Biology and Management of Dogfish Sharks

Abstract.—Spiny dogfish <em>Squalus acanthias </em>have been an important commercial species on Canada’s Pacific coast for more than 130 years. In this study we show that the spiny dogfish life history results in juveniles remaining in pelagic waters for 10–15 years after birth, with lengths up to about 60 cm. Abundance estimates show that the numbers of these young dogfish, as well as some older dogfish in the pelagic waters, appear to represent a relatively large percentage of the population in these two regions. Dietary analysis shows that while euphausiids and teleosts constitute the major food items, regardless of size/age, dogfish feed on a number of species within the ecosystem. After about 15 years, there is a movement into demersal habitats where individuals eventually mature. Because dogfish are long lived, and because they are found throughout the pelagic zone and demersal habitats, it is probable that they play a key role in the Strait of Georgia and Puget Sound ecosystems.

Biology and Management of Dogfish Sharks

Abstract.—Spiny dogfish <em>Squalus acanthias </em>have been an important component of the Strait of Georgia fisheries from the late 1800s to the late 1940s, when the fishery collapsed owing to overfishing and changes in market demand. The stock population levels have sustained a commercial fishery of approximately 2,000 metric tons since 1978. Recent concerns regarding the status of dogfish stocks worldwide have reprioritized the status assessment of dogfish in British Columbia. Longline research surveys were conducted for dogfish in the Strait of Georgia in 1986, 1989, and 2005. Additional sources of information are catch and effort data collected through logbook records from the commercial longline fishery. Recent improvements in gear configuration resulted in a switch in the mid-1990s from traditional J hooks to circle hooks, which makes direct comparison of catch rates difficult. In November 2004 a calibration experiment using J hooks and circle hooks demonstrated that, overall, spiny dogfish catch per unit effort (CPUE) for circle-hook gear was 1.6–1.7 times higher than that for J-hook gear. After applying this conversion to the commercial longline CPUE data available for 1980–1984 and 2000–2004, no significant trend in catch rate over time was detected. The catch rate observed in the longline research survey actually increased in 2005 compared to 1986 and 1989. In both fisheries and research data, the proportion of smaller spiny dogfish in the size distribution has increased, reducing the overall mean size. The decline in mean size is probably due to an increase in recruitment of juvenile fish. However, caution in management of this stock is warranted given that the current commercial fishery is now landing a large proportion (estimated 80%) of immature fish. Increased fishing pressure on juveniles could have implications for the abundance of mature fish in upcoming decades.

Biology and Management of Dogfish Sharks

Abstract.—The fishery for spiny dogfish <em>Squalus acanthias </em>within British Columbia (B.C.) has fluctuated greatly over the past 150 years. During the 1930s and 1940s it was one of the most valuable fisheries on the West Coast. Active management of this fishery began in 1977 after Canada extended its exclusive economic zone to 200 mi. The management of Pacific groundfish fisheries, including dogfish, is complex, and is further complicated by serious conservation concerns. Bycatch issues and the lack of full catch monitoring have been of particular concern. As a result, Fisheries and Oceans Canada (DFO) approached groundfish industry representatives to develop a plan to address these key issues. A program to make individual fishers more accountable for their harvest, to improve compliance with the DFO’s selective fishing and fishery monitoring policies, and to be consistent with Pacific fisheries reform was developed. This integration program was implemented in 2006 for commercial groundfish fisheries within B.C. As a result, at-sea monitoring was maximized to 100% and individual transferable quotas within each fishery allow fishermen to account for their groundfish bycatch on an annual basis. This new management system could help pave the way for other fisheries around the world to learn, adjust accordingly, and implement similar regimes.

Biology and Management of Dogfish Sharks

Abstract.—Spiny dogfish <em>Squalus acanthias </em>are an abundant and commercially important species of fish off both the Atlantic and Pacific coasts of North America. They are opportunistic feeders and have a varied diet that can include many fish species, especially small forage fish such as herring, capelin, and sand lance as well as crustaceans, worms, euphausiids, gelatinous zooplankton, and cephalopods. The purpose of our present study is to investigate the utility of the second dorsal spine in providing multiyear information on the feeding habits of dogfish using stable isotope (C and N) analysis. The outer dentine and enamel layers of a spine from three dogfish (caught off the coast of British Columbia) were analyzed to obtain their stable nitrogen and carbon isotope composition (δ¹⁵N and δ¹³C, respectively). Each sample had annuli from multiple years, allowing possible seasonal migrations to be averaged over samples. The δ¹⁵N ranged from a low of 11.6‰ to a high of 14.9‰ over the three spines and δ¹³C ranged from –11.5‰ to –18.4‰. The variable isotopic signatures along the spine indicate that the method may be used to assess ecological changes. Stable isotope measurements of dogfish spines could be a valuable means of determining long-term changes in habitat usage and feeding ecology.

