DOYLE: NEUSTONIC ICHTHYOPLANKTON 

ColCOFl Rep., Vol. 33,1992 

NEUSTONIC ICHTHYOPLANKTON IN THE NORTHERN REGION OF THE CALIFORNIA 

CURRENT ECOSYSTEM 

MIRIAM J DOYLE’ 

Department of Fisheries and Wildlife 

Oregon State University 

Corvallis, Oregon 97331-3803 

ABSTRACT 

Analysis of ichthyoplankton data collected off 

Washington, Oregon, and northern California during the 1980s indicates a neustonic assemblage offish 

eggs, larvae, and juveniles. This assemblage is most 

diverse over the shelf and continental slope. Diel 

variation in the occurrence and abundance of certain 

species of fish larvae in the neuston samples is striking. Three categories are apparent among the neustonic ichthyoplankton. Obligate members include 

larvae and early juveniles of nine species that occurred permanently and almost exclusively in the 

neuston but were scarce or absent in subsurface samples. Other taxa of larvae and juveniles were abundant at the surface only at night and are identified as 

facultative members of the neuston. Several taxa of 

fish eggs were abundant in the neuston; they seem to 

accumulate at the surface because of positive buoyancy. They are considered strays in the neuston. 

Fish larvae in the neuston were larger overall than 

those deeper in the water column; this is advantageous in terms of seeking prey and avoiding predators. Juveniles were also common in the neuston, 

but recently hatched larvae were largely absent. 

Several factors may limit the successful habitation 

of the neuston by fish eggs and larvae: high levels of 

damaging UV radiation, intensive wave action, a 

reduced biota, enhanced visibility to predators, and 

larval dispersal. However, adaptations to these potentially adverse factors are apparent among the species. Advantages to a neustonic existence may 

include enhanced growth, reduced levels of predation, and suitable concentrations of food. The main 

reason that larvae and juveniles of certain species 

select the neuston as a suitable ecological niche is 

probably the unique trophic conditions that prevail 

in this biotope. 

RESUMEN 

Andisis de datos de ictioplancton colectados en 

las costas de Washington, Oregon y en el norte de 

‘Present address: National Marine Fisheries Service, Alaska Fisheries Science 

Center, 7600 Sand Point Way, NE, Seattle, Washington 98115-0070 

[Manuscript received February 10,1992.1 

California durante la dtcada del 80 sefiala la existencia de un grupo neustonico de huevos de peces, larvas y juveniles. Este grupo tiene mAxima diversidad 

sobre la plataforma y el tal~d continental. La variaci6n diurna en la ocurrencia de algunas especies de 

peces en el neuston es sorprendente. El ictioplancton 

neust6nico puede dividirse en tres categorias. 

Miembros obligados, que incluyen larvas y juveniles tempranos de nueve especies que ocurren permanente y casi exclusivamente en el neuston, per0 

escasos o ausentes en las muestras sub-superficiales. 

Otro grupo de taxa de larvas y juveniles fut abundante en la superficie s610 de noche y se identifican 

como miembros facultativos del neuston. Varios 

taxa de huevos de peces fueron abundantes en el 

neuston donde aparentemente se acumulan debido a 

que poseen flotaci6n positiva; se considera que este 

es un grupo “extraviado” en el neuston. 

Las larvas de peces en el neuston fueron mas 

grandes que las encontradas a mayor profundidad en 

la columna de agua; se considera que esto es ventajoso a1 buscar presas y evitar depredadores. Los juveniles tambiCn se encontraron a menudo en el 

neuston, contrastando con larvas de reciente eclosion, quienes estuvieron ausentes. 

Varios factores podrian limitar a1 neuston como 

un hAbitat exitoso para el ictioplancton: altos niveles 

de radiaci6n ultravioleta, oleaje intenso, una biota 

disminuida, mayor visibilidad para 10s depredadores 

y dispersidn larval. Sin embargo, las especies muestran adaptaciones a esos factores adversos. Las ventajas de una existencia neust6nica incluirian mayor 

crecimiento, menores niveles de depredacih y concentraciones de aliment0 adecuadas. La raz6n principal por la cual larvas yjuveniles de algunas especies 

eligen a1 neuston como un nicho ecol6gico conveniente estriba probablemente en las condiciones trbficas tinicas que prevalecen en este biotopo. 

INTRODUCTION 

A diverse assemblage of planktonic organisms occurs in the uppermost surface layer (10-20 cm) of 

the oceans and is collectively referred to as the neuston (Zaitsev 1970; Peres 1982). The composition and 

abundance of neustonic organisms vary consider141 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

ably, both geographically and temporally. In general, concentrations of neuston are higher in neritic 

areas than in the open ocean at the same latitudes 

(Hempel and Weikert 1972; Peres 1982). Holdway 

and Maddock (1983a) also showed that tropical and 

subtropical neritic and upwelling areas supported 

greater concentrations of neuston than oceanic and 

boreal zones. Diel variation in occurrence and abundance of organisms in the neuston is well documented. Although many members of the neuston 

are permanently present in the surface zone (obligate 

members), a diverse range of organisms concentrates at the surface only during certain hours (facultative members), mostly at night (Zaitsev 1970; 

Hempel and Weikert 1972; Peres 1982; Holdway and 

Maddock 1983a, b). 

Fish eggs, larvae, and juveniles are abundant in 

the neuston, which is considered an important nursery ground for the early stages of many fish (Zaitsev 

1970; Hempel and Weikert 1972; Moser 1981; Peres 

1982). Although eggs of various fish species concentrate in the neuston, essentially because of their positive buoyancy, larvae and juveniles actively migrate 

to the surface zone and may be obligate or facultative 

members of the neuston. The importance of the 

neustonic realm in the ontogeny and ecology of larval fish populations varies with geographical area 

and local conditions. Factors such as latitude, surface 

water temperature, water depth, nutrient concentration, and upwelling all affect the diversity, age 

structure, and vertical migratory patterns of fish larvae in an area (Hempel and Weikert 1972; Tully and 

O'Ceidigh 1989a). 

Several studies of planktonic neuston in the northeast Pacific were carried out during the 1970s and 

1980s. Most were for the purpose of documenting 

fish larvae in the neuston. Richardson (1975) made a 

preliminary report on the occurrence and abundance 

of fish larvae and juveniles in the neuston along an 

east-west transect off the mid-Oregon coast. Ahlstrom and Stevens (1976) documented species composition and abundance of fish larvae in the neuston 

and in the water column over an extensive area of 

the northeast Pacific, including the coastal and 

oceanic zone from northern Washington to southern 

Baja California. In their account of the distribution 

of ichthyoplankton in the Southern California 

Bight, Gruber et al. (1982) compared the occurrence 

of larvae in neuston tows with their occurrence in 

oblique tows. These studies established that many 

species of fish larvae are abundant in the surface zone 

as well as deeper in the water column but that an 

additional group of species is almost exclusively 

neustonic. Brodeur et al. (1987) and Brodeur (1989) 

examined species composition and abundance of fish 

larvae and invertebrate components of the neuston 

in coastal waters of the northeast Pacific as part of a 

study ofjuvenile salmonids' feeding habits. Shenker 

(1985, 1988) was the first to carry out a biological 

and ecological investigation of neustonic larval and 

juvenile fishes in the northeast Pacific. That study, 

however, was restricted to a single transect of stations off the Oregon coast. 

From 1980 to 1987, a series of cooperative U. S. / 

U. S. S.R. ichthyoplankton surveys was conducted 

off the U.S. west coast from 48"N to 40"N (Dunn 

and Rugen 1989). These surveys were designed to 

determine spatial and temporal patterns in the ichthyoplankton. The neuston as well as the water column fauna was sampled, and hydrographic data 

were collected. Preliminary results from these surveys were given in Kendall and Clark 1982a, b; 

Clark 1984, 1986a, b; Bates 1984; Clark and Kendall 

1985; Clark and Savage 1988; and Savage 1989a, b. 

These data made it possible to investigate the occurrence and ecology of fish eggs and larvae in the neuston over a large area and in comparison with their 

occurrence deeper in the water column. 

In this investigation, species composition and 

relative abundance are documented, as are lengthfrequency distributions of larvae and diel variation 

in their occurrence and abundance in the neuston. 

Different categories of neustonic ichthyoplankton, 

such as obligate and facultative members, are identified. Horizontal patterns of distribution are described for the numerically dominant neustonic 

taxa. The ecological significance of a neustonic existence for early life stages of these fish is also 

discussed. 

MATERIALS AND METHODS 

The cooperative ichthyoplankton surveys conducted offthe U. S. northwest coast during the 1980s 

involved the U. S. Northwest and Alaska Fisheries 

Center in Seattle, and the U. S.S.R. Pacific Research 

Institute in Vladivostok. Over a period of seven 

years, ten cruises were made. During each cruise, a 

maximum of 125 stations was occupied (table 1). 

