Ibution of Cetaceans and Sea-Surface Chlorophyll Concentrations in the California Current

Marine Biology 91,385-402 (1986)

D1:::;ibution of cetaceans and sea-surface chlorophyll concentrations in the California Current

R. C. Smith ', P. Dustan ', D.Au3, K. S. Baker4 and E. A. Dunlap '

Universitj of California Marine Bio-Optics, Department of Geography, University of California at Santa Barbara; Santa Barbara, California 93106, USA * Department of Biology, The College of Charleston: Charleston, South Carolina 29424, USA National Marine Fisheries Service, Southwest Fisheries Center: La Jolla, California 92038. USA Univenity of California Marine Bio-Optics, Scripp5 Institution of Oceanography, UniverGty of California at San Diego: La Jolla, California 92093, USA

Abstract southern California. seaward of the borderland province (Shepard and Emery. 1941). A census of marine mammals was conducted off the coast The work reported here began ;is two separate research of California (USA) in 1979-1980. The distribution of sea- efforts on board the same ship aimed at obtaining a census surface chlorophyll was determined at the same time by of marine niammals in the California coastal region and at onboard fluorometry and by remote sensing using the obtaining surface-validation temperature and chlorophyll Coastal Zone Color Scanner on the Nimbus-7 satellite. data over this broad area in support of satellite sensors. Comparisons of species and chlorophyll distributions indi- The surface data included tlle abundance and distribution cate that marine mammals are not randomly distributed of marine mammals froni sightinss and the continuous with respect to chlorophyll. Cetaceans were more abun- along-track recordings of near-surface temperature and dant in the productive coastal waters than in the offshore chlorophyll concentration. The combined data sets allowed oceanic waters of the California Current. This supports the a quantitative evaluation of sighting with respect to the hypothesis that the distributions of some cetacean species temperature and chlorophyll characteristics of the waters may be related to the mesoscale features that are manifest surrounding the sites where mammals were observed. The in the patterns of chlorophyll as revealed in the satellite results demonstrate that cetaceans tend to be most abun- imagery. It is suggested that oceanic chlorophyll may be dant where chlorophyll is most concentrated. This is con- used as a habitat descriptor for selected marine mammals. sistent with the hypothesis that cetacean habitats are pri- and that remote sensing will provide complementary data marily defined by the coastal. surfiice water-mass which is useful in the interpretation of observed distribution pat- rich in chlorophyll. and that the mesoscale dynamics of terns of marine mammals and in the estimation of their these waters are important to the different cetaceans. It can abundance. further be hypothesized that the distribution of cetaceans is proximally related to the mesoscale distribution of primary productivity through links in the food web. These ideas are not new. Whalers have long known that Introduction wliales could be found where their food is plentiful (Fox- ion. 1956). In the Pacific. studies have shown that areas of The rich cetacean fauna off California. first described com- mixing. upwelling. and frontogenesis frequently attract prehensively by Scammon (1874). is the subject of increas- whales (Uda. 1954. 1962: Omura and Nemoto. 1955: Uda ing interest as human activities continue to intensify in and Nasu. 1956: Uda and Dairokuno. 1957; Uda and SU- coastal waters. Reviews (Norris et al., 1976: Morejohn, zuki. 1958; Nasu. 1957. 1963. 1966; Rovnin. 1969; Volkov 1977 a) have emphasized both the diversity and mobility of and Moroz. 1977: Berzin. 1978: Clarke e/ uL. 1978; Gaskin. these cetacean populations within the California Current. 1982). The same appears true for the smaller dolphins and This marine biome is well known for its rich biological pro- porpoises (Gaskin. 1968: Kasuya. 1971: Evans. 1974. 1975; duction (Owen. 1974) due to upwelling and the mixing of Miyazaki e/ (I/.. 1974: Miyazaki. 1977: Miyazaki and Nishi- surface water-masses (Reid et a/.. 1958). Although one of waki. 1978: Hui. 1979: Au and Perryman. in press). We the most intensively studied marine ecosystems in the suggest that if statistical relationships can be found be- world (Hickey, 1979), understanding of the extent and tween cetacean habitats. as distinguished by different tem- constitution of its cetacean fauna has remained sketchy. perature and/or chlorophyll regimes. then the spatial de- This is especially so beyond the continental slope. or off termination of these variables by remote sensors can quan- 386 R. C. Smith er a/.:Cetaceans and sea-surface chlorophyll titatively aid the estimation of abundance and distribution (generally < 150 km) and offshore components. The near- of marine mammals. While the data presented here were shore region is primarily related to the seasonal fluctuation not obtained expressly for this purpose, the methodology of wind-driven upwelling along the coast. The region off- discussed holds considerable potential for estimation of shore from the coast is more associated with the stronger populations in the sea. Indeed, a main objective of this southward flow of the California Current. For con- work is to suggest that combined ship and satellite sam- venience, we frequently refer to the inshore component as pling of the ocean may permit more quantitative as- “coastal” waters and the offshore component as “oceanic”. sessments of living marine resources. but emphasize that both components are part of the Cali- Both sea-surface temperature (Bernstein et al., 1977; fornia Current system. The coastal water tends to be chlo- McClain. 1981; Bernstein, 1982; Brown and Evans. 1982) rophyll-rich and is often differentiated sharply by fronts and chlorophyll concentration (Gordon and Morel, 1983) from the offshore, more oceanic water that grades into the can now be quantitatively determined by satellite sensors. core of the California Current. Both the oceanic boundary Sea-surface chlorophyll is related to the primary pro- of this coastal water and the water mass itself are charac- ductivity of the water column to the depth of the euphotic terized by dynamic mesoscale features. zone (Smith, 1981), so that surface chlorophyll measurements may be used to estimate the distribution and amount of oceanic productivity (Smith et a/., 1982; Smith, Materials and methods 1984; Brown et al., 1985: Eppley er al., 1985). These data can be obtained from both ships and satellites, providing A coastal marine mammal survey (Au and Duffy. 1979: alternate and complementary sampling schemes. Satellite Baker eta/., 1984) was conducted from the R. V. “David data are generally less accurate at single station points than Starr Jordon” between 27 September and 20 October 1979 those from ships, but provide almost real-time, synoptic between Cape Mendocino and the tip of Baja California coverage of large areas. The combination of ship and satel- (see Fig. 1 for the northern portion of the survey area). A lite sampling techniques permits a calibrated mapping of second marine mammal survey (Au. 1980) was made be- the regional distribution of sea-surface temperature and tween 17 June and l l July 1980. following a similar track chlorophyll concentrations (Smith and Baker, 1982; Smith pattern. but going south only to the latitude of Point Eu- et a/., 1982; Brown ef al., 1985). genia. There were additional legs on this cruise seaward of The purposes of the present work are: (I) to discuss the the previous September-October coverage, designed to in- relative abundances and distributions of cetaceans and vestigate the effects of deep-sea seamounts on cetacean dis- their relationships with ocean-water properties in Cali- tribution. fornia coastal waters; (2) tosuggest methodologies for the Each day. the scientific crew searched continuously for utilization of synoptic satellite images (and the statistics de- mammals as the ship cruised in an offshore direction. They rived therefrom) to optimize sampling strategies and im- used 25 X 150 mm Fuji binoculars mounted port and star- prove abundance/distribution estimates of cetaceans. board above the flying bridge. At night. the ship sailed to This study focuses on the California Current. which the shoreward start-point of the next day’s leg. Along-track brings cold subarctic water slowly southward along the temperature and chlorophyll measurements were made California Coast. The current merges with tropical water continuously. 24 h a day. Vessel speed was between 9 and around Latitude 23”N. Its western boundary. about 10.5 knots (1 knot = 1.85 km h-’), The observer’s horizon 700 km from the coast, is the variable transition region be- was approximately 12 km away. Upon sighting a cetacean tween subarctic and Eastern North Pacific Central water. school. position. distance, and bearing information were Seasonal coastal upwelling in spring and summer is driven recorded. Then the ship usually made a close approach for by prevailing northwesterly winds. The major centers of species identification, determination of school size. and upwelling occur at Latitude 41’N in the vicinity of Cape behavioral observations. Mendocino. at Latitude 35”N off Point Conception, and at Navigation and sighting fixes were provided by a Mag- Latitude 28”N off Point Eugenia. Within the Southern novox Satellite Navigational system with an accuracy of California Bight, islands and irregular bottom topography roughly one-half nautical mile. Along-track temperature, contribute to locally intense, highly variable mixing and salinity and chlorophyll concentration data were recorded upwelling. which is intensified in the fall months by in- continuously 011 strip-chart recorders and sampled at 1 min teraction with the seasonal Davidson Counter Current. intervals with a minicomputer (Hewlett Packard 9845). Thus, while the California Current may be envisioned as a Temperature and salinity were recorded from the output of “wide body of water which moves sluggishly toward the the onboard. calibrated thermosalinograph (Ocean Data southeast” (Sverdrup era/., 1942), its local structure is Equipment TSG- 102). Chlorophyll fluorescence was mea- characterized by highly variable swirls, eddies, and inter- sured with a flow-through fluorometer (Turner Designs) mingling of water masses (Bernstein el a/.,1977; Hickey. and calibrated periodically with discrete extracts of chloro- 1979). phyll (Smith et a/,, 1981). Reid et a/. (1958) and Hickey (1979) have discussed the Satellite imagery from the Coastal Zone Color Scanner California Current system, its seasonal variability. and aboard the Nimbus 7 satellite (Hovis et a/., 1980) was cap- cross-shore structure which can be divided into nearshore tured at the Scripps Satellite Oceanography Facility. Image R.C.Smith CI (I/.: Cetaceans and sea-surface chlorophyll 387

