227 



Abstract.— Po/.vpr/on oxygeneios (fam- 

 ily Polyprionidae) is fished commer- 

 cially and recreationally in the south- 

 ern Indian and Pacific Oceans. Esti- 

 mates of growth rate, age at maturity 

 and recruitment, and longevity are re- 

 quired for fishery management. We 

 used thin otolith sections to age P. 

 oxygeneios from New Zealand, where it 

 is known as hapuku. Growth bands 

 were difficult to count, leading to low 

 counting precision and, for some age 

 groups, to a small between- and within- 

 reader ageing bias. These problems, 

 however, had little effect on the shape 

 of growth curves fitted to length-at-age 

 data. An oxytetracycline injection ex- 

 periment supported our hypothesis of 

 annual deposition of an opaque-hyaline 

 band pair, but further validation is re- 

 quired. Independently derived von 

 Bertalanffy growth curves ( from length- 

 frequency data) and growth-rate esti- 

 mates (from tag-recapture data) for 

 young hapuku agreed well with esti- 

 mates from length-at-age data. 



Juvenile hapuku are pelagic and 

 most switch to a demersal habitat at 

 around 50 cm total length and at an 

 estimated age of 3^ years. They prob- 

 ably recruit to commercial trawl catches 

 at about the same age. Female hapuku 

 appear to grow slightly faster than 

 males. Both sexes mature at about 10- 

 13 years. The longevity of hapuku is 

 uncertain, but some individuals prob- 

 ably live longer than 60 years. 



Age and growth estimates for 



New Zealand hapuku, Polyprion oxygeneios 



Malcolm P. Francis 

 Kevin P. Mulligan 

 Nick M. Davies 



Michael P. Beentjes 



National Institute of Water and Atmospheric Research 

 P, O Box 14-901, Wellington, New Zealand 

 E-mail address (for M P Francis) m francisaniwacn nz 



Manuscript accepted 5 May 1998. 

 Fish. Bull. 97:227-242(1999). 



Polyprion oxygeneios (Schneider, 

 1801) (family Polyprionidae) is a 

 large demersal fish that inhabits 

 temperate and subtropical waters of 

 the southern Indian and Pacific 

 Oceans (Roberts, 1986; Fig, 1), It 

 supports significant fisheries off the 

 Juan Fernandez Islands, Chile, and 

 off New Zealand and is an impor- 

 tant bycatch in south-east Austra- 

 lian longline fisheries (Johnston, 

 1983; Pavez and Oyarziin, 1985; 

 Pizzaro and Yaiiez, 1985; Kailola et 

 al,, 1993; Annala and Sullivan, 

 1997). The closely related wreck- 

 fish, P. at7iericanus (Bloch and 

 Schneider, 1801) is found in the 

 North and South Atlantic Oceans, 

 Mediterranean Sea, southern In- 

 dian Ocean, and south-west Pacific 

 Ocean (Roberts, 1986; Sedberry et 

 al,, 1994) and supports fisheries 

 throughout its range (Sedberry et 

 al., 1994, 1996). 



The ability to age Polyprion spe- 

 cies is essential for proper manage- 

 ment of their widespread fisheries, 

 because it will enable determination 

 of growth rates, ages at maturity 

 and recruitment, longevity, and 

 natural mortality rates. Previous 

 attempts to age the two species have 

 had limited success. Age and growth 

 off, oxygeneios have been estimated 

 from otolith band counts in New 

 Zealand (McDougall, 1975) and 

 from scale annuli counts in Juan 

 Fernandez Island (Pavez and Oyar- 

 ztin, 1985). A study on the age and 



growth of P, americanus from the 

 north-west Atlantic is currently 

 underway (Sedberry et al., 1994, 

 1996; Manooch and PottsM. How- 

 ever, otolith bands have proven dif- 

 ficult to count in both species, scale 

 annuli are unreliable for older fish, 

 and the ageing techniques have not 

 been validated. 



In New Zealand, P. oxygeneios and 

 P. americanus are managed as a 

 single species-unit in the Quota Man- 

 agement System (QMS) (Paul and 

 Davies, 1988; Annala and Sullivan, 

 1997), Both species are fished com- 

 mercially and recreationally through- 

 out New Zealand, They are highly 

 sought after, but catches are rela- 

 tively low. Commercial landings of 

 both species combined peaked at 

 2700 t in 1983-84, but since the in- 

 troduction of the QMS, they have 

 been constrained by quotas to less 

 than 1500 t per year (Annala and 

 Sullivan, 1997), Despite these quo- 

 tas, commercial line and set-net 

 fisheries for Polyprion species have 

 been seasonally important for small 

 inshore fishing vessels in many parts 

 of New Zealand. Annual recreational 

 landings were about 500 t in 1991- 

 94 (Annala and Sullivan, 1997), 



This paper addresses age and 

 growth in New Zealand P. oxy- 



Manooch, C. S., and J. Potts. 1997. Na- 

 tional Marine Fisheries Service, 101 Pivers 

 Island Rd, Beaufort, NC 28516. Personal 



commun. 



