RECEIVED AUG 2 '; 1977
The Ecological Energetics of the California Sea Otter, Enhydra lutris
Final Report U. S. Fish and Wildlife Service Contract #14-16-0008-2047
Principal Investig~tor Dr. Kenneth Norri~ Research Assistant Daniel Costa
DRAFT 20 August 1977 Written by Daniel Costa liiTRODUCT I ON The trophic impact of mammals on terrestrial communities has been wdl documented (Galley, 1960; Galley, 1968; Chew, R. and Chew, A. 1970).
~~: \'tever, few investigators have attempted to quantify the impact of
rrnJn:1ls on marine communities (see Lavigne, et !]_. 1976 for review).
· =-··ological investigations of marin~ communities have yielded a
\•f ll th of information concerning energy flow in pelagic communities ) us se l-Hunter, 1970) and an understanding of competitive and predator p1 ey interactions (Connell, J. 1961; Paine, 1971; Dayton, 1974, 1975).
Tl:~ sea otter Enhydra lutris, in nearshore communities offers a
rH•ique opportunity to study and synthesize our current understanding of
pr,~dator~-prey and ecological energetics. The impact of the sea otter on nearshore communities has been well
{ 1 (·~umented (Ebert, 1968; Lowry and Pearse, 1973; Wild and Ames, 1973;
~:: ,cton, 1974; Estes and Palmisano, 1975). Sea otters act as keystone
p ·dators altering the community composition as a result of their for
a~ ing activity (Lowr·y, L. and Pearse, J., 1973; Estes. P. and Palmisano, 1c 'S). The sea otters predation is so efficient on macro-invertebrate
~' .~;~ers such as sea urchins that they significantly reduce the impact or those gr.uers on algae primary production (North, 1974; Lowry and . Pr•. rse, 1973; Estes and Palmisano, 1975). In addition, the sea otter 1'1 f'a1 ifornia has been shown to have a profound effect on commercially
cl'l~ recrc.:atlonally important shellfish resources (Wild and Ames, 1973; Mi ler, 1975; Miller, Hardwick and Dahlstrom, 1975). The purpose of this investigation was to measure the trophic impact
ol the sea otter in California. The energy consumption in calories per· ~<: our understanding of the sea otters impact of nearshore corrmunities. There are many techniques available for the measurement of free .. ,•nging energy consumption of mammals (see Gessamen, 1973 for review; :: loer11a ker, flagy and Costa, 1976). Mast of these techniques have been II' •'·i on small marrmals and are inappropriate for use on marine mammals. U Jy four studies have attempted to measure trophic impact on ·!.,rgP marmmls (lamprey, 1964; Buechner and Galley, 1967; Boulva, 1973; .•: ·.1 l.avignP., _et al_, 1976). Two of these papers estimated energy con ·:r rnption in seals, but were estimates based on few direct measurements _ft~ulva, 1973; Lavigne, et ~. 1976). In this investigation, an estimate of energy consumption was derived ·om P'Jbl ished data on activity patterns of wild otters and oxygen con- ' nptfon of captive sea otters (Loughlin, 1977; Morrison, Rosenmann and i ·:tee:, 1975). In order to convert the estimated free-ranging oxygen con ·;,; rrpt ion to prey consumption the assim11 at ion efficiency, diet and r:-iloric content of prey ingested by sea otters were measured. These d.rta were then converted to prey consumed by use of a simple equation. -3- Materials and Methods l~·n,ln!J Behavior: Thl! foraging pattern of sea otters, Enhydra lutrfs. feeding in the P!. 1 abr!llo kelp forest, Pacific Grove, California was observed from ,_;flo:"! with a 15-45 power spotting scope. The length of dive, success rate .Jr.d 1 ype of prey items recovered were recorded. Unidentifiable prey items "rr·~~ classified as unknown. In order to follow seasonal shifts in diet, r·l:~ :•· vations were made on two consecutive days per month, from dawn to dusk, for· r months. Observations were made on 3, 4 September; 5~ 6 October; 6, 7 r·:flv'·Hber; 6, 7 December; 10, 11 January, and 14 February. Observations were (!10''!0d into monthly diets, and the overall diet for the six-month period. :~: h·· ir: Content of Prey: The following prey items were collected for calorific and biomass measure- IW:n • !Jal_iot~ rufescens, ~· wallensis, Hinnites multirugosa, Tivela. stultoru~_, I·~!_: !!J .2Pi'.1~scen~-· Cancer antennarius, Pugettfa l?roducta, f. richii, Strongylo t'':!:_I'J_ _l!!~ fran.fJl~il..!l.Y~~ .?_. _Qurpuratus. Prey items were collected with scub11 in ~.h·• I ;lp forests of Pacific Grove and Santa Cruz, California. The length or width or 11,~ intact prey was taken, along with the wet weight edible biomass. Edible tdnnt>s was that portion of the food item either eaten or digestible by a sell Gt~Tt· Edible biomass for molluscs was assumed to be everything excluding the ::;hr~11; for urchins only the soft matter inside the test was considered edible; for all parts of the crab except the dorsal carapace, and for r11_~l~;:'. ~Ji_a ~.P..E..· the who 1e ani rna 1 was considered edi b 1e. nvertebrate prey species length or width can easily be measured in the fir·H Population, size data already exists for many .of tfle sea otters' prey. it· rr-> In the Pt. Cabdllo kelp forest (lowry & Pearse, 1973; Pearse, unpublished . ...,... __ (~'t;~ . In order to convert modal sizes of prey to biomass, a regression f•:r ~,,'ible biomass to length was derived for 7 of the most co1m10nly eaten r·~~ it~ms. Edible portions of the prey were weighed fresh and placed in a lnr~!(l air oven at 80°C (Paine, 1971} until dry (at least 24 hrs.). The dry •.·l'f ·~' fs of the samples were then taken for determination of the \'let weight. dry \I i ·I n1tio. Dried samples were ground either in a spex mixer mill ~,olfth the ~ ai·lr-ss steel grinding ball or in a Waring blender. Pellets of appt·oximately 1 gr • .,,,r• mflde for determination of caloric content on a Parr model 61341 oxygen bomb '; ,.,, imeter, following the procedure outlined by lieth (1975). Corrections for llt!CL~ production and fuse wire combustion were made. Oupl icate combustions were made for 'ach individual prey sample. If the two combustions differed by more than 2%, a lid r: combustion was made. Differences of less than 1% were encountered in most well t,!nn;enized samples. At least 10 individual Tegula .!E.E.·• 7 individual l· stultcrum, 'l i•l(ivirlual ~-· opa!_~scen~, and 3 individual i· purpuratu~ were ground together to ,~,;~ .!! r arlequate pellet size. Pellets of all other prey items were aliquots of ir:di-. idunl prey. !:q:ll.: ve Sea Otters: five capf·ive sea otters were maintained to measure foLd consumption and 1~,s n ilati0r1 efficiency. Otters one and two were held in a small concrete 1sol.3tion Litn\: '•et1.·1e~n 12 and 17 December, 1973, at Sea World, San Diego, California. Th·~Y u r"• fE~d .~ diet of conm1ercfa1ly obtained clam, Spi.sula solidissirra. These two 1:1 t'rS h~d been held in captivity since December, 1972, and the clam, Spisula s!•!_i( issi!ll_a, made up most of their staple diet. Otters three, four and five were I :·p'. red in the \dld in the waters off Pacific Gr·ove, California by use of a large salrron ·4~p · et. These otters were coaxed to the side of the boat with squid while the dip u·t ·as m.1neuvered underneath to net them. It must be mentioned that these ott1~rs 1.1r-' accu-; tcmed to being hand fed by humans. Ottr~;·s three, four and five were held in a holding tank constructed at the l!"pk ns Marine Station, Pacific Grove, California. The tank was made out r-f pywood and sealed with fiberglass resin (Figure 1). Otter three ~1as nlclinl ained in the tank from 16 to 26 May, 1977. Otter four was maintained in tl e tank concurrently with otter three from 20 to 26 May, 1977. Otter flvr~ v:as m~intained in the tank alone from 9 to 4 February, 1977. Food consumption was measured by hand feeding the otters;iood)from \, p:e~·;l ic buckets ~'lhich were weighed prior to and after each feeding. The ctt··r s ~1ere fed at least four times daily. Each otter had its own bucket fron VJhich it was fed. In this way each otter's indivic!ual food consumption couJ: be measured. Otter65would not eat while a person was in the tank so \~hol• abalone were left in the tank for the otter to eat when hungry. Most of t.i1 ~ r~. oct 1eft in the tank was eaten within two hours. Any food 1eft in the Inn\ for more than four hours was retrieved, weighed, food consumption rate ~~ tl e beginning and end of the feeding experiment with a spring scale. Otter fiv~~ ~as weighed on an Ohaus balance beam scale to within .05 kg. Otters three and four were fed conrnercially obtained frozen squid, loligo :';a.l, ?