Seasonal coverage was limited: six of the ten cruises 

were made in spring (March to early June); one 

cruise in summer (August 1980); one in winter (January 1987); and two in autumn (October-November 

1981 and November-December 1983). The station 

grid covered an area of approximately 249,000 km2 

off Washington, Oregon, and northern California. 

Stations were more closely spaced over the shelf and 

slope than in deep water west of the 1,000-m isobath 

(figure 1). 

142 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

TABLE 1 129 OOY 127 OOY 12s oou 123 OOY 

Sampling Schedule and Number of Stations Sampled 

for Ichthyoplankton 

Cruise 

TK80 

PO80 

PO81 

DA81 

PO82 

EQ83 

MF83 

PO84 

BA85 

MF87 

Vessel 

Tikhookeanski 

U.S.S.R. 

Poseydon 

U.S.S.R. 

Poseydon 

U.S.S.R. 

Mys Dalniy 

U.S.S.R. 

Poseydon 

U.S.S.R. 

Equator 

U. S. S.R. 

Miller Freeman 

U.S.A. 

Poseydon 

U. S. S.R. 

Mys Babyshkina 

U. S. S.R. 

Miller Freeman 

U.S.A. 

Cruise dates 

Apr. 20-May 15,1980 

Aug. 1-20.1980 

May 9-June 2,1981 

Oct. 24-Nov. 19,1981 

May 3-June 1,1982 

Apr. 23-May 15, 1983 

Nov. 11-Dec. 2,1983 

Mar. 11-Apr. 4, 1984 

Apr 19-May 11,1985 

Jan. 7-31,1987 

~~~~ 

Stations occuDied 

Neuston 

tows 

Bongo 

tows 

125 

91 

123 

125 

124 

124 

113 

124 

124 

88 

125 

91 

123 

125 

49 

124 

113 

124 

124 

88 

Total number of stations occupied 1161 1086 

During each cruise, plankton was sampled for fish 

eggs and larvae, and hydrographic casts were made 

to determine temperature and salinity at all stations. 

Water samples were collected with Niskin bottles at 

nominal depths ofO, 5, 10, 15, 20, 25, 30, 35, 50, 75, 

100, 200, 250, and 300 m, as depth permitted. For 

10 minutes at each station, paired neuston tows were 

made with Sameoto samplers (Sameoto and Jaroszynski 1969) with 0.3-m-high-by-0.5-m-wide 

frames and 0.505-mm mesh netting. The samplers 

were towed at a speed of 2.0 knots and sampled 

approximately the upper 15 cm of the water column. 

Following standard procedures, oblique tows to 

200-m depth, or 5 m from the bottom in water shallower than 200 m, were carried out at each station. 

For these tows, 60-cm-frame bongo samplers fitted 

with 0.505-mm-mesh nets were used (Smith and 

Richardson 1977). Flowmeters in the mouths of the 

samplers were used to determine the volume of 

water filtered by each net. 

The plankton samples were preserved in a 5% 

buffered Formalin solution. One of each of the 

paired neuston and bongo samples was retained by 

the Americans and the other by the Soviets. The 

American plankton samples were processed by the 

Polish Plankton Sorting Center in Szczecin, Poland, 

and subsequently by the Northwest and Alaska 

Fisheries Center, Seattle. Fish eggs and larvae were 

removed from the samples, identified to the lowest 

taxonomic level possible, counted, and measured. 

48 001 

47 001 

40 OW 

45 OON 

44 OW 

43 oow 

42 OOW 

41 OOll 

40 OW 

39 oow 

+++ 

+++ 

++++ 

++++ 

++++ 

++++ 

+++++ 

++++ 

++++ 

++++ 

+++ 

I CA 4 inc 

12) mu 127 OOU 125 OOY 125 oou 

Figure 1. Survey area, sampling stations, and bathymetry off the US. west 

coast. 

Counts of fish eggs and larvae were converted to 

numbers per 10 m2 of sea-surface area for the bongo 

samples and numbers per 1000 m3 for the neuston 

samples. 

OCEANOGRAPHIC ENVIRONMENT 

The oceanography of the survey area is characterized by the California Current system, a typical eastern boundary current regime (Hickey 1979, 1989). 

The main California Current is slow, meandering, 

broad, and indistinct, and it proceeds southwards 

along the U. S. west coast (figure 2). Subcomponents 

of the California Current include the northwardflowing California Undercurrent and Davidson 

Current (Hickey 1989). The California Undercurrent consists of a jetlike poleward flow with a subsurface maximum. Its core appears to be confined to 

143 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

130" 120"W 

30" - 

1 I I I I 

130" 120"W 

CC = CALIFORNIA CURRENT 

DC = DAVIDSON CURRENT 

SCC = SOUTHERN CALIFORNIA 

COUNTERCURRENT 

SCE = SOUTHERN CALlFORNlA EDDY 

130" 120"W 

50" 50" - 

- 

30" 30"- 

N N 

11 1 I I I 

1 30° 120"W 

130" 120"W 

50" 

40" 

30" 

N 

Figure 2. Seasonal variation in deep-ocean boundary currents off the US. west coast: Col. R. = Columbia River; CB = Cape Blanco; 

CM = Cape Mendocino; PC = Point Conception. From Hickey 1989. 

the continental slope. The northward-flowing Davidson Current that prevails on the coastal side of 

the California Current during winter is a seasonal 

surface current (figure 2). 

Coastal surface currents in this region are primarily wind-driven, with strong seasonal variability 

(Huyer et al. 1975; Hickey 1979; Strub et al. 1987). 

Spring and autumn transitions in prevailing winds 

and associated coastal currents are driven by largescale changes in atmospheric pressure systems over 

the North Pacific. In winter, southerly winds result 

in the northward-flowing Davidson Current, onshore Ekman transport of surface water, and downwelling close to the coast. In spring the winds shift 

from southerly to northerly, and by summer the 

prevailing conditions include a southward-flowing 

coastal current, offshore Ekman transport, and 

upwelling of cold oceanic water close to the coast. 

The autumn transition from northerly to southerly 

winds leads back to the winter conditions. 

The intensity of Ekman transport and associated 

upwelling varies along the coast. Mean monthly upwelling indices (derived from geostrophic wind 

stress; Bakun 1973) for four locations along the 

125"W meridian - from northern Washington to 

northern California - show that the extent and intensity of upwelling increases from north to south 

(figure 3). Off Washington and northern Oregon, 

the upwelling season is confined largely to summer, 

whereas winter is characterized by vigorous downwelling. Along the northern California coast, winter downwelling is weaker and less extensive, and 

144 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

ColCOFl Rep., Vol. 33,1992 

Upwelling Indices (m3/s/100m coastline) 

250 1 I 

- 48N 125W + 45N 125W +++ 42N 125W 4 39N 125W 

Figure3. Monthly upwelling indices (Bakun 1973), mean of years 1946 to 1989, 

for four locations along the west coast. 48N = northern Washington; 45N = 

northern Oregon; 42N = Oregon/California border; 39N = northern 

California. 

summer upwelling indices are considerably higher 

than off Washington and northern Oregon. The region of maximum upwelling along the U.S. west 

coast is between Cape Blanco in southern Oregon 

and Point Conception in southern California, with 

a local maximum at Cape Mendocino (Parrish et al. 

1981). 

The oceanography of waters off the U.S. northwest coast is modified significantly by the Columbia 

River, which divides the Washington and Oregon 

coastal regions (Hickey and Landry 1989). The Columbia River is the largest point source of freshwater flow into the eastern Pacific Ocean, and its water 

forms a low-salinity plume that extends outwards 

from the river mouth above a shallow halocline (<20 

m; Fiedler and Laurs 1990). The extent and orientation of the plume is variable and subject to seasonal 

changes in runoff (peak period in June) and coastal 

circulation patterns. 

RESULTS 

Species Composition and Relative A bundance 

Both fish eggs and larvae were abundant in neuston samples, but species diversity was lower than in 

the bongo samples. Twenty-five species of eggs representing 17 families were identified from neuston 

samples (table 2). In addition, three identifications 

were to generic level and five to family level. In 

terms of percentage occurrence and mean abundance in all samples, Engvaulis movdax, Tvachiptevus 

altivelis, Icichthys lockingtoni, the paralichthyids, and 

the pleuronectids dominated. The paralichthyids 

(Citharichthys spp.) were outstandingly abundant, 

with a mean density of 389 eggs per 1000 m3, even 

though they occurred in only 27% of neuston samples. The mesopelagic species Chauliodus macouni 

and Icosteus aenigmaticus were moderately abundant 

but occurred in approximately 10% of all samples. 

Taxonomic diversity was higher for larvae in the 

neuston samples. Forty-six species were identified 

in a total of 24 families (table 3). Among the nine 

identifications to generic level, Sebastes spp., representing numerous rockfish, was most important. 

Species composition, and particularly relative abundance, differed greatly from that recorded for eggs 

in the neuston. Engvaulis movdax was the only species 

for which both eggs and larvae were abundant. Although paralichthyid and pleuronectid larvae appeared in the neuston samples, occurrence and 

abundance were very low in comparison with their 

eggs. The numerically dominant taxa of larvae in 

the neuston included Engvaulis movdax, Cololabis 

saiva, Sebastes spp., Anoplopomajmbvia, Hexagvammos 

decagvammus, Hemilepidotus spinosus, and Scovpaenichthys mavmovatus. Less abundant, but also well represented, were Tavletonbeania cvenulavis, Hexagvammos 

lagocephalus, Ophiodon elongatus, Hemilepidotus hemilepidotus, Ronquilus jovdani, Cvyptacanthodes aleutensis, 

and Ammodytes hexaptevus. 

Eggs of all species that were prominent in the 

neuston were also prominent in subsurface bongo 

samples (tables 4 and 5). Except for Engvaulis movdax, 

larvae of the same species were absent or scarce in 

the neuston, but were generally prominent in the 

bongo collections. It seems, therefore, that species 

of fish eggs that are abundant in the neuston accumulate passively at the surface and on hatching into 

larvae migrate downwards into the subsurface zone. 

In contrast, many of the larval species that were 

abundant in the neuston were absent or scarce in the 

