ESCAPE BEHAVIOR OF THE HAWAIIAN SPINNER PORPOISE 



{Stenella cf. 5". longirostris) 



William F. Perrin and John R. Hunter^ 



ABSTRACT 



Incidental mortality of porpoise (Cetacea, Delphinidae) occurs in the tropical tuna seine fishery. Ex- 

 periments were carried out in a crowding chamber to determine behavioral responses of trained and naive 

 Hawaiian spinner porpoise (Stenella cf. S. longirostris) to barriers of purse-seine netting, monofilament 

 webbing, pol>winyl sheeting, rows of floats, and openings of various dimensions in a net wall. The object 

 of the experiments was to generate information to be used in development of rescue gear and methods 

 for the fishery. Openings of less than 1.5 m in width and/or 1 m in depth markedly inhibited escape. 

 Negative effect of a line of floats aci'oss an opening at the surface was pronounced. Barriers of visually 

 and acoustically relatively transparent monofilament webbing and polyvinyl sheeting were not appar- 

 ently detected by porpoise prior to physical contact. Recommendations pertaining to potential design of 

 rescue gear are presented. 



Incidental mortality of porpoise occurs in the 

 American purse-seine fishery for tropical tunas 

 (Perrin, 1970). In 1970, the National Marine 

 Fisheries Service began a program of research 

 to develop improved gear and methods to reduce 

 the porpoise mortality due to tuna seining. This 

 paper reports the results of experiments on the 

 responses to netting and other barriers by the 

 Hawaiian spinner porpoise {Stenella cf. S. longi- 

 rostris) , a form closely related to one of the 

 species involved in the tuna fishery." We studied 

 the response of the spinner porpoise to barriers 

 of net, transparent monofilament nylon webbing, 

 transparent polyvinyl sheeting, rows of floats, 



' National Marine P^isheries Service, Southwest Fish- 

 eries Center, La Jolla, CA 92037. 



^ Taxonomic note: The spinner porpoise of Hawaii 

 has been variously referred to Stenella longirostris Grav 

 1828, by Nishiwaki (1967) and Tomich (1970), and to 

 S. roseivcntris Wagner 1846, by Fraser (in Morris and 

 Mowbray, 1966) and Rice and Scheff"er (1968). The 

 spinner porpoise of the tuna grounds of the far eastern 

 Pacific has been referred to .S'. microps Gray 1846 (Miller 

 and Kellogg, 1955; Handlev, in Hester, Hunter, and 

 Whitney, 1963; Nishiwaki, 'l967; Pilson and Waller, 

 1970) and to .S. longiros^tris (Rice and Scheffer, 1968; 

 Harrison, Boice, and Brownell, 1969). No critical re- 

 view of the genus has been accomplished since True's 

 work on the Delphinidae in 1889. The usage here of 

 S. longirostris for the Hawaiian spinner is provisional 

 pending the I'esults of taxonomic studies underway at 

 the Southwest Fisheries Center and elsewhere. 



and to openings of different dimensions in a net 

 wall. The results of these studies will be ap- 

 plied in the design of an escape opening in the 

 tuna purse seine. The experiments were carried 

 out at Oceanic Institute, Oahu, Hawaii, in May, 

 June, and July 1970. 



METHODS AND MATERIALS 



THE ANIMALS 



Three of the five porpoise (Table 1) used in 

 the experiments had been in captivity at Oceanic 

 Institute and Sea Life Park for various lengths 

 of time and are referred to below as the "trained 

 porpoise"; the remaining two, referred to below 



Table 1. — Hawaiian spinner porpoise (Stenella cf. S. 

 longirostris) used in behavioral experiments. 



Name 



Date of 

 capture 



Sex 



Weight at 

 time of 

 capture 



Manuscript accepted September 1971. 



FISHERY BULLETIN: VOL. 70, NO. I, 1972. 



49 