Fig. 1. Northern area of marine mammal survey conducted from the R.V. “David Starr Jordon” between 27 Sep- Sin Diego tember and 20 October. 1979. Locations of the sighted cetacean schools (del- . Delphinids phinids and whales) are indicated by . Whales circles and triangles, respectively. The average hourly value of chlorophyll plus I’ , I Chl + Ph lye1 pheophytin, in units of mg pigment nP. 11 m ’ rng \\ is indicated by the along-track his- I tograms. Cruise track is labeled by daily 1 onshore to offshore transects. where I “Leg 1” corresponds to 27 September or \ Julian Day 270. No sightings were made during the “night-time legs” of the cruise 12s“ 120”

processing and analysis were carried out by means of at- Grntnpus griseus. Tursiups trunca~usand Glubiccphala sp.). mospheric correction and a chlorophyll algorithm (Smith Adjusted relative abundance was calculated by first taking and Wilson. 1980: Gordon and Clark. 1981: Gordon (’1 n/.. the mean perpendicular distance from the trackline of the 1983) using software of the RSMAS group at the University sightings of a given species and dividing by the same for of Miami. Statistical analysis of the images was carried out Didphinus delphis. The latter is a conspicuous species at the UCMBO computer and image processing facility at against which we reference the others. This ratio is a rela- Santa Barbara. Contemporaneous sea-truth data from the tive sightability correction term which was next divided in- along-track record were used to check the validity of values to the numbers of sightings of the species of interest to ob- obtained from the processed satellite images. tain an adjusted school abundance. For each species, an The examination of relative abundance of each adjusted measure of total individuals was then calculated cetacean species in different parts of the coastal habitat by multiplying the adjusted school abundance by the geo- was of primary interest in our work. However, data on rela- metric mean school size (Table 3). The mean perpendicular tive species-abundance collected from ships are potentially distance of sightings is widely used to correct for dif- biased. because small schools cannot be seen as far off as ferential sightability. although strictly speaking it is correct can larger schools. and each species has its different only if each species has a negative exponential detection characteristic school size and behavior. A correction index function (Gates ern/.. 1968: Burnham eta/., 1980). Our was devised to adjust for this undersampling effect among data were insufficient for rigorous testing of this as- species with small average school sizes (Phocuenoides d~//i, sumption. The geometric mean school size was used be- 388 R. C. Smith el ul.: Cetaceans and sea-surface chlorophyll

Table 1. Cetacean species sighted in California Current region, VI ? Species relative abundance between Cape Mendocino and tip of Baja California, during the 100 R. V. “David Starr Jordon” cruise between 27 September and 20 50 ,,[Dolphins October 1979. The key numbers are used in following tables 5 v Key No. Specific name Common name ;LO a Delphinus delphis cn .- rd Phocoenoides doll; Dolphins VI -VI Other delphinids 1 Delphinus delphis Common dolphin 8 30 2 Phocoenoides dalli Dall’s porpoise L uVI 3 Grampus griseus Grampus c 4 Tursiops lruncalus Bottle-nosed dolphin 0 20 L 5 Globicephalu sp. Pilot whale a n 6 Lugenorhynchus White-sided dolphin E obliquidens 3 10 7 Lissodelphis borealis Northern right-whale dolphin 8 Stenella coeruleoalba Striped dolphin 0 9 , Orsinus orca Killer whale 0 100 200 300 100 500 600 700 IO Unidentified delphinid Dolphins and porpoises Estimated individuals per school Whales/ pinnipeds Fig. 2. Number of cetacean schools sighted versus estimated individuals per school. Inset shows species relative abundance. Full I Balaenoprera musculus Blue whale specific names are given in Table 1 2 Balaenoptera physalus Fin whale 3 Balaenoptera edeni Bryde’s whale 4 Megaptera novaeangliae Humpback whale 5 Unidentified rorqual Large whales 6 Berardius bairdii Baird’s beaked whale age school size was only 5.7 individuals (Table 2). Most 7 Mesoplodon sp. Beaked whale schools among species were small (Fig. 2). Even among 8 Ziphius cavirostris Goosebeaked whale D. delphis, which had a mean school size of 200 individ- Unidentified ziphiid Beaked whale 9 uals, schools smaller than 20 were seen more often than IO Physeter macrocephalus Sperm whale I1 Kogia sp. Pygmy or dwarf any other size interval. Since sighting conditions during the sperm-whale second cruise were obtained under relatively adverse 12 Other unidentified whale Whales weather conditions compared to the first cruise, these and 13 Pinnipeds Seals, sea lions the following statistics are based only upon results north of 30.5” North from the first cruise. The adjusted species indexes of total individuals (Table 3) show that the dominant delphinid was Delphinus cause it provides a heavier proportional weighting of the delphis (57%), followed by Lagenorhynchus obliquidens or presumed undersampled, smaller school sizes. Since school Pacific white-sided dolphin (l6%), and Lissodelphis size may be log-normally distributed for reasons given by borealis or northern right-whale dolphin (14%). all being Williams (1964) and May (1975). the geometric mean species with relatively large average school size. The re- should estimate the median, or most typical, value of ac- maining species, including Phocoenoides dalli, were rela- tual school size. tively rare. These latter species are those that were adjusted Twenty identified cetacean species were encountered for differential sightability. The numerical dominance by during the cruises (Table I). Fig. 1 shows the locations of D.delphis is evident. regardless of whether adjusted or the sighted schools from the first cruise off southern and nonadjusted measures are used (Fig. 2). central California; the average hourly value of chlorophyll Among the whales, Balaenopfera musculus, the blue plus pheophytin is indicated by the along-track histograms. whale, was the dominant species with 20 schools and 40 individuals (Table 2, Fig. 2). Next were the ziphiid whales, with 18 schools and 43 individuals (among these were Be- Results rardius bairdii, Mesoptodon sp. and Ziphius cavirostris). The remaining 14 rorqual sighting, including Balaenoptera Cetacean population distributions physalus, B. edeni and Megaptera novaeangliae, con- stituted the least abundant grouping. Physefer macro- Cetaceans were most frequent off the California (USA) cephalus, the sperm whale, with 2 schools and 25 individ- coast. On the first cruise 87% and on the second cruise 79% uals, and Kogia sp. (probably the pigmy sperm-whale, of the schools encountered were north of 30.5” North. The K. breviceps), with 4 schools and 6 individuals, were two most frequently seen delphinid off California was Del- species encountered only on the outer legs. phinus delphis or common dolphin (38% of all delphinid Fig. 1 summarizes the first-cruise locations of sighted schools, Table 2) followed by Phocoenoides dalli or Dall’s cetacean schools; the average hourly values of along-track porpoise (25%). The latter, however, was a comparatively chlorophyll plus pheophytin (mg pigment m-3) were only rare species in terms of total abundance because its aver- obtained during daylight hours, so that only the numbered R.C. Smith et a/.: Cetaceans and sea-surface chlorophyll 389