~'!1_:-~, and otter five was fed abalone, Haliotus rufescens, collected with ·~::J 1 ! nPar Half ~-~oon Bay, California. All otters were maintained in the tanks at least ·' I, 'Jrs prior to the start of the experiment. -6- FIC:URE 1 FZ:gw'1~ 1 is an il-lustration of the holding facility cxmstruated out of plyz..Jood at the Hopkins Mc.rine Station, Monterey, California. Ot;c>rs,, 3, 4,and .s were held in this tank. Assimilation efficiency was determined for otters three and four on a diet of squ1d. Systematic fecal collection was not possible for otters 1, 2 and 5. Otters 1 and 2 produced feces which disintegrated 1rrrnediately upon excretion, and otter 5 was too disturbed by human presence to allm-1 fecal collection. Ottet·s three and four were suffi ciently tan1e and produced feces which were coherent upon the surface of the water for at least one minute. All feces excreted by these two ottr~t·s over a forty-e1ght hour period were collected by a pool skiiTIT1er net, deposited in a plastic pan, and the net rinsed with distilled water to rinse adherent feces into the pan. Upon completion of the fecal collecticn the feces in the pans were placed in a forced air oven at 80°C until dry. The dry weight was then taken. Aliquots of the feces were take~ for calorific determination, as outlined earlier. The assimilation effici••ncy was determined as follows: Assimilation Efficiency .. food Energy InFood (kcal)- Eneray FecalIn ______(kc.J'Hn•t:v · --· ·· ···· ... (kcal) Estimate of Free Ranging Energy Consumption: The free ranging energy consumption of sea otters was estirrated fron: ,, otter time-energy budget derived from available data on sea activity patterns ar,{ oxygen consumption (Loughlin, 1977; Morrison, Rosenman and Estes, 1973) . . Loughlin (1977) broke up the sea otters' activity patterns into three r.atuplrir: resting, grooming and foraging. He reported the mean length of time spent in each of these activities for six sea otters, followed by radio telemetry U' 1 h' for four consecutive days. Morrison, Rosenmann and Estes (1974) meCisured ~Jw standard metabolic rate of Alaskan sea otters and reported minimum and ma> iliun· rates of oxygen consumption for these otters within their thermoneut ra 1 zn:1! in - :J- water. They also reported mean values for four otters which were a 11 owed some freedom of movement wfthf n the metabo 1 i c chamber. The report :.( rates of oxygen consumption were: 0.85 cc/gr-hr. o2 basal level in water; 2.6 cc 02/gr-hr. o2 maximum metabolic rate; and 1.4 cc/gr-hr. o2 for non resting level. These values were judged to approximate the cost of restin:1. foraging and grooming as defined by Loughlin (1977). Rates of oxygen consumption in cc/gr-hr. were converted to kcal/kg-hr. by using the conversion factor 4.8 l Sui11Tiing ttle daily costs of these activities resulted in an estimate or tl1 t free. ranging dc.ily fasting metabolic rate (H1R). In order to convert the r-t!R tr the gross energy input a correction was made to take into account the specH'ic dynamic action (SDA) or the cost of utilizing the digested food energy and the otters' ability to metabolize the ingtsted food energy (Figure 3). An ir crease in the metabolic rate of 30% was assumed to represent the SOA of th:• hi-protein diet consumed by sea otters (Kleiber, 1975). The assimil.:ttion efficiency was measured for otters three and four in this study. Conversion of Free Ranging Metabolic Rate to Predation Rate: A simple relationship between the energy content of the prey and the number of rwey items consumed was used to convert ·sea otter field enerqy consumption to rates of individual prey ingestion (Figure 4). Equation or::· equates the otters' total energy consumption per unit time (E) to the cal~r c content (c) of each prey times the number of prey items consumed (X). Equation two expresses the number of prey items consumed (X) in terms of til~~ empir-Ically det(lrmfned relative percent CC'ntposition of the diet. If w• h<1 'i" detenninrd: 1. the mean calorific prey content 2. the percent composition of the diet 3. the otter/s daily energy consumption -10- FIGURE 2 ' : 9'' Y :; dw;cJ>ibes the equations used to aonveJ>t energy consumption ·, :. t!hl:.(hwl prey aonsu"!lption, E = C1X 1 + C2 X2 + · · · + Cn Xn PI X I = I - P ( X2 + X3 + . . . Xn ) 1 u'ho"'e·...... , . . E =: Energy consumed X= Number Prey Consumed C = Co Iori fie Content of Prey P = Percentage of Prey in Diet -12- FIGURE 3 Pigu.re 3 dieplays the frequency of oaau.renae of the prey item 'f'ecm.'ered by sea otters foraging in the Pt CabriZZo kelp forest. 'J!he abbrcviaticn~> ,zye as follcuJs: PP, E· produata; CA'!, Canaer sp.; TEG, Tegula §JZQ.; HAL, HaUoJyfi. ~·; SP, §._. purpuratus; SF, §_. [:ranaisaanus; UNK, unbwwn. PERCENT COMPOSITION OF DIET ..... w 0 0 , "'0 , :0 m :.J: ~ -< r· ~~~ ,(/) m 0 (") m , 1\) en z 1\) ..0 , C') c: z ~ -14- FIGURE 4 F .·~ :I 111 ,.... --4·---~t ~ n en () IJ.. _____.,.. • ...______,,! I . :I ~---·--~1~ .,. ..\ \, 0 :I '1'1 )> ...., • l:b •: ··- !'; 1:' r r· ~··! :I 0 111 .. ., • ~~ : f'i en ·r )'• ~------~----~IR ' . "" f.: :I , ...... ~--.....·---JI::, '""' co 1/) (: • f) t ~~ CD 0 -16 - We can then solve the necessary equations simultaneously for numbers of individual prey eaten per unit time. These equations can be derived from equations one and two. RESULTS foraging Behavior During the six-month period, 33 sea otters were observed makin9 a total of 409 foraging dives 1n the Pt. Cabrillo kelp forest; of these dives 75.1% (309) were successful tn obtaining a food item. Prey species were identified in 77% of the successful dives. Foraging bouts lasting from 1 minute to 2 hrs., 46 mins. were observed. The overall diet for the 6-month period can be seen in Figure 2. The kelp crab fE9ettia producta was the most coi'11Tlonly captured prey item followed by Te9ul~~·· Strongylocentrotus~·· Haliotus ~~-·· Cancer ~-·• unidentified clam and Pisaster giganteus. The monthly dietar) breakdown can be seen 1n Table 1. September, 1976, had the most observa tions of any month. No otters were observed foraging on the two observat' ~J 1 days in December, 1976. To test for ,:, seasonal trend in diet all the observations of otters · O"iHl'i q 1n September, 1976, were compared to the pooled observations of otters fot 3Jinq in October, 1976; November, 1976; January, 1977, and February, 1977. Poo·l1n done of the data wasAdue to the small sample sizes in October, November and Fel r.J The number· of otters observed fn September, 1976, was 15. The total ('lf 1't· observed foraging for the other months combined was 18. A qualitative exi·nin.•· tion of the prey taken in September·, 1976, seemed to indicate that this rH·nth was different than the other months examined separately or combined. A h ohly significant (P.>).Ol) difference between the diet of otters fn Septer:ibcr. fl7t', and October, 1976 through February, 1977 was found to exist. (Contingency 2 table analysis for independence x = 99, V = 5, Hoe1, 1971 ). A compariso·1 between September, 1976 and January, 1977 also showed a highly significant 2 difference in dietary composition (x = 99 V = 5). The most commonly captured prey item in September, 1976, was f_. Rroc!_~ ~J!! ..: In order to test if abundance of f... producta in the diet was different between the five months, a comparison between f. producta and the pooled observation of all other food Hems was made. Each month was treated sepa ··at!~l_y. A highly significant (P«•Ol) difference in the occurrence of.!:_. produc_~ :r the diet 1vas found to exist (/=70 V = 4). These results indicate that a seasonal trend may exist in the otters' predation upon f. producta. Then! was a highly significant (P<•Ol) difference between the length nf dive and the prey item recovered (Figure 3, one-way analysis of variance, SoH:at & Hohlf, 197 ) • The mean length of a dive when Tegula !E.E.