bongo samples and therefore may be considered almost exclusively neustonic (obligate members of the 

neuston). These include Cololabis saira, Anoplopoma 

_fimbria, the hexagrammids, the cottids, and Cvyptacanthodes aleutensis. Because their eggs were absent 

from the neuston (table 2), these larvae must actively 

migrate to, and remain in the surface zone. Ronquilus 

jordani and Ammodytes hexapterus were recorded frequently in the bongo samples, although they were 

not abundant. Their incidence of occurrence in neuston samples was, however, higher than in the bongo 

samples. These larvae are considered to be more facultative than obligate neustonic types. The remaining taxa that were prominent in the neustonincluding Engvaulis movdax, Tavletonbeania cvenulavis, 

and Sebastes spp. -were also abundant, and had a 

higher incidence of occurrence, in the bongo samples, which indicates that they are essentially facultative in the neuston. 

145 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

TABLE 2 

Percentage Occurrence and Mean Abundance of All Taxa of Eggs in Neuston Samples Collected during All Cruises 

Family 

Unidentified 

Engraulidae 

Argentinidae 

Bath ylagidae 

Chauliodontidae 

Melanostomidae 

Myctophidae 

Gadidae 

Scom beresocidae 

Trachipteridae 

Scorpaenidae 

Carangidae 

Icosteidae 

Ammodytidae 

Centrolophidae 

Tetragonuridae 

Paralichthyidae 

Pleuronectidae 

Species 

Engraulis mordax 

Unidentified 

Nansenia candida 

Nansenia crassa 

Unidentified 

Bathylagus spp. 

Bathylagus orhotensis 

Chauliodus macouni 

Tactostoma macropus 

Unidentified 

Merluccius productus 

Theragra chalcogramma 

Cololabis saira 

Unidentified 

Trachipterus altivelis 

Sebastolobus spp. 

Trachurus symmetricus 

Icosteus aenigmaticus 

Ammodytes hexapterus 

Zcichthys lockingtoni 

Tetvagonurus cuvieri 

Citharichthys spp. 

Unidentified 

Errex zachirus 

Hippoglossoides elassodon 

Pleuronectes isolepis 

Eopsetta exilis 

Microstomus pacificus 

Pleuronectes vetulus 

Platichthys stellatus 

Pleuronichthys coenosus 

Pleuronichthys decurrens 

Psettichthys melanostictus 

~~ -~ ~ ~~~~ ~~ 

- 

~. -~ 

Diel Variation in Catches of Larvae 

For larvae in the neuston, it is important to consider diel variation in catches, especially for the 

facultative members that are only occasionally 

abundant in the surface layer. The pattern of diel 

variation in total catches differs significantly between the two sampling gears (figure 4). There is 

very little variation over 24 hours for the bongo 

samples, whereas in the neuston, catches were considerably lower during daylight than at night. Between 0800 and 1900 hours, catches in the neuston 

were always <3% of total catch; from 2000 to 0600, 

catches per hour ranged from approximately 5% to 

12% of the total larval fish catch (figure 4a). Two 

possible factors may contribute to this diel pattern: 

(1) vertical migration of larvae into the neuston at 

night causes an increase in catches during darkness, 

and (2) enhanced avoidance of the neuston sampler 

during daylight reduces catches during the day. One 

or both of these factors may operate among the individual species of larval fish in the neuston. 

Oh occurrence Mean no./1000 m3 

(all samples) (all samples) ~~ ~. __~ ~ 

2.83 3.10 

2.74 32.28 

0.19 0.02 

0.28 0.04 

0.38 0.07 

1.51 0.60 

1.42 0.26 

0.28 0.04 

10.21 2.23 

2.65 4.88 

0.09 0.02 

0.09 0.01 

0.19 0.07 

1.04 2.70 

0.66 0.12 

39.98 37.77 

1.51 57.49 

0.19 0.08 

10.21 5.54 

0.09 0.02 

30.15 43.48 

0.47 0.13 

27.03 389.37 

10.40 76.18 

8.88 13.05 

0.57 0.13 

1.80 0.55 

5.86 4.13 

14.75 42.19 

3.50 3.13 

1.13 0.81 

0.76 0.17 

3.02 1.15 

4.44 3.43 ~______~___~_____~.~.- 

There was little variation in catches of Cololabis 

saiva over 24 hours, with only a slight reduction during daylight (figure 5a). Given that it occurred almost negligibly in the bongo samples (table 6), this 

species appears to be a permanent resident in the 

neuston. Anoplopoma fimbria larvae were less abundant in neuston samples during the day than at night 

(figure 5b), and their occurrence in bongo samples 

was, although low, higher than for Cololabis suivu 

(table 6). There may be some migration of these larvae 

out of the immediate surface zone during the day. 

The incidence of occurrence of hexagrammid larvae in bongo samples was very low (< 1 "/o) or, in the 

case of Hexagvummos lagocephulus, zero (table 6), implying that they are obligate neustonic species. Diel 

variation in catches, however, indicates that these 

larvae were slightly more abundant at night than 

during daylight (figure 5c-e). The cottid Hemilepidotus spitzosus, which accounted for approximately 

25% of all larvae caught in the neuston (table 6), was 

considerably more abundant in nighttime neuston 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

TABLE 3 

Percentage Occurrence and Mean Abundance of All Taxa of Larvae in Neuston Samples Collected during All Cruises 

Family Species 

O/O occurrence 

(all samplesj 

Mean no./1000 m3 

(all samples) 

Clupeidae 

Engraulidae 

Osmeridae 

Argentinidae 

Bathylagidae 

Myctophidae 

Merluccidae 

Gadidae 

Scomberesocidae 

Scorpaenidae 

Anoplopomatidae 

Hexagrammidae 

Cottidae 

Agonidae 

C yclopteridae 

Carangidae 

Bathymasteridae 

Stichaeidae 

Cr yptacanthodidae 

Pholidae 

Ammodytidae 

Centrolophidae 

Paralichthyidae 

Pleuronectidae 

Clupea harengus pallasi 

Engraulis mordax 

Unidentified 

Nansenia candida 

Unidentified 

Bathylagus spp. 

Bathylagus ochotensis 

Unidentified 

Ceratoscopelus townsendi 

Diaphus theta 

Lampanyctus regalis 

Protomyctophum crockeri 

Protomyctophum thompsoni 

Stenobrachius leucopsarus 

Symbolophorus calijorniense 

Tarletonbeania crenularis 

Merluccius productus 

Microgadus proximus 

Theragra chalcogramma 

Cololabis saira 

Unidentified 

Sebastes spp. 

Sebastolobus spp. 

Anoplopomafimbria 

Unidentified 

Ophiodon elongatus 

Pleurogrammus mouopterygius 

Hexagrammos spp. 

Hexagrammos decagrammus 

Hexagrammos lagocephalur 

Hexagrammos stelleri 

Unidentified 

Artediusfenestralis 

Artedius harringtoni 

Cottus asper 

Hemilepidotus hemilepidotus 

Hemilepidotus spinosus 

Leptocottus armatus 

Radulinus spp. 

Radulinus asprellus 

Scorpaenichthyr marmoratus 

Unidentified 

Unidentified 

Trachurus symmetricus 

Bathymaster spp. 

Ronquilus jordani 

Unidentified 

Delolepisgigantea 

Cryp tacanthodes aleu tensis 

Pholis spp. 

Ammodytes hexapterus 

Icichthys lockingtoni 

Citharichthys spp. 

Citharichthys sordidus 

Citharichthys stigmaeus 

Eopsetta jordani 

Errex zachirus 

Pleuronectes isolepis 

Microstomus pacifcus 

Pleuronectes vetulus 

Platichthys stellatus 

Pleuronichthys decurrens 

Psettichthys sp. 

Psettichthvs melanostictus 

0.58 

3.88 

1.23 

0.09 

0.09 

0.09 

1.13 

0.19 

0.09 

0.28 

0.09 

0.19 

0.09 

1.42 

0.19 

5.95 

0.09 

0.09 

0.09 

31.29 

0.09 

18.05 

0.09 

22.02 

0.19 

4.16 

0.19 

0.19 

19.01 

5.01 

0.09 

0.28 

0.28 

0.28 

0.09 

3.02 

13.14 

0.76 

0.09 

0.09 

16.54 

0.09 

0.94 

0.09 

0.19 

3.49 

0.09 

0.09 

1.42 

0.09 

4.06 

0.39 

0.57 

0.19 

1.51 

0.28 

0.09 

0.28 

0.19 

1.42 

0.19 

0.28 

0.09 

0.28 

0.19 

9.99 

1.07 

0.01 

0.02 

0.02 

0.25 

0.02 

0.02 

0.04 

0.02 

0.05 

0.01 

0.65 

0.03 

5.56 

0.02 

0.01 

0.01 

16.71 

0.19 

19.86 

0.05 

26.46 

0.14 

3.39 

0.04 

0.06 

15.16 

1.61 

0.04 

0.04 

0.08 

0.08 

0.01 

1.24 

40.84 

0.21 

0.16 

0.01 

8.38 

0.01 

0.16 

0.09 

0.03 

1.75 

0.22 

0.01 

1.83 

0.02 

7.11 

0.07 

0.44 

0.03 

0.24 

0.09 

0.43 

0.22 

0.03 

0.44 

0.02 

0.35 

0.01 

0.06 

147 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

TABLE 4 

Dominant Ichthyoplankton Taxa in Neuston and Bongo Samples Collected during All Cruises 

Family 

Engraulidae 

Osmeridae 

Bath ylagidae 

-- ~ 

Chauliodontidae 

Melanostomidae 

Myctophidae 

Scomberesocidae 

Trachipteridae 

Scorpaenidae 

Anoplopomatidae 

Hexagrammidae 

Cottidae 

Bathymasteridae 

Cryptacanthodidae 

Icosteidae 

Ammodytidae 

Centrofophidae 

Paralichthyidae 

Pleuronectidae 

Species ~~~~ ~~~~ ~~~ ~ 

E~igraiilis rnordax 

Unidentified 

Unidentified 

Bathylagrrs ochoterrsis 

Chariliodiis maroroii 

Tactosforna rnaeropits 

Unidentified 

Diaphiis theta 

Protoni yctopliiirn crockrri 

Protorn yctophiirn thotnpsoiii 

Tarletorrbearria crertrilaris 

Sle~iobrach iris /errcopsariis 

Cololabis saira 

Trachipterits altiivlis 

Sebastes spp. 

Arroplopoirmfirnbria 

Hexagrarnrnos decagrairinirrs 

Hexagramtnos iagoeephdirs 

Ophiodoir eloirgatiis 

Hemilepidotus hetnilepidottis 

Hernilepidottis spi~~osris 

Scorpaenirh th ys marrrioratrrs 

Roriqriiliisjordani 

Cryptacanthodes aleritensir 

Icosteus aeriigrnaticrrs 

Amrnodytes hexapterris 

Icichthys lockirrgtorii 

Citharichthys spp. 

Citharichtli ys sordidits 

Citharichthys stiginaerrs 

Unidentified 

Errex zachirtrs 

Eopsetta exilis 

Microstomus pacifitiis 

Pleiirorrectes iwtitliis 

Psettichthys melanostictiis 

Bathylaglts spp. 

Bath ylagrts pac.ifcrrs 

S~bflS~ll/fl/Jfts Spp. 

~ ~~~~ ~~ ~ ~~~~~ 

X 

Y 

Y 

X 

X 

X 

Y 

X 

X 

X 

Bongo ~~ -~ ~~ ~ 

Larvae Eggs ~ ~~ 

X X 

X 

X 

X 

X X 

X 

X X 

X X 

X 

Y 

X 

Y 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

TABLE 5 

Relative Abundance of Dominant Taxa of Eggs in Neuston Samples 

Family Species 

Engraulidae Engraulis rnordax 

Chauliodontidae Chauliodus maroutti 

Melanostomidae Tactostoma macroprrs 

Scomberesocidae Cololabis saira 

Trachipteridae Trachipterus altivelis 

Scorpaenidae Sebastolobus spp. 

Icosteidae Icosteus aenigmaticits 

Centrolophidae Icichthys lockirigtotii 

Paralichth yidae Citharichthys spp. 

Pleuronectidae Unidentified 

Eopsetta exilis 

Errex zarhirus 

Microstomus pacificus 

Pleuronectes uetulrrs 

Psettichthys melanostictus 