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Table 3. School size and relative abundance ofcetacean species offCalifornia. September-October 1979. Table entries listed in order from the largest number oftotal individuals sighted to the smallest number. Data is a subset from Table 2 and is based upon Legs 1-14.23. and 25 off southern and central California (Fig. I). “School size” gives arithmetic means (IA).logarithmic nieans (i~).standard deviations (stdL) and geometric mean. “Perp. dist.” gives perpendicular distance in nautical miles. based upon sightability characteristics of each species and weighlings factors. All delphinids except P. dalli, Grampus griscus, Gluhicepliulu sp. and T. rruncums are given the same weighting factor (wt= I): of the latter group. Glubicephu sp. and T. truncurus are given equivalent weights. The weighting factnr for a given species is the mean perpendicular distance. 2. divided by the same for D. delpliis (d= 1.759). “Tot. individs” gives adjusted index of total individuals= (n)(geometric mean) + (wt): whales were not adjusted. as school and sample sizes were miell

Species Sight- School size Perp. dist. (nni) Tot. individs ings (n) .i-A XL stdL &Om. d wt non-adj. adj. mean (arith.) (geoiii.)

Dolphins Delphinus delpliis 38 20 1 .o 1.89 0.745 71.6 1.759 1.00 7639 2950 Lagenorhynchus ubliquidens 3 298.3 2.44 0.213 275.4 1.759 1.00 895 826 Lissodelphis borealis 5 I65 .O 2.15 0.265 141.3 1.759 1.00 825 706 Phocoenoides dalli 29 5.7 0.64 0.325 4.36 0.617 0.35 165 361 Grampus griseus 8 21.3 1.17 0.433 14.8 1.336 0.76 170 156 Globicephala sp. 3 30.0 1.44 0.231 27.5 1.348 0.77 90 107 Tursiops truncatus 4 13.8 0.94 0.489 8.7 1.348 0.77 55 45 Stenella coeruleoalba 1 3.0 0.48 - 3.02 1.759 1.00 3 3 Orsinus orca 1 2.0 0.30 - 1.99 1.759 1.00 2 2 Whales

- - Baluenoptera musculus 19 1.95 - 37 - Other rorquals IO 1.50 - - - 15 - Ziphids except Berardius bairdii 12 2.08 - - - 25 - Berardius bairdii 2 4.00 - - - 26 Physeter niacrocephalus 3 8.67 - - - 26 - Kogia sp. 4 1.50 - - - 6 -

daytime legs of the cruise have sightings indicated, whereas count for a “nominal sighting radius”. which provided val- chlorophyll measurements were made both day and night. ues of an average and a variance (see below) of chlorophyll Many of the sightings or groups of sightings (Fig. 1) were for the vicinity of the sighting location. Fig. 3. using all main the vicinity of seafloor topographical changes and re- rine mammal sightings. shows the number of (a) sightings gions of relatively persistent. high chlorophyll. For in- versus chlorophyll concentration in five intervals stance. the sightings at the ends of Legs 1 and 2 were in the (0.01 <0.03, 0.03<0.l, 0.1<0.3. 0.3< 1.0, l.O< IO) in units vicinity of the Tanner and Cortez Banks. an area important of mg pigment m-3. (b) daylight transect blocks for each of to fishermen. On Leg 5, the whale sightings occurred near these same five chlorophyll intervals. and (c) the cor- Pioneer Seamount, an area that once supported a near- responding number of sightings normalized by the number shore whaling industry (Rice, 1963 b). Sighting along Leg of daylight transect blocks. 8 occurred along the topographically complex Mendocino Also shown in Fig. 3 a, by the dashed histogram values. Escarpment. Thus, casual observation would suggest that are the number of sightings that would be expected in each cetacean schools are concentrated in waters of relatively chlorophyll interval if the mammals had been randomly rich productivity and are not distributed at random among distributed with respect to chlorophyll concentration and different chlorophyll concentrations. would thus have been sighted in proportion to the distance There is, however, a stochastic element to the shipboard searched (Le., in proportion to the number of daylight observations, which might explain the above. To test transect blocks in each chlorophyll interval as shown in whether cetaceans have a random distribution with Fig. 3 b). A chi-square test of the hypothesis that the respect to chlorophyll in space, all sightings were divided cetaceans were sighted in proportion to the number of day- into several chlorophyll concentration in;:rvals. The sight- light transect blocks in each range led to rejection of the ings within chlorophyll concentration intervals were then hypothesis of a random distribution of sightings with re- averaged or normalized by the different number of day- spect to chlorophyll concentrations at the 99% confidence light transect blocks within each concentration interval. level (DF-4. f=33.6). The number of sightings per day- Transect blocks are one-minute time intervals of integrated time transect block was also regressed against the mean along-track chlorophyll data (including time intervals chlorophyll concentration of each interval (Fig. 3 c) and without cetaceans), each corresponding to a distance or gave a sample correlation coefficient of 0.92. A Student’s roughly 300 m (at IO knots). The chlorophyll value used to &test indicated that the slope of this regression was signifi- represent a sighting was the mean of 25 transect blocks, cantly different than a slope of zero (DF=3, equal to k 12 min from the actual point of sighting to ac- 0.05 z P> 0.01). providing further evidence for rejection of R.C. Smith er ul.: Cetaceans and sea-surpace chlorophyll 39 1