· was recovered Has significantly different (P <·Ol} from a dive when Haliotus ~·. Cancer.~, t· producta or Strongylocentrotus ill· were recovered (students' two samplt ' t-test, SoHal & Rohlf, 197 ). A significant difference (P<•OS) was obser1 :d between dives returning w1th Tegula !EE..· and unidentified clam, and betw~ ?1 Haliotus spp. and Str..£1:!.9..Y.locentrotus !EE..· Calorific Content: The mean calorific content of twelve species of sea otter food items ( .1n be found in Table 2. A linear regression was done on a plot of the prey length to natural logarithm of prey edible bio.mass, yielding the follmJing t?xponential equations where x = prey length in mm and y = prey \'let edible t ior·as· 2 3070 0 02239 In gr.: Ualiotus rufescens, y = e • + · X size ranqe 82 mm- £'18 .... ,, -3 0777 + 0 1419x n = 14, r = .967; Tegula_ ~pp., y = e • • , size ranqe 15 rmt - ~ll·m, 6327 0 1419 n = 14, r = .919; £u9ett~ producta, y = e1· + ~ X size ranqe 4~rmn- 9143 0 03397 91.3mm, n + 8, r + .935; Cancer 2£·• y = e1. + · X, size range 6Bn t-P0 rn:, -18- TABLE 1 'ab~e 1 lists the relative peraer:t aomposition of the diet of soa otters . ~oraging in the Pt. C(zbrillo kelp forest from September, 1976 tJzrough .·'ebruar-y, 1977. '11ze numbers in parenthesis are the aatua l numbe1• of 1 )beerva.tions mad!? for that aategor>y. PERCENT CO~WOSITION OF THE DIET 'RE? SPECIES SEPT OCT NOV JAN FEB . -· ------·---·--·------59.2 22.2 30.8 30.6 16.? (97) (4) (4) (11) (2) 16.5 0 0 3.8 50.0 (2?) (4) (6) 7_~l.'P!.!£Hli?~ 4.3 11.1 0 22.6 0 :_q_~L.P.PcJ:~s ?_2!?_· (7) (2) (24) 2.4 22.2 15.4 13.2 0 (4) (4) (2) (14) 1. 8 22.2 0 13.2 8.3 (3) (4) (14) (1) 0.6 0 0 2.8 'J(~'?l (1) (3) 0 1.2 [l 0 0 0 (2) 14.0 22.2 54.9" 34.0 25.0 (23) (4) (7) (36) (3) ---- .... _. ______-19- TABLE 2 !.'able 2 lists th.-=! mean calorific content of 10 sea otter prey ite:na. !'he nu.rnbers in parenthesis underneath the calorific content are the wr[[icimzt of t.'at>iation for the mean. The number in parm1thesis mdcr'•zeath the nunber of individ!laf.J sampled ,ia the numbm• of total !cm.Z-·ustimzs made for that prey iteM. Dry Wet fl Kcal/gr Kcal/gr Ind ' 2.20 :. cmtcnna:r•·ius 0.662 ·6 (0.34) (12) 2.11 0.641 6 (0.06) (14) 1.95 2 (2) 3.35 0.402 10 * (0.0]) (?) 4.45 0.623 13 (0.16) (26) 4.5? 0.983 17 (0. 02) (40) 4.67 0.894 4 (0.02) (8} 4.36 1.190 30 * (0.05) (6) 4.11 ? (2) 4.83 * I . (0. 08) 1.091 30 (14) ~.~ iJrJatcr: that the indivtdua t samples wer•e pooled into one p( llet .·'P ,,or··busfi,m. -20- . 0 5997 + 04155 '' ,., 1, r = .998; Strongylocentrotus franciscanus y • e · • ~ x, dz·' range 33.2mm-127mm, n- 15 r • .924; §.. purpuratus v ,, , -1.6077 + 0 · 0906 Rx size range 20. 2mm-44mm, n = 22, r • . 962. M~an sizes of the prey items available as sea otter prey as \··r 1 t as the wet \ \, ·r t ''nt (from Table 2) can be seen in Table 3 (size data from ,.,.,!1 ~~e, unpublished data; and Lowry and Pearse, 1973). Ert('1 gy J.letabolism: The mean food energy consumed for the five otters studied was '.' ~n + t~3 kcal/kg-Day. The energy consumption for the individual tJt. ~s cnn be seen in Table 4. Assimilation efficiency on a diet ·· r ! (~uid, ]:.oligo opalescens, was 82.3% and 76.2"/o, otters number r:d L~ respectively (mean = 79.3%). Utilizing conversions for the loss of energy in the metabolie t<'tl ·of 107? for SDA (McGilvery, p. 522, 1970), a loss of 11.3'7o ICc·~t~, l976) for energy lost as urea in the urine and an assimi- 1 a 1 Lon e ffici.ency of 79. 2%, the FMR of 175 kcal/kg-Day converts to ;• r. d.ly field energy consumption of 275 kcal/kg-Day. This is a 1 f.: increase over captive conditions. The rate of prey consumption for a 25 kg otter can be seen in 1ahle 5. These rates were determined by solving the five r:qt "' ti ons generated from equations one and two with the dietary ·I<~. a in Figure 2 (without unidentified food i terns) , the caloric 'hta in Table 2 and the estimate of field energy input derived ·.~. • 1 l i er. TABLE 3 t:hlt> J Z.£ r;~s the mean length ([Porn Lourry & Pearse, 1973.- Pearse, mrublisltc:>d data) of the pt•ey item avaitibZ.e to sea otters foraging 1:n tJu: Pt: Cabrillo kelp forest. LENGTH WET WEIGHT CALORIFIC CONTEN.T ';PFCIES Tm1 gr Kcat 148 145 275 182 r'. oroducta 56 . 67 43 ·~----,---- 10. 6.5 4 1. 6 3.6 TABL,E 4 1 'i"'z ; 7•. 4 tints th.~ se.x, weight, dai Zy r»eight loss, and the measured focd Pl:e •' :'f eounsu77ed • ...... •• ... ------DAILY 1 INITIAL /! '' tfAI~ SEX WEIGHT FOOD ENERGY CONUSUMED WEIGElT LOSS Kaal/Day Kadl/Kg-Da.y Kg Kg/Day . ______.... -~------·------"" le 5 ohcws the :\zZ:.,;.e::; to :;e ::.:s .. "r;:.~~ :75 ~:c:::.Z,lkg-:iv.."'Y dai Zy ~~ng "'1et"'JJolic :--ate ::>f ;'Y.ee "!'W"I.qing sea otters. For carr:parison the rela-cive percent of -cr..e o-cters time and energ'd budgets are ;resented. * W.ta from Loughlin(1977). ** Data from Mornson, Rosenman and Estes (19?4). TIME* Energ-y Cost** Daily Coar; Peraent Peraent A.CTIFI'J!Y hr K.cal/kg-hi' KcaZ/kg-d:r:::J Energy Budget .4ati vi ty Budget* Feeding 8.26 12.5 103 59 34.4 GJ.>ooming 2. 98 6. ?1 ..."ll .., 11 12.4 I N w Resting 12. 7'1 4.08 52 30 53.2 I TABLE 6 7'cUe 6 'li[:ta tl1e daily predt.1tion rate for a 25kg sea otter [C1'ogt"ng {n the Pt. CabriUo kelp forest. The relative energy ''!('ntt•tbutimz cf the prey is compared to the prey contribution by ~w!IJJer. '* .Indicates actual number of prey ingested if six Z'f.fl!lla. !!.f'Q· are ingested per dive. *" Indicates percent of dives ":1 :.erved r,;{ th 'l'f.£l.Y:l:E:. !ll212..· recovered, not the actual nwnl•er of : Tt'IJ £Jtot>rn' ed. - ·- ···------·------Daily P1'ey Consumption Relative Con tribut1:o;1 ·!lumber Energy Number KcaZ Indil)iduals % % 2580 60 38 49 2020 .11 29 9 400 1.l2 4 6 15"* 1?60 12 26 10 t'ru;tr:-iscanus .20 2 14 ,._., ______~----- 128 DISCUSSION The diet of sea otters observed in the Pt. Cabrillo kelp for~st is indicative of an area which has been utilized by Pt~: 'rs for some time. Sea otters have been seen in the Pt. •: a!' -U.lo kelp forest for at least 14 years (Lowry and Pearse, . 1973). The diet of sea otters in an established foraging area Is 1sunlly quite diverse with many prey species contributing to ~ h:• ovcr;lll diet (Hall and Schaller, 1964, Vandervere, 1969). ld.~~ s of sea otters in areas which are newly occupied are usually cor·!>OSE~d of one or two major prey species, abalone, Halictus ~· p. ·:·r .arge red sea urchins, S. franciscanus (Ebert, 1968, Boolootium, 19 ~. ', Vandervere, 1969). In Table 7 the diets observed in newly - i ~·t·: tgcd areas, Cambria, and Pieo Creek, can be compared with the d l :•I from areas foraged upon by otters for many years such as Pt. Lobos, Pt. Cabrillo, and China Row. Sea otters have been observed taking as many as ten individual .X~~,">':_~l. §££· in one dive (Vandervere, 1969). In Figure 2 and TablE! 1 :_l,e percent occurrence of Tegula ~· refers Clnly to the number r.J f ~lives in which Tegula .§.££.· were recovered. The percent occt:,rrence d•>t" I'.ot relate the actual number of Tegula Jffi.E.· recovered since it n~~ too difficult to accurately observe. If an otter took six ]',.~, l.a Sll_Q. per dive this would change the percent occurence to nr', P. p roducg, 53% Tegula !.E£. , 7. 9% Strongylocentrotu~ .!J2.E.. , ~~. T~ 11<.!.1 iotus §.£.2.. and 5. 3% Cancer §.2£. TARLE 7 Table ? coPq)a.res t1t(} diet of sea otte1'8 fomging at Pt Lobos., ;alifornia (1963, Hatl and SchaUer1 1964; 19691 Vande:rvere, 1969); Pt:. Cabrillo, California (this study); China RotJ,Mont ?rey, California (Harris, 19?? J; Cambria, Califo:rrria (Va'1der %!r'e, 1969) and Pico Creek, California (Ebert., 1968). Al.l :'17tH>..': rE'rrPsent tlU?. obse:rved frequency of occu.rence iu per ·•cnt. Pt Lobos Pt Cabrillo China Row Cambria Pico Creek 196,3 1969 197'1 1977 1969 1968 9.9 5. 1 10.1 5.9 88.2 69.4 ' :~ / ' u.s 11.8 58.8 34.8 11. 8 28.8 ~ . • : ): '1: "' ••• '* ~ .. '. 32.8 2. 7 13.9 1. 4 6 .~. 9 15.5 20.0 2.4 !' ' •. 1 1.? 3.6 2. ? l . 