~~~ ~~~~~ ~~~~~ 

-. ~~ . ~~ ~~~ ~~~ 

Based on data from all cruises. 

Common name 

Northern anchovy 

Pacific viperfish 

Longfin dragonfish 

Pacific saury 

King-of-the-salmon 

Thornyheads 

Ragfish 

Medusafish 

Saiiddabs 

Righteye flounders 

Slender sole 

Rex sole 

Dover sole 

English sole 

Sand sole 

~~ -~ ~ 

~ ~~~~ 

YO total 

egg 

abundance 

4.44 

0 30 

0.69 

0.36 

5.19 

7 93 

0.76 

5.99 

56.28 

10 48 

0.55 

1.79 

5.80 

0.93 

0.42 

~ ~ 

~ ~ -~ 

~~ 

YO occurrence 

(all samples) ~ - 

Bongo 

-~ Neuston 

2 74 2 17 

10 21 20 69 

2 65 2 17 

1 04 0 94 

39 98 32 61 

151 0 76 

10 21 13 04 

30 15 20 71 

27 03 26 00 

10 40 11 91 

8 88 15 12 

5 86 21 83 

14 75 14 37 

3 50 3 59 

4 44 4 82 - ~ ~ ~~~ 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

(a) Total Fish Larvae in Neuston Samples (b) Total Fish Larvae in Bongo Samples 

% of Total Catch over 24hrs % of Total Catch over 24hrs 

12 3 4 6 0 7 8 01011121314151817181~2021222321 12 3 4 5 8 7 8 01011121311151017181~2021222324 

Local Time (Hours) Local Time (Hours) 

Figure 4 Diel variation in total catch of fish larvae in neuston (a) and bongo (b) samples For each hourly interval over 24 

hours, abundance was summed for all stations (10 cruises combined) where larvae were found The percentage of total catch 

(24 hours combined) accounted for by each hourly interval was then calculated Numbers above the bars are the total number 

of samples collected during each hourly interval 

samples than in daytime ones (figure 50, indicating 

a possibly significant migration out of the surface 

layer. The incidence of occurrence of H. spinosus larvae in the bongo samples was still low (approximately 1.9’/0), however, but higher than for the 

obligate neustonic species (table 6). An unusual pattern of diel variation was apparent for the cottid 

Scovpaenichthys mavmovatus (figure 6a). Its larvae were 

most abundant in the neuston after midnight until 

early afternoon (1400 hours); after that, hourly 

catches made up less than 3% of the total catch. 

These larvae may migrate out of the neuston during 

the latter period. 

Diel variation in larval abundance was most dramatic for Ronquilus jovdani, Engvaulis movdax, Tavletonbeania cvenulavis, Sebastes spp., and Ammodytes 

hexaptevus (figure 6b-0. Daytime catches of these 

larvae were usually insignificant. It seems that high 

numbers of these larvae migrate into the surface 

zone at night, which indicates a facultative association with the neuston. For E. movdax, 7: cvenulavis, 

and Sebastes spp., this facultative association is further emphasized by the much higher occurrence and 

abundance of these larvae in the bongo samples than 

in the neuston collections (tables 4 and 6). Ronquilus 

jovdani and A. hexaptevus occurred in fewer bongo 

than neuston samples, and their overall abundance 

in the bongo samples was low (tables 4 and 6). 

Categories of Neustonic Ichthyoplankton 

The patterns of occurrence and abundance of eggs 

and larvae in the neuston collections, and the diel 

variation in catches indicate three categories of neustonic occurrence for west coast ichthyoplankton (table 7). 