125 Sightings of individual species were too few, once they a were divided into appropriate chlorophyll concentration intervals, to allow for meaningful statistical testing of their $‘expected” on basis of distance distributions in space. However, separate tests were done number of mammal searched In each for the combined mysticeti or baleen whales and for the observations in each chlorophyll Interval combined odontoceti or toothed whales. There were only chlorophyll interval A3 30 observations of the former, and a chi-square test of the hypothesis that they were distributed randomly with respect to the chlorophyll concentration gave a value just below the YO% level of confidence (DF=4, ~”7.3). Also, a t-test of the slope of this regression indicated that it was not significantly different from zero (DF=3, P> 0.10). Thus. at this level of confidence, one could not decisively reject the hypothesis that mysticeti were distributed randomly with respect to chlorophyll concentration. In contrast, a chi- transect blocks In each chlorophyll square test of the odontocete sightings led to a rejection of interval (%) the hypothesis of a random distribution at greater than the 97.5% confidence level (DF=4. ?=12.6). The number of .64 ”’ sightings of odontocetes per daytime transect block was al- 0 .01 .03 0.1 0.3 1.0 ~~(mgm-5 so regressed against chlorophyll concentration, giving a sample correlation coefficient of 0.81. A t-test of the slope c- 2.ia of this regression against zero showed it to be in a bor- derline area between significance and nonsignificance (DF=3, O.lO>P>O.O5). These results are consistent with number of sightings r =.92 in each chlorophyll the hypothesis that toothed whales are found more fre- 1% Interval per daytime ’’O quently at higher chlorophyll concentrations. transect block

0.0 Cetaceans and chlorophyll variance .Ol .03 Or1 0.3 1rO 15 ‘Chl(rn9 m3)

Fig. 3. (a) Number of marine mammal sightings versus chloro- Shipboard observations of along-track chlorophyll concen- ph) II concentration divided into five logarithmic intervals tration and marine mammal schools suggested that some (0.0I<0.03.0.03<0.1. 0.1<0.3.0.3<1.0. 1.0<10, in unitsofmg species were not only associated with regions rich in chlo- pigment tK3); dashed “expected” lines show number of ob- rophyll but also with areas where major changes in the sur- servations based on assumption of a random distribution in proportion to number of daytime transect blocks searched in each in- face characteristics occurred, e.g. at interfaces such as drift terval of chlorophyll concentration. (b) Number of daylight tran- lines, shear zones, convergences and the coastal-offshore sect blocks (%) in each chlorophyll interval for all mammal sight- water boundary. ings: transect blocks are one-minute intervals of shipboard ob- Our along-track data provided a measure not only of servations. (c) Number of sightings per daytime transect block (ar- bitrary normalization) versus chlorophyll concentration (n= 223, the concentration of chlorophyll but also of its variance. r=0.92) Continuously recorded along-track data can, for con- venience of analysis, be integrated into I-min intervals the hypothesis of no dependence. This also provides a mea- which we refer to as transect blocks. Any number of these sure of the degree of correlation between sightings per day- transect blocks can be further averaged to obtain a mean time transect block and chlorophyll concentration, and is and standard deviation of the along-track data for some consistent with the hypothesis that more sightings occur at distance in a given time interval over which the ship has higher chlorophyll concentrations. traveled. The mean and standard deviation of all pigment The robustness of these statistics was tested by dis- recorded k 12 min of each sighting was calculated. Twenty- tributing the data into several different numbers of equally five min is approximately equal to 4 nautical miles of track spaced (on a log scale in order to span three orders of data and is equivalent to 7 km or 5 satellite pixels (picture magnitude in chlorophyll concentrations) chlorophyll in- elements) at a speed of 10 knots. This provided a “nominal tervals and also by selecting the chlorophyll intervals with sighting radius’’ of a circle encompassing the sighted mam- the requirement of obtaining an equal number of transect mals. The radius was chosen small enough so that chloro- blocks per chlorophyll interval, again for several different phyll variance would be sensitive to sharp frontal bound- numbers of intervals. In all these cases, chi-square tests of aries yet large enough so that mean chlorophyll would be the data and t-tests of the corresponding regression slopes representative of the region around the sighting. A dou- against zero lead to rejection of the hypothesis that the ma- bling or halving of the chosen radius did not significantly rine ir.amnial sighting were independent of chlorophyll influence the statistical results. Thus, for each sighting lo- concentration. cation an average and a coefficient of variation of the 392 R. C. Smith rr (I/.; Cetaceans and sea-surface chlorophyll

