384 Abstract—Although the Atlantic Food habits of Atlantic white-sided white-sided dolphin (Lagenorhynchus acutus) is one of the most common dolphins (Lagenorhynchus acutus) dolphins off New England, little has been documented about its diet in off the coast of New England the western North Atlantic Ocean. Current federal protection of marine James E. Craddock (contact author)1 mammals limits the supply of animals 1 for investigation to those incidentally Pamela T. Polloni caught in the nets of commercial fish- Brett Hayward2 ermen with observers aboard. Stom- 3 achs of 62 L. acutus were examined; of Frederick Wenzel these 62 individuals, 28 of them were Email address for contact author: [email protected] caught by net and 34 were animals 1 Biology Department stranded on Cape Cod. Most of the Woods Hole Oceanographic Institution net-caught L. acutus were from the Woods Hole, Massachusetts 02543 deeper waters of the Gulf of Maine. A 2 Integrated Statistics, Inc. single stomach was from the continen- 16 Sumner St. tal slope south of Georges Bank. At Woods Hole, Massachusetts 02543 least twenty-six fish species and three cephalopod species were eaten. The 3 Protected Species Branch predominant prey were silver hake Northeast Fisheries Science Center (Merluccius bilinearis), spoonarm National Marine Fisheries Service octopus (Bathypolypus bairdii), and 166 Water Street, Woods Hole, Massachusetts 02543 haddock (Melanogrammus aeglefinus). The stomach from a net-caught L. acutus on the continental slope con- tained 7750 otoliths of the Madeira lanternfish (Ceratoscopelus maderen- sis). Sand lances (Ammodytes spp.) were the most abundant (541 otoliths) The Atlantic white-sided dolphin second collected in 1976, likely a dis- species in the stomachs of stranded (Lagenorhynchus acutus) is restricted carded incidental take from a gillnet L. acutus. Seasonal variation in diet to the temperate and subpolar North set near Jeffreys Ledge (Katona et was indicated; pelagic Atlantic her- Atlantic Ocean, ranging from west al., 1978), were taken in summer and ring (Clupea harengus) was the most Greenland (approximately 64°N) to contained the same species of fish and important prey in summer, but was North Carolina (about 35°N) in the squid. These records indicated that rare in winter. The average length of western North Atlantic, and from Atlantic herring (Clupea harengus), fish prey was approximately 200 mm, Norway to the Bay of Biscay in the silver hake (Merluccius bilinearis), and the average mantle length of eastern North Atlantic (Leopold and and northern shortfin squid (Illex il- cephalopod prey was approximately Couperus, 1995). There are thought ) could be significant com- 50 mm. lecebrosus to be three populations in the western ponents of the diet. A single animal North Atlantic—the Gulf of Maine, driven ashore in Trinity Bay, New- Gulf of St. Lawrence, and Labrador foundland, also contained Atlantic Sea populations (Palka et al., 1997). herring and northern shortfin squid Seasonal shifts in the Gulf of Maine (Sergeant and Fisher, 1957). population have been reported; high- Other observations have reported est numbers are found in summer and a few more prey species for L. acu- fall and lowest numbers in winter tus. Stomachs of 14 of 40 stranded L. (Northridge et al., 1997; Palka et al., acutus examined from Cobscook Bay, 1997). Most of our animals, however, Maine, contained one silver hake, were obtained during the winter. nine shortfin squid, five rainbow smelt This study is the first detailed (Osmerus mordax), and fragments of analysis of the food habits of the unidentified decapod shrimp (St. Au- Atlantic white-sided dolphin in the bin and Geraci, 1979; Sergeant et al., western North Atlantic Ocean, here- 1980). Katona et al. (1978) reported after referred to as L. acutus rather probable feeding on sand lances (Am- Manuscript submitted 18 September 2008. Manuscript accepted 5 May 2009. than the more cumbersome Atlantic modytes spp.) by L. acutus associated Fish. Bull. 107:384–394 (2009). white-sided dolphin. Previously, only with feeding humpback (Megaptera three live-caught specimens from off novaeangliae) and fin whales (Balae- The views and opinions expressed New England have been examined noptera physalus). The only L. acutus or implied in this article are those for stomach contents and reported in feeding incident recorded was on De- of the author and do not necessarily reflect the position of the National the literature. A single specimen col- cember 20, 1997, on Stellwagen Bank, Marine Fisheries Service, NOAA. lected in 1954 (Schevill, 1956) and a southwestern Gulf of Maine, when a Craddock et al.: Food habits of Lagenorhynchus acutus off the coast of New England 385 72°W 71°W 70°W 69°W 68°W 67°W 44°N 44°N Maine Gulf of Maine 43°N New Hampshire m 43°N 200 Massachusetts 