0.6 6.9 0.8 When otters move into a previously unforaged area they find ~n tbundance of their preferred iood items, i.e. abalone and sea c:rc 1lins (Ebert, 1968; Vandervere, 1969). As the otters continue to . ·orage the abundance of their preferred food items becomes n.:d11ced resulting ln a shift in the diet from the preferred prey to he more available and thus more desirable prey such as Tegula \... sp.) Subtidal transects through areas foraged upon by sea otters ha.,.,. shmm a noti.ceable reduction in the abundance of the sea r·tf,•r-'s preferred food items (Ebert, 1968; Wild and Ames, 1973; Lo .. , y and Pearse, 1973; Estes snd Palmisano, 1975). These reduc Li '".S in prey densl.ty have resulted in profound changes i.n the •:p .,·ics composition of these newly sea otter dominated conununities (Wi'd and Ames, 1973; Lowry and Pearse, 1973; Estes and Palmisano 1 l g / ') . \·.'hat: are the i.mportant factors determing prey select1.on by c;•:- 1 otters and why do we see seasonal changes in diet? A sea ': t t ~ r probably acts like many other predators and optimizes the t iw· !>pent searching for prey against the benefit gained or ' II.·. I • J 'l I. t r·y of its prey (HcArthur and P i anka, 1966; Emlen, 1966). , ..~-~~-.eM-~ ) I ; .l I. it :1 can be defined as the value of the prey in supplying the 1 ~~tl . pf. •f •• t t~"; :· :_r ·-: it ional or energetic needs of the predator. Em len (1975) has '? P'.1 i ,.tf·rl out that in species with a high weight specific metabolism, ·n · gy may be the limiting quantity, since most if not all of the '''I:: it i.onal needs of the animal will be met prior to the fulfill- _____ !f ,, '1 t~{ the Pnergy demnnd. Conversely, in animals with low weight ·• ,, ··! iIi c me t<1 holism, nutritional requirements may become important sj1·ce the energy turnover is relatively low. The weight specific •n(~t <~holism of sea otters is extremely high. A sea otter's meta bc.:t I.e rate more closely resembles that of a desert jack rabbit dtw1 an equally-sized terrestrial carnivore (Shoemaker, Nagy and Couta, 1976). It then follows, that optimization of time and 0m· rgy are probably the determining factors in prey selection '•) se.1 otters. From Table 2 we can find the caloric density of 10 important ;E:~ otter prey items. Dry weight caloric density alone does not tel] us much about the quality of the prey, sin6e the prey items 1~''0 differing water contents and tends to increase (crabs) or (11;_ ,. rease (ttrehins) their wet weight caloric densities. As previously · !i !: ·us sed, prey selection is a trade off between caloric payoff and ·~.: ':lifficulty required to obtain the prey. Haliotus .§_E£. has a IiI'') caloric content and is probably more completely assimilated ·~/I 1 ~:~1_~c~ !~P..·, the prey with the highest caloric payoff in the l't Cnbr-Lllo kelp fo;:2st (Table 3, Fausett, 1976). However, .1 t ·1 Lone is one of the more difficult prey items to recover requir ir~· a mean dive time of 71 sec. (Figure 4). compared to 64 sec • .! c 1· P. Produc ta and 2 7 sec. for Tegula !E£. In addition, as many .1~ tt,•enty unpr0ductive dives in the same spot have bee_!l __ o}?_served ...... __ ...., __ ·---~ ~· P-<' •••·~••·-·~ ..... - < ------·' u•••~·-·---•-• ~-. -·------~--•F • t. c :,e necessary to obtain an abalone, whereas the crabs h producta and Lororhynchus crisputus are usually I "l: t a inc>d on single dives (Vandervere, 1969) . Obviously then, there iE 1 tradeoff between the time necessary or difficulty in obtain ir L prey items and· their caloric content. Figure 5 displays the , ~~ lric content, the prey density, and the relative occurrence of t!tn: prey in the diet. This relationship can also be examined f rt • able 8 with the addition of the observed mean live time ,.•,!' nJ~"'d "1hen each prey was recovered. Notice that Tegula ~· i ,, 1 ) far the most abundant species, being 9 times more common 1 1 t< 11 f;~ron_gy_!r~~e_ntrob:!.S ~· and 288 times more abundant than the '.: l "'·, ~. PEoclt!_C t~ and Cancer .E.E.· Sea otters have been observed 1. ·t ., rning to :::he surface after a shallow canopy dive with 10 ., ~T,ll I. a _§.EJ~.. ( V<1ndervere, 1969) . However, the caloric yield ; ·•·'le ~~0f~!2. .;;~J~· is only 2.0'%, of the energy obtained from a f ·. '!. c ,;! ..::?..P. or 2. 5% of the energy contained in Haiiotus .£1~. How ··. ·r t~·c. compare the relative time spent searching to energy payoff? l • >.r' a:.sume a sea otter can obtain six Tegula .§E.£.· in one 27 sec. ,: ; \ ,. and one P. producta in one 64 sec. dive with a success rate ,,, J ')l)"/, for the Tegula ~· and 77"lo for P. producta (Figure 4), thE~n 1'1' C'lfi COmpare the time Spent underwater to obtain 2580 kcal (the (Ld I" P. _pn~_dL!cta energy consumed by a 25 kg otter Table 6) of prey ' ( 1 l'. j~_Egd~~£-~a nnd 720 Tegula §.£.£.· (Tegula .§E.£.· 119 di.. ves, 78 <· ~ v: ~ fer !:_. P..!'_()duct~). Capturing 60 P. producta requires about ): ;, ·linutes stwnt foraging underwater compared to 54 minutes requirecl ',, 1ll••ct 720 T~la. If it takes less time to collect the same :•J.c rc:ta? J t is possible that the assumptio~s made to derive these time.s '1Jf: ; tt.1':'cuulte nnd more time is required to obtain 720 T€'J1_ula .§E.£.· fl(·~.· ,'Pr, a mor~ plausible explanation is that it takes more time I'' )w>•lrn(~ 720 1'£~la then 60 f. produc ta. Table 11 displays the -30- FIGURE :; 1 1F' ' 5 rrr•ap!zs thA population density, caloric content, and the frequency of "'"~ · ·'IUC of thr. mast common prey items of the sea otter foraging in the Pt. · [ l:• l j DIET% .... 14 z ... 40 ....LIJ z 0 (J 1 + V/~ ~ 1/"..11 V/.l ~ I (J 3 a: 0 ,.. 0_, 1~ ~ 1- < -U) (.) z ~ m ~ ~ m I LIJ J 0 z_, _,z I fil m ~ ~ m 12 .... 20 1 1 10 2 3 i t>§Wbf¥3 t«r/£4i? 00//&§§1 ~ ~ ffi t»p'~ I 0 0 pp TEG SP SF PREY SPECIES TABLE 8 Table 8 lists tJte prey density calorific content, frequtm~J of O(~mwence in the diet, and the observed length of a div~ when that !n'cy ,: te'71 z.1as "I'ecovered. Density data is from Pearse (unpublished data). * Frequency for both spec,.>ies. H caloric conhm.t of ind{v~~- . _•f:~E}_prey_, 21Kca l [or six Tepula spp. assumed to be captured per dive. lknsity Calorific Frequency Dive Time . 'R~'Y srE crss Content Ind!m2 Kcat I Sec ----·-· f?.l'Oduat<~ 0.1 43 49.2 64 . ' ~ · .t'!liLg_ £'££_· 28. 8 3.6u 15.4 27 r' e,_; ~~ sv. ··---·- 0.1 182 9.2 55 " [£ .:~ ~!£2. QEE..· 0. 3 145 10.0 71 r_;~rJ~!!:rat us ,3. 2 1. 6 13.8 ... 53* £:.~!!.'!!:: m: can~ o. 1 6.5 -33- '\!/; ~ :' '\f. :l ') t' t ,}l t:irn' underwater required to fulfill the energy demand of a 25 kg \ (~( 'J, nt~ ~:r, assuming it only forages for one food item. From Table 11 '/~ f ( J~ i_ t :~tJu_l.d seem more advantageous for a sea otter to feed exclusively , ·1 . ..:·nl·' pnrtially reflects the actual time required to capture these Another aspect of difficulty in obtaining a given prey item is :he depth required to obtain prey. Most of the dives observed ·,;rw 1 P. roducta or Tegula .§.!?.E.· were taken were very shallow dive!). Jn ftese dives the sea otters would "comb" through the kelp grounds, ''it 1in the first meter of the kelp canopy searching for P. producta. Jhr distribution of P. producta is very patchy and dives lasting ns l.ong as four minutes or as short as 15 sec. were observed f,e f Jre a crab was recovered. Whereas, dives when Haliot~lS !!PJ!.·, (1r .~ancer l?.E.·· were recovered were of long duration and probably (lf ccAsorwble depth to an otter (10-20 meters), and wen~ often pr 1. .:edec1 by unsuccessful dives. 1\nson Hines (personal communication) has observed a seasonal ~·tu.:tunt:ion in the apparent abundance of P. producta. He thinks '~'It ~· rr_Cld~lCta may give birth and m~tUre intertidally, and then ' r 1 r.. ·r the subtidal kelp canopies to reproduce and forage. This hrv~thcs is would account for the monthly difference observed in • •J•t• .. 