Spiny Dogfish, , Piked Dogfish, Spurdog.
A slender squaloid shark with a long snout, fairly large eyes, and a narrow anterior nasal flap. Snout length greater than mouth width. Two dorsal fins with short anterior spines. Second dorsal fin much smaller than first dorsal. First dorsal fin origin posterior to free rear tip of pectoral fin. Second dorsal origin midway between pelvic fin insertion and free rear tip. Pectoral fins have mildly concave posterior margins and rounded free rear tips. Anal fin absent. Pectoral fins broad with rounded free rear tips.
Dorsal coloration grey or greyish-brown, usually with a few small, white spots along lateral line and upper back. Ventrum pale. Tip of first dorsal and upper caudal lobe often dusky or black. Posterior margins of pectoral fins and caudal fin often pale.
Maximum length 200cm but most adults do not exceed 100cm. Size varies significantly by region. Size at birth 18-33cm.
A temperate water species. Found inshore in enclosed bays and estuaries, to well offshore along the continental and insular slopes. From the surface to 1,978m.
The spiny dogfish has a wide distribution in the temperate coastal regions around the North Atlantic Ocean and Mediterranean Sea. There are also isolated populations in the southern hemisphere, on both sides of South America, on the southern tip of Africa, along the south coast of Australia, and in New Zealand.
The Spiny Dogfish is taken as targeted and incidental catch by hand line, demersal gillnet, trawl, dredge, and longline in artisanal, industrial, and recreational fisheries. While targeted fishing pressure in the Atlantic Ocean has declined markedly, the species is still susceptible to capture as bycatch in multi-species fisheries (Rago and Sosebee 2014, da Silva et al. 2015, ICES-WGEF 2018, FNZ 2019). Aggregative behaviour increases the catchability of mature (and usually pregnant) females (ICES-WGEF 2018). In European Union (EU) industrial fisheries, the species is generally discarded due to bans on retention, transshipment, and landing (e.g. ICES-WGEF 2018). Post-release mortality varies depending on handling techniques and gear type (e.g up to ~30% in trawl fisheries); at vessel mortality has been estimated as high as ~39% for gillnet fisheries (Ellis et al. 2017).
Historically, the species has been intensively fished off Europe since the early 1900s (mainly in the North and Irish Seas), primarily by British and Norwegian fleets, and later by French and Irish fleets (Bonfil 1994). As of 2010, science-based regulations ended EU industrial fisheries targeting Spiny Dogfish in the Northeast Atlantic; landings are still reported from Norway (between 216–313 t annually since 2011) (ICES-WGEF 2018). Some ICES member countries may be reporting landings of the Spiny Dogfish under a generic name (e.g. Squalus sp.) In the Mediterranean, most targeted fishing ceased in the 1970s with the decline in stock; however, unregulated and incidental capture still occurs in the Mediterranean and Black Seas (e.g. Ţoţoiu et al. 2016, Bonanomi et al. 2018). In the Mediterranean, Spiny Dogfish is considered a bycatch species, but catches are fully commercialized (Serena et al. 2009b, Farrugio and Soldo 2013). Targeted fisheries in the Black Sea were once operated by Turkey, Russia, and Ukraine; following reductions of Spiny Dogfish stock in the region observed in the 1990s, most of the fisheries closed and today Bulgaria is the only country with a targeted fishery in the region (Shlyakhov and Daskalov 2008).
Landings of Spiny Dogfish from the Northwest Atlantic peaked in 1974 at ~25,000 t, and again in 1996 at ~28,000 t; the majority of landings between 1979–2000 were reported from the United States fisheries. The driver behind these fisheries has been international trade to satisfy the European market demand (Dell’Apa et al. 2013). The species is currently not commercially fished in Canada, but is reported as bycatch in industrial and recreational fisheries (DFO 2020). Spiny Dogfish is still fished commercially in U.S.waters, but according to the 2018 stock status update, the population is not currently overfished or subject to overfishing (NOAA 2019).
In Africa, Spiny Dogfish is infrequently reported (<1 t between 2010–12) from South African industrial demersal longline fisheries, including those targeting sharks (da Silva et al. 2015). Some African countries, particularly Mauritania, appear to be intensifying Spiny Dogfish fishing to supply the European market demand in recent years (FAO 2009, Dell’Apa et al. 2013).