Obligate members of the neuston permanently 

live in the surface zone. Among the west coast ichthyoplankton, larvae and early juveniles of the species Cololabis saiva, Anoplopomafimbvia, Hexagvanzmos 

decagvammus, H. lagocephalus, Ophiodon elongatus, 

Hemilepidotus hemilepidotus, H. spinosus, Scovpaenichthys nzavmovatus, and Cvyptacanthodes aleutensis are assigned to this category (table 7). 

Facultative members of the neuston are occasionally abundant in the surface layer. In the study area, 

larvae and early juveniles of Engvaulis movdax, Tavletonbeania crenulavis, Sebastes spp., Ronquilus jovdani, 

and Ammodytes hexaptevus belong to this category. 

They are abundant in the neuston only at night and 

migrate vertically in a diel pattern, remaining in the 

subsurface zone during daylight. 

A third category of neustonic ichthyoplankton, 

strays,” includes a wide variety of fish eggs and 

larvae. Most of the species assigned to this category 

were most abundant in the subsurface zone of the 

water column, but some also appeared in the neuston. The species listed in tables 2 and 3 but not included in tables 4-6 (dominant neustonic taxa) are 

considered strays. In contrast, several species of eggs 

accumulate passively and abundantly in the surface 

zone. They float to the surface because they are positively buoyant. Eggs of the paralichthyids Cithavichthys spp. are the most prominent members of this 

category, accounting for over 50% of all eggs in the 

neuston collections (table 5). Other species of eggs 

that were relatively abundant in the neuston included Engvaulis movdax, Tvachiptevus altivelis, Sebastolobur spp., Icichthys lockingtoni, and various 

pleuronectids. 

“ 

Horizontal Patterns of Distribution 

Patterns of distribution described here for neustonic fish larvae are based on data combined for the 

ten sampling cruises; no adjustment is made for daynight differences in catches. The distribution maps 

represent general patterns of horizontal distribution 

149 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

(a) Cololabis saira (b ) Anoplopoma fimbria 

Yo of Total Catch over 24hrs Yo of Total Catch over 24hrs 

30 

26 

20 

16 

37 - 

- 

- 

30 

26 

15 

iI 

1 2 3 4 6 8 7 8 9 10 11 12 13 14 15 18 17 18 19 20 21 222324 1 2 3 4 6 8 7 8 9 10 11 12 13 14 15 18 17 18 19 20 21 22 2324 

Local Time (Hours) Local Time (Hours) 

( c) Hexagrammos decagrammus ( d ) Hexagrammos lagocephalus 

96 of Total Catch over 24hrs -~ Oh of Total Catch over 24hrs 

30 T12 3 4 6 8 7 8 9101112131415181718192021222324 1 2 3 4 5 8 7 8 9 10 11 12 13 14 15 18 17 18 19 20 21 22 23 24 

Local Time (Hours) Local Time (Hours) 

( e) Ophiodon elongatus ( f ) Hemilepidotus spinosus 

% of Total Catch over 24hrs 30 - YO of Total Catch over 24hrs 

26 - 

20 - 13 

3 

10 

12 3 4 6 8 7 0 9101112131415101718192021222324 12 3 4 6 0 7 8 01011121314151017181S2021222324 

Local Time (Hours) Local Time (Hours) 

Figure 5. Diel variation in catches of fish larvae in neuston samples. For each hourly interval over 24 hours, abundance was summed for all stations 

(10 cruises combined) where larvae were found. Numbers above the bars are the total number of stations at which fish larvae were caught (with 

either gear) during each hourly interval. The total number of neuston samples collected during each hourly interval is given in figure 4a. 

in the sampling area rather than accurate plots of pelagic Engvaulis movdaa and the demersal hexamean larval abundance. Most taxa of fish larvae oc- grammids, cottids, Ronquilus jovdani, Cvyptac~ncurred close to the coast over the shelf and slope and thodes aleutensis, and Ammodytes hexaptevus. Adult 

were absent or scarce in the deepest part of the populations of these species are essentially coastal. 

oceanic zone (figures 7 and 8). This is true of the Some, such as Hexagvammos decagvammus, H. lagoce150 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

TABLE 6 

Relative Abundance of Dominant Taxa of Larvae in Neuston Samples 

Family 

Engraulidae 

Osmeridae 

Myctophidae 

Scomberesocidae 

Scorpaenidae 

Anoplopomatidae 

Hexagrammidae 

Cottidae 

Bathymasteridae 

Cryptacanthodidae 

Species ~ ~~ 

Engraulis mordax 

Unidentified 

Tarletoribeania crenularis 

Stenobrachius leucopsarus 

Cololabis saira 

Sebastes spp. 

