DOYLE: NEUSTONIC ICHTHYOPLANKTON ColCOFl Rep., Vol. 33,1992



### NEUSTONIC ICHTHYOPLANKTON IN

### THE NORTHERN REGION OF

### THE CALIFORNIA CURRENT ECOSYSTEM

MIRIAMJ DOYLE’ Department ofFisheriesand Wildlife Oregon StateUniversity Corvallis, Oregon97331-3803



### ABSTRACT Analysis of ichthyoplankton data collected off Washington, Oregon, and northern California duringthe 1980sindicates aneustonic assemblageoffish eggs, larvae, andjuveniles. This assemblageis most diverse over the shelf and continental slope. Diel variation in the occurrence and abundance ofcertain species offish 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 neustonbutwere scarceor absent in subsurface samples. Other taxa of larvae and juveniles were abundant at the surfaceonly 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 surfacebecause ofpositive 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 ofthe 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 adversefactors areapparentamongthe species. Advantages to a neustonic existence may include enhanced growth, reduced levels of predation, and suitable concentrations offood. Themain
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 SandPoint Way, NE, Seattle, Washington 98115-0070 [Manuscript received February 10,1992.1 California durantela dtcada del 

### 80 sefialala existencia deun grupo neustonico dehuevos depeces, larvas yjuveniles. Este grupotiene 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 yjuveniles 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 aparentementese 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 quelas encontradas a mayor profundidad en la columna de agua; se considera que esto es venta

### joso a1 buscar presas y evitar depredadores. Losjuveniles tambiCn se encontraron a menudo en el neuston, contrastando con larvas de reciente eclosion, quienes estuvieron ausentes. Varios factores podrian limitar a1 neuston como unhAbitatexitosopara el ictioplancton: altos niveles de radiaci6n ultravioleta, oleaje intenso, una biota disminuida, mayorvisibilidad 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 dedepredacih y concentraciones de aliment0 adecuadas. La raz6n principalpor la cual larvas yjuveniles dealgunasespecies eligen a1 neuston como un nicho ecol6gico conveniente estriba probablemente en las condiciones trbficas tinicas que prevalecen en estebiotopo.



### INTRODUCTION

A diverse assemblageofplanktonic 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).Thecomposition and abundance of neustonic organisms vary consider

### 141DOYLE: 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
arepermanentlypresentin the surfacezone (obligate members), a diverse range of organisms concentrates at the surfaceonly during certainhours (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 ofvarious fish speciesconcentratein theneuston, essentially because of their positive buoyancy, larvae andjuveniles actively migrate to the surfacezone and maybe 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 andlocal conditions. Factors suchas latitude, surface water temperature, water depth, nutrient concentration, and upwelling 

### all affect the diversity, age structure, and vertical migratorypatterns offish larvae in an area (Hempel and Weikert 1972;Tully and O'Ceidigh 1989a). Severalstudiesofplanktonic neuston in the northeast Pacific were carried out during the 1970s and 1980s. Most were for the purpose of documenting fish larvaein the neuston. Richardson (1975)made a preliminary report onthe occurrence and abundance of fish larvae andjuveniles in the neuston along an east-west transect off the mid-Oregon coast. Ahlstrom and Stevens (1976) documented species composition and abundance 

### offish larvae in the neuston and in the water column over an extensive area of the northeast Pacific, including the coastal and oceanic zone from northernWashingtonto 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

### offish larvae areabundantinthe surfacezone 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 speciescompositionand abundanceoffish larvae and invertebrate components of the neuston in coastal waters of the northeast Pacific as part of a study ofjuvenilesalmonids' 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 offthe 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. Theneuston 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 madeit possible toinvestigatethe occurrence and ecology offish 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. 

