FISHERY BULLETIN: VOL. 84, NO. 1 



grass beds (Lyons and Kennedy 1981) might occur 

 at accelerated rates in the relatively more sparse 

 ocean environment. If food is sufficiently scarce, ac- 

 celerated weight loss may lead to starvation and in- 

 creased mortality within the observed 4-wk period. 



Traps in these experiments had their entrances 

 boarded over to prevent escape, whereas lobsters 

 that escape from traps used in the fishery are likely 

 to recover from effects of starvation. Escape rates, 

 though, are quite low, ranging from 0.8 to 1.8%/d 

 (Yang and Obert 1978; Davis and Dodrill 1980; Lyons 

 and Kennedy 1981). 



We offer no explanation for our observation that 

 highest mortality rates are associated with 1-h ex- 

 posures nor for the persistent background mortality 

 among oceanside controls. Nevertheless, neither 

 seem to be artifacts of experimental design and, in- 

 stead, probably represent other yet-to-be understood 

 physiological reactions to stress caused by exposure, 

 handling, or confinement. If so, they represent other 

 effects of baiting with shorts and are justly included 

 among estimates of total fishery-induced mortality. 



Economic Effects of Mortality 



Baiting traps with shorts results in significant 

 economic loss to the fishery. Although use of shorts 

 is an effective means of attracting other lobsters 

 without requiring out-of-pocket expenses for bait, 

 each bait lobster that dies is one that potentially will 

 not enter fishery landings. In addition, repair of 

 broken legs, antennae, and other injuries caused by 

 handling may retard growth by as much as 40% 

 (Davis 1981), increasing the time required for a 

 lobster to attain legal size and extending the time 

 during which it may be used as bait. An injured 

 lobster that escapes from a trap where it was placed 

 will direct energy toward repair, not growth, thereby 

 reducing the probability that it will attain legal size 

 during its next molt. If the lobster does not attain 

 legal size, it is again vulnerable to capture and to 

 use as bait. Confinement itself also results in reduced 

 lobster growth rate (Kennedy 1982), which doubt- 

 lessly extends the period during which a lobster may 

 be vulnerable to use as bait. 



The hidden costs of baiting with shorts needs to 

 be considered in future management efforts. The 

 following model, based only upon observed mortali- 

 ty rates, estimates that cost: 



Y = AxBxCxD 



where Y = seasonal mortality of shorts used as bait; 

 A = number of traps in the fishery; 



B = average number of shorts per trap; 



C = season length (in months); 



D = average monthly mortality rate. 



Because the actual allocation of fishery traps 

 among Florida Bay and Atlantic sites is unknown 

 but believed to be relatively equal, we selected the 

 unweighted average cumulative 4-wk mortality rate 

 to estimate monthly mortality throughout the 

 fishery. By using a range of values for other 

 variables, several estimates of the average number 

 of shorts that die seasonally because of fishery bait- 

 ing practices may be obtained (Table 4). Thus, if each 

 trap in the fishery is baited with only 1 short/mo and 

 all fishermen leave the fishery after only 4 mo, more 

 than 600,000 sublegal lobsters may die as a result 

 of their use as bait. If all traps are deployed for the 

 full 8 mo and each trap uses 3 shorts as bait, more 

 than 3.6 million shorts may die as a result of that 

 use Both examples probably represent extreme 

 cases, and actual fishery-induced mortality probably 

 lies somewhere between these estimates. 



The problem is really more complex. Some lobsters 

 that die because they were used as bait would prob- 

 ably fall victim to other causes, but natural mortal- 

 ity among lobsters of sizes appropriate for use as 

 bait (65-75 mm CL) may be low, particularly since 

 incidence of their principal predators, large ser- 

 ranids, has been greatly reduced in the fishery area. 

 Furthermore, not all traps are baited with shorts 

 because shorts are not readily available in some 

 peripheral areas of the fishery. Both of these factors 

 suggest that the model may overestimate fishery- 

 induced mortality. However, values used in the model 

 for numbers of shorts per trap are probably low. 

 Fishermen prefer to use 3-5 shorts/trap (Gulf of Mex- 



Table 4. — Estimates of the economic effect of baiting with 

 shorts in the south Florida spiny lobster fishery. 



'Unweighted average cumulative 4-wk mortality rate from this study. 



2 Number of traps in 1981 (E. J. Little, Jr., Southwest Fisheries Center 

 Resource Statistics Office, National Marine Fisheries Service, NOAA, 

 P.O. Box 269, Key West, FL 33041, pers. commun. November 1982). 



3 The season is 26 July-31 March, 8+ mo; some fishermen begin 

 removing their traps after November, and many have left the fishery 

 by the end of January, causing a considerable reduction in the number 

 of traps fished during February and March. 



^Conservative estimates; fishermen try to put as many shorts as 

 available into traps. 



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