Tethering as a Technique for 

 Assessing Predation l?ates in Different 

 Habitats: An Evaluation using Juvenile 

 Lobsters Homarus amehcanus 



Diana E. Barshaw 



Rutgers University Marine Field Station 

 Great Bay Boulevard. Tuckerton. New Jersey 08087 

 Present address: Center for Maritime Studies 

 University of Haifa. Mount Carmel. Haifa 31999, Israel 



Kenneth W. Able 



Rutgers University Marine Field Station 



Great Bay Boulevard. Tuckerton. New Jersey 08087 



Tethering has been used successful- 

 ly to assess predation rates of a 

 variety of predator-prey systems in 

 several different habitats. The ma- 

 jority of these experiments have 

 used tethered crabs as prey (Heck 

 and Thoman 1981, Wilson 1985, 

 Wilson et al. 1987, Heck and WOson 

 1988, Wilson et. al. 1990, Barshaw 

 and Able In press). Fish have also 

 been tethered in different habitats; 

 however, in these experiments the 

 tethered fish could not act natural- 

 ly, and therefore the technique only 

 showed the differences in predator 

 encounter rate in different habitats 

 (Shulman 1985, Mclvor and Odum 

 1988). Other organisms are present- 

 ly being used in tethering experi- 

 ments including molluscs (R.N. Lip- 

 cius and L.S. Marshall, Jr., Coll. 

 William and Mary, Va. Inst. Mar. 

 Sci., Gloucester Ft., VA 23062, un- 

 publ. data) and spiny lobsters 

 (Herrnkind and Butler 1986). 



We determined if tethering was 

 an appropriate technique to assess 

 predation on species that burrow 

 (i.e., juvenile lobsters Homarus 

 americanus). Lobsters were chosen 

 for this study, in part, because their 

 behavior has been well studied and, 

 therefore, a basehne of "normal" 

 behaviors is available (Botero and 



Atema 1982, Barshaw and Bryant- 

 Rich 1988). 



Lobsters use different methods of 

 constructing burrows in different 

 habitats; therefore we tested three 

 habitats known to be important for 

 early juvenile lobsters: mud, cobble, 

 and Spartina peat (Able et al. 1988, 

 Barshaw and Lavalli 1988). 



Methods and materials 



Six "ant farm" aquaria (10 cm wide, 

 30 cm long, 45 cm deep) were 2/3 

 filled with either cohesive mud, cob- 

 ble of a natural size distribution, or 

 Spartina peat substrates (two repli- 

 cates per substrate type) and pro- 

 vided with running, unfiltered sea- 

 water. Early juvenile lobsters (8-14 

 mm carapace length) were individu- 

 ally tethered to monofilament line 

 using "super glue" to attach it to 

 their carapace. Individual tethered 

 lobsters were placed into half the 

 tanks while similar-sized untethered 

 control lobsters were placed into the 

 remaining tanks. 



A discrete reading of each lob- 

 ster's behavior was recorded every 



Reference to trade names does not imply en- 

 dorsement by the National Marine Fisheries 

 Service, NOAA. 



minute for the first 20 minutes, 

 every 5 minutes for the next 35 

 minutes, and then every hour for 6 

 hours. A final assessment of each 

 lobster's burrow was made after 24 

 hours. Therefore, each lobster was 

 observed 33 times over 24 hours in 

 each test. Seven tests were run 

 using all the substrates, with two 

 extra tests run only with mud; thus 

 observations were made on a total 

 of 14 lobsters in cobble, 14 in peat, 

 and 26 in mud. The behaviors ob- 

 served are described in Table 1. 



The behaviors of the tethered and 

 untethered lobsters were compared 

 by calculating the percent of the 33 

 observations in which the lobsters 

 were engaged in each of the behav- 

 iors for each test. Since this experi- 

 ment was designed only to compare 

 tethered and untethered lobsters, 

 no comparisons were made between 

 different behaviors or between dif- 

 ferent substrates (comparisons of 

 that nature were studied in Bar- 

 shaw and Bryant-Rich 1988). The 

 percent of observations was trans- 

 formed using the arc-sign trans- 

 formation, and analyzed with a Stu- 

 dent's t test. The numbers of the 

 tethered and untethered lobsters 

 that had burrows at the end of the 

 experiment were analyzed for each 

 substrate using 2x2 contingency 

 tables and chi-square tests. 



Results 



The tethering of juvenile lobsters 

 resulted in substrate-specific dif- 

 ferences in behavior and the ability 

 to construct burrows. There were 

 no significant differences between 

 the behavior of tethered and unteth- 

 ered lobsters in the peat or cobble 

 substrates (Fig. 1); in both peat and 

 cobble, all the tethered (7/7) and all 

 the untethered (7/7) lobsters had 

 burrows that they constructed and 

 maintained throughout the experi- 

 ment. 



Manuscript accepted 22 January 1990. 

 Fishery Bulletin, U.S. 88:415-4:7. 



415 