Biology and Management of Dogfish Sharks

Abstract.—The first tagging program for spiny dogfish <em>Squalus acanthias </em>in Washington State was conducted in the early 1940s, coinciding with the period of the highest landings in the history of the fishery, when annual landings in the Northeast Pacific grew to over 50,000 metric tons (mt). A second tagging program in Puget Sound began in 1969, when landings in the Northeast Pacific were below 500 mt. Patterns of recaptures from the two tagging experiments are reanalyzed and compared using a common set of spatial areas for the first time. The fraction of dogfish remaining in each basin and moving between each pair of basins is reported, along with the fraction of dogfish recaptured in Canadian waters. Seasonal movement north and south in coastal waters is considered. Differences in length compositions between inside and outside waters are described, and possible causes of this difference are discussed. The potential use of these tagging results in a population dynamics model is considered.

Biology and Management of Dogfish Sharks

Abstract.—The spiny dogfish <em>Squalus acanthia</em>s is one of the world’s best-studied and heavily fished sharks, yet one of the hardest to protect from overexploitation. The life-history characteristics, serious stock depletion, and significant international trade associated with dogfish are exceptionally welldocumented. The conservation mandates under the U.S. Magnuson Fishery Conservation and Management Act (MFCMA) and the goals of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) are also clear. Still, dogfish conservation efforts are hampered by the shark’s relatively low economic value, reputation as a pest, and general lack of appeal. The level of public support required to secure and sustain dogfish restrictions has been much higher than for other, more charismatic sharks. This paper documents the 15-year-long quest for science-based management of Northwest Atlantic dogfish fisheries and restrictions on dogfish international trade under CITES. Specifically, it reviews the process and hurdles associated with developing and effectively implementing fishery management plans (FMPs) for dogfish by the Mid-Atlantic and New England Fishery Management Councils (MAFMC, NEFMC), National Marine Fisheries Service (NMFS), and Atlantic States Marine Fisheries Commission (ASMFC). The relevant work of CITES and its Animals Committee as well as Germany’s efforts to list dogfish under CITES Appendix II are also discussed in detail. Specific recommendations to ensure dogfish sustainability, through improving fisheries policy development and employing complementary conservation tools, are offered.

Biology and Management of Dogfish Sharks

Abstract.—The Northeast Atlantic contains one stock of spiny dogfish <em>Squalus acanthias </em>(also known as spurdog), which has been in decline since the 1960s. Landings reached a peak of 55,600 metric tons (mt) in 1963; 24 years later they had fallen to 44,600 mt and 12 years after that to 9,800 mt. The last phase of steep decline commenced in 1987 and coincided with heavy landings from mainly the Celtic Seas of which Ireland took a substantial share in a gill-net fishery off its southwest coast. At first the Irish gill-net fishery harvested predominantly female and pregnant spiny dogfish but the characteristics of the landings rapidly changed.

Biology and Management of Dogfish Sharks

Abstract.—Spiny dogfish <em>Squalus acanthias </em>biomass has increased in the Gulf of Alaska, yet little is known about the ecological niche that dogfish fill in this ecosystem. Trophic position is an important indicator of the ecological role of an organism. To explore the trophic position of dogfish we analyzed the nitrogen and carbon stable isotope ratios of 60 dogfish from five locations between Washington and the Gulf of Alaska. The mean δ¹⁵N values for dogfish ranged from 12.0‰ (central Gulf of Alaska) to 13.4‰ (Howe Sound, British Columbia) and the mean δ¹³C values ranged from –21.3‰ (Yakutat Bay, Alaska) to –17.9‰ (Puget Sound, Washington). Sites to the north tended to be significantly depleted in the heavy isotopes of both nitrogen and carbon. The differences in nitrogen isotope ratios among sites were attributed to potential changes in dogfish feeding behavior and trophic position. Differences in carbon isotope ratios suggested that dogfish utilize different food webs along the northeastern Pacific Ocean shelf. Additionally it was hypothesized that feeding differentially in offshore versus inshore food webs or targeting pelagic versus benthic prey species may explain the isotopic variability. These results are preliminary and require additional tests before conclusions can be made about the trophic position of dogfish in this region. Future work will explore stable isotope variability at lower trophic levels to test the hypothesis that entire food webs are isotopically shifted owing to differences in isotopic fractionation at the base of the food web. Also, trophic level differences among dogfish size classes and between sexes will be explored among a greater diversity of locations to better describe the ecological consequences of increased biomass of dogfish in the northeastern Pacific Ocean.

Biology and Management of Dogfish Sharks

Abstract.—Spiny dogfish <em>Squalus acanthias </em>is distributed in the Southwest Atlantic Ocean between 34°S and 55°S. Information on size, sex, stomach contents, presence of gravid females, oocyte size, embryo size, and sex ratio were collected from bottom trawl surveys in eight of the years between 1986 and 2004. The species was recorded from a depth range of 66 to 165 m, with maximum densities found between 86 and 105 m. Female length was in the range of 46 to 101 cm and male length from 48 to 94 cm. Gravid females had lengths between 69 and 98 cm, and contained 4 to 11 embryos each (mean = 7.8, SD = 1.7). In 1996 intrauterine embryo growth was observed between August (females: 19.9 cm; males: 19.9 cm) and November (females: 22.3 cm; males: 22.6 cm). The sex ratio of embryos was 1:1. Litter size and near-term embryo length increased with the size of the pregnant female. Embryo sizes were not significantly different with respect to sex. A 2-year gestation cycle appears consistent with the data. Dogfish is a top predator in the San Matías Gulf ecosystem, feeding on fish species important to local fisheries.