and Ezzi, 1985, 1990, 1992). 

 The switch between filter and particulate feeding can 

 be predicted from the relationship between energy 

 gain and expenditure as the plankton size spectrum 

 changes (Crowder, 1985; James et al., 1989; Gibson 

 and Ezzi, 1992). In contrast, Atlantic menhaden are 

 less flexible in their feeding behavior and conse- 

 quently may be restricted to coastal and estuarine 

 waters of high production because energetic costs of 

 filter feeding are high and because a relatively small 

 volume of water is searched with mode of feeding 

 (Durbin and Durbin, 1983). 



Table 4 



Partitioning of metabolism during filter feeding in Atlantic menhaden Brevoortia 

 tyrannus, swimming at their preferred speed of 41.3 cra/s at 20°C. Components of 

 the energy budget: total metabolism during feeding (/Jp^^j); total metabolism 

 nonfeeding but swimming at the same speed '.^Nonfeed'' standard metabolism (^s,j>; 

 metabolism associated with swimming li?s„.,n,>; metabolism associated with fdter 

 feeding l^p,!,^^ '; metabolism associated with digestion and transformation of the food 

 '^sda'- -^Feed fro"i Durbin et al. (1981); remaining data from this study. 



mg 02/(g wet wt h) 



Percent of 

 total 



•'^Std + ^Sw,m + ^Filter + ^SDA 



■^Std + ^S»>m 



= R. 



0.480 

 0.197 

 0.087 

 0.110 

 0.283 



100 



18.1 

 22.9 

 59.0 



1000 



500 



3 



00 



E 



100 



10 



I  



20 



 I 



30 



cm/s 

 40 



50 



60 



 I  



70 



Filtering +SDA 

 59.0% 



Swimming speed, BL/s 



Figure 7 



The energy budget of Atlantic menhaden during foraging 

 at the preferred swimming speed. 41.3 cm/s (Durbin et al., 

 1981) partitioned by the vertical dotted line into the en- 

 ergy required for standard metabolism (horizontal dotted 

 line), swimming (solid line), and feeding (dashed line) = 

 filtering + SDA. 



However, menhaden flourish in their chosen habi- 

 tat, and as omnivores specializing in the smaller size 

 spectrum of particulate material, they have no im- 

 portant competitors among the fishes. Herring and 

 mackerel eat larger zooplankton and live further off- 

 shore. The small anchovies that live in the men- 