### MATERIALSAND METHODS The cooperative ichthyoplankton surveys conductedoffthe

### U.S. northwest coast during the 1980s involved the 

### U.

### S. Northwest and Alaska Fisheries Centerin Seattle, and the 

### U.S.S.R. PacificResearch 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). Seasonalcoveragewas limited: six ofthe ten cruises
were made in spring (March to early June); one cruisein 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. Stationswere more closely spaced over the shelfand slope than in deepwater west ofthe 1,000-m isobath (figure 

### 1).



### 142DOYLE:NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep.,Vol. 33,1992

129 OOY 127 OOY 12s oou 123 OOY TABLE 1 Sampling ScheduleandNumber 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. MysDalniy U.S.S.R. Poseydon U.S.S.R. Equator U.S.S.R. Miller Freeman U.S.A. Poseydon U.S.S.R. MysBabyshkina U.S.S.R. MillerFreeman U.S.A. Cruisedates 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 ~~~~ StationsoccuDied 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 stationsoccupied 1161 1086

During eachcruise, 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 10minutes ateach 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 theupper 15cm 

### ofthe 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 10m2 

### of sea-surface area for the bongo samples and numbers per 1000 m3for the neuston samples.


### OCEANOGRAPHIC ENVIRONMENT The oceanography ofthe 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 theU.

### S. west coast (figure2). Subcomponents of the California Current include the northwardflowing California Undercurrent and Davidson Current (Hickey 1989). The California Undercurrent consists of ajetlike poleward flow with a subsurfacemaximum. Its core appears tobe confined to



### 143DOYLE: 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 = SOUTHERNCALIFORNIA COUNTERCURRENT 

### SCE = SOUTHERNCALlFORNlA EDDY 130" 120"W 50" 50" 

### -

- 30" 30"- 

### N N

11 1 I I I 130° 120"W
130" 120"W 50"

40"

30" 

### N

Figure2. Seasonalvariation in deep-ocean boundary currentsoff 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 surfacecurrent (figure

### 2). Coastal surfacecurrents in this region areprimarily 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 atmosphericpressure 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 upwellingvaries along the coast. Mean monthlyupwelling 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, theupwelling 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



### 144DOYLE: 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), meanof years 1946to 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 offWashington 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 significantlyby 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 shallowhalocline 

### (<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 RelativeA

### bundance Both fish eggs and larvae were abundant in neuston samples, but species diversity was lower than in thebongo samples. Twenty-five species ofeggs 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. Speciescomposition, 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, Ophiodonelongatus, 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

### 4and 

### 5).Except for

### Engvaulismovdax, 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 subsurfacezone. In contrast, many of the larval species that were abundant in the neuston were absent or scarcein the bongo samples and therefore may be considered almost exclusivelyneustonic (obligatemembers of the neuston). These include 

### Cololabis saira, Anoplopoma _fimbria,the hexagrammids, the cottids, and 

### Cvyptacanthodes aleutensis. Because their eggs were absent from theneuston (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. Theirincidenceofoccurrence in neuston samples was, however, higher than in the bongo samples. These larvae are considered tobe 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.



### 145DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep.,Vol. 33,1992

TABLE 2 Percentage Occurrence andMeanAbundance ofAll Taxa ofEggsinNeuston 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 Chauliodusmacouni Tactostoma macropus Unidentified Merluccius productus Theragrachalcogramma Cololabissaira Unidentified Trachipterusaltivelis Sebastolobus spp. Trachurussymmetricus Icosteus aenigmaticus Ammodyteshexapterus Zcichthys lockingtoni Tetvagonuruscuvieri Citharichthys spp. Unidentified Errexzachirus Hippoglossoides elassodon Pleuronectes isolepis Eopsetta exilis Microstomuspacificus Pleuronectes vetulus Platichthys stellatus Pleuronichthys coenosus Pleuronichthysdecurrens Psettichthys melanostictus ~~ -~

~ ~~~~ ~~

-

~. -~



### Diel Variationin Catchesof 

### 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% oftotal 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 speciesoflarval fish in theneuston. Ohoccurrence 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 24hours, 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 abundantinneuston 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 maybe some migration ofthese larvae out ofthe immediate surface zone during the day. Theincidence ofoccurrence of hexagrammid larvae in bongo samples was very low (< 1"/o) or, in the
case 

