these values are also shown in table 1. The model was quantified for "average" 



conditions, and seasonality was ignored; thus model forcing functions were 



constants. Values in the literature and fisheries statistical data were used 

 for the quantification. 



Standing stock estimates are specific to the area offshore the Mississippi 

 Delta. Fishery standing stocks were estimated from fishery landings data for 

 1975, using the relationship: 



N = C/F, 



Q = N(D/M), 



where N is population number, C is landings, F is instantaneous fishing mortality, 

 D is average dry weight of individuals, and M is the area inside 93 m (50 

 fathoms) covered by the landings, or, in the case of migrating species, area 

 covered in migrations. The F values used in these calculations were crude 

 approximations and may be sources of error. 



Pelagic forage fish standing stock was based on menhaden catches for 

 Louisiana and doubled to take into account other forage fish species in the 

 area. The shrimp standing stock was also based on Louisiana landings. Bottomfish 

 standing stock was based on landings and estimated bycatch of croaker and other 

 bottomfish species in the area from Point Au Fer, La., to Perdido Bay, Fla. 

 The model is quantified for the area from the eastern Louisiana border to Point 

 Au Fer, with respect to the above three groups. 



The standing stock of migratory pelagics was based on king and Spanish 

 mackerel catches for the entire U.S. Gulf coast. The mackerels are not fished 

 commercially to any extent in the north-central Gulf, but those stocks fished 

 commercially elsewhere probably spend about half the year in the northern Gulf. 

 By dividing estimated total Gulf standing stocks by total area of the Gulf, I 

 obtained an estimate for an "annual average" standing stock of mackerels in the 

 model area. This value was doubled to provide an estimate of coastal pelagics 

 standing stock, which includes other species in this same trophic group for 

 which there are no commercial landings on which to base standing-stock estimates. 



Animal respiration rate-coefficients were specific to each compartment of 

 the model and were based on values for a representative species in each 

 compartment or a related or similar type species. Calculations of nitrogen 

 flows are based on body nitrogen concentration of a representative species in 

 each compartment or a related or similar type of species. For zooplankton, the 

 N/NF ratio used (in the initialization routine) for setting nitrogen release 

 rates relative to excretion rates was 0.3 to 0.7. The routine calculated a 

 nitrogen concentration ratio in fecal pellets of 0.06455 at steady state (com- 

 pared to a value of 0.0448 calculated from Johannes and Satomi (1966)). For 

 bottomfish, the N/NF ratio employed was 0.99 to 0.01 (compared to a value of 

 0.9942 to 0.0058 from Darnell and Wissing (1975) for pinfish, Lagodon rhomboides ). 

 Specific nitrogen information of this type was not available for the other 

 animal compartments. The production of feces by the three higher trophic 

 compartments (migratory pelagics, marine mammals, and large scavengers) was 

 considered to be insignificant in the model, and all nitrogen loss was designated 

 to excrement. For the other animal compartments, the N/NF ratio was 0.8 to 

 0.2. 



198 



