NOTE Gilman: An energy budget for Ammodytes dubius 



649 



where AE = assimilation efficiency (%); 

 T = temperature ( C ). 



Ration estimation 



Annual ration was estimated by summing the meta- 

 bolic requirements, somatic growth requirements, 

 and reproductive requirements, and then by taking 

 assimilation efficiency into account. Because assimi- 

 lation efficiency was found to increase with increas- 

 ing temperature (Larimer, 1992), ration was calcu- 

 lated on a monthly rather than an annual basis. 



Seasonal water temperatures (and therefore fish 

 activity levels) and food availability on Georges Bank 

 were used to estimate a monthly ration for sand lance 

 based on the energy budget requirements. I assumed 

 that the fish are inactive during January, February, 

 and March. Other species of Ammodytes (A. tobianus, 

 Reay, 1970; A. marinus, Macer, 1966) are known to 

 spend the winter months buried in the sand. This 

 behavior has not been recorded for A. dubius but 

 catches of these fish during the winter months are 

 low (Nelson, 1990) and they have been observed to 

 spend extended periods buried in the sand in the labo- 

 ratory, apparently without feeding 3 (personal observ., 

 1991 ). I assumed that the metabolic requirement for 

 January, February, and March and the annual re- 

 productive requirement were assimilated from May 

 through September when food availability is high and 

 water temperatures are still warm. 



Monthly gross energy requirements were esti- 

 mated by summing monthly energetic costs and 

 multiplying by the percent of consumed calories lost 

 as waste based on monthly assimilation efficiencies. 

 These were divided by the caloric content of the ra- 

 tion (6.11 ± 0.77 kcalg" 1 for Calanus ftnmarchicus; 

 Larimer, 1992) to determine the actual grams of ra- 

 tion required per month. The sum of these monthly 

 estimates is the yearly ration requirement. 



Population energy budget 



The energy budget for 'individual adult northern sand 

 lance was extrapolated to the population level by 

 multiplying overall production (growth + repro- 

 duction) and consumption (predicted ration) by the 

 number of individuals estimated to be present on 

 Georges Bank from 1977 through 1986. Northern 

 sand lance population size was estimated from spring 

 sand lance biomass estimates for 1977-86. 2 Mean 

 sand lance weight per tow was divided by mean in- 

 dividual adult fish wet weight (see above) and the 

 average tow volume to estimate the number of indi- 



:i Halavik, T. NOAA, Nat. Mar. Fish. Ser., Northeast Fish. Sci 

 Center, Narragansett Lab, Narragansett, R.I. 02882. Personal 

 eommun., September 1991. 



viduals present per unit volume on the Bank. There 

 were no sand lance abundance data for 1979. The 

 energy budget parameters of the population were 

 then compared with estimates of secondary produc- 

 tion on Georges Bank. 



Macrozooplankton production (including Calanus 

 ftnmarchicus, Pseudocalanus minutus, Centropages 

 species, and Metridia lucens) on Georges Bank was 

 calculated from population estimates measured dur- 

 ing the MARMAP surveys from 1977 to 1986 

 (Sherman et al., 1987). Zooplankton volumes were 

 reported in Kane. 1 These were transformed into an- 

 nual production values following Sherman et al. 

 ( 1987) where volume is converted to biomass using 

 the following equation (Wiebe et al., 1975): 



log lf| (dry weight) = log 1(J ( volume + 1.828 )/0.848. 



A value of 5.25 kcal-g" 1 (Laurence, 1976) and a pro- 

 duction-to-biomass ratio (P:B) of 7 (Steele, 1974; 

 Crisp, 1975 ) were used to convert zooplankton biom- 

 ass to production. Annual production was estimated 

 for each year of available zooplankton data ( 1977- 

 86) and compared with the calculated annual con- 

 sumption by northern sand lance. 



Results and discussion 



Predicted ration and individual budget 



The ratio of production to consumption (P:C) deter- 

 mined from an individual energy budget represents 

 the gross ecological growth efficiency of an animal 

 within a trophic level (Slobodkin, 1960). This ratio 

 was determined from the individual energy budget 

 for the northern sand lance. Monthly growth esti- 

 mates calculated from Reay's ( 1972) data range from 

 0% from September to March to 36% dry body weight 

 in May (Table 1) and from 0.00 kcal, from Septem- 



Table 1 



Monthly somatic growth of northern sand lance, 

 Ammodytes dubius, on Georges Bank estimated from 

 measurements of A. tobianus growth rates in length 

 (Reay, 1972) and the availability of food on the Bank. 

 Reay measured no net growth September through 

 March. 



Month 



r 'f Growth (wt) 



Growth (kcal) 



April 



May 



June 



July 



August 



0.14 

 0.36 

 0.19 

 0.07 

 0.24 



1.15 

 2.90 

 1.50 

 0.56 

 1.97 



