The Role of Cetaceans in the Shelf-Edge Region of the Northeastern United States

JAMES H. W. HAIN, MARTIN A. M. HYMAN, ROBERT D. KENNEY, and HOWARD E. WINN

Introduction ploration and development added to from Cape Hatteras, N.C., and the present fishing and shipping ac­ from the center of the Northeast Man has been, and continues to tivities, this role may be on the in­ Channel at the eastern tip of be, a part of the ecosystem along the crease. After 3 years of field studies, Georges Bank (Fig. 1). This region outer margin of the outer continen­ the role of another group of apex straddles the shelf break (200 m tal shelf (OCS). With oil and gas ex- predators, marine , can be depth contour), is about 40 km (21.6 characterized. These findings have n.mi.) wide, and includes about application to decisions about 62,100 km 2 (18,100 n.mi. 2). The authors are with the Graduate School of resource utilization, habitat use, This paper summarizes aspects of Oceanography, University of Rhode Island, and the impacts of offshore ac­ the findings from a large and Kingston, RI 02881; the present address of tivities. multifaceted study. Details on J. H. W. Hain is Associated Scientists at Woods Hole, Box 721, Woods Hole, MA 02543. Views In this study, the shelf-edge sampling and data collection not in­ or opinions expressed or implied are those of the region was defined as bounded by cluded here are given in the final authors and do not necessarily reneet the posi­ tion of the National Marine Fisheries Service, the 91 and 2,000 m depth contours, report of the Cetacean and Turtle NOAA. and by lines extending southeast Assessment Program (CETAP),

Three sperm (two adults and a calf) sighted by survey aircraft in deep water south of Georges Bank.

47(1),1985 13 University of Rhode IslandI. Addi­ tional findings on cetacean biomass and energetics in waters of the northeastern U.S. are reported in Scott et al. (1983). A review of mor­ phology and energetics in relation to the food requirements of marine mammals is provided by Brodie (1984). The principal findings reported here are: 1) Twenty species or species groups were reported in the region. Of these, 12 are common and 8 are uncommon or rare. Three species, the sperm , Physeter catodon; fin whale, Ba/aenoptera physa/us; and pilot whales, G/obicepha/a Figure I. - The shelf-edge spp., together constitute 75 per­ > region of the northeaster~5° cent of the cetacean biomass. U.S. outer continental shelf 2) During the season of peak (lined area). Depth contours abundance, spring, a minimum of are labelled in meters. 47,565 cetaceans may inhabit or transit the region. This represents a cumulative biomass of 26,506 metric tons (t). Table l.-Cetaceans reported from the shell edge region of the northeastern U.S. 3) The food requirement of the DCS. Data from CETAP field studies, November 1978-January 1982. shelf-edge cetacean component is Species Common name No. of sightings estimated to be between 64,000 and 960,000 tlyear. The current best Mysticetes-baleen whales physalus Fin whale 91 estimate within this range is 480,000 B. acutorostrata Minke whale 34 B. borealis Sei whale 27 tlyear. This value converts to a ceta­ Megaptera novaeangliae 6 cean consumption of 9.7 Kcall Eubalaena glacialis 3 2 m /year, which is in the same range Odontocetes-toothed whales as values reported for the highly Tursiops truncatus Bottlenose 531 Globicepha/a spp.' Pilot whales 347 productive Georges Bank region. Grampus griseus Grampus 332 4) If our assessment is correct, Delphinus delphis Saddleback dolphin 197 Physeter catodon 156 then cetaceans must be considered a coeruleoalba Striped dolphin 48 Stenella spp. (spotted)' Spotted dolphin 27 major component of the ecosystem. acutus Whitesided dalphin 22 Their impact on resources of the phocoena Harbor 17 Mesop/odon spp.' Beaked whales 6 region is substantial- perhaps equal Orcinus orca 3 to, or comparable to, that of man. Ziphius cavirostris Goosebeaked whale 3 Lagenorhynchus albirostris Whitebeaked dolphin 3 Hyperoodon ampullatus Northern 1 Species Present Pseudorca crassidens 1 In the 39 months of field studies Unidentified large whales' 144 from November 1978 through Unidentified small whales' 520 January 1982, 2,519 cetacean Total sightings 2,519 sightings were reported from the 'Identification to genus level only due to difficulty in field identification and/or defined shelf-edge region. These unresolved taxonomy. , Categories used to group unidentified or partially·identified sightings: Large whales, sightings are listed in Table 1 by ,,25 feet (7.6 m) in length; small whales, < 25 feet (7.6 m) in length. species or species groups, along with two categories into which unidentified

