352 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 1. — Projected bottom area off the Gulf of Mexico 

 coast from Marathon, Florida, to Cabo Catoche, Yucatan ' 



[Square nautical miles] 



> Source: Charts issued by U.S. Coast and Geodetic Survey and U.S. 

 Navy Hydrographic Office. Untrawlable bottom not delineated. 

 2 Refer to figure 1. 



estimates of individual vessel and fleet trawling 

 time. Secondly, the assumption that all vessels 

 operating out of or landing at a particular port 



fish in close proximity may not always be valid. 

 It is acknowledged, however, that portions of the 

 fleet fishing a specific locale usually tend to 

 aggregate on shrimp concentrations occurring 

 there. The question of how fishing positions and 

 effort are assigned to vessels operating in periods 

 during which interview data cannot be obtained 

 remains unreconciled. 



LANDINGS 



Equivalent in importance to the variable, 

 "effort," is the corresponding variable, "catch." 

 The present statistical survey attempts to account 

 for all commercial shrimp landings through a 

 daily or weekly canvass of processing plants. 

 From dealers' receipts, port agents transcribe the 

 details of landings for each vessel-trip on a 

 "Shrimp Schedule" form. An estimated 97-100 

 percent of all Gulf shrimp landings are so reported 

 each year. Contrasted to other types gathered 

 by the survey, data of commercial landings may 

 be considered complete and, in addition, quite 

 precise, since they are factors in business transac- 

 tions. Unfortunately, recorded landings may not 

 always represent the amount of shrimp actually 

 caught. This is usually attributable to the period- 

 ically widespread practice of discarding at sea 

 small or otherwise undesirable shrimp. 

 Origin 



Each landing is coded according to its known or 

 "estimated" origin in the same manner as that 

 described earher for coding a vessel's fishing 

 position. 



Prorating landings by depth of capture is one 

 procedure here that could lead to misrepresenta- 

 tion ot tabulated data. If a captain states that 

 he trawled in several depth zones but cannot 

 specify how his trawling time and catches were 

 apportioned among them, his total effort and cor- 

 responding catch will be coded, respectively, as 

 having been expended in and taken from the zone 

 of greatest depth fished. Accumulations of catch- 

 by-depth data obtained by interview for a very 

 small proportion of the commercial shrimp fleet, 

 and by projection therefrom for the greater part 

 of tlie fleet, have limited usefulness in depth dis- 

 tribution studies of commercial species. Some 

 will be falsely described as having been avail- 

 able in larger quantities over a greater depth 

 range than they actually were. 



