RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE 



1972, sometimes by an order of magnitude (Figure 

 5). These differences are exemplified further by 

 the mean standardized number of larvae per tow 

 (Table 7). 



In March- April, five of the six dominant (BI 5* l) 

 taxa were more abundant in 1971 than 1972 (Ta- 

 ble 7). The exception was Sebastes spp., which was 

 6.5 times more abundant in 1972 based on mean 

 standardized number per tow. The greatest de- 

 crease occurred for P. vetulus, which was 24.9 

 times more abundant in 1971. The low numbers of 

 P. vetulus in 1972 may have been partly due to an 

 early spawning; small larvae were taken as early 

 as September and October 1971 (Table 6) and 

 many larvae may have settled out by the March- 

 April 1972 period. Or 1972 may have been a year 

 of reduced larval survival for P. vetulus. Am- 

 modytes hexapterus was also more abundant in 

 1971 with 12.2 times more larvae being taken 

 than in 1972. Dominance shifted fromP. vetulus in 



1971 to the Osmeridae in 1972 even though os- 

 merids were less abundant in 1972 than 1971. The 

 number of taxa taken was similar each year 

 although the species richness value was higher in 



1972 (Table 7). 



During the May-July period, the five dominant 

 taxa were all more abundant in 1971 than in 1972 

 (Table 7). The largest decline occurred in M. 

 proximus where 13.5 times more larvae were 

 taken in 1971. Osmerids were 10.6 times more 

 abundant in 1971. Their decline in numbers had a 

 major impact on overall abundance in 1972. In 

 1971, an average of 143 osmerids were taken per 

 tow and they contributed 71% to the total larval 

 abundance. While still the dominant taxon in 

 May-July 1972, they were less abundant and 

 made up 57% of the total. Considerably fewer 

 taxonomic groups were taken in 1972. This may 

 have been a result of fewer samples taken and a 

 corresponding reduction in numbers of rare taxa. 



TABLE 7. — Comparison of data on larval fishes collected off Oregon in 1971 and 1972. 

 [BI = Biological Index modified from Fager (1957)]. 



Taxa 



(dominants 



listed separately) 



No. samples 



BI 



1971 



1972 



Mean no./ 10 m 2 



1971/1972 



% total abundance 

 1971 1972 



Species richness 

 (D =S - 1/ln N) 



1971 



1972 



March-April 2-28 km 12 22 



Parophrys vetulus 

 Isopsetta isolepis 

 Ammodytes 



hexapterus 

 Microgadus proximus 

 Osmeridae 

 Sebastes spp. 

 All other species 



Total (41 in 1971; 

 48 in 1972) 



May-July 2-28 km 34 20 



Osmeridae 

 Isopsetta isolepis 

 Microgadus proximus 

 Lyopsetta exilis 

 Artedius sp. 1 

 All other species 

 Total (46 in 1971; 



24 in 1972) 



March-April 37-111 km 

 Sebastes spp. 

 Stenobrachius 



leucopsarus 

 Tarletonbeania 



crenularis 

 Hemilepidotus 



spinosus 

 All other species 



Total (16 in 1971; 

 16 in 1972) 



May-July 37-111 km 38 28 



Stenobrachius 



leucopsarus 

 Sebastes spp. 

 Lyopsetta exilis 

 Tarletonbeania 



crenularis 

 Engraulis mordax 

 All other species 



Total (32 in 1971; 



25 in 1972) 



16 



20 



44.40 



33.80 



24.90 

 3.85 



12.20 

 2.64 

 1.34 

 0.16 

 3.12 



3.36 



10.60 

 8.10 



13.54 

 6.24 

 2.37 

 3.78 



8.59 



0.89 



4.46 



5.44 



0.52 

 4.56 



1.31 



100.0 



100 



5.24 



6.41 



4.94 



3.30 



2.52 



248 



3.66 



3.35 



— 175.30 



76.98 



2.27 



100.0 



100.1 



137 