1 h sc.a otter's diet at Pt. Cabrillo. P. producta may become rad ficiently abundant seasonally to make it a prime prey ltem ; t' ~ertain ti.mes of the year, whereas its abundance may become rc low during other times of the year to preclude sea otters ct·1ging upon it. The ways in which sea otters have optimized their prey selec t :f r t 5 n two different habitats can be seen in Tables 9 and 10. I :i c > Creek wHs an area in which ab·alone were of large size (Table 9) ! r:· ·;tingly, Pt. Cabrillo is an area in which otters have been ct 1 gtng for sometime. Abalones and cancer crabs have been limit·?.d ' c '•'t·p rock crevices, .in order to avoid predation by sea otters. !·i! f~rence {n the size distribution of these prey items are 'r: l led.ed by their caloric content (Table 9). In areas \vhere sea ''t: r ~r':; fr:lrnge the size age class distribution is shlfted to a ~·ot. tgcr population with a high recruitment (Lowry and Pearse, 1973; 1st !S and Palmisano, 1975). The differences in number of prey , c•·;umed between these two areas also reflects the difference in ~·i7~ distributions of the populations. Pico Creek abalone are '.-:rse, representing 89% of the energy consumed. by a sea otter . M. ,,t. Cabrillo more abalone are consumed (12 vs 9), but they only t c t·resent ?6~~. nf the sea otter's energy consumption. Since the l't ,. : if: smnlJer the energy yield per prey is much less, so the ·:.c1 .. number of a given prey species may be taken, 1::--ut the relative ,.,, y en('rgy consum~d and contributed to the sea otter's energy 1n11·u.,t J~; rdgnifidmtly less. This is a very important difference -J!>- TABLE 9 ?'able 9 showll the prey ealorific oontent used to determine prey (!cnsumpticn by s~a otters at Pi co Creek and Pt Cabri Uo. The data in table 2 1Jas utJed to eonvert the hlet hleight biomass values for se?J. otte:r.• prey at Pieo Creek reported by Ebert( 1968}. * no data we.t•e avaiUble for Canaer !!E.· at Pico Creek so these values are fr>'Jm Pt · Cabril.lo. "'* asswning six individuals taken per dive. l'Ji'FY SrE'ClBS Piao Creek Pt Cabrillo Kaal/Ind Kool/Ind 43 .. 182 182 695 145 F:ra:naisacrnus_ 232 6.5 65 1'. nu;~talli 314 .... --.~---- .... ---··------',11 t: nr.. ::·· r:; Teo Ze 10 shotJ. Per-cer:t Contribution /lumber Prey Consumed PF?EY SPECIES 2nergy Nwnber Pt. Cabr>i ZZo Pico Creek .p ...... Cabril.lo ~~co Creek Pt. Cabr";zzo Pico Creek P. producta 60 - 38 - 49 Can.cer :!E.· 11 3.3 29 8. 7 9 28.4 Tegu.la !!EP..· 112 - 5 - 15** Hal io tus !!EE..· 12 9 26 89 10 89.4 •, S. [rancisaanus 20 - 2 - 14 H. 111UZtii'Ugosus - 0.4 - 0.3 - 2.3 . Tresus nuttaZli - 0.3 - 1.2 - 2.7 • I TABLE 11 'l'able 11 shows tJ1e number of dives and time underuater required to captur>e each of the prey spedes to fulfill the otters eneT'(JlJ requiremen t:f; if only that prey "'as being consumed. 'f11e 1wtual r~ompo:~ition of tl2e diet by percent occurence is for> ref~rence . .•)lcr•rr.f demand of a 25 kg otter 1:s estimated to be 6880 Kcal/day. Time Dives PHJ-7Y SFE Cil78 Underuater Diet Required min % Ccl!ZCC:J: ~· 49 45 9.2 Ha}iotus_ ~· 61 73 10.0 r. E!_•oducta 208 222 49.2 ,T_i;_;,_p l a s £E· 319 144 15. 4 §_f::_Pm!.Ey]o- 1380 1220 13.8 _q;::..:_!_0_·ottts_ sop_. ····-·---· -38- to ote. If we were modelling energy flow through these two sys te•a•, we might overlook the increased turnover in individual prey. 'Th; • difference in increased turnover is due to differences in t:h J·h i' pnper can then be used to plug into population and competi U.· ,. r:1odcls. I feel that a synthesis of ecological energetics, p·>J• lation and competitive modelling will be necessary for a •.l·m r:d.c underst;mding of community structur:e and function. The mean assimilation efficiency of 79.3% for the two captive ·;·~ 1 Dtters is in good agreement with the 81% reported by Fausett ( Ft"()). Assimilation efficiency in sea otters is the lowest yet ,,, •rl ed for a carnivore. The lowest assimilation efficiency 1:·~· 1: •rted for a terrestrial carnivore is· 90% for the least weasel, l ..:,l ! ela nivai:es (Galley, 1969). Assimilation efficiencies as hi~~~~ as 95% have been reported in the Arctic fox, Alopex leucopus (1!1derwood, 1971). Unfortunately no data are available for compara t: 1. VI' purposes on the assimilation efficiency of other marine •r• '11F 1:11 s. The low assimilation efficiency of sea otters may be a ' ~-:--lrlt of the rather fast food passage rate of three hours St.11lken and Kirkpatrick, 1955) and/or the co::-.:':>osition of their f o ., 1. The primary food of sea otters consists of marine inverte- l't"l f~S whi.ch have three times the electrolyte concentrati.on of •,er t·bral:e tissue (Gordon, 1972). Mgso forms a significant fraction 4 -39- t) [ 1 he electrolytes in invertebrates body fluid. It is possible · '· t:t 'A'q_=:n. ... 1nrl .,.,.._.,P..r ~ 1-P-c:'!:.r~ tytP.:~ r:.-=~at:!'! .:tn. '1-Jtnat:..:i!: :•tH loNering the assimilation efficiency. Another possibility is tIE :: the high mucous content of the squid diet reduced the diges- 1 f[,.J by acting as a barrier to the digestives fluids, thereby 1 e•: td ng the assimilation efficiency. In addition arthropod prey {'on ·ai ns a chitinous exoskeleton which may also tend to reduce th•~ • 1 1;~ ~stability of this prey. Fausett (1976). observed assimilation ~·ff :cicncic~ as high HS 96.5% for one animal on 1 diet of abalone ''wl aF lm·1 as 66. )'7,, for an anlmal eating crab. The prey type and ~ ':or )os:i ti.on may be an important factor in determing the assimilation) : f ·· c ien·~Y in seA otters. The mean energy consumption of 234 kcal/kg-day for the captive ·: -:c:1 otters ls well wi.thin the values pr~viously reported (189 kcal/ i:~~·d.1y, ~~enyon, 1969; 307 kcal/kg-day, Fausett, 1976). The rela- r i ···~ ·ly low energy consumption of Otter 3 may be due t:o a lower 1 ' 1 1 mnl load since he spent most of the time hauled out on the d·~ :; . The low energy consumption of 11tter 5 may be a result of the :1 )1' ible higher assimilation efficiency on an abalone diet t r; 1 ~H: t, 1976). The mean daily captive energy consumption was ) I 1 . . } : i mes the basal metabolic rate reported by Morrison, Rosenmann .md !:~tes ( 197!~) or 8 times the predicted basal rate for a terres- \ '# J ;mim ,. t i ~: unlquC' among mustelids but seems to be a. common occurrence t ti· 1', l'lilri.ne 1'[lmm;tls (Harrison, Rosenmann and Estes, 197/~). Hy estimate of free ranging food consumption is probably a gon( approximation of a sea otter's daily energy demands. The r:lo' e agreement between the captive and estimated free ranging r·1w r gy consumption is not unexpected. Mullen and Chew (1973) found ,,.er·) close agreement between the direct oxygen-18 doubly labelled ~.~a1 • r technique and a time energy budget derived in much the same rrnwer as done in this paper. Mullen and Chew (1973) felt the c·x('• llcnt agreement between the two techniques was due to the i 11·; e percentage of the energy budget devoted to temperature n~r.' lation. The sea otter also devotes a large percentage of its (· 1 w·~ gy budget to thermoregulatlon. I feel that my estimate of free ! i ,, i ng energy consumption would also share the close agreement as r:lttl d by Hullen and Chew (1973). An increase of 18% in the sea '•::t r rs energy consumption for the cost of foraging for their own 1 H j s appropriate when we consider that sea otters only spend ''·~ of tbeir total time foraging (Loughlin, 1977). The only aspect ,,r •he estimate which is subject to an appreciable error is the · •n·.E·rsion for SDA. SDA is very difficult to estimate without 'I i 1·1 c t measurement. The SDA could be as high as 25% (Kleiber, 19 75) ,.,·rL: ng the estimate of field energy consumption 333 kcal/kg-day . If Morrison, Rosenmann and Estes, (1974) are c·t~·rcct in postulating that the SDA of sea otters is spread through !. ·tt the day and was included in their measurement of fasting meta- b: d ·. c rate , the energy consumption estimate would be 250 kcal/kg- · tt ,, rs. The value of 275 kcal/kg-day is a respectable figure. td :J.l f.zlng an established conversion for the SDA of 10% (McGilvery, ·19}[ i. Lamprey (1964) and Buechner and Golley (1967) used three tfnK: the basal metabolic rate (BMR) for estimates of the energy , ···s ~- of free ex:f.stence in large African mammals. My estimate of r ~1e1 ;y cost of free existence is 2.9 times the measured tn1R. Un .