SHENKER: OCEANOGRAPHIC ASSOCIATION OF NEUSTONIC MEROPLANKTON 



38.8 mm (A^ = 10) in early April to 51.2 mm 

 {N = 72) during the first June cruise. 



Brown Irish lord juveniles were the numeri- 

 cally most abundant and the second most fre- 

 quently occurring species (Table 1). Early juve- 

 niles (10-20 mm) were taken with both nets in 

 April and May only at the offshore (40-50 km) 

 stations. Larger juveniles (20-30 mm) were 

 patchily distributed from April through mid-June 

 all along the transect (CD. = 14.1). Although 

 47% of the total number of trawl caught speci- 

 mens were taken in densities below 15/1,000 m-^, 

 repeated sampling in one large aggregation ac- 

 counted for the bulk of the catch. Three sequen- 

 tial tows at the 50 km station on 5 May had juve- 

 nile densities of 15-39/1,000 m*^ , but distinctive 

 hydrographic characteristics at the station were 

 not detected. 



The only species with a characteristic offshore 

 distribution prior to upwelling was sablefish, 

 Anoplopoma fimbria. Small juveniles (10-45 

 mm) were effectively taken by the Manta net, 

 while the neuston trawl was more efficient at col- 

 lecting 30-70 mm specimens (Fig. 6c). The 10-50 

 mm fish were collected primarily at the 50 km 

 station from April through mid-June, although 

 several specimens were taken closer inshore. The 

 50-75 mm fish were captured only on 8-10 June 

 from the Columbia River plume water at the 50 

 km station. After the onset of upwelling, two indi- 

 viduals ( 120-130 mm) were taken 80-90 km from 

 shore. 



Upwelling Species 



Three taxa were abundant on only one of three 

 cruises made after the onset of upwelling in mid- 

 June (Table 1). Distributions of northern an- 

 chovy, Engraulis mordax, larvae; rockfish (Se- 

 bastes spp.) larvae; and adult blue lanternfish, 

 Tarletonbeania crenularis, overlapped at some 

 offshore stations on 8 and 9 July. The offshore 

 portion of the transect was characterized by a 

 drop in salinity and an increase in temperature 

 between 60 and 70 km offshore (Fig. 5a, b), indi- 

 cating a transition from coastal to Columbia 

 River plume water. 



Of the 814 rockfish larvae collected throughout 

 the survey, 87% were taken at the 50-90 km sta- 

 tions on this cruise, with a peak density of the 

 3.5-7.0 mm larvae of 684/1,000 m^. Adult blue 

 lanternfish were present in densities up to 315/ 

 1,000 m"^ at the 60-90 km stations. Lanternfish 

 from simultaneous Manta and neuston trawl tows 



displayed no difference in length-frequency dis- 

 tributions, although a significant change in the 

 size structure of the catches between stations was 

 observed (K-S test, P < 0.01). Mean size of the 

 fish decreased approximately 10% between adja- 

 cent stations, from 50.9 mm at 60 km to 37.8 mm 

 at 90 km. Anchovy larvae (3-9 mm) were re- 

 stricted to the lower salinity plume water at the 

 70-90 km stations, with peak and mean densities 

 of 368 and 210/1,000 m^, respectively. 



Persistant Species 



Only northern ronquils, Ronquilus jordani, 

 were abundant in both pre-upwelling and up- 

 welling periods. The elongate larvae and juve- 

 niles were collected with the Manta net starting 

 in mid-April, with abundances peaking at 40/ 

 1,000 m*^ in July. Mean lengths over this time 

 interval increased from 8.7 mm (n = 8) to 26.6 

 mm (n = 43). Ronquils were relatively dispersed 

 along the transect (CD. = 7.6), and size or sea- 

 sonal patterns of distribution were not detected. 



Dungeness Crab Megalopae 



Dungeness crab megalopae were the dominant 

 component of the catches throughout the survey, 

 with an estimated total of 350,000 megalopae col- 

 lected in 249 hauls. The megalopae were found at 

 most stations during all cruises (Fig. 7), although 

 they were rare seaward of 50 km in July. Megalo- 

 pae were present in 71.4% of the Manta net day- 

 time tows and 93.8% of the nighttime tows, and in 

 90.9% and 98.9% of the day and night neuston 

 trawl collections, respectively. All twilight hauls 

 captured megalopae. 



Despite the higher frequency of occurrence of 

 megalopae in the neuston trawl, the Manta net 

 was a more accurate estimator of their abun- 

 dance. For 58 pairs of nighttime catches with den- 

 sities under 2,000/1,000 m-^, the Manta net caught 

 approximately 3 times as many megalopae per m^ 

 as the neuston trawl. The 4.8 mm mesh of the 

 neuston trawl apparently enabled some megalo- 

 pae to pass through the mesh, and some escape- 

 ment was observed while the trawl was sitting on 

 deck after retrieval. More similar estimates be- 

 tween the nets were obtained when higher densi- 

 ties of megalopae were sampled, probably because 

 of clumping of the large (11 mm total length) 

 spiny megalopae into large masses which clogged 

 the mesh. 



In general, densities of megalopae caught by 



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