I Final Report of the Cetacean and Turtle Assessment Program, University of Rhode or partially identified sightings were were common (10 or more sightings) Island, to the Bureau of Land Management, U.S. Department of the Interior. Ref. No. grouped. Twenty species or species and 8 were uncommon or rare ( < 10 AA551-CT8-48, 568 p. groups were reported. Of these, 12 sightings). Sperm whales and fin

14 Marine Fisheries Review Table 2.-Estimated abundance, biomass, and food requirements for cetaceans in the shelf edge region of the northeastern U.S. OCS. species groups, B. borealis, T. trun­ catus, Grampus griseus, D. delphis, Percent Food Total of total require- and Stenel/a spp., each accounting for 4 Abundance estimate' 1 biomass cetacean Weight' ment 3-9 percent of the total biomass, bring Species (No. +/- 95% GI) (t) biomass (t) (tlyear) the total to 99 percent. The remaining P. calodon sp 215 +/- 256 4,300 16 20.0 6,016 species together account for about 1 wi 65 +/- 197 1,300 18 percent of the total biomass. (This B. physa/us sp 292 +/- 426 8,760 33 30.0 10,250 wi 60 +/- 102 1,800 24 treatment does not include the two B. borealis sp 237 +1- 327 3,081 12 13.0 3,686 unidentified whale categories.) wi 0 0 0 Therefore, of the 20 species reported, B. acutorostrata sp 47 +/- 57 212 1 4.5 330 wi 0 0 0 three species form the principal com­ H. ampullatus sp 9 na 42 < 1 4.7 65 ponent of the cetacean biomass, and wi 0 0 0 Unidentified sp 2 +/- 6 41 <1 '20.5 44 eight species account for nearly the large whales wi 0 0 0 entire biomass. T. truncatU$ sp 6,431 +1- 4,001 965 4 0.15 4,320 wi 1,458 +1- 1,885 219 3 G/ob/cephala spp. sp 6,823 +1- 6,934 5,800 22 0.85 19,137 wi 2,693 +1- 3,817 2,289 31 Food Requirements: Grampus griseus sp 3,543 +1- 4,350 1,205 5 0.34 3,952 wi 364 +/- 1,254 124 2 Estimated Minimum Values D. de/phis sp 13,881 +/- 19,734 902 3 0.07 8,652 wi 15,703 +1- 24,071 1,021 14 The role of cetaceans in the shelf­ Slenella spp. sp 13,210 +/- 11,334 713 3 0.05 4,317 edge ecosystem can be further wi 3,754 +1- 3,004 203 3 described through the calculation of L. acutus sp 1,231 +1- 1,931 148 < 1 0.12 570 wi 0 0 0 the food requirements of this compo­ P. phocoena sp 140 +1- 163 6 <1 0.05 34 nent. Following the methods of Brody wi 15 +1- 34 1 <1 Unidentified sp 1,504 +1- 2,206 331 1 '0.22 2,593 (1945) and Hinga (1979), the small whales wi 2,050 +1- 7,529 451 6 minimum metabolic demands, and

Total sp 47,565 26.506 63,966 thus the minimum food requirements, wi 26,162 7,408 can be calculated from the following , Estimates based on individuals sighted at or near the surface and do not account for missed due to equation: submergence. Additional discussion in text. 2 Estimates and biomass data shown for peak values in spring (sp) and minimum values in winter (wi). 'Weight values are from Kenney et ai. (text footnote 3). Resting or basal metabolism (~:l) • Calculation based on 6 months at high spring abundance and 6 months at low winter abundance. Definition of seasons follows calendar conventions, e.g., spring = 20 March-20 June. , Estimated body weight for this grouping is a weighted mean from the identified large or small whales. = 70 x (body wt. in kg)o.75.