Anoplopomafim bria 

Hexagrammos decagrammus 

Hexagrammos lagocephalus 

Ophiodon elongatus 

Hemilepidotus hemilepidotus 

Hemilepidotus spinosus 

Scorpaenichthys marmoratus 

Ronqu ilur jordani 

Cryptacanthodes __ aleutensis 

Ammodytes hexapterus ~~ Ammodytidae 

Based on data from all cruises 

Common name 

Northern anchovy 

Smelts 

Blue lanternfish 

Northern lampfish 

Pacific saury 

Rockfish 

Sablefish 

Kelp greenling 

Rock greenling 

Lingcod 

Red Irish lord 

Brown Irish lord 

Cabezon 

Northern ronquil 

Dwarf wrymouth 

Pacific sandlance 

~_________~ 

O/O total 

larval 

abundance 

5 96 

0 26 

3 33 

0 26 

10 08 

11 99 

15 97 

9 15 

0 91 

1 95 

0 74 

24 65 

5 06 

1 05 

1 00 

4 16 

TABLE 7 

Categories of Neustonic Ichthyoplankton 

% occurrence 

(all samples) ~~ 

Neuston Bongo 

3.88 

1.23 

5.95 

1 42 

31.29 

18.05 

22.02 

19.01 

5.01 

4.16 

3.02 

13.14 

16.54 

3.49 

1.42 

4.06 

5.67 

4.91 

34.40 

56.33 

0.47 

43.57 

1.23 

0.66 

0.00 

0.47 

0.28 

1.89 

0.85 

2.08 

0.19 

1.80 

Strays 

Accumulate passively in the neuston because 

ofneutral or positive buoyancy, or because of 

occasional forays to the surface 

~~ ~~ 

Obligate Facultative 

Permanently in the neuston- most abundant 

in the surface zone Neustonic larval niche 

~- 

Occasionally abundant in the neuston because 

of diel vertical migration 

~ ~~ ~~ ~ ~~~~~~ ~~____ ~ ~~_______________ 

Larvae andjuveniles of Larvae andjuveniles of Eggs of 

Cololabis saira Engradis mordax Gzgraulis mordax 

Anoplopomafimhria Tarletoribeania crenularis Trachipteriis altivelis 

Hexagrammos decagrammus Sebastes spp Sebastolobris spp 

Hexagrammos lagocephalus Ronquiltisjordani Icichthys lockingtoiri 

Ophiodon elongatus Ammodytes hexapterus Citharichthys spp 

Hemilepidotus hemilepidofus Pleuronectidae 

Hemilepidotus spinosus 

Scorpaenichthys marmoratus 

Cryptacanthodes aleuterisir 

Other less abundant eggs and larvae of 

various species ~~ ~ ~~~ ~ ~~~~ ~~~ ~~~~~~___

~~~ 

phalus, Hemilepidotus spinosus, and Scovpaenichthys 

maumovatus, are most abundant close to shore, where 

they spawn from the intertidal zone to a maximum 

depth of 100 m (Hart 1973; Matarese et al. 1989). It 

seems unusual, then, that the larval distribution of 

S. mavmoratus extends as far offshore as it does, with 

occurrences over the slope and adjacent deep water 

and sometimes over the deepest water of the sampling grid (figures 7f,g and 8b,c). Obviously larval 

drift is extensive; larvae in the neuston are subject to 

wind-generated transport as well as the prevailing 

patterns of water circulation. Because the station 

grid began three miles offshore, the highest larval 

densities of the shallow-water species were probably 

missed by this sampling program. 

The occurrence of highest densities of Engvaulis 

rnovdax larvae over the shelf, slope, and immediate 

deepwater zone off Washington and northern Oregon (figure 7a) reflects the known association of this 

species with the Columbia River plume. The northern subpopulation of E. movdax spawns in the nearsurface waters of the Columbia River plume during 

summer (Richardson 1980). 

Larvae that occurred extensively in the neuston of 

the shelf, slope, and oceanic zones include the myctophid Tavletonbeania cvenulavis (figure 7b), the Pacific 

saury (Cololabis saiva; figure 7c), the rockfish complex (Sebastes spp.; figure 7d), and the sablefish (Anoploponza jimbvia; figure 7e). Larval distribution 

accurately reflected the distribution of adult popu151 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

(a) Scorpaenichthys marmoratus 

90 of Total Catch over 24hrs 

30 

25 

1 

- -7 

20 - 

15 - 

12 3 4 6 8 7 8 0101112131415181718182021222324 

Local Time (Hours) 

(c) Engraulis mordax 

% of Total Catch over 24hrs 

--I 4 

12 3 4 6 8 7 8 0101112131416181718102021222324 

Local Time (Hours) 

(e) Sebastes spp. 

% of Total Catch over 24hrs 30 7 I 

2o li 36 I 

12 3 4 6 0 7 8 B101112131415181718102021222324 

Local Time (Hours) 

( b ) Ronquilus jordani 

% of Total Catch over 24hrs 

-- I I 25 i 

I 4 I 

12 3 4 6 8 7 8 8101112131415181718192021222324 

Local Time (Hours) 

( d Tarletonbeania crenularis 

"1 24 

% of Total Catch over 24hrs 

30; 

- 1218 

18 18 

12 3 4 6 8 7 8 0101112131415181718102021122324 

Local Time (Hours) 

30 

25 

10 

0 

( f Ammodytes hexapterus 

of Total Catch over 24hrs 

61.43 3 

2 

1 

90 0 0 10-0 01 

12 3 4 6 8 7 8 8101112131415181718102021222324 

Local Time (Hours) 

Figure 6. Diel variation in catches of fish larvae in neuston samples (continued). For each hourly interval over 24 hours, abundance was summed for 

all stations (10 cruises combined) where larvae were found. Numbers above the bars are the total number of stations at which fish larvae were caught 

(with either gear) during each hourly interval. The total number of neuston samples collected during each hourly interval is given in figure 4a. 

lations only in the case of the mesopelagic T cYemlavis, which is an oceanic species. Sebastes spp., C. 

saiva, and A. jimbvia are most abundant as adults 

along the outer shelf and over the slope, and their 

larvae are advected extensively into deep water. 

Early Life-History Characteristicsfor Species with 

Neustonic Larvae 

Larval length distributions are compared between 

the neuston and bongo collections for the facultative 

neustonic species with larvae abundant in the water 

152 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

130 OOU 122 45u 

38 45N 

(a) Engraolis mordax (b) Tarleronbeania crenularis (c) Cololabis saira (d) Sebasfes spp. 

(e) Anoplopoma fimbria (1) Hexagrammos decagrammus (9) Hexagrammos lagccephahs (h) Ophiodon elongatus 

Figure 7. Patterns of distribution for dominant taxa of fish larvae in the neuston. Data are combined for 10 cruises, and mean abundance of 3 NUMBER PER 1000 fl larvae (no.11000 ma) is calculated for each grid square. 

00 

column (figure 9a-j). A broader size range of specibongo samples. Neustonic specimens were significantly larger, and many were juveniles. Most of the 

larvae taken in the bongo samples were less than 10 

~ ::: 

< IO0 

::..: s500 

.:..::: < 1 . 000 

< 5.000 

mens was encountered in the neuston than in the .... 

..... 

.. .. 

. .. ....... 

.. . 

=.::: / 

____ mm long, or in the case of A. hexaptevus less than 15 

mm, whereas neustonic larvae were mostly longer 

than 10 mm (figure 9). The difference was greatest 

for Tuvletoribeania cvenuluvis: its smallest neustonic 

specimens were 19 mm (figure 9c,d). Length at 

transformation for this species is given at 19-21 mm 

(Matarese et al. 1989). It seems, therefore, that 

among the facultative neustonic species, mainly the 

well-developed, large larvae and young juveniles 

migrate to the surface zone at night. 

Among the obligate neustonic species, a wide size 

range of larvae and early juveniles was encountered, 

and most larvae were larger than 10 mm (figure 10ai). Catches of early juveniles varied among species. 

Length at transformation to juvenile stage varies 

among these species. For some, such as the hexagrammids and cottids, the transition stage is prolonged, and a prejuvenile, neustonic stage is 

153 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

130 OOU 122 4% 

40 3011 

38 45N 

(i) Hemilepidotus hemikpidotus 

u 

(I) Ronquilus jordani 

(i) Hemilepkforus spinosus 

(m) Ctyptacanrhodes aleurensis (n) Ammodytes hexaperus 

3 NUWBER PER 1000 W 

0 

< 20 

< 50 

< 100 

500 

< 1 .ooo 

* 5.000 

Figure 8. Patterns of distribution for dominant taxa of fish larvae in the neuston (continued). Data are combined for 10 cruises, and mean abundance of 

larvae (no./1000 m’) is calculated for each grid square. 

recognized (Kendall et al. 1984). This prejuvenile 

stage differs from both the larval and the adult stage, 

and the morph resembles a herring, with silvery 

sides. 

By the time Cololabis saiva have reached a body 

length of 25 mm, most adult characters are present. 

These juveniles (>25 mm) were well represented in 

the catches, although less abundant than the larval 

stages (figure loa). Large larvae and early juveniles 

(>30 mm) were scarce for Anoplopomajimbviu (figure lob). Prejuvenile stages (>20-25 mm) for the 

hexagrammids Hexagvammos decagvammus, H. lagocephalus, and Ophiodor-l elongatus were present but in 

low concentrations, and specimens longer than 40 

mm were rare. Lengths at transformation for the 

cottids Hemilepidotus hemilepidotus (19-23 mm), H. 

spinosus (19 mm), and Scovpaenichthys mavmovatus (14 

mm) are less than for the hexagrammids (Matarese 

et al. 1989). Prejuveniles of these species were scarce, 

and specimens longer than 40 mm were absent from 

the neuston samples (figure 10f-h). 

Obligate neustonic larvae and larvae that are 

abundant deeper in the water column differ strikingly in their levels of pigmentation, particularly 

on the dorsal surface (Zaitsev 1970; Hempel and 

Weikert 1972; Moser 1981). The obligate neustonic 

larvae (Cololabis saiva, Anoplopoma jimbvia, hexagrammids, cottids, and Cvyptacanthodes aleutensis) all 

have heavy melanistic pigmentation along the dorsal 

surface, particularly at the late larval and juvenile 

stage (Matarese et al. 1989). The intensity of pigmentation and beginning of its development, how154 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

(a) Cololabis saira 

Neuston samples 

Total No. Larvae (N-1250) SO 

I 

I I 

0 5 10 15 20 25 30 35 40 45 50 55 

Size mm 

(c) Hexagrammos decagrammus 

Neuston samples 

Total No. Larvae (N.1054) 

Size mm 

(e Ophiodon elongatus 

Neuston samples 

Total No. Larvae (N.248) 40 

35 

30 I 

Size mm 

( g Hemilepidotus spinosus Neuston samples 

Total No. Larvae (N-2756) 

300 

Size mm 

(i) Cryptacanthodes aleutensis 

Neuston samples 

Total No. Larvae (N-138) 20 1- 

0 6 10 15 20 25 30 35 40 45 50 55 

Size mm 

(b) Anoplopoma fimbria 

Neuston samples 

Total No. Larvae (N-1707) 200, 