·he bas:l.s of these arguments, 275 kcal/kg-day is a good r ( n: ·n.•.:1tlve estimate of the free living energy consumption of the :ea otter, Enhydra lutris in California. LITERATURE CITED t·rqlootian, R. 1965. The Sea Otter and its Effect upon the Abalone Resource in Senate Permanent Fact Finding Comn1ttee on Natural Resource, pp. 129-144, third Progress Report to the legislature, 1965, regular session, Section I, Senate, State of California, Sacramento. E~ 1lva, J., 1973. The Harbor Seal, Phoca vitulina concolor, in eastern Canada, Ph.D. thesis, Dalhousie Untv.,~~. Nova Scotta, Canada. Eu,!chner, H. K. & Golley, F.B., 1967. Preliminary Estimation of Energy Flow in Uganda Kob. In K. Petrusewicz (ed) Secondary Productivity of Terrestrial Ecosystems. Waszawa-Krakow, pp. 243-254. OH~w, R. M. and Chew, A.E. 1970. Energy Relationships of the Mammals of a Desert Shrub Community. Ecol. Monogr •.40{1 ): 1-21. (n1111ell, J. 1961. The Influence of Interspecific Competition and Other Factors on the Distribution of the Barnacle Chthamalus stellatus. Ecology 42:710-723. · Co: ta, D., 1976. Water Balance of the Sea Otter, Enhydra lutris. A paper presented to the 56th Annual Meeting American Society of Mammalogists, lubbock, Texas. Oa:·ton, P. K., 1974. Experimental Algal Studies of Algal Canopy Inter actions in a Sea Otter Dominated Kelp Community at Amchitka Island, Alaska. Fishery Bull. 73(2) pp. 230-237 .• (Ja;·ton, P. K., 1975. Experimental Evaluation of Ecological Dominance in a Rocky Intertidal Algal Community. Ecol. Monogr. 45(2):137-159. Eb1 r·t, E. , 1968. A Food Hab fts Study of the Southern Sea Otter, En hydra lutris nereis. Calif. Fish &Game 54{1):33-42. -- !>n· en, J., 1966 •. The Role of Time and Energy in Food Preference. Amer. Natur. 100(916):611-617. E,,· en, J. and Emlen, M., 1975. Optimal Choice in Diet: Test of a lfypothesis. Amer. Natur. 109(968):427-435. E~les, J. and Palmisano, 1975. Sea Otters: Their role 1n structuring nearshore communities. Science 185:1058-1060. F~ ~ett, J., 1976. Assimilation Efficiency of Captive Sea Otters, ~nhydra lutris. M. A. thesis, Calif. State Untver·sity, long Beach. G G:~lley, F.B., 1960. Energy Dynamics of a Food Chafn of an Old-field Community. Ecol. Honogr. 30:187-206. Go' ley, F. B•• 1968. Secondary Productivity in Terrestrial Contnunities. Amer. Zool. 8{1):53-59. G:lldon, M., 1972. Animal Physiology, MacMillen Co., N.Y. H~·1, K. and Schaller, G., 1964. Tool-Using Behavior of the California Sea Otter·. Jour. Mantna 1 • 45 {2): 287-298. Ha1ris, R., 1977. Feeding and Other Activities of the Sea Otter, Enhydra lutris along Cannery Row, Monterey, California. B.A. Thesis, Environmental Studies, Univ. of Calif. at Santa Cruz. 1 K~,yon. K., 1969. The Sea Otter in the Eastern Pacific Ocean, Dover, N.Y. Kl!iber, M., 1975. The Fire of life, Robert Kieger Publ. Co., N.Y. l:p·:prey, H. F., 1964. Estimation of the large Marrnnal Densities, Biomass and Energy Exchange in the Tarangire Game Reserve and the Masai Steppe in Tang·anyika. E. Afr. Wildl. J. 2:1-46. l:t. igne, D.; Barchard, W.; Innes, S; and Or1tsland, N., 1976. Pinniped Bioenergetics Scientific Consultation on Marine Mammals, ACHRR/MM/ SC/112, FAO. . U: th, H., 1975. The Measurement of Caloric Values in Primary Productivity of the Bio3phere (Ed.), lieth, H. and ~hittaker, R. Springer-Verlag, N.Y. L)" r·y, L. and Pearse, J., 1973. Abalones and Sea Urchins in an Area In habited by Sea Otters. Marine Biology, 23:213-219. L.:t1 ghlin, T., 1977. Activity Patterns and Habitat Partitioning and Grooming Behavior of the Sea Otter, Enhydra lutris in California. Ph.D. theses, Univ. of Calif. at Los Angeles. M::' rthur, R. and Pianka, E., 1966. Optimal Use of a Patchy Environnent. Amer. Na tur. 100( 916): 603-609. MJilvery, 1970. Biochemistry: A Functional Approach. W. B. Saunders, Philadelphia. "'illet·. D., 1975. A Review of the Taxonomic Status, Life History ,1nd Some Ecological Interactions of the Sea Otter, Enhydra lutris. Leaflet #7, Calif. Dept. Fish and Game. Mi llert D.t Hardwick, J., and Dahlstrom, W., 1975. Pismo Clams and Sea Otters. Calif. Dept. Fish &Game. Marine Resources technical report No. 31. ~!,,rison. P., Rosenmann, M. & Estes, J., 1974. Metabolism and Tlu!rmo regulation in the Sea Otter. Physiol. Zool. 47{4):218-229. 11,;1 len, R. and Chew, R., 1973. Estimating the Energy Metabolism of Free-Living Perogna thus _1 on_gj_menbrus: A Compa ri sort of 01rect and Indirect Methods. Ecology 5~(3}:633-637. rlc•,·th, vi., 1974. Kelp Habitat Improvement Project Anmwl Report. W.~L t:eck labor·atory, California Institute of Technology. f'; ine, R. T., 1971A. A Short Term Experimental Investigation of Resource Partitioning in a NeH Zealand Rocky Intertidal Habitat. F:cology 52(6)1096-1'106. l'i·.ine, R., 1971B. The Me(l.sur·ement and P.pplication of the Calorie to Ecological Problems. Ann. Rev. Ecol. Systematics 2:115-164. 11''"se11-Hunter, W. 0., 1970. Aquatic Productivity. MacMillan f'1Jbl. N.Y. ~d Jemaker, V.; Nagy, K.; and Costa, W., 1976. Energy Utilization and Temper~ture Regulation by Jackrabbits in the Jojave Desert. Physiol. Zool. 49(3)364-375. :Hr~n, D. cmcl Kirkpatrick, C., 1955. Physiological Investiqat.ion of Captivity Mortality in the Sea Otter. Trans. 20th N. Arner. Wi 1dl. Con f. '!. df'tviOod, 1.., 1971. The Bioenergetics of the Arctic Fox (AJ~.PC.?£.l.M~2J· Ph.D. thesis. Pensylvania State University, Pl t tsl1urg, 1'enna. '=rdrrvnrr, J., 1969. Feeding Behavior of the Southern Sea Otter. pp. 87-90. Proc. 6th Conf. on Biol. Sonar and Diving t·1ammals, Stanford Research Institute. :'ld, P. and Ames, J., 1973. A Report on the Sea Otter, Enhydra lutris in California. Marine Resources Technical Report ~o. 20, CaHT- Fish & Game. Date Submitted------ Renewal Proposal Proposal Submitted to: U. S. Fish & Wildlife Service Project Title: The Ecological Energetics of the California Sea Otter, Enhydra lutris Support Requested: $19,459 Total Amount Requested Desired Starting Dnte: Apri 1 1 , 1977 Submitted by: The Regents of the University of California Institution Address: University of California Santa Cruz, California 95064 Principal Investigator: Kenneth S. Norris (408) 429-2001 Submitted: Kenneth S. Norris Professor of Natural History Approval: Dav1 d E. Dorfan Dean, Division of Natural Sciences The enactment of the Marine Mammal Protection Act has initiated an ecosystem approach to marine mammal management. Consequently, the estima tion of the trophic impact and trophic relationships of marine mammals to their ecosystem has become an important aspect of the management of marine mammal populations. This construct is especially true whenever there is a resource conflict between man and marine mammal. The impact of the sea otter on the abalone, pismo clam, crab and sea urchin fisheries in California has resulted in such a conflict. In our first year proposal we reviewed the literature regarding the ecology of the California sea otter. The literature has been primarily limited to observations of the dietary composition of sea otters (Fisher, 1939; Limbaugh, 1961; Hall & Schaller, 1964; Ebert, 1968; Vandervere, 1969), compari sons of sea otter dominated and non-dominated communities in Alaska (Estes and Palmisano, 1974) and a description of the invertebrate macro-fauna of a sea otter dominated kelp bed in California (lowry and Pearse, 1973; Pearse and Lowry, 1974). No study has dealt with the trophic dynamics of sea otters in terms of energy flow and related community productivity. It is the emphasis of our current research on sea otter ecological energetics to describe the rate of energy flow and exchange in the sea otter with respect to its ecosystem. Our work, coupled with Or. John Pearse's (U.C.S.C.) measurement of energy flow of macro-invertebrates and dominant kelps in the Pt. Cabrillo kelp bed, will provide a detailed description of the trophic dynamics and energy flow within a sea otter dominated kelp bed. Not only will this study make possible a more informed decision concerning the management of the sea otter in California, it will also provide techniques which will