In Argentina, the Spiny Dogfish is reported as bycatch in industrial fisheries (e.g. Cedrola et al. 2012, Crespi-Abril et al. 2013). Catches have been difficult to monitor since the species may be misidentified, reported under a generic category of “shark”, or processed at sea (making species identification not possible) and historically, the species was discarded for lack of commercial value (Chiaramonte 1998). Increased commercial landings of the species were first noted in the early 2000s after the collapse of Argentina’s primary fishery, hake (Merluccius hubbsi). It has not been possible to estimate the volume of Spiny Dogfish landings, but it is known that the species is not as frequently landed as other regional sharks (Narrownose Smoothhound, Mustelus schmitti, and Tope, Galeorhinus galeus) (G. Chiaramonte pers. comm. 22/04/2020). Retention of the species is largely influenced by international market forces (Chiaramonte 2006). Increased exploitation from South American countries (e.g. Argentina, Brazil, Uruguay, and Chile) is expected if European demand increases; exports of the species from Argentina increased after strict management measures began to take effect in the US around 2000 (Dell’Apa et al. 2013). In Argentina, fisheries are characterized by declining catches, a shift to species of lower trophic levels, and an increase in catch coming from overexploited stocks (Pauly and Zeller 2015). Nearly two thirds of all Argentina stocks were overexploited or collapsed in 2014 (Pauly and Zeller 2015). The species is reported in both Chilean (SUBPESCA 2017) and Argentinian hake fisheries (Núñez et al. 2018); the latter of which has 566 trawlers in operation.
In the Southwest Pacific, New Zealand data pre-1980 are unavailable, but landings were likely to be negligible given its low value (Francis 1998, FNZ 2019). Landings increased in the late 1980s and 1990s, but fluctuated considerably depending on market forces and the species availability and the amount of effort directed at target species (Francis 1998). Spiny Dogfish is one of the primary bycatch species in New Zealand offshore fisheries (Finucci et al. 2019) and the most reported chondrichthyan from New Zealand fisheries (Francis 2015). In Australia, the species has been reported from Tasmanian recreational gillnet fisheries (Fordham 2005), as well as industrial trawl, dropline, and longline fisheries; average annual industrial catch is low (<4 t) and it is thought the species has minimal exposure to fishing gear (Walker and Gason 2007).
In addition to fishing activities, Spiny Dogfish may be threatened by habitat loss and degradation. Coastal development, pollution, dredging, and bottom trawling affect coastal or demersal habitat that the species’ prey relies on (ASMFC 2002). In Chile, spatial overlap of nursery areas and aquaculture farms have been identified; the effect of this interaction appears to influence the diet of the Spiny Dogfish, but any effect on the species’ reproductive output is unknown (Gaitán-Espitia et al. 2017).
Citations and References
Finucci, B., Cheok, J., Chiaramonte, G.E., Cotton, C.F., Dulvy, N.K., Kulka, D.W., Neat, F.C., Pacoureau, N., Rigby, C.L., Tanaka, S. & Walker, T.I. 2020. Squalus acanthias. The IUCN Red List of Threatened Species 2020: e.T91209505A124551959. https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T91209505A124551959.en. Downloaded on 08 January 2021.
An aplacental viviparous species. Litter size 2-16. Gestation ranges between 12-24 months depending on the region.
Spiny dogfish are opportunistic predators that will feed on whatever is locally available. Stomach content analysis has included a wide range bony fishes (including species that are larger than themselves) and squids, shrimps, crabs, amphipods, snails, and worms. When food is scarce, they will even consume calorie-poor prey such as jellyfishes and ctenophores. Spurdogs are generally bottom feeders but they will rise to the surface to gorge on clouds of krill.
North American Spiny dogfish migrate northward in the summer. They may be solitary but when a particular food is abundant they form immense feeding schools.
Reaction to divers
Sy and difficult to approach, but occasionally makes close passes. Will become much bolder in baited situations, even wrestling for fish directed from a divers hand.
Sightings in European waters are rare, but is possible to run into dogfish while wreck diving in New England. When this occurs, the encounters are usually brief and more distant than one would like.
Spiny dogfish can easily be baited in, by chumming around shallow wrecks in the summer months. I tried chumming on a wreck off of Rhode Island and managed to attract around a dozen sharks. They were initially shy but soon became very comfortable around our small group, even accepting food by hand.