The conversion of caloric demand to whales were the most common large sightings within the genus Stenel/a, weight value of prey species is from whales present. The majority of small since species were virtually in­ Sissenwine et al. (1984a): whale sightings were made up of four distinguishable in the field. Also, species (or species groups): Tursiops while humpback whales, Megaptera 1 Kcal/g wet weight. truncatus, Globicephala spp., Gram­ novaeangliae, and right whales, pus griseus, and Delphinus delphis. Eubalaena glacialis, are known to oc­ The calculated annual food re­ Together these six taxa made up 89 cur in the area (Table 1), none were quirements are given in the righthand percent of the identified sightings. sighted on census tracks, and are column of Table 2. Here, individual therefore not included in Table 2. food requirements have been Abundance and Biomass These data suggest that during the multiplied by the estimated abun­ Table 2 summarizes abundance and season of peak abundance, spring, the dance. The seasonal fluctuation in biomass data for cetaceans in the shelf-edge region may be inhabited by numbers has been accounted for in shelf-edge region. These abundance 47,565 individuals with a combined the calculations: The total require­ estimates are based on aerial survey biomass of 26,506 t. This inhabitance ment is based on 6 months at the high data with calculations following the is seasonal, and the low value for spring estimate and 6 months at the methods of Burnham et al. (1980). estimated biomass in winter is about low winter estimate. This treatment Because these data are based solely on 28 percent of the spring season high. achieves our aim of a concise presen­ aerial surveys in a rigorously defined Averaged over the whole year, three tation of findings, yet is consistent census mode, they are from a subset species or species groups, P. catodon, with the larger and considerably more of the total data given in Table 1. B. physalus, and Globicephala spp., detailed data set. Several differences will be noted. For constitute 75 percent of the total ceta­ The summed values suggest that the example, aerial observers pooled all cean biomass. Five more species or minimum food requirement of the

