Michael J. Dadswell

Effect of stocking density on growth, production, and survival of the giant scallop, Placopecten magellanicus, held in intermediate suspension culture in Passamaquoddy Bay, New Brunswick

Abstract The effect of stocking density on the growth of juvenile giant scallops, Placopecten magellanicus (Gmelin, 1791) (Bivalvia: Pectinidae), was assessed for 1 year in Passamaquoddy Bay, N.B., Canada. Scallop spat (initial shell height = 10–15 mm) were held in suspension culture (pearl nets) at six different stocking densities ranging from 136 to 818 spat m −2 ( 15–90/net). Scallops were sampled initially and at 5, 8, and 12 months in order to measure growth, yield, production, and survival. An inverse relationship was found between growth (shell height, meat weight, and whole weight) and stocking density, with a substantial amount of growth occurring at all densities. A similar relationship occurred between stocking density and production (kJ year −1 ) and yield (g) per individual. Overall survival was 91% and was not influenced by density. The optimal stocking density for giant scallops is dependent on the overall cultivation strategy and is thus influenced by the desired final market product, market size, type of grow-out technique, and timing of transfer from the pearl nets.

A Review of the Status of Atlantic Sturgeon in Canada, with Comparisons to Populations in the United States and Europe

Abstract Anadromous Atlantic sturgeon (Acipenser oxyrinchus) occur in most large rivers and in the sea of Atlantic Canada. They are recorded as far north as George River, Labrador, but spawning is unknown north of the St. Lawrence River. In Canada, spawning is in freshwater, usually close to tidehead, during June-July. To maintain a population, this iteroperous species requires access to rivers with medium to large estuaries and the sea. Juveniles inhabit the mesohaline region of estuaries (5–25 ppt salinity), usually over a mud-sand bottom. After 1–12 years, they migrate to sea where they spend another 5–10 years before reaching sexual maturity, after which they return to rivers to spawn every 1–5 years depending on sex and latitude of the natal stream. Migration is extensive, north and south on the Atlantic coast, and seaward to the edge of the continental shelf. There are five known spawning populations in Canada and probably numerous unknown ones. Spawning populations in the United States occur from M...

The North Atlantic subpolar gyre and the marine migration of Atlantic salmon Salmo salar: the ‘Merry‐Go‐Round’ hypothesis

One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62 degrees N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62 degrees N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high-seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium-137 ((137)Cs) levels in S. salar returning to a Quebec river suggested 62.3% had fed at or east of Iceland, whereas levels in 1 sea-winter (SW) Atlantic Canada returnees indicated 24.7% had fed east of the Faroes. Lower levels of (137)Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open-ocean migrations of epipelagic fishes.

Life History and Population Characteristics of Striped Bass in Atlantic Canada

Abstract Populations of striped bass Morone saxatilis occur in three regions of Atlantic Canada: the St. Lawrence River and estuary in Quebec; the Gulf of St. Lawrence from Chaleur Bay through Northumberland Strait; and rivers in New Brunswick and Nova Scotia draining into the Bay of Fundy. At least nine rivers are known or believed to sustain spawning populations: the St. Lawrence River (where the spawning stock may be extirpated); the Nepisiguit River in Chaleur Bay; the Tabusintac, Miramichi, Kouchibouguac, and Richibucto rivers in the western Gulf of St. Lawrence; the Saint John and Annapolis rivers in the outer Bay of Fundy; and the Shubenacadie–Stewiacke river system in the inner Bay of Fundy. Historically, commercial striped bass landings in Atlantic Canada were lower than those of the U.S. eastern seaboard, the largest landings being made in New Brunswick. Angling catches are substantial but difficult to verify. Spawning occurs in tidal streams several weeks after ice leaves the system. Adults exh...

Stock Origin of Migratory Atlantic Sturgeon in Minas Basin, Inner Bay of Fundy, Canada, Determined by Microsatellite and Mitochondrial DNA Analyses

Abstract Five distinct population segments of Atlantic sturgeon Acipenser oxyrinchus were recently listed (April 2012) as endangered or threatened under the U.S. Endangered Species Act. Atlantic sturgeon are anadromous, spawning occurs in rivers from the St. Lawrence River, Quebec, to the Satilla River, Georgia, and subadults and adults undertake extensive coastal migrations. Bycatch of Atlantic sturgeon in coastal fisheries may have resulted in the slowed or failed rebuilding of many populations despite the imposition of a U.S. federal moratorium on their harvest in 1998. Canadas Bay of Fundy hosts weir and trawl fisheries which bycatch Atlantic sturgeon of unknown origin. Additionally, tidal power development projects for the Bay of Fundy have been proposed which could detrimentally impact migratory sturgeon. We hypothesized that the Atlantic sturgeon that occur in Minas Basin in the Bay of Fundy are of local Saint John River, New Brunswick, origin with little or no U.S. contribution. We used microsate...

