130 



Fishery Bulletin 100(1) 



70 

 60 



50 



? 



"D 



S 30 

 a 

 20 



10 



1982 1984 



1986 1988 1990 



Year 



1992 



1994 



1996 



Figure 3 



Annual estimates of the reported discard rate of lobsters in the NWHl lobster fishery. 

 1983-95 



berried spiny and slipper lobsters that occurred within 

 two days after capture under handling methods known to 

 have been used in the NWHI lobster-trap fishery. 



Methods 



Studies of handling-induced mortahty ( referred to as "han- 

 dling mortahty" in the remainder of this note) for spiny 

 lobster were conducted at Necker Island onboard the 

 NOAA ship Towitsend Cromwell during the NMFS Hono- 

 lulu Laboratory's 1996 NWHI lobster sui-vey from 21 to 

 26 June 1996 and for slipper lobster at Maro Reef from 4 

 to 11 July 1996 (see Fig. 1). These locations were chosen 

 because of their historically high lobster catches and their 

 overall importance to the commercial lobster fishery over 

 the past 13 years. 



Handling mortalities were estimated for two handling 

 methods: "dry" and "wet." The effects of on-deck exposure 

 time on handling mortality were also estimated for spiny 

 lobsters handled by the dry method. We defined a particu- 

 lar combination of factors (method and exposure time) as 

 an experimental treatment. For dry treatments, lobsters 

 were held on deck in 30-gallon containers without water 

 and in direct sunlight for 1, 2, or 3 hours. In the wet treat- 

 ment, lobsters were held on deck for 3 hours in shaded 

 30-gallon containers with circulating seawater. The 2- and 

 3-h dry treatments represent prevailing commercial fish- 

 ing practices (Anderson'^), whereas the 1-h dry treatment 



^Anderson,?. 1997. Personal commun. University of Hawaii, 

 Marine Option Program, 1000 Pope Road, Honolulu. HI 96822. 

 Kazama, T. 1997. Personal commun. Honolulu Laboratory, 

 Southwest Fisheries Science Center, 2.570 Dole Street, Hono- 

 lulu, HI 96822-2396. 



and the 3-h wet treatments represent possible handling 

 alternatives or mitigative measures. 



Spiny and slipper lobsters were collected in baited com- 

 mercial lobster traps and sorted (legal, sublegal, and ber- 

 ried). All sublegal and berried lobsters were held in tanks 

 of circulating water until a sufficiently large paired exper- 

 imental treatment sample («=200 lobsters) was collected. 

 Experiments with the 3-h wet and dry treatments were 

 done first, followed by experiments involving 1- and 2-h dry 

 treatments. For each treatment, 100 lobsters (sublegal and 

 berried) were randomly chosen from the tank and placed 

 into two 30-gaUon treatment containers (dry or wet). 50 

 lobsters/container After the exposure time (1, 2, or 3 hours), 

 lobsters were removed from the treatment containers, their 

 condition recorded as active (i.e. lobsters were capable of tail 

 flexion), weak (incapable of tail flexion but able to move ap- 

 pendages when prodded), or dead. Five lobsters were placed 

 in each of 20 lobster-holding traps (commercial lobster traps 

 with sealed entrances) and held in two 1320-gallon bait- 

 wells with recirculating seawater (21 gallons/minute) for 2 

 days. It was assumed that the 2-d holding period would al- 

 low ample time for latent effects from a treatment to man- 

 ifest and that each lobster holding trap was a replicate 

 (7! =20 replicates/treatment). To check for possible baitwell 

 effects, five control traps, each containing five previously 

 untreated lobsters, were placed in the baitwells (two traps 

 in the port baitwell and three traps in the starboard bait- 

 well) at the beginning of the holding phase, and their condi- 

 tion was recorded at the beginning and end of the holding 

 phase. At the conclusion of the holding period, the condition 

 of the treated lobsters was again assessed. 



Handling mortality for each treatment was computed 

 as the arithmetic mean of the percent mortality (dead/ 

 total or (dead -i- weak)/total — see below) observed in the 20 