0 5 10 15 20 25 30 35 40 45 50 55 

Size mm 

(d Hexagrammos lagocephalus 

Neuston samples 

Total No. Larvae (N-108) 

14 

0 5 10 16 20 25 30 35 40 45 60 55 

Size mm 

( f ) Hemilepidotus hemilepidotus 

Neuston samples 

Total No. Larvae (N-81) 

I I 

Size mm 

( h ) Scorpaenichthys marmoratus 

Neuston samples 

Total No. Larvae (N-646) 120, 

0 6 10 15 20 25 30 35 40 45 SO 55 

Size mm 

Figure 9. Length-frequency distributions among 

obligate neustonic fish larvae and juveniles in 

neuston samples. Catches combined for 10 

cruises. N = total number of larvae caught for 

each species. 

155 
DOYLE: NEUSTON IC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

700 

800 

600 - 

400 - 

300 - 

200. 

100 - 

o -~,Dl~,~~~TT~,~,!~!,~ 

1200 

1100- 

1000- 

000 - 

800. 

700. 

em - 

600 - 400 - 

300 

200 - 100 - 

0 

Size mm 

~~TT!~~!!!!!!~!~!~~ 

(i) Ammodytes hexapterus 

Neuston samples 

Total No. Larvae (N.546) 70 , 70 

eo - 

60 - 

40 - 

30 - 

20 - 

10- 

Size mm 

Figure 10. Length-frequency distributions 

among facultative neustonic fish larvae and juO& Ill.%, 

(b ) Engraulis mordax 

Bongo samples 

Total No. Larvae (N-3229) 

Size mm 

( d) Tarletonbeania crenularis 

Bongo samples 

Total No. Larvae (N-1238) 

100 

0 5 10 15 20 25 30 35 40 45 60 65 

Size mm 

(f) Sebastes spp. 

Bongo samples 

Total No. Larvae (N-3155) 1200 

1100 I 

1000 - 

000 - 

800 - 

700 - 

eo0 

600 - 

i! Lllll,,,,...... 0 5 10 15 20 25 30 35 40 45 50 55 

Size mm 

( h Ronquilus jordani 

Bongo samples 

Total No. Larvae (N-53) 20 

0 6 10 75 20 25 30 35 40 45 50 65 

Size mm 

156 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

TABLE 8 

Habitat and Spawning Strategies among Species with Obligate Neustonic Larvae 

Species Habitat 

Cololabts satra Epipelagic 

Anoplopomafim brta Semidemersal 

Hexagrammos decagrammus Demersal 

Hexagrammos lagocephalus Demersal 

Ophrodon elongatus Demersal 

Hemilepidotus hemileptdotus Demersal 

Hemilepidotus spinosus Demersal 

Scorpaenichthys maimoratus Demersal 

Cryptacanthodes aleutensis Epi/meso-benthal 

Life-history information from Matarese et a1 1989 

Shelf and slope 

Shelf and slope 

Coastal-inshore 

Coastal-inshore 

Coastal and shelf 

Coastal and shelf 

Coastal-inshore 

Coastal-inshore 

Shelf and slope _____~ 

Spawning season 

Winter-autumn 

Peak Feb -July 

Winter-spring 

Peak Feb -March 

Autumn-spring 

Peak Dec 

Autumn-winter 

Peak Dec -Jan 

Winter-spring 

Peak Dec -Feb 

Winter-spring 

Peak Dec -Jan 

Winter-spring 

Peak Dec -Feb 

All year 

Multiple spawning 

Winter-spring 

Peak Jan -March 

~~ ~ ~ 

~- 

ever, varies among species. In contrast, in the 

facultative neustonic larvae identified here dorsal 

melanistic pigmentation is poorly developed. 

Habitat and spawning strategies among the west 

coast species with obligate neustonic larvae are similar (table 8). Except for Cololabis saiva, which is epipelagic, all live on or close to the bottom, mainly in 

coastal waters. Cololabis saiva, A. jimbvia, and C. 

aleutensis extend into deeper water than the other 

species, and they are common near the slope. The 

spawning season for most species is short, with a 

winter peak, usually from December to March. In 

contrast, C. saiva has an extended spawning period 

from winter to autumn, with a peak from February 

to July, and Scovpaenichthys mavmovatus is a multiple 

spawner throughout the year. Cololabis saiva and A. 

fimbria are the only species that do not have demersal 

eggs. Eggs of C. saiva are epipelagic and are usually 

attached to flotsam, whereas A. jimbvia eggs are 

bathypelagic. Hexagrammids and cottids tend to 

have adhesive eggs that are attached to the substratum, either rocks or seaweed. Size at hatching 

among the obligate neustonic larvae is greater than 

5 mm, and may be up to 10 mm, except for S. mavmoratur, which hatches at a minimum size of about 

4 mm. These sizes are relatively large in comparison 

with most species that hatch at sizes (5 mm. For 

instance, E. movdax hatches at 2.5-3 mm and 7: cvenularis at (3 mm (Matarese et al. 1989). Obligate 

neustonic larvae therefore tend to be relatively well 

developed at hatching. 

Spawning mode 

Epipelagic, eggs attached 

Bathypelagic 

Demersal, shallow 

water, adhesive eggs 

Demersal, shallow 

water, adhesive eggs 

Demersal, shallow 

water, adhesive eggs 

Demersal, shallow 

water, adhesive eggs 

Demersal, shallow to 

moderately deep water 

Demersal, shallow 

water, adhesive eggs 

Demersal, moderately 

deep water 

to flotsam 

Larval hatch 

size (mm) 

6-8.5 

6 

7-9 

7-9 

7-10 

5-6 

5 

4-6 

lo? 

DISCUSSION 

Data from this study and from previous ichthyoplankton investigations indicate a neustonic assemblage of fish eggs and larvae off the coasts of 

Washington, Oregon, and northern California 

(Richardson'; Ahlstrom and Stevens 1976; Gruber et 

al. 1982; Brodeur et al. 1987; Shenker 1985, 1988). 

This assemblage is most diverse over the shelf and 

continental slope, but several species are also distributed throughout the oceanic zone. 

The three categories of neustonic occurrence 

among the ichthyoplankton follow the general classification scheme for neustonic organisms (Zaitsev 

1970; Hempel and Weikert 1972; Peres 1982). Obligate and facultative members of the neuston include 

larvae and early juveniles that actively seek out the 

surface zone. 

The nine species of fish larvae assigned here to the 

obligate neustonic category appear to live permanently in the surface zone. These species occupy an 

exclusively neustonic niche during their larval and 

early juvenile or prejuvenile stages. Their larvae 

are scarce or absent in subsurface ichthyoplankton 

collections from coastal and oceanic waters off 

Washington, Oregon, and northern California 

(Richardson 1973; Richardson and Pearcy 1977; 

Richardson et al. 1980; Boehlert et al. 1985; Brodeur 

'S. L. Richardson. 1975. Oregon's coastal ichthyoneuston: a preliminary report. 

Unpublished report presented at American Society of Ichthyologists and Herpetologists, Williamsburg, Virginia. 

157 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

et al. 1985; Doyle et al. in press). The reduced abundance of some of these larvae in neuston samples 

collected during daylight is attributed primarily to 

their visual avoidance of the sampling gear. It is also 

possible, however, that some larvae migrate vertically out of the surface layer during the day. 

The facultative members differ from the obligate 

members in that they do not remain permanently in 

the neuston but migrate vertically in a diel pattern, 

moving up to the surface around dusk and remaining there until the onset of daylight. 

Fish eggs are present in the neuston as “strays,” 

accumulating at the surface because of positive 

buoyancy. Also included in this category are many 

species of larvae that appear frequently in the neuston but are much more abundant in the subsurface 

zone. For these species, the neuston represents the 

upper extreme of their vertical range. 

In their review of the neuston of the subtropical 

and boreal northeast Atlantic Ocean, Hempel and 

Weikert (1972) documented the scarcity of very 

young fish larvae in the surface zone. Their neuston 

net caught mainly late larval and juvenile stages. The 

same was true for Shenker’s (1985, 1988) ichthyoneuston collections off the Oregon coast. Comparing the length-frequency distributions of larvae 

caught in the bongo samples with those of the 

neuston collections in this study, I found that neustonic larvae are generally larger than those in the 

subsurface zone. The difference was particularly 

striking among the facultative larvae, indicating that 

those that migrate to the surface at night are welldeveloped larvae and early juveniles. Tully and 

O’Ceidigh (1989a) made the same observation for 

facultatively neustonic species of fish larvae in 

Galway Bay on the west coast of Ireland. 

The scarcity of larvae less than 10 mm long among 

the obligate ichthyoneuston can be related to the 

strategies displayed by these species. Except for Cololabis saiva, which is an epipelagic spawner, these 

species either deposit their eggs on the bottomfrequently in gelatinous masses that adhere to rocks 

or weed-or spawn bathypelagic eggs, e.g., Anoplopoma jmbvia (Matarese et al. 1989). After hatching, larvae migrate to the surface, and small yolksac larvae are therefore likely to be dispersed 

throughout the water column rather than concentrated in the neuston. Their scarcity in the bongo 

samples may be attributed to the inefficiency of the 

gear in sampling relatively low densities of larvae 

scattered throughout the water column, in comparison with neuston nets, which efficiently sample larvae that are concentrated at the surface. Fecundity is 

also relatively low among the species with obligate 

158 

neustonic larvae, and the larval hatch size is correspondingly high (Matarese et al. 1989), further contributing to the larger larval sizes in the neuston. 

The implication from these length-frequency observations is that it is advantageous for larvae in the 

neuston to be well developed. With increasing size, 

fish larvae become more agile at seeking food and 

avoiding predators, thus enhancing their chances of 

survival. The size range of available food organisms 

also expands with increasing larval size. Hempel and 

Weikert (1972) observed that because phytoplankton 

seems to be scarce in the immediate vicinity of the 

surface, neustonic fish larvae are carnivorous or omnivorous. On depletion of the yolk sac, small firstfeeding larvae may therefore be more vulnerable to 

starvation than they would be deeper in the water 

column. 

Eggs that adhere to the substratum help retain 

young fish close to the adult habitat. The commencement of a planktonic existence is postponed 

to the larval phase, considerably reducing the period 

