Abstract. — Commercial and 

 scientific bottom longline catches of 

 alfonsino, Beryx splendens, from 

 seamounts off New Caledonia were 

 sampled to study length-frequency 

 distributions. A total of 14,674 fish 

 were measured. CPUE of Beryx 

 splendens on two seamounts is mod- 

 elled in terms of length and depth. 

 The data show that mean length in- 

 creases with depth; this is well de- 

 scribed by a bivariate normal model 

 that estimates catch for a given sea- 

 mount. In addition, the data show 

 that mean length also varies with 

 the depth of the top of seamounts; 

 this is described by a recursive 

 model that is designed to predict ap- 

 proximate catch for any seamount. 

 The limitations of both models are 

 discussed, particularly with regard 

 to temporal variation. 



Modelling the distribution of 

 alfonsino, Beryx splendens, over 

 the seamounts of New Caledonia 



Patrick Lehodey 

 Paul Marchal 

 Rene Grandperrin 



Centre ORSTOM, BPA5, Noumea. New Caledonia 



Manuscript accepted 31 March 1994. 

 Fishery Bulletin 92: 748-759. 



A bottom longline fishery operated 

 on the seamounts of the Exclusive 

 Economic Zone (EEZ) of New Cale- 

 donia from February 1988 to July 

 1991. ' Three vessels were involved 

 but only one vessel was operated at 

 any given time. The fishing effort, 

 which totalled 4,691,635 hooks, fo- 

 cused on five seamounts (B, C, D, 

 J, and K) whose summits are lo- 

 cated at depths ranging from 500 

 to 750 m (Fig. 1 ). The target species, 

 alfonsino, Beryx splendens, ac- 

 counted for 92% of the catch by 

 weight. This species has a world- 

 wide distribution, from the equator 

 to the temperate latitudes, and is 

 fished by bottom trawl or longline. 

 Alfonsino generally occupies waters 

 between 200 and 800 m, although 

 it has been caught at depths of only 

 25 m and as deep as 1,240 m 

 (Busakhin, 1982). Some authors 

 have noted an increase in mean 

 length with depth 2 (Yamamoto et 

 al., 1978, Seki and Tagami, 1986), 

 a trend which has been observed in 

 other fishes (Heincke, 1913), par- 

 ticularly some deep-water demersal 

 species 3 ' 4 - 5 (Ralston and Williams, 

 1988). There have been few studies 

 relating the size distribution of 

 alfonsino to depth. The objective of 

 this paper is to describe an ap- 

 proach for estimating the abun- 

 dance of alfonsino by modelling its 

 distribution in terms of fork length 

 and depth of capture. A bivariate 

 normal model describes this distri- 

 bution for a given seamount and a 



recursive model predicts catch on 

 any seamount. 



Material and methods 



Data 



Alfonsino were captured with long- 

 line gear (Fig. 2). The main line, 

 averaging 4,000 m, was held on the 

 bottom by means of terminal an- 

 chors and regularly spaced heavy 

 sinkers that delimited five equal 

 line sections. During a fishing trip 



1 Grandperrin, R., and P. Lehodey. 1993. 

 Etude de la pecherie de poissons profonds 

 dans la zone economique de Nouvelle- 

 Caledonie. Rapport final. Contrat de re- 

 cherche ORSTOM /Territoire de Nouvelle- 

 Caledonie. Noumea: ORSTOM, Conv. Sci. 

 Mer, Biol. Mar. 9, 321 p. 



2 Masuzawa, T., Y. Kurata, and K. Onishi. 

 1975. Results of group study on population 

 of demersal fishes in water from Sagami 

 Bay to the southern Izu Islands — popula- 

 tion ecology of Japanese alfonsin and other 

 demersal fishes. Japan Aquatic Resources 

 Conserv. Assoc. Fish. Res. Paper 28, 105 

 p. (English translation held at Fisheries 

 Research Centre Library, MAF, P.O. Box 

 297, Wellington]. 



:t Brouard, F, and R. Grandperrin. 1985. 

 Deep bottom fishes of the outer reef slope 

 in Vanuatu. South Pacific Commission 

 17th Regional Technical Meeting on Fish- 

 eries, W P 12, 127 p. 



4 Clark, M. R., and K. J. King. 1989. Deep- 

 water fish resources off the North Island, 

 New Zealand: results of a trawl survey, 

 May 1985 to June 1986. N.Z. Fish. Tech. 

 Rep. 11, 55 p. 



5 Dalzell, P., and G. L. Preston. 1992. Deep 

 reef slope fishery resources of the South 

 Pacific. South Pacific Comm. Inshore Fish. 

 Res. Project. Tech. Doc. 2, 299 p. 



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