42°N 42°N Georges Bank 41°N 41°N 50 m 100 m 40°N 200 m 40°N Kilometers 1000 m 75 37.5 0 75 72°W 71°W 70°W 69°W 68°W 67°W Figure 1 Occurrences from 1991 to 2006 of 62 Atlantic white-sided dolphins (Lagenorhynchus acutus) collected in the Gulf of Maine and south of Georges Bank and examined for stomach contents in this study. Circles are locations of net-caught dolphins; triangles are locations of stranded dolphins. group was observed circling and feeding on a school of MA, and one from Naushon, Elizabeth Islands, Dukes sand lance (Weinrich et al., 2001). County, MA (Table 1). We have examined every available stomach of net- caught L. acutus. All were taken in the U.S. commercial Materials and methods fishery and sampled aboard ship by fisheries observ- ers of the National Marine Fisheries Service (NMFS), This study records stomach contents from 28 inciden- Northeast Fisheries Science Center (NEFSC, Woods tally caught and 34 stranded L. acutus from the Gulf of Hole, MA), Northeast Fisheries Observer Program (NE- Maine population off the coast of New England (Fig. 1). FOP). NEFOP is the permitting and monitoring agency The animals examined were collected between 1991 of the commercial fishing fleet in compliance with the and 2006, most of them from 2004–5. The incidentally Marine Mammal Protection Act (MMPA) and the U.S. caught (hereafter referred to as net-caught) animals Endangered Species Act (ESA). were taken either by otter trawl (22 stomachs) or by Stranded animals were obtained by volunteers of sink gillnet (six stomachs). Of these, 26 were from the the Cape Cod Stranding Network, currently known as Gulf of Maine, one was from deep water (500 m) on the International Fund for Animal Welfare (IFAW), Yar- continental slope south of Georges Bank near Munsen mouth, MA. Most of the stomachs were initially frozen Canyon, and one was from the continental shelf south and curated by the NEFSC. of Narragansett Bay. Thirty-four stomachs were from Contents from stomachs determined to be intact (reli- strandings: 33 from outer Cape Cod, Barnstable County, able) were examined for frequency, relative abundance, 386 Fishery Bulletin 107(3) Table 1 Summary comparison of numbers, sex, and stomach contents of 34 stranded vs. 28 net-caught Atlantic white-sided dolphins (Lagenorhynchus acutus) collected in the western North Atlantic Ocean off the coast of New England, between 1991 and 2006; and seasonality of the net-caught individuals. Total net-caught includes two calves with empty stomachs; seasonal net-caught excludes the two calves; S. of Georges = South of Georges Bank. Nontrace = whole prey. Seasonal net-caught Strandings Total net-caught Winter Summer S. of Georges Number of dolphins 34 28 22 3 1 Depth where captured (m), mean (range) 0 189.8 (55–503) 186.9 (71–265) 107.0 (55–187) 503 Number of males 22 9 9 0 0 Length of males (cm), mean (range) 227 (156–280) 208 (173–260) 208 (173–260) 0 0 Adult males (>230cm) 10 2 2 0 0 Number of females 12 16 12 3 1 Length of females (cm), mean (range) 205 (168–219) 199 (161–253) 203 (171–253) 178 (161–203) 252 Adult females (>200cm) 10 6 4 1 1 Number unsexed 0 3 1 Number of stomachs containing food 22 (65%) 25 (89%) 20 (91%) 3 (100%) 1 (100%) Number of empty stomachs 12 (35%) 3 (11%) 2 (9%) 0 0 Number of otoliths 856 10287 2157 287 7843 unidentified 231 54 51 2 1 Number of fish species 8 21 17 6 7 Number of cephalopod beaks 34 535 519 11 5 Number of cephalopod species 3 3 3 2 1 Number of identified prey Nontrace fishes 0 50 35 15 0 Near nontrace fishes (skulls) 7 56 38 4 14 Total fishes 332 5179 1120 135 3924 Nontrace cephalopods 0 2 0 2 0 Near nontrace cephalopods 0 1 0 1 0 Total cephalopods 20 282 274 4 4 and size (length, weight) of prey. Two net-caught dol- mantle length for cephalopods). Otoliths were removed phins examined and subsequently eliminated from the from skulls of both nontrace and trace fishes and then analysis were one partly decomposed female with a cleaned, dried, and measured. The remaining contents mud-filled stomach and thoracic cavity and virtually no were soaked overnight in hot water, if necessary, or food in the stomach, and a partially decomposed male elutriated directly through a series of sieves to remove with an almost empty stomach taken on the continental soft tissue and retain hard parts. All items found were shelf south of Narragansett Bay. identified to the lowest taxonomic level possible (usu- Stomachs were weighed whole, divided into their ally to species) by using our own reference collection three components (forestomach, main, and pyloric), and published guides (Campana, 2004; Clarke, 1962, emptied of contents, and weighed again to determine 1986; Collette and Klein-MacPhee, 2002; Gregory, 1933; both the size of the stomach and the mass of its con- Harkönen, 1986; Smale et al., 1995; Vecchione, 2002).