of drift in the plankton. It therefore seems contradictory that the dominant hexagrammid and cottid 

species inhabiting the coastal and inshore zone off 

Washington, Oregon, and northern California have 

larvae that are essentially neustonic. Their presence 

in the neuston subjects them to wind transport as 

well as to surface currents. In the dynamic surface 

zone they are much more likely to be widely dispersed away from suitable habitats for settlement 

than if they were concentrated deeper in the water 

column. The distribution patterns documented for 

all the neustonic larval species during this study indicate that larval drift is generally extensive in the 

surface zone of this region. Even among some of the 

inshore species such as Hexagvammos decagvammus, 

H. lagocephalus, and Hemilepidotus spinosus, the distribution of neustonic larvae extends well into the 

slope and oceanic zone. Larvae of these species encountered over deep water probably are lost to the 

adult populations and do not survive to recruitment. 

The widespread dispersal of larvae in the neuston 

may be facilitated by various mesoscale oceanographic features as well as wind transport and prevailing patterns of circulation. Eddies, offshore jets, 

meanders in the alongshore currents, and surface 

slicks associated with internal waves may contribute 

significantly to the onshore-offshore dispersal of 

ichthyoplankton (Shanks 1983; Kingsford and 

Choat 1986; Shenker 1988). 

The prevalent spawning season among species 

with obligate neustonic larvae, however, is such that 

the larvae are most abundant when Ekman surface 

transport is onshore, and downwelling is occurring 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

along the coast. The peak period of spawning for 

most species is winter; for the coastal species this 

favors retention of their larvae in the coastal zone, in 

the vicinity of the adult habitats. In their review of 

reproductive strategies among fish species in the 

California Current system, Parrish et al. (1981) observe a correspondence to the major features of surface transport that minimizes larval advection out of 

suitable habitats. Richardson et al. (1980) and Doyle 

et al. (in press) document a coastal assemblage of 

fish larvae in the plankton along the Washington, 

Oregon, and northern California coasts. This assemblage is present during winter and spring and, 

for the most part, absent from summer to autumn, 

when upwelling and offshore Ekman transport prevail. The spawning seasons among species with exclusively neustonic larvae therefore reflect the 

general correspondence between spawning strategies in this region and the prevailing circulation 

patterns. 

By the time the neustonic larvae have developed 

to the juvenile stage, the transition to offshore Ekman transport and upwelling of oceanic water may 

have taken place along the coast. If young juveniles 

are still present in the neuston, they are likely to be 

transported away from the coastal zone. Postlarvae 

and juveniles of Cololabis saiva and Anoplopoma jimbvia remain at the surface (Hart 1973; Kendall and 

Matarese 1987) and therefore are widely distributed 

in deep water as well as along the coast. Among 

coastal and inshore hexagrammids and cottids, there 

is some evidence to suggest that large prejuveniles 

and juveniles migrate out of the neuston with the 

onset of upwelling, thus largely avoiding offshore 

transport. Shenker (1985,1988) documented the disappearance of hexagrammid and cottid juveniles 

from neuston collections off Oregon in association 

with the beginning of upwelling and offshore Ekman transport. He proposed that upwelling triggers 

these fishes’ settlement to the demersal habitat used 

by older juveniles and adults and that a possible 

stimulus for this transition is the breakdown of the 

thermocline. 

Several factors that may limit the successful habitation of the neuston by fish eggs and larvae characterize the surface layer (Zaitsev 1970; Hempel and 

Weikert 1972). They include high levels of UV radiation, which may cause physiological stress or genetic damage; intensive wave action, which may 

cause mechanical damage to organisms; and a reduced biota, which may mean a diminished availability of prey. In addition, the high light intensity at 

the surface during the day is likely to make neustonic 

fish eggs and larvae more visible to predators. Surface transport mechanisms that disperse larvae away 

from a suitable adult habitat are another disadvantage associated with the neuston. 

Adaptations to these potentially adverse factors 

are, however, apparent among neustonic ichthyoplankton in general (Zaitsev 1970; Hempel and Weikert 1972; Moser 1981) and specific to the U. S. west 

coast. For instance, the heavy melanistic pigmentation on the dorsal surface of larvae and early juveniles in the obligate neustonic category is considered 

to be a protective adaptation in response to high 

light intensity and associated UV radiation. Mechanical resistance of fish eggs is high, and eggs are 

believed to be endangered by wave action only during the first few hours after spawning (Hempel 

1979), when they are deeper in the water column. 

Recently hatched larvae are likely to be much more 

vulnerable to mechanical damage, but - as observed off the U. S. west coast and elsewhere (Hempel and Weikert 1972) - in most species these larvae 

are absent from the neuston. The well-developed 

nature of neustonic larvae may be adaptive both in 

terms of seeking prey - which may be scarce in the 

neuston - and avoiding predators, to which they 

may be more visible than if they were deeper in the 

water column. As mentioned previously, the detrimental effects of surface transport along the west 

coast are reduced by the synchrony of spawning seasons. The demersal spawning mode is also an adaptive feature in this respect. 

Given the hazardous conditions that may prevail 

in the sea-surface layer, it is interesting that certain 

species of fish along the U.S. west coast use this 

biotope as the ecological niche for their young. Advantages to a neustonic existence for ichthyoplankton may include enhanced growth and reduced levels 

of predation. For instance, accelerated embryogenesis is characteristic of fish eggs in the neuston, where 

temperatures are higher because of the intensive absorption of solar radiation in the upper 10 cm of the 

water column (Zaitsev 1970; Peres 1982). Positive 

buoyancy among certain species of fish eggs, resulting in their concentration in the neuston, may therefore be considered adaptive. Larval growth is also 

likely to be enhanced at the surface, shortening the 

most vulnerable early stage. For example, AnoplopornaJimbvia larvae are known to grow rapidly (up 

to 2 mm per day) during spring off the U.S. west 

coast (Kendall and Matarese 1987). Hempel and Weikert (1972) propose that the surface layer of the ocean 

serves as a refuge from predators, particularly during the daytime, because of the relative scarcity of 

invertebrates and fishes, making it a less attractive 

hunting area for large predators. Hempel and Wei159 
DOYLE: NEUSTONIC ICHTHYOPLANKTON 

CalCOFl Rep., Vol. 33,1992 

kert suggest that the few enduring neustonic metazoa, including fish larvae, encounter relatively little 

predatory pressure during the daytime. 

Based on their investigations of feeding among 

fish larvae and juveniles in the neuston of Galway 

Bay (west coast of Ireland), Tully and O’Ceidigh 

(1989b) conclude that feeding conditions at the surface are unique and that neustonic species are 

adapted to feed more successfully in this environment. It is likely that the most important advantage 

to a neustonic existence for fish larvae is the suitability of the surface layer as a trophic niche. Evidence 

that facultatively neustonic species of fish larvae migrate to the surface with the onset of darkness and 

return to deeper layers in the morning supports this 

hypothesis. A feature common to all investigated 

regions in the world ocean is that many plankton 

organisms migrate into the surface zone as daylight 

fades, thus making the neuston a much richer biotope at night, with higher concentrations of food 

suitable for fish larvae (Zaitsev 1970; Hempel and 

Weikert 1972; Peres 1982; Holdway and Maddock 

1983a, b). 

Apart from the high densities of zooplankton that 

may occur in the neuston at night, mesoscale physical features such as fronts, convergence zones, and 

surface slicks can cause aggregations of plankton at 

the surface, bringing high concentrations of fish larvae together with high concentrations of suitable 

prey. Kingsford and Choat (1986) found that small 

fish and zooplankton from surface waters off New 

Zealand were denser in slicks than in the rippled 

waters adjacent to them. Off Oregon, Shenker 

(1988) documented aggregations of Dungeness crab 

megalopae and fish larvae and juveniles in association with nearshore surface convergence zones and 

the periphery of the Columbia River plume. High 

concentrations of neustonic ichthyoplankton and 

zooplankton have also been found in association 

with the frontal structure around the discharge 

plume of the Mississippi River (Grimes and Finucane 1991). Clearly, the neuston biotope offers 

unique trophic conditions for young fish, and Moser 

(1981) proposes that the neustonic zone may be a 

permanent food patch available to larval fish. The 

feeding habits of the neustonic fish larvae described 

in the present study need to be investigated thoroughly, however, for a more complete understanding of the neustonic realm’s importance in the early 

life history of fishes off the U. S. west coast. 

ACKNOWLEDGMENTS 

Suggestions and comments by three anonymous 

reviewers and by Art Kendall and Ann Matarese of 

the Alaska Fisheries Science Center in Seattle are 

gratefully acknowledged; they helped considerably 

with the final draft of this manuscript. 

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