47(1), 1985 15 shelf-edge cetaceans is on the order of Applying the cumulative correc­ (NEFC, 1983; footnote 2). (As above, 64,000 t/year. tions, the actual requirements are values are for entire shelf, Gulf of almost certain to be 2-3 times greater Estimated Food Requirements: Maine to Cape Hatteras, and not only than the calculated minimums. For A Best Estimate and the shelf-edge region.) species which ordinarily spend a good If an Upper Boundary our assessment is correct, the portion of their time submerged and food requirement of shelf-edge ceta­ The figures presented in the forego­ also require additional food intake to ceans is 480,000 t/year and could ap­ ing are thought to be an under­ build up substantial stored food proach I million t/year. Even after all estimate. This is due to a number of reserves, the requirement could be qualifications have been considered factors: from 6 to 16 times greater. Particular­ (e.g., cetaceans feeding at various I) Metabolic rate. Our calcula­ ly since sperm and fin whales are trophic levels, cetaceans feeding on tions provide values for basal shown to be a major component of species other than those considered by metabolism. The actual metabolic re­ the total cetacean biomass - both the foregoing National Marine quirements will be greater, between species with storage requirements and Fisheries Service assessments), the im­ 1.5 and 3 times the basal rate (Brodie, apparently considerable submergence pact of cetaceans on the available 1975; Brody, 1945; Hinga, 1979). times - the upward correction to our food resource is substantial, and is 2) Assimilation efficiency. An minimum estimate will be a substan­ likely comparable with man's take. cannot utilize all of the energy tial one. To arrive at a best estimate, To relate these findings to existing in its food. Lockyer (1981) gives an we select correction factors from values, these estimates were converted assimilation efficiency of 80 percent within the ranges given as follows: to consumption per unit surface area for cetaceans, resulting in a feeding a) Metabolism beyond basal following the methods of Cohen and rate of 1.25 the metabolic re­ metabolism-2 x, b) assimilation ef­ Grosslein (In press). Dividing total quirements. ficiency - 1.25 x, c) food storage re­ consumption by the shelf-edge area 3) Food storage. Many cetacean quirements -1.5 x, and d) noncen­ and assuming, for the purposes of species store food energy in the blub­ susing of submerged animals - 2 x . consistency, that I g wet weight equals ber and elsewhere for periods of Summing these values yields a total 1.25 Kcal, cetacean consumption con­ reduced feeding common to their upward correction of 7.5 x and a best verts to 9.7 Kcallm2/year, with an seasonal cycles. Building up this estimate of 480,000 t/year as the an­ upper estimate of 19.3 Kcallm2 /year. reserve requires increased food intake nual food requirement of cetaceans Calculations based on estimates given while in productive feeding areas. The within the defined region. in Winn et al. (In press) yield com­ correction for this factor very likely Using a less conservative selection parable values for Georges Bank of lies in the range of 1.25-2.00. of correction factors and similarly 6.3 and 12.6 Kcallm2 /year. Allowing 4) Submerged animals missed by summing the values (total correc­ for uncertainties in the estimates, in­ surveys. Aerial surveys result in tion = 15 x ) yields an upper boundary dications are that consumption by estimates based on individuals sighted to our estimates of 960,000, or about marine mammals in the shelf edge at or near the surface. The estimates I million t/year. region is in the same range as for the are negatively biased by individuals These estimates will almost surely Georges Bank region. not sighted due to submergence. At be improved upon as additional data As fishery scientists and managers present, this factor can only be gaug­ become available. For the present, seek to improve their understanding ed in a preliminary way. In one study, they provide an advance over what of the biology of the resource and its fin, humpback, and right whales were has previously been known, and a successful management, an area of shown to spend 25-65 percent of their useful measure of the role of ceta­ current interest is in the improved time at the surface (footnote I). Short ceans in the shelf-edge region. estimation of natural mortality and dive routines of 2-6 minutes were Conclusions the partitioning of its components. reported to be common in fin whales, Recent work has shown predation by although dives of 6-14 minutes (or The role of marine mammals in the marine mammals to be an important longer) were also observed (Watkins, ecosystem is likely greater than has element (Kenney et aJ.3; Scott et al., 1981). In the Caribbean, dives of an been previously recognized. For the hour or more were not unusual for period 1979-82 (corresponds to the sperm whales, and estimates based on cetacean data), the current best 'The fisheries estimates are for all commercially exploited species of finfishes and squids except underwater sounds were nearly four estimate for the abundance of squid highly migratory species such as billfishes, times higher than those based on sur­ and finfish in the shelf waters of the tunas, and large sharks, and inshore species face sightings made from a small northeastern United States (includes such as menhaden, American eel, and white perch. research vessel (Watkins and Moore, other than the defined shelf-edge 'Kenney, R. D., M. A. M. Hyman, and H. E. 1982). This factor is clearly highly region) is on the order of 3.4 million Winn. 1983. Calculation of standing stocks and variable (Leatherwood et aI., 1982), t/year (NEFC, 1983). The commer­ energetic requirements of the cetaceans of the northeast United States outer continental shelf. and a correction lies in the range of cial fishery catch for this same period Nat!. Mar. Fish. Servo Rep. NA-83-FA-C-0009, 1.5-5.0. was on the order of 0.5 million t/year 154 p.