### ofHexagvummos 

### lagocephulus, zero (table6),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 

### Hemilepi

### dotus spitzosus, which accounted for approximately 25% ofall larvae caught in the neuston (table6),was considerably more abundant in nighttime neustonDOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep., Vol. 33,1992

TABLE 3

Percentage Occurrence andMean AbundanceofAll Taxa ofLarvae 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 Cyclopteridae Carangidae Bathymasteridae

Stichaeidae Cr

yptacanthodidae

Pholidae Ammodytidae Centrolophidae Paralichthyidae

Pleuronectidae Clupea harenguspallasi 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 Microgadusproximus Theragra chalcogramma Cololabissaira Unidentified Sebastes spp. Sebastolobus spp. Anoplopomafimbria Unidentified Ophiodon elongatus Pleurogrammus mouopterygius Hexagrammos spp. Hexagrammosdecagrammus Hexagrammos lagocephalur Hexagrammosstelleri Unidentified Artediusfenestralis Artedius harringtoni Cottusasper Hemilepidotus hemilepidotus Hemilepidotusspinosus Leptocottus armatus Radulinus spp. Radulinus asprellus Scorpaenichthyr marmoratus Unidentified Unidentified Trachurus symmetricus Bathymaster spp. Ronquilus jordani Unidentified Delolepisgigantea Cryp tacanthodesaleutensis Pholis spp. Ammodytes hexapterus Icichthys lockingtoni Citharichthys spp. Citharichthys sordidus Citharichthys stigmaeus Eopsetta jordani Errex zachirus Pleuronectes isolepis Microstomuspacifcus 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



### 147DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep., Vol. 33,1992

TABLE4 DominantIchthyoplanktonTaxa in Neuston and Bongo Samples Collected duringAll Cruises

Family Engraulidae Osmeridae Bathylagidae --

~

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 Tactosfornarnaeropits Unidentified Diaphiistheta Protoni yctopliiirn crockrri Protornyctophiirn thotnpsoiii Tarletorrbearria crertrilaris Sle~iobrach iris /errcopsariis Cololabissaira Trachipteritsaltiivlis Sebastes spp. Arroplopoirmfirnbria Hexagrarnrnosdecagrairinirrs Hexagramtnos iagoeephdirs Ophiodoir eloirgatiis Hemilepidotus hetnilepidottis Hernilepidottis spi~~osris Scorpaenirh th ysmarrrioratrrs Roriqriiliisjordani Cryptacanthodes aleritensir Icosteus aeriigrnaticrrs Amrnodytes hexapterris Icichthys lockirrgtorii Citharichthysspp. Citharichtliyssordidits Citharichthysstiginaerrs Unidentified Errex zachirtrs Eopsetta exilis Microstomuspacifitiis Pleiirorrectes iwtitliis Psettichthys melanostictiis Bathylaglts spp.

Bathylagrtspac.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 ofDominant Taxa ofEggsin Neuston Samples

Family Species Engraulidae Engraulis rnordax Chauliodontidae Chauliodusmaroutti Melanostomidae Tactostoma macroprrs Scomberesocidae Cololabissaira Trachipteridae Trachipterus altivelis Scorpaenidae Sebastolobus spp. Icosteidae Icosteusaenigmaticits Centrolophidae Icichthys lockirigtotii Paralichth yidae Citharichthys spp. Pleuronectidae Unidentified Eopsetta exilis Errexzarhirus Microstomuspacificus Pleuronectes uetulrrs Psettichthys melanostictus ~~~ ~~~~~ ~~~~~

-.