MYSTICETE d show similar data for odontocetes. The CV was subdi- a vided into intervals such that there were an equal number of transect blocks per CV interval. so that if the ob- number of baleen ______expected servations were randomly distributed in space, one would whales observed 5 number expect an equal number per CV interval. This “expected” per CV interval (6) number of sightings per CV interval is indicated on Fig. 4 a and c by dashed lines. 0 cv For mysticete whales, a chi-square test comparing the observed and expected frequency of sightings for each in- 2.0 terval gave a chi-square of 7.10 (DF=4, P=0.14) so that 1.67 b I the hypothesis of a random distribution with respect to number of baleen r2z .a8 chlorophyll variation could not be rejected at the 90% level whales observed 1.0 of confidence. It is still of interest, however, to note that a in each CV interval per daytime transect block regression of normalized observations versus CV (Fig. 4 b) gave a correlation coefficient of r=-0.94. A t-test of the slope of this regression with that of zero indicated that it is 0.0 cv significantly different from zero (DF= 3. 0.05 > P). If this tendency for mysticete observations to be more numerous ODONTOCETE 1 39 __ in areas of low chlorophyll variation were to be confirmed C 3047 I by further research. it would indicate a sharp contrast in _-____. this habitat descriptor as compared to that for odontocetes. number of toothed For odontocetes. a chi-square test comparing the ob- whales observed 20 c per CV interval servations against the hypothesis of an independent distribution with respect to chlorophyll CV indicated that the null hypothesis could be rejected (DF=4, x2= 19.7. 0.01 > P). In contrast to the baleen whales, the normalized sightings of toothed whales showed a positive‘ correlation d 2.0 1 (r= +0.70) with CV. This suggests that higher num- J 1.43 1.43 r - 7n bers of odontocete sightings occurred in regions ofrelative- number of toothed whales observed ly high chlorophyll variability. 1.0 in each CV interval per daytime transect block Cetaceans and physical water types 0.0 The above chlorophyll statistics. which may serve as habi- Fig.4. Nuntber of mysticete (baleen) whale sightings (a) and tat descriptors, are also associated with the conventional number of odontocete (toothed) whalc sightings (c) versus chloro- physical parameters used to characterize water masses. For phyll coeficient of variation (CV) divided into equal frequency in- example. a major break in surface temperature and salinity tervals. Expected number of observations based on assumption of a random distribution with respect to CV is shown by dashed line. often occurred at the coastal-offshore water boundary (b) and (d) Number of mysticete (N=30, r=-0.94) and odontocete which also often differentiated regions of low and high (IV= 136. r=0.70) whale sightings per da) tinie transect-block chlorophyll concentration (Fig. 5). This boundary tended to correspond to the surface-density isopleth. u,= 23.8. Sig- ma-i is determined from temperature and salinity (see along-track pigment concentration within this “nominal Sverdrup et a/.,1942) and. off California. decreases with radius” was calculated. These calculations are both mean- offshore distance (see Lynn el al., 1982). A classification of ingful for sighting statistics and useful in providing a the cetacean sighting data as coastal or oceanic, on.the means whereby both ship and satellite data can be directly basis of interrelationships between temperature. salinity intercompared (see “Discussion”). and chlorophyll, and the relationship to fronts. tended to We compared the number of schools of Mysticeti and be separable by this sea-surface density interface. Fig. 5 of Odontoceti at five different levels of coefficient of vari- shows that Delphinus delphis were encountered in outer ation (CV) of chlorophyll concentration. The CV will be coastal and in oceanic waters. while Phoecoenoides dalli relatively large in regions of high chlorophyll variability. were encountered primarily in coastal waters. as indicated such as frontal regions. and relatively small in areas where by the dashed envelope lines relative to the 0,=23.8 line. the chlorophyll concentration is homogeneous. Fig. 4 a and In the satellite imagery a persistent color/temperature b show the data for mysticete whales; Fig. 4a the num- front was also recognizable. Water inshore of this color/ ber of these whales observed as a function of the CV of temperature front (high density, salinity and chlorophyll chlorophyll concentration, Fig. 4 b the number observed but low temperature) had characteristics of recently up- per daytime transect block with respect to CV. Fig. 4 c and welled ’ atcr. The water offshore this front was character- R. C.Smi~het ol.; Cetaceans and sea-surface chlorophyll 393 istic of subarctic water of the California Current system data showed that strong fronts were most apparent in the (Hickey. 1979). This break between oceanic and coastal along-track data where the ship entered or left these meso- waters was often accompanied by abrupt changes in the scale features and crossed one water type, or habitat. to an- encounter rate of birds and mammals. We have therefore other. used this color/temperature front as the seaward boundary The field investigation sampled relatively less of the off- of coastal water. This front is shown in two satellite chloro- shore oceanic water, so there are fewer data concerning the phyll images in Figs. 6 a and 7. It persisted more or less co- importance of that province as a cetacean habitat. If the incident with the slope break (2 000 m isobath) for the en- coastal water were the major habitat, there would be tire period of the cruise. greater numbers and more species seen in coastal versus The ship sampling-intensity by itself was not adequate oceanic water, relative to the allocation of sampling effort to give a detailed areal picture of the complexity of the in the two kinds of water. This follows because, as dis- coastal-oceanic boundary. However, mesoscale features cussed above. most cetaceans were found in higher chloro- were indicated by abrupt changes in the along-track data. phyll waters which, in these areas and at this time, were From the satellite data. these mesoscale features can be usually coastal waters. Cetacean schools were indeed more identified (Fig. 6 a). Comparison of the ship and satellite frequently encountered in coastal waters than expected on the basis of sampling effort. but the statistical significance of this difference varied according to the stratification of the sample, as shown by several chi-square tests (Table 4). Significantly more cetaceans were sighted in coastal waters than oceanic waters (P

Table 4. Cetacean distribution by water type. Water type was determined by inspection of along-track records of temperature and salinity; chi-square tests were based upon miles sampled in the two kinds ofwater. Miles searched were along Legs I- 14. 23 and 25

Area Miles searched Schools observed

All cetaceans Dolphins only' Whales only Coast- Oce- Total Coast-Oce- Total xz Coast- Oce- Total xz Coast- Oce- Total xz al anic al. anic al anic a1 anic ~ ~ SouthernCali- 1186 3895 5081 I8 32 50 3799 9 II 20 4098' 9 21 30 0419 tornia Bight Central 65962436 9032 82 17 99 4341: 61 13 74 2863 21 4 25 1019 Caltfornid Pooled 7782 633 1 1411 3 100 49 149 8 I%** 70 24 94 1343.' 30 25 55 I316

Family Delphinidae * Pi0.05 ** PcO.OI 394 I and sea-surface chlorophyll 395

Fig. 6. (elontinu< xi)

I’lfnlcn‘ (111s Clll ill 3)

K.ln~e \ i .Sill

-3 x 0.0I4 -2.40 0 36 t 0.40 I12 27 Y 0.64+0.52 ni 0.57k0.29 50 z9 I).I3 2.80 0.89 20.76 86 78 I 0.50 0.60

8 n 6 I ~ 0.83 0.7 I +o 09 13 II 3 L2Ik 1.12 Y 3 0.77f0.36 47 6 0 I? -1.81 0.4ii0.47 104 60 I 0.35 0.36 7 0.43 2.4Y 0.YltO.62 6X 25 2 0.42 10.04 9 0.51 +0.0s 9

I6 0.16 -0.x) o45ko.20 59 IO 14 0.3s!r0.22 58 0.47f0.17 37 6 O.I? -0.86 0.3lt0.28 92 13 6 0.83 c 1.28 I54 0.40-0.32 SO 7 0.12 0.Y7 0.31t0.14 7Y 52 4 0.50_t0.19 38 0.60k0.31 52 2 0 12 -0.33 0.17~0.0Y 54 7 0. I8 ?z 0.04 21 0.16+0.04 25 56 0.08 1.87 0.60i0.4Y 82 24 16 0.63? 0.46 73 0.55f0.23 42 __~ 396 K <' Siiii~liei ul: (7et,iceans and sea-surficc chlorophyll

