Observations of Adult Atlantic Cod (Gadus morhua) Overwintering in Nearshore Waters of Trinity Bay, Newfoundland

1994 ◽  
Vol 51 (1) ◽  
pp. 142-150 ◽  
Author(s):  
J. S. Wroblewski ◽  
Wade L. Bailey ◽  
Kristine A. Howse
Keyword(s):  
Minimum Distance ◽  
Short Range ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Nearshore Zone ◽  
Island Region ◽  
Northern Cod ◽  
Near Shore ◽  
Surgical Implantation ◽  
Trinity Bay

In the Random Island region of Trinity Bay, Newfoundland, individual adult Atlantic cod (Gadus morhua) with surgically implanted sonic transmitters were repeatedly relocated during the winter of 1990–91. Cod remained near shore, where seawater temperatures were as low as −1.5 °C. These fish did not move in the fall to offshore continental shelf waters as do most northern cod, nor did they move into the deeper waters of Trinity Bay that were slightly warmer than those in the nearshore zone. Of 12 cod released with transmitters in the fall and early winter, two were caught by local inshore fishermen the following spring, providing evidence that adult cod that overwinter nearshore become available to the spring inshore fishery. Another three were caught within a year of release. One fish was hooked in Fortune Bay on the southern coast of Newfoundland, having traveled a minimum distance of 305 nautical miles. These results demonstrate that northern cod can survive the surgical implantation of transmitters for at least a year and that this method is a valid technique for studying the behavior of northern cod. The main limitation to our sonic tracking was the relatively short range of signal reception (<1 nautical mile).

Survival of Northern Atlantic Cod (Gadus morhua) Eggs and Larvae when Exposed to Ice and Low Temperature

1992 ◽  
Vol 49 (12) ◽  
pp. 2588-2595 ◽  
Author(s):  
Paul F. Valerio ◽  
Sally V. Goddard ◽  
Ming H. Kao ◽  
Garth L. Fletcher
Keyword(s):  
Low Temperature ◽  
Newfoundland And Labrador ◽  
Direct Contact ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Ice Crystals ◽  
Freeze Resistance ◽  
Northern Cod ◽  
Northern Atlantic ◽  
Eggs And Larvae

Freeze resistance of eggs and larvae of Atlantic cod (Gadus morhua) from the northern cod stock was investigated to determine whether ice contact could affect survival during the spring spawning season off Newfoundland. Egg and larval homogenates did not appear to contain antifreeze proteins (mean freezing points −0.78 and −0.88 °C, respectively). However, cod eggs did not freeze at −1.8 °C in icy aerated seawater, could be undercooled to −4.0 °C in ice, and froze at temperatures between −4.1 and −1 7 °C; freeze resistance depended on the integrity of the chorion. Larvae withstood undercooling to −1.8 °C, provided they were not brought into direct contact with ice crystals, if directly touched with ice, larvae froze at −1.36 °C (feeding stage) or −1.34 °C (yolk-sac), approximately 0.5 °C lower than would be expected from the freezing temperatures of their body fluids. The nature of their external epithelium and delayed development of sensitive gill structures below 0 °C may contribute to larval freeze resistance. Cod eggs and larvae are found in spring off Newfoundland and Labrador, when sea temperatures can be as low as −1.8 °C and ice cover extensive. While cod eggs are remarkably freeze resistant, such environmental conditions may cause freezing mortalities in larval cod.

Indices of Total Stock Biomass in the "Northern" and Gulf of St. Lawrence Atlantic Cod (Gadus morhua) Stocks Derived from Time Series Analyses of Fixed Gear (Trap) Catches

1992 ◽  
Vol 49 (2) ◽  
pp. 202-209 ◽  
Author(s):  
G. A. Rose
Keyword(s):  
Time Series ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Moving Average ◽  
Stock Biomass ◽  
Northern Cod ◽  
Cross Correlations ◽  
Time Series Analyses ◽  
Trap Catches ◽  
Total Stock

The hypothesis that annual catches of fixed gear fisheries are cross-correlated with stock biomass at lags predictable on the basis of the relative ages of fish comprising the catch and biomass was verified for the trapnet fisheries of the northeastern Newfoundland "northern" (NAFO 2J3KL) and northern "Gulf" of St. Lawrence (NAFO 3Pn4RS) Atlantic cod (Gadus morhua) stocks. Time series indices of stock biomass were derived from these cross-correlations. For northern cod, the index was a 3-yr weighted and lagged moving average of catch. For the years 1972–81 (the first half of the available data) the trap index (Ti) was regressed on the stock biomass (Bi) determined by sequential population models (SPA) (Ti = 0.477Bi0.638, r = 0.99, P < 0.01). Biomass forecasts for 1982–90 derived from this function (inverted) were positively correlated with recent SPA-based estimates (r = 0.94, P < 0.02). For Gulf cod, the index was a 4-yr weighted and lagged moving average of catch. This index was regressed on SPA-determined biomass for the years 1974–81 (Ti = −3.19 + 0.0217Bi, r = 0.99; P < 0.01). Biomass forecasts for 1982–90 were positively correlated with (but lower than) SPA-based biomass estimates for the Gulf stock (r = 0.91, P < 0.05).