~~ . ~~ ~~~ ~~~ Based on data from all cruises. Commonname 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 -~

~ ~~

~ ~~~~ YOtotal 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 ~ ~

~ ~ -~ ~~ YOoccurrence (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 1304 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 123 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, abundancewas summedfor all stations(10 cruisescombined)where larvaewere found The percentageof total catch (24 hours combined) accountedfor by each hourly intervalwas then calculated Numbersabovethe bars arethe total number of samples collectedduring each hourly interval

samples than in daytime ones (figure 

### 50, indicating a possibly significant migration out of the surface layer. Theincidence ofoccurrence of

### H.

### spinosus larvae in the bongo samples was still 

### low (approximately 1.9’/0), however, but higher than for the obligate neustonic species (table6). An unusual pattern of diel variation was apparent for the cottid 

### Scovpaenichthys mavmovatus (figure6a). Its larvaewere 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, Tavle

### tonbeania 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 emphasizedby the muchhigher occurrence and abundance ofthese 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). 

### Categoriesof 

### Neustonic Ichthyoplankton Thepatterns ofoccurrence and abundance of eggs and larvae in the neuston collections, and the diel variation in catches indicate three categories ofneustonic occurrencefor west coast ichthyoplankton (table 

### 7). Obligate members of the neuston permanently live in the surface zone. Among the west coast ichthyoplankton, larvae and earlyjuveniles of the species 

### Cololabissaiva,Anoplopomafimbvia,Hexagvanzmos decagvammus, H. 

### lagocephalus, Ophiodon elongatus, Hemilepidotus hemilepidotus, 

### H.spinosus, Scovpaenichthys nzavmovatus, and 

### Cvyptacanthodesaleutensis are assigned to this category (table

### 7). Facultative members 

### ofthe neuston are occasionally abundant in the surfacelayer. In the study area, larvae and earlyjuveniles 

### 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 ofthe 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

### ofeggs accumulate passively and abundantly in the surface
zone. Theyfloat to the surface becausethey arepositively buoyant. Eggs of the paralichthyids 

### Cithavichthys spp. are the most prominent members ofthis 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

### ofDistribution Patterns of distribution described here for neustonic fish larvae are based on data combined for the ten samplingcruises; noadjustmentis madefor daynight differences in catches. The distribution maps represent general patterns ofhorizontal distribution



### 149DOYLE: 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 

# 37 30 

# iI

26 -

20 -

16 - 26

15

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

# T123 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

123 4 6 8 7 0 9101112131415101718192021222324 123 4 6 0 7 8 01011121314151017181S2021222324 Local Time (Hours) Local Time (Hours) Figure5. Diel variation in catches of fish larvae in neuston samples. Foreach hourly intervalover 24 hours, abundance was summedfor 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 eithergear) during each hourly interval.The total numberof neuston samplescollectedduring each hourly interval is given infigure4a.

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 slopeand 

### 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. lagoce

### 150DOYLE:NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep.,Vol. 33,1992

TABLE 6 Relative Abundance ofDominant Taxa ofLarvae in Neuston Samples

Family Engraulidae Osmeridae Myctophidae

Scomberesocidae Scorpaenidae Anoplopomatidae Hexagrammidae

Cottidae

Bathymasteridae Cryptacanthodidae Species

~ ~~ Engraulis mordax Unidentified Tarletoribeania crenularis Stenobrachius leucopsarus Cololabissaira Sebastes spp. Anoplopomafim bria Hexagrammos decagrammus Hexagrammos lagocephalus Ophiodonelongatus Hemilepidotus hemilepidotus Hemilepidotus spinosus Scorpaenichthys marmoratus Ronquilur jordani Cryptacanthodesaleutensis



### __ Ammodytes hexapterus

~~ Ammodytidae Based ondata from all cruises Common name Northern anchovy Smelts Blue lanternfish Northern lampfish Pacific saury Rockfish Sablefish Kelp greenling Rock greenling Lingcod Red Irishlord BrownIrish 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 ofNeustonic 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 Accumulatepassively in the neuston because ofneutral or positivebuoyancy, orbecause of occasional forays to the surface ~~ ~~ Obligate Facultative Permanentlyinthe neuston- most abundant in the surfacezone Neustonic larval niche ~- Occasionally abundantin the neustonbecause ofdiel vertical migration