\ve could reject the hgpothe\is hj F-test that its sightings were lioin iircas with tlic siiiii~mean chlorophyll level, i.e.. within the chlorophyll range for a species. fidelity to a spe- citic chlorophg ll habitat \,\a\ lo\v. Estimate of \vitliin-liabitat heterogeneity (CV of the me;in \ari;ince of the chlorophyll concentrationl showed there wcrc dilTcrences betu een species not correlated with ;ibsolute pigment Ie\.els. For example. Dekhinus delphis wi\ widely distributed in heterogeneous. niedium-chlorophyll environinents. while Rtrltrciioptrrtr niitsculus was 5iglited predominately in le\> cariablc. medium-chloro- phq'll regions. ~'lioi.or/i,)irh,.r ihi//i and Liigenorlijwclius oh- /~quidemwere \ighted primarily in medium-to-high chloro- ph! II w;itei-s. \\IIo\c incan\ exhibited significant chloro- ph!lI ditlercncet ii~c,ich sighticg (chlorophyll concentra- R.C. Smith el ol.: Cetaceans and sea-surface chlorophyll 397 tions ranged from 0. I3 to 2.8 and 0.4 to 2.5 mg pigment the pixels within a 7 kmX7 km (5X 5 pixel) box centered n~-~.respectively: Table 5). on the sighting location. and then taking a mean of all In contrast. pigment differences between Grampus these data. This area on the satellite image is approximate- griseus sighting suggest that this mammal is attracted to ly the area within the “nominal sighting radius” discussed much more constant environments (0.61 to 0.83 mg pig- above. and therefore provides an analogous mean. stan- ment m-3). Comparison of its between and within sighting dard deviation and coefficient of variation for comparison CVs supports the hypothesis (0.05 > P) that the sighting w,ith the ship data. Although the satellite data are consis- were in waters with the same mean chlorophyll concentra- tent with the ship data. there are fewer sighting statistics tion. However. this result is primarily suggestive since the because satellite passes and/or cloud-free imagery did not number of sightings is few. exist at the time of all shipboard sightings. Interestingly. the more geographically restricted Pho- Fig. 6 a shows a chlorophyll image of the California coenoides dalli commonly occurred over a wider range of coastal region during the period of the cruise. The absolute absolute chlorophyll levels within the generally high chlo- accuracy of this image is estimated to be (by comparison rophyll areas off northern central California than did the with ship data) k40R. Our point of departure for the work widespread Delphinus delphis, which tended to occur in reported here is the derived chlorophyll image. The black offshore waters. Evidently the more productive habitat of areas of these images are either land or clouds which have P. dalli is also characterized by large and changing vari- been set to zero value. Landmarks (e.&. Point Conception, ations in pigment level. Also. the data suggest that Santa Barbara, San Diego. the offshore islands) are easily Lagenorhynynchus obliqtridens and Lissodelphis borealis are identifiable by comparing Fig. 1 with the images. Phy- primarily coastal water species. On the other hand. Physe- toplankton pigment concentrations ranging from 0.0 I to ter macrocephalus (Rico. 1977) and Kogia sp. are clearly 10.0 mg pigment are represented by 18 equally-spaced oceanic by geography and water type. Other species. es- logarithmic steps from low (dark) to high (light) concentra- pecially ones occurring in or near the Southern California tion. corresponding to the grey scale on the images. The Bight (an area of much water-mass mixing). occurred in ship track (annotated for each leg of the cruise) has been both kinds of water. superimposed on the image. and also can be compared with Fig. 1. Note that each processed image not only rep- resents a synoptic view of the relative chlorophyll concentra- Satellite images tions in the area observed, but also is a matrix of quantitative information: the chlorophyll concentration at each Both qualitative experience and our statistics suggest that pixel (each “picture element” corresponds to a surface area oceanic chlorophyll concentrations and sea-surface tem- of roughly 1.5 kmx 1.5 km) location. As a consequence, peratures. as well as the variance of these properties. can statistical analyses can be carried out using such images be used as “habitat descriptors” for living marine re- (Smith and Baker. 1982; Smith e/ al., 1982). The variance sources. As a working hypothesis, it could be assumed that based on the image displayed in Fig. 6a is depicted by habitats of some Cetacea are primarily defined by areas Fig. 6 b. This “variance image” clearly demonstrates the with relatively high chlorophyll concentrations. In Cali- area of high chlorophyll variability (lighter) and the area of fornia waters at this time of year these are primarily de- more constant habitats (darker). Note that the offshore fined by the coastal. high-chlorophyll and low-temperature oceanic region is represented as a much more constant en- surface waters. It follows that the mesoscale dynamics of vironment than many inshore coastal regions. Again, the these waters, especially those determining distribution and offshore clouds which have been masked black during pro- relative productivity. are important to the different species cessing must be disregarded. of Cctacea. Ottr results indicate that this hypothesis holds Estimates of the distributions and abundances of when all observations are aggregated; however it is quite cetaceans are usually imprecise owing to the methods of likely that this habitat-descriptor hypothesis will also hold surveying their habitats. Airplane searches provide data at some level of generality for some individual species. We from low-flying, fast-moving platforms, while ships allow would also emphasize that the data necessary to ad- for more careful observations from a slower-moving plat- equately test, and to optimally use, this hypothesis have form. Both assume that all animals in the path are seen, not yet been collected. while realizing that many of them may avoid the ship or Table 5 also shows the characterization of marine mam- may be underwater at the time of the overflight. In addi- mal habitats by pigment concentration as derived from tion, it is known that the time that a cetacean spends at the satellite (CZCS) imagery. The table lists sighting for which surface is highly variable and somewhat species-specific. contemporaneous satellite imagery was available i6 h of a Using current techniques. a species abundance may be es- shipboard sighting. The mean pigment concentration from timated from counts of schools per unit area adjusted for the satellite picture elements (“sigle pixel”) corresponding detectability (Burnham er ai., 1980) and then multiplied by to the sighting locations are given, along with the standard mean school size and the total area searched to obtain an deviation and coefficient of variation of this pigment con- esimate of total abundance. Alternatively. if our habitat- centration from the average of all sighting locations. The descriptor hypothesis holds and if a cetacean species could “sighting area” data were obtained by first averaging all be associated with a given range of chlorophyll concentration. then the number of individuals per track-line area Discussion of the specific habitat searched (to total track-line iirea searched) could be normalized by the specific habitat iirea Cetaceans were sighted in coastal wter more lrequeiitly (to total area searched) for the region under study to obtain than expected on the basis of sampling allocation. Oui an estimate of total abundance. d,‘ita , strongly, stiggcst that in Ca1iforni;t coastal \\;rtcrs tlic For example. the image in Fig. 6a has been divided numerous cetace:in sightings were associated u ith cliloro- into three grey scale levels (Fig. 7) corresponding to low phyll-rich uaters nhich. in turn. are linked to both high (<0.3 nig pigment m-3). medium (0.3 to 1.0 mg pigment primary production (Chvcn. 1974) and rich and diver\? m-’) and high (> 1.0 mg pigment nV3) chlorophyll concen- fisheries and ichthyofiiuna (Horn. 1980). Tlicse water5 thur trations. These habitat divisions are based on the ship- appear to be a major habitat ofcetaceans. While our uork board data as well as upon the clearly delineated color/ is exploratory. it suggests that more extensive \hiplair- temperature front as seen in Fig. 6. An immediatc result craft/satcllite 5tratified sampling will be required for niorc from this habitat image is a quantitative estimate of the reliable statistics on cetacciin populations. turther. th,s three habitat areas. The non-cloudy area shown in this im- work indicates that more extensive. quantitative iiifornw age is approximately 21 1 000 kmz. and the areas of low. tion on ocean water types and posible habitat descriptorr medium and high chlorophyll correspond to 79 000. should be obtained in conjunction with distribution ;iiid I14 000. and 18 000 kmz or 37. 54 and 97 of the total abundance surveys. Although the possibility that \pecic\ cloudless area. respectively. A second observation from the ageregate in response to habitat productivity and vari,ibili- satellite imagery is that the color/temperature front was ty IS not the oiily plausible hypothesis consistent with cur relatively persistent (t 10 km of mean position) during the observations. the methodology discussed show\ the possi- two weeks of the survey in this region off the Cali- bility of quantitatively testing this and alternati\ e liypoth- fornia coast. indicating that these habitats may be rather eses. persistent. Total cetacean sightings per daytinie transect blocE, were highly correlated with increasing chloropliyll conceii- If shipboard observations can establish characteristics trations (r=0.92. Fig. 3 e). While a stratification by siiboi- of species habitats. satellite iniagcry can then be used to der suggested (the chi-quare test was not significant al the estimate habitat areas for calculating species abundances 907 level) that mysticetc whales are only weakly correlatcd within these areas. For example. Grcr/npu.s griseus was (r=0.62) with surface chlorophj II concentrations. the odonto found to be associated with a relatively narron range of cctes were significantly and positively correlated (r=O.S!) chlorophyll waters (Table 5). If we assume that the habitat with chlorophyll concentration. A chi-square test t~ deter- for this species is “medium” chlorophyll waters. then its mine if these whales had a random distribution with respe1:t abundance may be more accurately estimated from an ex- to chlorophyll allowed rejection of this null hypothesis at t!i, pansion of density calculated from the miles searched in 97.5% confidence level. Although it is clear that a signiti- that habitat and expanded to the total areal extent of only cant correlation exists behveen cetacean sightings and pri- medium chlorophyll waters. Thus. the total nautical miles mary production (as measured by pigment biomass). the (nm) searched within medium chlorophyll waters was degree of “coupling” and the ecological signiticancc ot 12 465 nm (or 41.3% of the total miles searched). Since the these observations is not obvious. A possible hypothc\is ii area of this habitat was 54% of the total habitat. we might that the distribution and abundance of’ cetaceans ;ire de- expect G. griseus schools to be 30% (0.54 t 0.41) more fined by the coastal surface-water mass. which is rich in abundant than an estimate that assumed the species habi- chlorophyll. and the link is via the food web. lloueier. tat was the total area. these “links” are likely to he species-specilic and ilia) he Other cetaceans seem to be associated with high chloro- indirect. For example. Evans (1981) suggested that Del- phyll areas (e.g. Phoceoenoides dallr and Lagenorph.wchus ~/I~IILI.Tdelpliis were concentrated at seamounts and along obliquidens). When sightings for these species were super- escarpments. not necessarily because of the high concen- imposed on the satellite imagery. it could be seen that they trations of chlorophyll there. but because thih species \bas occurred in near-shore. high-chlorophyll regions or in the using multisensory environmental cues related to the\<: high-chlorophyll areas of color fronts. If we were confident landmarks to orient during migration. of the fidelity of these marine mammals to these habitats. We have also shown that there is a significant relatioii- population estimates could be based on the areas of high- ship between the sightings of certain cetaceans and the co- chlorophyll water only. efficient of variation (CV) of chlorophyll. Further. wlicii During our survey, Mesoplodon sp.. P/i,vseter macro- stratified to suborder. the toothed whales werc significantly cephalus and Kogia sp. were associated with low-chloro- correlated with areas of relative high CV. ivhile the baleen phyll waters on the seaward side of the color/temperature whales showed a weak. but non-significant, negative corw front. This habitat is estimated as 47.5?; of the total area. lation (Fig. 4). The similar results obtained for chlorophyi! based upon the miles searched in such waters. but only concentration and CV may be due simply to tlic fact hat 37% of the area as determined from satellite imagery. We chlorophyll is. in many regions. correlated with its own CV. would therefore assume that abundance estimates of these The cetacean fauna was numerically dominated h~,Del- species would be adjusted down by 22% (1.0-0.37 t 0.475). phiriirs &/phis among the delphinid odontocetes and by 399