be applicable to the measurement of - 2 - the trophic dynamics of other marine mammal populations. Work Carried Out to Date: In our first year of study we have or intend to have measured: 1) the size biomass and caloric content relationship of 15 selected sea otter prey items; 2) the assimilation efficiency of eight sea otters on four different food items; 3) the captive food consumption of eight sea otters on four different food items; and 4) an estimate within 50% of the free-ranging metabolic rate of free ranging sea otters based on the behavioral and physiological literature. In addition, we have designed an inexpensive method of measuring directly the food consumption and metabolic rate of free ranging sea otters by the use of tritiated water. We have begun an analysis of the seasonal variation of sea otter foraging efficiency and prey choice at the Pt. Cabrillo kelp bed. We have collected some baseline data on the basic blood parameters of wild sea otters in order to diagnose their physiological condition. We have also designed a fast and efficient method of radiotelemeter attachment to the hind flipper. Information concerning the effectiveness, and dosage of Ketamine hydrochloride as a chemical immobilizing agent has been collected. lastly, we have attempted to measure the free ranging food consumption of two sea otters with tritiated water. Research Planned for the Second Year: In the second year of our research we plan to measure directly free ranging food consumption of 10-15 sea otters with tritiated water; complete the seasonal analysis of foraging efficiency; find a suitable immobilizing - 3 - agent; and collect sufficient blood baseline parameters so as to establish the normal for healthy sea otters. Food consumption of free ranging sea otters will be measured by utilizing a modification of the tritiated water technique as described by Nagy (1975). Tritiated water is used to label the total body water pool. The dilution of the tritium through time in the body water, as determined by the specific activity of tritium in the blood wate~ is proportional to the total water flux. The rate of water input (or tritium dilution) is directly proportional to the amount of food water (water contained in the food) ingested by the animal while eating. If we measure the water content of the various food items that the sea otter is likely to eat and then observe the various food items the labeled individual is eating, we can then estimate the total amount of food consumed during the field measurement period. Data on captive indi viduals collected during the first year of the study {Costa 1976) indicates that with a small correction for sea water ingested with the food, this technique will allow a 20% estimate of the actual food consumed. It is hoped that with a study of more captive individuals in the next few months we may be able to reduce the estimate of field food consumption to within 10% of the actual food consumed in the wild. Sea otters will be captured and injected with lmC tritiated water. The animals will then be held for three hours so as to permit the tritiated water to equilibrate. Upon equilibt·ation a blood sample and body weight will be taken. A radio telemeter will be attached to the animal {Cedar Creek Bioelectronics Lab telemeters) and the animal will then be released. Only two animals will be injected at any one time Upon release, the otter will be radio tracked and observations as to the dietary composition of the tagged individuals will be made. After five - 4 - days, recapture efforts will be initiated and will continue for 14 days or until the animal(s) is/are recaptured. After 14 days the tritium level in the blood water will be insufficient to measure (Costa, 1976). In our original Fish and Wildlife Permit (PRT 22-C) we were allowed to take 10 sea otters for scientific research. We have applied for a permit amendment which would allow us to take up to 25 additional sea otters. It is hoped that by injecting and tracking up to 15 sea otters we will be able to recapture a significant number of tagged otters. We have already attempted this technique on two sea otters in September 1976. However, we were not able to recapture the tagged animals due to their increased awareness to the scuba divers' bubbles after their initial capture. In order to alle viate this problem, we are making arrangements to borrow a closed circuit breathing system from Dr. Glen Egstrom (U.C.L.A.) which does not release air bubbles. We have also asked for a permit amendment that would permit us to recapture the otters with a large net which could be used to encircle the otters. With either of these two techniques we feel confident that we may be able to recapture at least 50% of the injected otters. In the process of carrying out our research on live captive sea otters, it has become apparent that some form of chemical immobilizing agent is neces sary to safely handle the otters and attach radio telemetry collars. Due to the morphology of the sea otter it is very difficult to attach radio collars which are not too tight so as to cause trauma to the animal (Last year, in a behavioral research project, one otter died as a result of the radio collar being too tight), or too loose, enablint it to fall off as soon as the animal enters the water. We have initially experimented with Ketamine Hydrochloride •• ;J - as an immobilizing agent in three otters with very good success. However, these animals later died of other non-related causes. {One died of shark bite; one died of a radio collar laceration; and one died of pneumonia.) Due to the highly sensitive nature of an otter death in California, no plans have been made to chemically immobilize any more animals until the safety and dosages are thoroughly known. For this reason we are asking for funds to work in Alaska with Ancel Johnson of the U.S. Fish &Wildlife Service in order to test safety and dosage of immobilizing agents Ketamine Hydrochloride, Inovar (which has an antidote naline) and halothane. This work will be carried out under the direction of Dr. Thomas Williams, D.V.M. Dr. Williams has been associated with our project as a consulting veterinarian and is on contract to the California Department of Fish and Game to treat injured or sick sea otters and to necropsy dead otters in order to determine the cause of death. During the Sea Otter Horkshop on 23 and 24 February 1976, the need for normal baseline blood parameters was expressed. Since this time we have collected blood from every sea otter handled under our permit. These blood samples have. been sent to a commercial clinical laboratory where the complete blood count, differential blood count and a profile of 13 metabolites and 7 enzymes have been run. To date we have accumulated blood profiles for 7 individual sea otters. This information has proven to be an excellent measure of the animals' physiological condition upon capture. It has allowed us to diagnose the illness of two otters and cure one. He have found that there may be a stress reaction to captivity which may be able to be monitored by these blood parameters. These data are valuable not only to researchers interested in ascertaining whether they are working on healthy sea otters, but to public display facilities which must be able to monitor the health of their captive sea otters and diagnose any disease in animals recently captured. - 6 - In order to get a significant normal value for clinical work, we need a sample of at least 20 individuals. In the second year of our research we are planning to collect blood from all of the individuals captured. These blood samples will be sent to the Veterinary Reference Laboratory (San Jose, California) for analysis of the complete blood count, differential blood count, SGPT, alkaline phosphatase, BUN, cholesterol, total protein, LOH, total bilirubin, creatinine, phosphorus, calcium, albumin, glucose, amylase, co2, CPK, lipase, potassium, sodium, T-3 and T-4 levels. Upon completion of the second year's research we should have normal blood values for 37 animals. (We