Consequences of Incidental Otter Trawl Capture on Survival and Physiological Condition of Threatened Atlantic Sturgeon

Abstract Atlantic Sturgeon Acipenser oxyrinchus aggregate in Minas Basin in the inner Bay of Fundy, Nova Scotia, during summer, presumably to feed on abundant intertidal invertebrates. The Atlantic Sturgeon aggregation is composed of multiple stocks from Canada and the USA. Government agencies from both nations have recently recognized Atlantic Sturgeon as threatened or endangered due to overfishing and habitat degradation. Little is known about the fate of Atlantic Sturgeon that are captured as bycatch in fisheries targeting other species, making it difficult to determine the extent to which bycatch is contributing to the Atlantic Sturgeon populations decline. To characterize the effects of otter trawl capture and release on Atlantic Sturgeon, we calculated a minimum survival rate for fish after catch and release by using acoustic telemetry, and we examined physiological indicators of stress. The minimum postrelease survival rate from otter trawl capture events was high (94% survival). Results also demo...

Mortality of Juvenile Clupeids during Passage through a Tidal, Low-Head Hydroelectric Turbine at Annapolis Royal, Nova Scotia

Abstract Migrant juvenile clupeids passing through the tidal, low-head hydroelectric turbine at Annapolis River, Nova Scotia, were monitored during the fall of 1985 and 1986. Although there were two fishways adjacent to both sides of the turbine intake, 98% of the clupeids passed through the tidal-power turbine. Total mortality of clupeids from turbine passage was estimated to be 46.3% for both years combined. Injuries observed were attributed to pressure effects (64.5%), mechanical strike (33.9%), and hydraulic shearing (1.7%).

Identification by Scale Analysis of Farmed Atlantic Salmon Juveniles in Southwestern New Brunswick Rivers

Abstract A procedure was developed to identify whether the natal origin of juvenile Atlantic salmon Salmo salar in the Magaguadavic River, New Brunswick, was farmed or wild. Farmed juveniles enter this river as escapees from commercial hatcheries. The discriminant function was developed using measured scale characteristics for the first year of growth, as determined from samples of farmed and wild juvenile Atlantic salmon of known origin. Eight scale characteristics proved to be significant predictors of origin. In a jackknife cross-validation, the discriminant function was 90% accurate in predicting the origin of juvenile Atlantic salmon in the Magaguadavic River. The procedure was then applied to juvenile Atlantic salmon of unknown natal origin sampled from the Magaguadavic and neighboring Waweig and Digdequash rivers, which also support salmon hatcheries. Of the juvenile Atlantic salmon sampled in the Magaguadavic River in 1996, 1997, and 1998, 36, 59, and 43%, respectively, were estimated to be of far...

Intertidal Habitat Use, Population Characteristics, Movement, and Exploitation of Striped Bass in the Inner Bay of Fundy, Canada

Abstract Striped bass Morone saxatilis were sampled from intertidal weirs in Minas Basin and Cobequid Bay, Bay of Fundy, to determine tidal behavior, population characteristics, movements, and exploitation. During 1985 and 1986, 1,864 striped bass ranging from 69 to more than 600 mm in fork length were captured in three commercial weirs from May to December along the north shore of Minas Basin and Cobequid Bay. Catches were lowest during early summer and highest in late summer and fall. Catches were greatest when low tide occurred from dusk to midnight (1800-2400 hours), a second peak being observed when low tide occurred from dawn to late morning. Largest weir catches at a clear-water site (Minas Basin) were associated with spring tides (0.5-0.9 m above mean low water [MLW]), but at turbid water sites (Cobequid Bay) the best catches were during neap tides (1.0-1.7 m above MLW). The largest striped bass were captured from June to August (280-610 mm), but age-0 (69-94-mm) and age-1 (141-240-mm) fish domina...

The annual marine feeding aggregation of Atlantic sturgeon Acipenser oxyrinchus in the inner Bay of Fundy: population characteristics and movement

Atlantic sturgeon Acipenser oxyrinchus aggregate to feed from May to October in Minas Basin (45° N; 64° W), a large, cul-de-sac embayment of the inner Bay of Fundy. The aggregation consists mainly of migrants from the Saint John, NB and Kennebec Rivers, ME (99%). During 2004-2015, 4393 A. oxyrinchus were taken as by-catch by commercial fish trawlers or at intertidal fishing weirs, and 1453 were marked and/or sampled and released. Fork length (LF ) ranged from 458 to 2670 mm, but 72·5% were <1500 mm. Mass (M) ranged from 0·5 to 58·0 kg. The mass-length relationship for fish ≤50 kg was log10 M = 3·32log10 LF - 5·71. Observed growth of unsexed A. oxyrinchus recaptured after 1-8 years indicated fish of 90-179 cm LF grew c. 2-4 cm a year. Ages obtained from pectoral spines were from 4 to 54 years. The Von Bertalanffy growth model predicted K = 0·01 and L∞ = 5209 mm LF . Estimated annual mortality was 9·5-10·9%. Aggregation sizes in 2008 and 2013 were 8804 and 9244 individuals, respectively. Fish exhibited high fidelity for yearly return to Minas Basin and population estimates indicated the total at-sea number utilizing the Basin increased from c. 10 700 in 2010 to c. 37 500 in 2015. Abundance in the Basin was greatest along the north shore in spring and along the south shore in summer, suggesting clockwise movement following the residual current structure. Marked individuals were recaptured in other bays of the inner Bay of Fundy, north to Gaspé, Quebec, and south to New Jersey, U.S.A., with 26 recoveries from the Saint John River, NB, spawning run. Fish marked at other Canadian and U.S. sites were also recovered in Minas Basin. Since all A. oxyrinchus migrate into and out of the Basin annually they will be at risk of mortality if planned tidal power turbines are installed in Minas Passage.