Lehodey et al.: Modelling the distribution of Beryx splendens 



751 



ing two other commercial cruises conducted by the 

 longliners Hokko Maru and Fukuju Maru, observers 

 recorded the maximum and minimum depths reached 

 by the longline 7 - 8 (Fig. 3D). 



Fork length (FL) was measured on a total of 14,674 

 alfonsino. During the commercial fishing trips, fish 

 to be measured were randomly sampled from each 

 set. When there were only a few fish, they were all 

 measured. As the samples varied in size between sets, 

 the length-frequency distribution of all the alfonsino 

 caught was estimated by multiplying the number in 

 the sample by the ratio of the total number of 

 alfonsino caught to the total number of alfonsino 

 measured for each longline set. During several sci- 

 entific cruises all of the fish were measured. 1 Because 



7 Anonymous. 1988. Rapport de la campagne de peche a la 

 palangre profonde dans la zone economique de la Nouvelle- 

 Caledonie. Hokko Maru 107: fevrier-mai 1988. Territoire de 

 Nouvelle-Caledonie, Service Territorial de la Marine Marchande 

 et des Peches Maritimes, 57 p. 



8 Laboute, P. 1989. Mission d'observation halieutique sur le 

 palangrier japonais Fukuju Maru du 21 nov. au 12 dec. 1988, 

 Noumea. ORSTOM Rapp. Missions, Sci. Mer Biol. Mar. 2, 15 p. 



all the depth zones were not sampled in the same way, 

 catch per unit of effort (CPUE=number offish caught 

 per 100,000 hooks) was taken as the abundance index. 

 The data collected during the Humboldt cruise was 

 used to model the distribution of CPUE in terms of 

 length and depth over seamounts. The models were 

 validated with data generated by the scientific 

 cruises and with data collected on board the two ad- 

 ditional commercial boats, Hokko Maru and Fukuju 

 Maru. These commercial data are less precise be- 

 cause only maximum and minimum longline depths 

 were recorded. 



Preliminary data analysis 



Table 1 shows the mean fork length by depth zone 

 for each seamount sampled during the Humboldt 

 cruise. This table suggests a significant increase in 

 mean length with depth on each seamount. In order 

 to model this increase, the data must be as repre- 

 sentative as possible of the fish population over its 

 depth range. For this reason, only data recorded for 

 seamounts B and J were used for modelling the in- 

 crease in length with depth. 