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

~ Larvae andjuveniles of Larvae andjuveniles of Eggs of Cololabis saira Engradis mordax Gzgraulismordax Anoplopomafimhria Tarletoribeania crenularis Trachipteriis altivelis Hexagrammos decagrammus Sebastes spp Sebastolobris spp Hexagrammos lagocephalus Ronquiltisjordani Icichthys lockingtoiri Ophiodonelongatus Ammodytes hexapterus Citharichthys spp Hemilepidotus hemilepidofus Pleuronectidae Hemilepidotusspinosus Scorpaenichthys marmoratus Cryptacanthodes aleuterisir Otherless abundant eggs and larvaeof various species

~~~ ~ ~~~~ ~~~ ~~~~~~____~

~ ~~~ ~~



### phalus, Hemilepidotus spinosus, and 

### Scovpaenichthys maumovatus, aremost 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;larvaein 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 ofthe shallow-water species were probably missed by this samplingprogram. The occurrence of highest densities of 

### Engvaulis rnovdax larvae over the shelf, slope, and immediate deepwater zone off Washington and northern Oregon (figure7a) reflects the known association ofthis species with the ColumbiaRiver plume. Thenorthern subpopulation of

### E. movdax spawns in the nearsurface waters ofthe 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 (figure7b), thePacific saury 

### (Cololabis saiva; figure 7c), the rockfish complex 

### (Sebastesspp.; figure 7d), and the sablefish 

### (Anoploponza jimbvia; figure 7e). Larval distribution accurately reflected the distribution of adult popu

### 151DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep., Vol. 33,1992


### (a) 

### Scorpaenichthys marmoratus

90 of Total Catch over 24hrs

30 

# 1 

# -7

25 

### -

20 -

15 -

12 3 4 6 8 7 8 0101112131415181718182021222324 LocalTime (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 307 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

123 4 6 8 7 8 8101112131415181718192021222324 LocalTime (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
123 4 6 8 7 8 8101112131415181718102021222324 Local Time (Hours) Figure 6. Diel variation in catches of fish larvae in neuston samples (continued).Foreach hourly intervalover 24 hours,abundancewas summedfor

all stations (10cruisescombined)where larvaewerefound. Numbersabove the bars arethetotal number of stations atwhichfish larvaewere caught (with eithergear) duringeach hourly interval.The total numberof neuston samplescollectedduring each hourly intervalisgiven infigure4a.

lations only in the case 

### of the mesopelagic 

### T cYem

### lavis, 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 extensivelyinto deep water. 

### Early Life-History Characteristicsfor Species with NeustonicLarvae Larval length distributions are compared between theneuston and bongo collections for the facultative neustonic species with larvae abundant in the water



### 152DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep.,Vol. 33,1992

130 OOU 122 45u

38 45N (a) Engraolis mordax (b) Tarleronbeaniacrenularis (c) Cololabis saira (d) Sebasfesspp.

(e)Anoplopoma fimbria (1) Hexagrammos decagrammus (9) Hexagrammoslagccephahs (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.11000ma)is calculatedfor 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 ofthe 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

....

.....

.. ..

. ..
.......

.. . =.::: /



### ____ mmlong, or in the case ofA. 

### 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. Amongthe obligateneustonic species, a wide size range oflarvae and early juveniles was encountered, and most larvae were larger than 10mm (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



### 153DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep.,Vol. 33,1992

130 OOU 122 4%

40 3011

38 45N (i) Hemilepidotus hemikpidotus



# u

(I) Ronquilusjordani (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 distributionfor dominant taxa of fish larvae in the neuston (continued). Data are combined for 10 cruises, and mean abundance of

larvae (no./1000m’) is calculatedfor each gridsquare. recognized (Kendall et al. 1984). This prejuvenile stagediffers 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 of25 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 earlyjuveniles 

### (>30 mm) were scarce for 

### Anoplopomajimbviu (figure lob). Prejuvenile stages (>20-25 mm) for the hexagrammids Hexagvammos 

### decagvammus, H. lago

### cephalus, and 

### Ophiodor-lelongatus 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 mmwere 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 andjuvenile stage (Matarese et al. 1989). The intensity 

### of pigmentation and beginning of its development, how

### 154DOYLE: 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.



### 155DOYLE: NEUSTONIC 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 amongfacultative neustonicfish larvae andjuO& 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



### 156DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep., Vol. 33,1992

TABLE 8 Habitatand Spawning Strategiesamong Species with Obligate Neustonic Larvae

Species Habitat Cololabtssatra Epipelagic
Anoplopomafimbrta 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 _____~ Spawningseason 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 specieswith obligate neustonic larvae are similar (table 8). Except for 

