migrating out of the Whitewater-Coot Bay- 

 estuary (via Buttonwood Canal) in Everglades 

 National Park and to deternnine the environ- 

 nnental and biological factors that influence 

 this abundance. 



Estimates of relative abundance are based 

 on the catches of emigrating shrimp col- 

 lected in a large channel net fished in Button- 

 wood Canal. Regular monthly sannples have 

 been taken since January 1963. Inmost months, 

 we sampled ebb tides on consecutive nights 

 and made an abundance estimate from the 

 combined sannples of 2 nights. These data 

 show that if weather rennains reasonably- 

 steady, the abundance from night to night 

 shows only nnoderate variation, especially 

 around tl;e time of the full moon. From our 

 analysis of 2 yr. of data, it appears that 

 periods of high relative abundance occur in 

 spring, summer, and early fall, but that inter- 

 year variation is considerable. 



Periods of low relative abundance occur 

 during the late fall or winter and in the 

 spring. In 1963 and 1964, the spring low fol- 

 lowed immediately after the spring peak of 

 relative abundance. 



During 2 yr. of sampling, the monthly nnean 

 size of the shrimp (sexes combined) ranged 

 from 9.9 to 18.0 mm. (0.38 to 0.71 in.) 

 carapace length and averaged 14 mm. (0.55 

 in.). In general, the snnallest shrimp appear 

 at times of high relative abundance. Annual 

 sex ratios were very close to 1:1 in 1963 

 and 1964. 



Secondary objectives of the study are to 

 examine the relation between the abundance 

 of shrimp migrating out of the nursery area 

 and subsequent commercial catches on the 

 Tortugas fishing grounds and to develop gear 

 and techniques that can be used to measure 

 shrimp migrations from an estuary. 



The relation of relative abundance of juvenile 

 shrimp in Buttonwood Canal catches to com- 



mercial landings of the smallest size category 

 of pink shrimp (68 count and over) shows 

 wide variation. It is best described by using 

 a 2-mo. lag for migrating shrimp of less 

 than 12 mm. (0.47 in.) and by using a 1-mo. 

 lag for shrimp of 12 mm. (0.47 in.) or larger. 

 Although variations do exist, the numbers of 

 small shrinnp moving through Buttonwood Canal 

 may provide a reasonably reliable index from 

 which to predict numbers of shrimp that will 

 subsequently appear on the fishing grounds. 



One yr. of sampling, with 13 small nets 

 placed from top to bottom across the canal, 

 has provided information on the distribution 

 of migrating pink shrinnp in Buttonwood Canal. 

 Results of this study, made during all moon 

 phases, suggest that nnost consistent numbers 

 of shrimp are on the surface during fullnnoon. 

 During the new moon the percentage of shrimp 

 taken in surface nets averaged 76 percent 

 (range 47 to 98 percent) of the total catch, 

 and during the full moon the numbers aver- 

 aged 92 percent (range 79 to 99 percent). 

 The considerable variation found in earlier 

 wing-net samples (obtained in the top 1 m. 

 (3.3 ft.) of water) was probably caused by 

 sampling without regard to nnoon phase. Re- 

 cent wing-net and channel-net samples taken 

 sinnultaneously during the time of the full 

 moon in February, March, and April have 

 shown a consistent relation. The variation in 

 abundance estimates observed fronn wing-net 

 samples can be reduced by fishing during 

 full-moon periods when the shrimp are close 

 to the surface. 



C. P. Idyll, E. S. Iversen, and 

 B. Yokel, Project Leaders 



Institute of Marine Science, 

 University of Mianni 



(Contract No. 14-17-0001- 

 99) 



SHRIMP DYNAMICS PROGRAM 



This program is concerned with developing 

 a sound basis for management of shrimp 

 resources in the Gulf of Mexico. The general 

 philosophy underlying our work is that shrinnp 

 fisheries should be regulated to provide the 

 maximunn return to fishermen, in terms of 

 the weight or value of shrimp harvested, but 

 under conditions that do not reduce future 

 returns. In this context, future returns refer 

 to production in years to come as well as to 

 harvests that might be made if a brood of 

 shrimp were permitted to grow to a larger 

 size. 



Management regulations currently applied 

 to shrimp stocks in the Gulf include minimum 

 size laws, net size and mesh regulations, 

 catch quotas, and closed seasons. Most regu- 



lations apply to inshore waters and are de- 

 signed to protect small shrimp until they 

 reach a size acceptable to local nnarkets. 

 Pressures that occasionally develop from 

 changes in marketing practices or in con- 

 sumer demands cause groups in the shrimp 

 industry to challenge the rationale behind such 

 regulations or to insist that more restrictive 

 laws be enacted and enforced. Conflicts nnost 

 commonly arise when a stock of shrinnp nnust 

 supply two types of markets--one that requires 

 small shrimp and another that deals in large 

 shrinnp. To answer problems of this nature 

 and to evaluate the merits of various regula- 

 tory measures, we must make critical studies 

 of shrimp stocks from several points of 

 view. 



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