16 Marine Fisheries Review 1983; Winn et aI., In press; and this management of the shelf-edge region Kinter, and R. M. Truppo. 1982. Respiration patterns and sightability of whales. Rep. Int. paper). This factor has, for example, of the northeastern U.S. outer con­ Whaling Comm. 32:601-613. been recently addressed by Sissenwine tinental shelf. Lockyer, C. 1981. Estimation of the energy et aI. (1984b) in analyzing the decline costs of growth, maintenance, and reproduc­ tion in the female minke whale (Balaenoplera of the Georges Bank herring stock. Acknowledgments aculOroslrala) from the Southern With respect to offshore oil and gas These data are from a study funded Hemisphere. Rep. Int. Whaling Comm. development, the effects of man's in­ 31 :337-343. by the Bureau of Land Management, NEFC. 1983. Status of the fisheries resources teraction with marine mammals are U.S. Department of the Interior, off the northeastern United States. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., not yet clear. Several preliminary under Contract AA551-CT8-48 to the studies indicate a lack of conspicuous Northeast Fish. Cent., NOAA Tech. Memo. Cetacean and Turtle Assessment Pro­ NMFS-F/NEC-22, 128 p. negative impacts on marine mammals Scott, G. P., R. D. Kenney, T. J. Thompson, 4 gram, University of Rhode Island. (Geraci and S1. Aubin ; Sorensen et and H. E. Winn. 1983. Functional roles and We thank P. F. Brodie, M. J. Fogar­ ecological impacts of the cetacean community aI., 1984). However, other parts of ty, and W. A. Watkins for their in the waters of the northeastern U.S. con­ these same studies also suggest possi­ critical review of the manuscript. tinental shelf. Int. Counc. Explor. Sea C. M. ble problems due to ingestion and 1983:(12). Sissenwine, M. P., E. B. Cohen, and M. D. contact, as well as long-term chronic Grosslein. 1984a. Structure of the Georges 4 effects (Geraci and S1. Aubin ). Literature Cited Bank ecosystem. Rapp. P.-v. Reun. Cons. Int. Explor. Mer 183:243-254. On both counts, the conservation Brodie, P. F. 1975. Cetacean energetics, ____, W. J. Overholtz, and S. H. and wise management of marine an overview of intraspecific size variation. Clark. 1984b. In search of density mammals is a national policy (Marine Ecology 56: 152-161. dependence. In B. R. Melteff (workshop _--,-_-,-' 1984. Review of status of knowl­ coordinator), Proceedings of the workshop Protection Act of 1972, En­ edge of energetics. In on biological interactions among marine dangered Species Act of 1973). In ad­ B. R. Melteff (workshop coordinator), Pro­ mammals and commercial fisheries in the dition, the effective management of ceedings of the workshop on biological in­ Southeastern Bering Sea, p. 119-137. Univ. teractions among marine mammals and com­ Alaska Sea Grant Rep. 84-1. our fishery resources requires an mercial fisheries in the southeastern Bering Sorensen, P., R. Medved, M. Hyman, and understanding of the role played by Sea, p. 149-156. Univ. Alaska Sea Grant Rep. H. Winn. 1984. Distribution and abundance 84-1. of cetaceans in the vicinity of human activities marine mammals. The assessments Brody, S. 1945. Bioenergetics and growth. along the continental shelf of the nor­ reported here should contribute to a Hafner Publ., N.Y., 1,023 p. thwestern Atlantic. Mar. Environ. Res. wider view of the ecosystem, and to Burnham, K. P., D. R. Anderson, and J. L. 12:69-81. Laake. 1980. Estimation of density from line Watkins, W. A. 1981. Activities and under­ forthcoming decisions about the transect sampling of biological populations. water sounds of fin whales. Sci. Rep. Whale Wildl. Monogr. 72, 202 p. Res. Inst. 33:83-117. Cohen, E. D., and M. D. Grosslein. In press. _--,-__, and K. E. Moore. 1982. An Production on Georges Bank compared with underwater acoustic survey for sperm whales other shelf ecosystems. In R. H. Backus (Physeler calOdon) and other cetaceans in the 'Geraci, J. R., and D. J. St. Aubin. 1982. Study (editor), Georges Bank. MIT Press. southeast Caribbean. Cetology 46: 1-7. of the effects of oil on cetaceans. Final report to Hinga, K. R. 1979. The food requirements Winn, H. E., J. H. W. Hain, M. A. M. the Bureau of Land Management, U.S. Depart­ of whales in the southern hemisphere. Deep­ Hyman, and G. P. Scott. In press. Whales, ment of the Interior. Ref. No. AA551-CT9-29, Sea Res. 26A:569-577. , and . In R. H. Backus 274 p. Leatherwood, S., K. Goodrich, A. L. (editor), Georges Bank. MIT Press.

47(1), 1985 17