168 



Abstract— The prowfish (Zaprora sile- 

 nus) is an infrequent component of 

 bottom trawl catches collected on stock 

 assessment surveys. Based on pres- 

 ence or absence in over 40,000 trawl 

 catches taken throughout Alaskan 

 waters southward to southern Cali- 

 fornia, prowfish are most frequently 

 encountered in the Gulf of Alaska and 

 the Aleutian Islands at the edge of the 

 continental shelf Based on data from 

 two trawl surveys, relative abundance 

 indicated by catch per swept area 

 reaches a maximum between 100 m 

 and 200 m depth and is much higher 

 in the Aleutian Islands than in the 

 Gulf of Alaska. Females weigh 3.7% 

 more than males of the same length. 

 Weight-length functions are W (gl = 

 0.0164 L 292 (males) and W = 0.0170 

 L 292 (females). Length at age does not 

 differ between sexes and is described 



by L = 89.3(1 - e 



-0 181i;+0554l 



), where 



L is total length in cm and t is age in 

 years. Females reached 50 r /f maturity 

 at a length of 57.0 cm and an age of 5.1 

 years. Prowfish diet is almost entirely 

 composed of gelatinous zooplankton, 

 primarily scyphozoa and salps. 



Manuscript approved for publication 

 20 September 2003 by Scientific Editor. 



Manuscript received 20 October 2003 

 at NMFS Scientific Publications Office. 



Fish. Mull. 102:168-178 (2004). 



Distribution and biology of prowfish 

 (Zaprora silenus) in the northeast Pacific 



Keith R Smith 

 David A. Somerton 

 Mei-Sun Yang 

 Daniel G. Nichol 



Alaska Fisheries Science Center 



National Marine Fisheries Service 



7600 Sand Point Way NE 



Seattle, Washington 98115 



E-mail address (for K. R. Smith, contact author) Keith.Smith@noaa.gov 



Current taxonomy distinguishes the 

 prowfish (Zaprora silenus, Fig. 1) as 

 the only species and the only genus of 

 the family Zaproridae. Other families in 

 the encompassing suborder Zoarcoidei 

 include Bathymasteridae (ronquils), 

 Cryptacanthodidae (wrymouths), Pholi- 

 dae (gunnels), and Stichaeidae (prick- 

 lebacks). Systematics of most families 

 within Zoarcoidei, and of the suborder 

 itself within the order perciforms, is 

 uncertain (Nelson, 1994). Prowfish 

 (adult) physical features include an 

 elongate, laterally compressed body; a 

 high convex brow and interorbital area 

 ending with a short blunt snout; and 

 a distinctive protruding area below a 

 slightly upturned terminal mouth. 

 Fins consist of: a long, moderately high 

 dorsal fin; a moderately long anal fin; 

 a discrete truncate caudal fin with a 

 short, broad peduncle; and moderately 

 large, rounded pectoral fins (pelvic fins 

 are absent). Teeth are small, sharp, and 

 close-set in a single row attached only 

 to the jaws. Scales are ctenoid. Numer- 

 ous distinctive large round pores occur 

 on the sides and top of the head. Color 

 is olive-gray to brown dorsally, shading 

 lighter below, suffused on the sides 

 and back with many small dark spots 

 (Clemens and Wilby, 1961; Eschmeyer 

 et al, 1983; Hart, 1973; Kessler, 1985). 

 The maximum length reported is more 

 than 1 m (Tokranov, 1999). 



Since its original description (Jordan, 

 1897), the prowfish has been observed 

 infrequently despite numerous and 

 extensive bottom trawl surveys com- 

 prising thousands of net deployments 

 off Alaska and the west coast of North 



America. It is not clear whether this 

 lack of documentation indicates a spe- 

 cies of low abundance or a preference 

 by prowfish for a habitat, such as rough 

 rock substrate or steep bottom gradi- 

 ents, that is poorly sampled by bottom 

 trawl surveys. Nevertheless, the spe- 

 cies is common enough to be considered 

 representative of the ichthyofauna of 

 certain benthic biotopes within its 

 range (Allen and Smith, 1988; Tokranov, 

 1999). It has been encountered at loca- 

 tions along the outer continental shelf 

 and upper slope ranging in a long arc 

 from San Miguel Island, California, 

 north through the Gulf of Alaska, west 

 through the Bering Sea and Aleutian Is- 

 lands to the Asiatic shelf, thence south 

 to Hokkaido, at depths of 10-675 m 

 (Allen and Smith, 1988; Hart, 1973). In 

 addition to occurring in the catches on 

 biological surveys, prowfish have been 

 taken incidentally, and occasionally 

 processed, in commercial fishing op- 

 erations on the outer continental shelf 

 (Smith, pers. obs.; Berger 1 ). 



Prowfish are known to be pelagic 

 as pre-adults (Hart, 1973; Doyle et al, 

 2002). After larval transformation at 

 30 mm (Matarese et al., 1989), juve- 

 niles maintain close proximity to the 

 medusae of pelagic cnidarians (Schef- 

 fer, 1940). Brodeur (1998) observed 

 juveniles swimming near the bells of 

 scyphomedusae Cyanea capillata and 

 Chrysaora melanaster and retreating 



1 Berger, J. 2002. Personal commun. 

 Alaska Fisheries Science Center, National 

 Marine Fisheries Service, 7600 Sand Point 

 Way NE, Bldg 4, Seattle, WA 98115-0070. 