will have 12 by the end of the first year.) This informa tion will then be published in an appropriate journal and be made available to any researchers or marine aquaria interested in these data. Measurement of the seasonal changes in foraging efficiency, diet and foraging intensity at the Pt. Cabrillo kelp bed was begun in September, 1976, and will continue through August, 1977. From sun-up to sun-down on two consecutive days during the first week of every month, we have observed the prey type, dive times, and success rate of otters foraging in the Pt. Cabrillo kelp bed. These data will be correlated with the quarterly samples of macro-invertebrate densities conducted by Dr. John Pearse (U.C. Santa Cruz). We have already observed some interesting changes in the foraging pattern of sea otters in the Pt. Cabrillo kelp bed. Puggettia producta.the kelp crab, has declined as an important prey iten1 as its density in the canopy has also declined. As the kelp crab's dominance in the sea otter's diet declined, we have noticed an increase in the numbers of sea urchins taken. This observation is especially interesting since a large set of juvenile urchins from last winter are now becoming of sea otter prey size and have been expected to show up in the sea otters' diet. LITERATURE CITED Costa, Daniel, 1976: The Water Balance of the California Sea Otter, Enhydra lutris, Technical paper, 56th annual meeting of the American Society of Mammalogists. Abstract published. Ebert, E., 1968. A Food Habits Study of the Southern Sea Otter, Enhydra lutra nereid, Calif. Fish & Game 54:33-42. Estes, J.A. and J.F. Palmisano, 1974. Sea Otters: Their Role in Struc turing Nearshore Communities, Science 185:1058-1060. Fisher, E., 1939. Habits of the Southern Sea Otter, Jour. Mammal. 20:21-36. Hall, K. and G. Schaller, 1964. Tool Using Behavior of the California Sea Otter, Jour. Mammal. 45:287-298. Limbaugh, C., 1961. Observations of the California Sea Otter, Jour. Mammal. 42:271-273. lowry, l. and J. Pearse, 1973. Abalones and Sea Urchins in a Sea Otter Habitat, Marine Biol. 23:213-219. Pearse, J. & L. Lowry, 1974. An Annotated List of the Benthic Algae and Invertebrates in the Kelp Forest Community at Pt. Cabrillo, Pacific Grove, California. Technical Report fL, Coastal Marine Laboratory, University of California, Santa Cruz. Nagy, K., 1975. Water and Energy Budgets of Free-living Animals: Measure ment Using Isotopically Labeled Water. In Environmental Physiology of Desert Organisms, ed. N. Hadley, Halstead Press, Stroudsberg, Penn. Vandervere J., 1969. Feeding Behaviour of the Southern Sea Otter, Proc. Sixth Ann. Conf. Biol. Sonar and Div. Mamm., SRI, Menlo Park, CA., p. 221-227. RENEWAL RESEARCH GRANT PROPOSAL BUDGET YEAR BEGINNING APRIL 1, 1977 THROUGH MARCH 31, 1978 BUDGET CATEGORY PROPOSED AMOUNT A. Salaries and Wages 1. Senior Personnel a. Principal Investigator Or. Kenneth Norris 2. Other Personnel (non-faculty) a. Graduate student (research assist.) Daniel Costa 100% time for 3 summer months $ 2,880 50% time during 9 months in acad. year 4,230 b. Diving Assistants II, unnamed 3 hours/day @ $5.36/hr x 56 total days during summer 900 Total Salaries and Wages $ 8,010 B. Fringe Benefits 1. 0.92% of Res. Assist.'s salary during acad. year 39 2. 1.72% of Res. Assist.'s and Diving Ass't's summer salary 65 C. Total Salaries, Wages and Fringe Benefits $ 8,114 0. Permanent Equipment 1. Scuba equipment 500 Total Permanent Equipment 500 E. Expendable Supplies and Equipment 1. Miscellaneous supplies, chemicals, anesthetics 800 2. Outboard fuel 400 3. Sea otter food, shipped to Alaska (charter flight) 1,600 @ $1.60/1 b. Total Expendable Supplies and Equipment $ 2,800 F. Travel and Per Diem 1. Local travel -Monterey Area 400 2. Round trip each for 3 persons (Oan Costa, veterinarian and diving assistant), San Francisco to Anchorage to Cordova, Alaska@ $387 R.T. each 1 '161 3. Per diem in Alaska - 3 persons @ $41/day for 41 days 1 ,681 Total Travel and Per Diem $ 3,242 G. Publication Costs 250 H. Other Costs 1 • Veteri na ria n - - - $1 00/ day for 8 days 800 2. Duplicating, long distance phone, postage, misc. 300 3. Blood analysis, 15 samples @ $32/sample 480 Total Other Costs $ 1,580 Budget Category Proposed Amount I. Total Direct Costs $16,486 J. Indirect Costs 1. Off-campus research rate, 18.6% of modified total direct costs 2,973 K. Total Estimated Project Costs $19,459 I University of California, Los Angeles (B.A.), 1948 University of California, Los Angeles (}f. A.), 1951 Scripps Institution of Oceanography (Ph.D.), 1959 POSITIONS Past Vice President, Marine Park Corporation Curator, ~mrinelnnd of the Pacific, 1953-1960 Director, Oceanic Institute, Hawaii, 1968-1971 Professor of Natural History, U.C.L.A., 1968-1972 Director, Coastal 7'-hrine Laboratory, 1972-1975 Deputy Director, Coastal !'-Iarine Laboratory, 1975- . 'AJ'IARDS, FELLOWSIIIPS A~D AFfiLIATIONS Brain Research Institute ;\t..rard, University of California, Los Angeles, 1966 Mercer -~~nrd, Best ncsearch in A•~ricru< Icology, 19G3, 1964 Stoye Award, American Society of Ichthyologists and Herpetologists, Best Research Paper, Ichthyology, 1950 Stoye Award, American Society of Ichthyologists and Herpetologists, Best Research paper, Herpetology, 1951 Fellah', California Academy of Sciences Fellow, Los Angeles Cmmty Museum Board of Governors, runerican Society of Ichthyologists and Herpetologists President, Herpetologists League ~~~rnber, Ecological Society of America Fellow, American Association for the Advancement of Science Fellow, American Fisheries Society Sustaining ~~nver, Americru1 Institute of Biological Sciences Omrter J-!ember, Society for the Study of Evolution Member, American Society of Mammalogists Memher, Nil de mess Society Member, National Parks Association t-fembcr, National i'li ldlifc Federation Associate r.rcmbcr, American ~luseum of Natural History Member, l\aturc Conservancy ~!ember, i1.'orld Population Council f.bmbcr, Si!-,'111'1 XI P.cmbcr, Wcstcm Society of Natur'alists l-bmbcr, Rcseardt Council of SJn Diego Zoo and Insti tutc for Compara tive Biology Associate ~tcmbcr, 1\dvisory Council, ~tission Bay Re~earch Foundation Member, BLM Califomia State t.ful tiple-Use Advisory Board Goven1or's (California) Conrnission of Sea Otter-Abalone Controversy Editor-in Olicf, 1st International Sympositnn of Cetacean Research, · Whales, fulphin :md Po!poises, University of California Press J.bmbcr, Biological Instn.nnentation Cotmcil (AIBS) ~1cmbcr, Brain Research Institute, U.C.L.A. Member, Mayor's Allvisory Corrnni ttee on Space and Oceanography (Los Angeles) J.1cmber, IBP Planning Cotmci 1, ~Iarine Mammals Program Member, Bioinstrumentation Advisory Cotmcil, American Institute of Biological Sciences, 1968 J.tcmber, Ecological Society of ;\merica Study Corrnnittee (desiw1 of Inter-American Institute of Ecology), 1969-1971 M:!mber, National Science Fotmdation Advisory Panel for Environmental Biology, 1969-1971 Governor's (Hmmii) Committee to Prepare a Program for the Preser vation of Scientific Areas, 1969-1970 Research 1\_c;sociate, Herpetology, Ichthology and Harine Mammalogy, Los Angeles County ?--Iuset.nn of Natural History Conservation Council for Hmvaii, Oceanography Corrnni ttee Chairman, 1969-1970 Member, Executive ConUJli ttee, Marine l>farrnnal Council, U.S. International Biological Program (IBP) Member, International IBP Panel on Higher Trophic Levels (Marine 1-1~rmnals) Chainnan, Dcpart.11ent of the Interior Conference on Biology of W'nales, Shenandoah, Virginia, 1971 Member, National Oceanic &Atmospheric Administration Task Force on Tuna-Porpoise Problem Founder, l.h1i vers i ty of California Natural Land and Water Reserves System Founder, Hm.;aii Environmental Simulation Laboratory · ~rnber, Scientific Advisory Corrnnittee, Marine ~Tammal Corrnnission, 1973-1975 Member, Advisory Corrnnittee, Friends of the Sea Otter, 1973- Associate Director, Institute of ~Iarine Resources Member, Scientific Advisory Board, Sailing Education Association, 1972-1974 • . 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