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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: salmon shark

Synonyms and Other Names: mackerel shark

Taxonomy: available through www.itis.gov

Identification: Lamna ditropis is a large heavy-bodied lamnid (mackerel) shark with a dorsum (back) that is dark blue to greyish-black in color, with a white underside and dispersed dark blotches (Goldman and Musick 2008). It has a large black eye, short conical snout, homocercal (equal-lobed) caudal (tail) fin, large first dorsal fin, and a small second dorsal fin (Goldman and Musick 2008, Nagasawa 1998). Lamna ditropis can be distinguished from the similar species L. nasus (Porbeagle shark) by its blotched abdomen, shorter snout, significantly shorter snout-to-nostril and snout-to-eye lengths, and shorter second dorsal fin (Hubbs and Follet 1947, Tanaka 1980).

Size: Ranging from 180 cm to 210 cm precaudal length and weighing up to 220 kg (Goldman 2002).

Native Range: Subarctic and temperate waters of the Northern Pacific Ocean (Hubbs and Follet 1947, Nagasawa 1998).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Lamna ditropis is a highly migratory opportunistic predator that feeds on fish, squid, and benthic crustations (Nagasawa 1998, Sano 1960, Sano 1962). This species is a seasonal migrant and is known to breed and overwinter in temperate waters and migrate to subarctic regions during other parts of the year (Nagasawa 1998). Lamna ditropis is ovoviviparous and reproduction includes an oophagous (egg eating) stage (Nagasawa 1998). Mating occurs in the late summer to early fall with an estimated gestation time of nine months and a litter size of up to five pups (Tanaka 1980, Nagasawa 1998, Goldman 2002). Like other species in the genus Lamna, L. ditropis is endothermic and thus capable of regulating its body temperature via oxidative metabolic processes (using specialized arteries call retia mirabilia) (Carey et al. 1981, Goldman et al. 2004).

Means of Introduction: The individual was likely dead upon release (Barker 2023).

Status: Failed introduction

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: It is suspected that the specimen found in Riggins, Idaho was placed there as a prank (Barker 2023).

References: (click for full references)

Barker, E. 2023. Official says shark found near Riggins, Idaho, wasn't a local. The Observer. La Grande, OR. https://www.lagrandeobserver.com/outdoors/official-says-shark-found-near-riggins-idaho-wasnt-a-local/article_5b92f2de-3cfa-11ee-9439-6b3fd455c56c.html. Created on 08/19/2023. Accessed on 1/24/2024.

Carey, F. G., J.M. Teal, & J.W. Kanwisher. 1981. The Visceral Temperatures of Mackerel Sharks (Lamnidae). Physiological Zoology, 54(3): 334–344. http://www.jstor.org/stable/30159948

Goldman, K. J. 2002. Aspects of Age, Growth, Demographics and Thermal Biology of Two Lamniform Shark Species. Ph.D. dissertation, College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, Gloucester Point, VA, 220 pp.

Goldman, K.J., S.D. Anderson, and R.J. Latour. 2004. Homeothermy in adult salmon sharks, Lamna ditropis. Environmental Biology of Fishes 71: 403–411. https://doi.org/10.1007/s10641-004-6588-9

Goldman, K.J. and J.A. Musick. 2008. The biology and ecology of the salmon shark, Lamna ditropis. Sharks of the open ocean: biology, fisheries and conservation, pp.95-104.
Hubbs, C. L., and W.I. Follett,. 1947. Lamna ditropis, new species, the salmon shark of the North Pacific. Copeia 1947(3): 194.

Nagasawa, K. 1998. Predation by salmon sharks (Lamna ditropis) on Pacific salmon (Oncorhynchus spp.) in the North Pacific Ocean. Bulletin of the North Pacific Anadromous Fish Commission 1: 419–433.

Sano, O. 1960. The investigation of salmon sharks as a predator on salmon in the North Pacific, 1959. Bulletin of the Hokkaido Regional Fisheries Research Laboratory, Fisheries Agency 22: 68–82.

Sano, O. 1962. The investigation of salmon sharks as a predator on salmon in the North Pacific, 1960. Bulletin of the Hokkaido Regional Fisheries Research Laboratory, Fisheries Agency 24: 148–162.

Tanaka, S. 1980. Biological investigation of Lamna ditropis in the north-western waters of the North Pacific. In: Report of Investigation on Sharks as a New Marine Resource. Japan Marine Fishery Resource Research Center, Tokyo, Japan.

Other Resources:

Author: Reaver, K.M.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.