### Cololabissaiva, 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 toJuly, and 

### Scovpaenichthys mavmovatus is a multiple spawner throughout the year. 

### Cololabissaiva and 

### A. 

### fimbria arethe only species that donot 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 

### 4mm. 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 athatching. Spawningmode 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 toflotsam 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 severalspecies are alsodistributed 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 earlyjuveniles that actively seek out the surface zone. Thenine species offish 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'scoastal ichthyoneuston: apreliminary report. Unpublished report presented atAmerican Society ofIchthyologistsand Herpetologists,Williamsburg, Virginia.



### 157DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep.,Vol. 33,1992

et al. 1985;Doyle et al. in press). Thereduced abundance of some of these larvae in neuston samples collected during daylight is attributed primarily to their visual avoidance ofthe sampling gear. It 

### is also possible, however, that some larvae migrate vertically out ofthe surfacelayer during the day. Thefacultative 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 ofdaylight. 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

### oftheir 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 surfacezone. Their neuston net caught mainlylatelarval andjuvenile 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 amongthe facultative larvae, indicatingthat 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 onthe west coast ofIreland. Thescarcity

### oflarvaelessthan 10mmlong among the obligate ichthyoneuston can be related to the strategiesdisplayedby 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., Ano

### plopomajmbvia (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 samplelarvae 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 (Matareseet al. 1989),further contributing to the larger larval sizesin the neuston. Theimplication from these length-frequency observationsis 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. Thesizerange of availablefood organisms alsoexpandswith increasing larval size. Hempel and Weikert (1972)observed that becausephytoplankton
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 theperiod ofdrift 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 someofthe 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 donot survivetorecruitment. The widespread dispersal of larvae in the neuston may be facilitated by various mesoscale oceanographic features as well as wind transport and prevailing patterns ofcirculation. Eddies, offshore jets, meanders in the alongshore currents, and surface slicks associated with internalwaves 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 occurringDOYLE: 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 favorsretention oftheir larvaein 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 surfacetransport 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 youngjuveniles are still present in the neuston, they are likely to be transported away from the coastal zone. Postlarvae andjuveniles of 

### Cololabis saiva and 

### Anoplopomajim

### bvia 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 inshorehexagrammids and cottids, there is some evidence to suggest that large prejuveniles andjuveniles 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. Heproposed 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 includehigh 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 ofprey. In addition, the high light intensity at the surfaceduring thedayis likely tomake neustonic fish eggs and larvae more visible to predators. Surfacetransport 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 specificto the U.

### S. west coast. For instance, the heavy melanistic pigmentation on the dorsal surface of larvae and earlyjuveniles 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 offthe 

### 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 featurein 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 enhancedgrowth and reduced levels ofpredation. For instance, acceleratedembryogenesis is characteristicoffish eggs in theneuston, 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 offish 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)proposethat the surface layer ofthe 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 Wei

### 159DOYLE: NEUSTONIC ICHTHYOPLANKTON CalCOFl Rep., Vol. 33,1992

kert suggest that the few enduring neustonic metazoa, including fish larvae, encounter relatively little predatorypressure during the daytime. Based on their investigations of feeding among fish larvae andjuveniles 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 offish 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 thehigh densities ofzooplankton 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 offish 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 ofDungeness crab megalopae and fish larvae andjuveniles 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 conditionsfor 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 offishes 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 ofthis manuscript.


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Translated from Russian by Israel Program for Scientific Translations,Jerusalem, 207 pp. 86~299-317.

100 pp.



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