Hrr/iienop/i~txiniir.wir/m among the whales. D.tki~lphis is daily foraging. although its seasonal distributional changes gcncrallj considered the most abundant cetaccLin off Cali- are conspicuous (Brown and Norris. 1956: Brownell. 1971: foruia (Rice. 1963 b: Norris et (I/.. 1976). The abundance of Norris P/ id., 1976: Morejohn. 1977 b). and may be deter- H. n~iucu/u,srelative to other whale species was not eupect- mined in part by the seasonal movements ofwater masses. eJ. as the blue whale has been thought to be an infrequent. The dissimilarities between these delphinids sugge\t a transient species iii Calihrnia waters (Rice. 1963 b: Norris strong environmental effect upon their ecology. an effect c’t o/.. 1976: Morejohn. 1977 a). The ,remaining cetacean directly related to the contrasting nature of coastal and species showed a tendency for geometric decline in rclative oceanic waters. The latter is a less productive habitat. .rbuiidance iimong apecics (Fig. 2). Similar results were oh- where animals may be less specialized (MacArthur. 1972: taiiied during the second coastal cruise. with D. ~/c//J/~/.sand Pianka. 1976). iiiore far ranging in their foraging. and like- B. niil.scu/irs again dominating the cetacean fauna (Au. ly to form larger and iiiore complex social groupings. On 1980). This dominance pattern is a frequent attribute of the other hand. species of productive habitats can “afford” ecologiciil communities (McNuughton and Wolf: 1970) and to he more specialized and some may tend to occur in m:iy have utility in assessing the status of disturbed smaller groupings. These distinctions may explain the dif- bicmies. Doniinance inay arise from “niche preemption” ferences between De/phitiirs de/p/iis and Phocoenoides du//i. competition in a species guild whose ecology is dominated and may be analogous to the ecological differences seen by some single fiictor (Whittaker. 1972: May. 1975). For between primates (e.g. baboons) from sparse. resource-lim- cetaceans off California. this factor niay well be the suit- ited savanna and from productive forest (Crook. 1970). ability of the phyhical environment dominated by lateral A similar speculation would he premature lor the and vertical mixing processes. Variation in the pigment species of whales. considering the relatively small numbers content of mesoscale water-inasses is related to this mixing encountered. We niay point out however. that the aiid miij be associated with differences in prey arailahility. Boloenoptem tiiic.rcirlirs, a very specialized “swallowing” The contrasts in distribution. morphology and behavior feeder of krill (Nemoto. 1970) was encountered in greater hetw een Delphinu.s i/e/phi.s, Pl~ocooioiiie.~tkulli and even concentration in two general area where increased bio- Lupcnorli~ncliusoh/iyuic/eiz.s (for which few schools were logical production is typical. i.e.. the vicinity of Tanner- seen) may be examples of niche separation on the basis of Cortez Banks and the Pioneer Seamounts. Similarly. foraging differences. There are large populations of de/- D. humpback whales feed on krill and a variety of small fishes phi., in the subtropics and large populations of D. dull; in (anchovies. sauries. sardines) and were sighted in green. the subarctic. California waters represent range extensions high-chlorophyll waters. The fin whales also feed on small where these two populations meet and overlap. D. cki,lphi.s fishes in addition to krill but tend to be somewhat more was widespread in the outer coastal and oceanic Maters off cosmopolitan in distribution. California. On the second niarine mammal cruise. 11. delphit were encountered on sonie of the firthest legs offshore Phytoplankton. as measured by chlorophyll content. (out to 300 km). However. they appeared not to have been and Cetacea represent the opposite ends of the marine attracted by seamounts. Fishing observers aboard albacore food web. Co-occurrence would suggest that the distri- boats have also reported this species in offshore oceanic bution of organisms that comprise the intermediate levels waters. in one case 375 kni from the coast (M. Laurs. un- of the food web are also tied closely to the distribution of published data). D. delphis feeds opportuni\tically (Evans. primary productivity. Our observations suggest that the 1975). although with a preference for mesopelagic prey thin ribbons of increased biomass along fronts or stream- (Fitch and Browncll. 1968). It is diurnally active and niay line intersections are exploited by foraging cetaceans. form large schools. D.delphis is often associated with other Coastal fronts are often characterized by an enrichment of spcciec. notably Lugenorl?vni.hus ohliquidens, Li.ssodc~lpliis phytoplankton seauard of the front at shallow depths horeoli~.aiid the pinniped Zakopliirs colif0,nicrt~u.s.which (Mooers. 1978). These features might explain our ob- are all species that also form large aggregations (Leather- ‘servation that cetaceans frequently occurred seaward of the wood and Walker. 1977). Although the species appears to first frontal zone between coastal and nearshore waters. travel widely. seasonal migration is apparently not pro- Tilting and subsequeut shallowing of the mixed-layer near- nounccd (Norris et al., 1976). On the other hand. the mor- fronts could also increase the availability of food to for- phologically different P. dull/, perhaps the third most aging mammals. abundant cetacean off California (Rice. 1963 a). was abun- The general importance of bottom topography to ceta- dant only in the northern survey area and apparently ceans is unclear. Most cetaceans encountered in this study prefers the structurally complex coastal water having high were well offshore ofthe continental slope. In the Southern and vaping chlorophyll levels (Figs. 1 and 6). This species California Bight, the complex topography makes it difficult also feeds opportunistically on squids and schooling fish to generalize about topographic effects. We suspect that in- (Kajiinura et (I/., 1980). niay he capable of extra deep div- creased turbulence and the extension of coastal water with ing (Ridgeway and Johnston. 1966). and may feed at night increased phytoplankton biomass. e.g. as in the Southern (Morejohn, 1977 b). f’. dulli schools were small (averaging California eddy system (Owen, 1980). are the main reasons 5 to 6 individuals) in our study (Table 2). and were not for reported relationships between cetacean concentratioiis with other dolphins. The species may not travel widely in its and topography (Rice. 1963 a: Evans. 1975: Hui. 1979). 400 R.C. Smith et (J/,; Cetaceans and sea-surface chlorophyll

Thc Coastal Zone Color Scanner (CZCS). an rnstru- DS80-5, 1-9 (1980). (Southwest Fisherie\ Center. La Jolla, inent aboard the Nimbus 7 satellite. was especially de- California) signed to measure oceanic chlorophyll levels. and hence Au, D. W. K. and T. Dufty: Report of the first coastal marine mammal survey. Sept. 27-Oct. 24. 1979. Cruise No. DS79-10. provides information on the mesoscale features of coastal Rep. SW Fish. Cent. DS79-10. 1-11 (1979). (Southwest waters. Figs. 6 and 7 are satellite images from the CZCS Fisheries Center. La Jolla. California j taken during the cruise period. They show the richness of Au. D. W. K. and W. L. Perryman: Dolphin habitat5 in the East- detail and the spatial complexity of this marine en- ern Tropical Pacific. Fish. Bull. U.S. (In press) Baker. K. S. P. Dustan and R. C. Smith: Coastal marine mammals vironment. and illustrate the potential of the satellite tor survey October 1979. Ref Rep. Scripps Instn Oceanogr. 84-29. studying living marine resources. By conventional method- 1-49 (1984). (Scripps Institution of Oceanographq. La Jolla. ology. random sampling. irrespective of species sub- C‘aliliirnia) habitats. produces population estimates. However, the Bcrnstcin. R. L.: Sea surface temperature estimation using the above cctaCcan-environnient associations suggest that the NOAA 6 satellite advanced very high resolution radiometer. J. geophys. Res. 87,9455 -9465 (1982) variations in temperature. salinity and chlorophyll-pig- Bernstein. R. L.. L. Breaker and R. Whritner: California Current ment levels can delimit species habitats in order to improve eddy formation: ship. air and satellite results. Science. N.Y. such estimates. For instance. an appropriate sampling IYS, 353-359 (1977) atratcgy could be developed for enumerating species Berrin. A. A,: Whale distribution in tropical eastern Pacific waters. Rep. int. U%al. Coinnin 28. 173-177 (1978) strongly associated with frontal areas. Real-time satellite Brown. 0. B. and R. H Evans: Visible and infrared satellite re- imagery could direction ship and/or aircraft sampling to mote senaing: a status report. Nav. Res. Rev. 29, 7-24 (1982) these highly productive and highly variable. limited areas, Brown. 0. B.. R. E. Evans, J. W. Brown. H. R. Gordon. R. C. optimizing search patterns and the statistical data there- Smith and K. S. Baker: Blooming off the U.S. east coast: a from. The upwelling and frontal. high-chlorophyll areas in satellite description. Science. N.Y. 229, 163- 167 (1985) Brown, D. ti. and K. S. Norris: Observations of captive and wild Fig. 7 comprise less than 10% of the total area. yet between cetaceans. J. Mammal. 37, 31 1-326 (1956) 20 and 301 of the sighting were in. or in close proximity Brownell. R. L.: Observations of odontocele\ in central California to. these waters. Thus. the satellite images allow these high- waters. Norsk Hvalfangsttid. 53, 60-66 (197 1) ly dynamic and relatively small areas to be identified and Burnham. K. P.. D. R. Anderson and J. L. Laake: Estimation of sampled. and their areal extent. as a function of time. to be density from line transect sampling of biological populations. Wildl. Monogr.. Jefferson City 72, 1-202 (1980) quantitatively determined. Clarke. R., L. Anelio Aguayo and S. B. Del Campo: Whale ob- To the extent that the abundance of selected cetaceans servation and whale marking off the coast of Chile in 1964. Sci- can be shown to have statistically significant associations ent. Rep. Whales Res. Inst.. Tokyo 30, 117- 177 (1978) with habitat descriptors. more reliable estimates of their Crook, J. H.. The socio-ecology of primates. In: Social behavior in birds and mammals; essays on the social ethology of animals distribution and abundance can be made using contempo- and man. pp 103-166. Ed. by J. H. Brook. London. New York: raneous ship and satellite data. The synoptic overview pro- Academic Press 1970 vided by satellites also enhances the understanding of the Dixon. W. J. and F. J Massey: Introduction to statistical analysis. dynamics and scale of the biological and physical features 638 pp. New York: McGraw-Hill 1969 Eppley. R. W.. E. Stwart. M. P. Abbott and V. Heyman: Estimat- characterizing the habitats of Cetacea. This may lead to a ing ocean prima9 production from satellite chlorophyll: in- more fundamental understanding of cetacean ecology and troduction to regional differences and statistics for the evolution. Southern California Bight. J. Plankton Res. 7, 57-70 (1985) Evans. W. E.: Radio-telemetric studies of two species of small Acknow~ledgernents.This work was accomplished with the odontocete cetaceans. In: The whale problem: a status report, pp 385-394. Ed. by W. E. Schevdl. Cambridge. Mass.: Harvard help of many individuals. The authors would like to ex- University Press 1974 press their appreciation to the cruise leader T. Duffy. the Evans, W. E.: Distribution. differentiation of populations and marine mammal spotters including R. Pitman. S. Sinclair. other aspects of the natural history of Delphit1u.s delphis in the G. Friedrichsen and R. Clarke, the crew. and the captain of Northeastern Pacific. 145 pp. PhD dissertation, University of California at Los Angeles 1975 the R. V. “David Starr Jordan”. R. Evans. 0. Brown and J. Evans. W. E.: Orientation behaviour or delphinids: radio tele- Brown (RSMAS) provided help and software for image metric studies. Ann. N.Y. Acad. Sci. 188, 142- 160 (I 98 I j processing. C. Epstein and R. Lenard helped with the Filch. J. E. and R. L. Brownell: Fish otoliths in cetacean stomachs manuscript preparation and data analysis. J. Michaelson and their importance in interpreting feeding habits. J. Fish. contributed to the statistical analysis. The constructive Res. 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