scholarly journals Otolith chemistry and redistributions of Northern cod: evidence of Smith Sound – Bonavista Corridor connectivity

2018 ◽  
Vol 75 (12) ◽  
pp. 2302-2312 ◽  
Author(s):  
Victoria Neville ◽  
George Rose ◽  
Sherrylynn Rowe ◽  
Robyn Jamieson ◽  
Glenn Piercey
Keyword(s):  
Oxygen Isotope ◽  
Gadus Morhua ◽  
Direct Evidence ◽  
Atlantic Cod ◽  
Otolith Chemistry ◽  
Stable Oxygen Isotope ◽  
Metapopulation Structure ◽  
Northern Cod ◽  
Stable Oxygen ◽  
Placentia Bay

Stable oxygen isotope assays of otoliths (δ18Ooto) from migrant Atlantic cod (Gadus morhua Linnaeus, 1758) that overwintered in Smith Sound, Newfoundland, during 1995–2006 differed from those of nonmigrating summer residents and cod from Placentia Bay and Halibut Channel but did not differ from those of cod from the adjacent offshore Bonavista Corridor in summer. All fish sampled were of the 1990 year class (founder of the Smith Sound aggregation) at ages 8–10 years. Hence, overwintering Smith Sound and summering Bonavista Corridor cod likely experienced similar temperatures and salinities in each year of life, representing different migration stages of an intermixed group. Moreover, predictions of δ18Ooto from near-bottom ocean temperatures and salinities differed between inshore and offshore sites and, in general, matched observed signatures of inshore and offshore cod. The Bonavista Corridor cod, however, were an exception, having δ18Ooto signatures suggestive of inshore exposure. Our findings provide direct evidence of metapopulation structure in the Northern cod and are consistent with offshore rebuilding having been spurred by dispersal of cod from inshore Smith Sound.

scholarly journals Is recovery of northern cod limited by poor feeding? The capelin hypothesis revisited

2014 ◽  
Vol 71 (4) ◽  
pp. 784-793 ◽  
Author(s):  
Darrell R. J. Mullowney ◽  
George A. Rose
Keyword(s):  
Newfoundland And Labrador ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Wild Fish ◽  
Fish Growth ◽  
Small Fish ◽  
Performance Trends ◽  
Northern Cod ◽  
Capelin Mallotus Villosus ◽  
Prime Condition

Abstract The slow recovery of the “northern” Atlantic cod (Gadus morhua) stock off Newfoundland and Labrador has been ascribed to many factors. One hypothesis is poor feeding and condition as a consequence of a decline in capelin (Mallotus villosus), their former main prey. We compared the growth and condition of cod from known inshore (Smith Sound) and offshore (Bonavista Corridor) centres of rebuilding in wild subjects versus captive subjects fed an unlimited diet of oily rich fish. Wild fish in these areas have had different diets and population performance trends since stock declines in the early 1990s. Captive cod from both areas grew at the same rates and achieved equivalent prime condition, while their wild counterparts differed, with smaller sizes, lower condition in small fish, and elevated mortality levels in the offshore centre. Environmental temperature conditions did not account for the differences in performance of wild fish. Our results suggest that fish growth and condition, and hence rebuilding in the formerly large offshore spawning components of the northern cod, have been limited by a lack of capelin in their diet. Furthermore, we suggest that these groups are unlikely to rebuild until a recovery in capelin occurs.

Movements of Atlantic Cod (Gadus Morhua) Within the Spring Thermocline in Trinity Bay, Newfoundland

1995 ◽  
Vol 75 (2) ◽  
pp. 265-284 ◽  
Author(s):  
J.S. Wroblewski ◽  
Sally V. Goddard ◽  
R. Kent Smedbol ◽  
Wade L. Bailey
Keyword(s):  
Surface Waters ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Antifreeze Protein ◽  
Early Spring ◽  
Subzero Temperature ◽  
Cold Adapted ◽  
Protein Levels ◽  
Trap Fishery ◽  
Trinity Bay

Using depth-telemetering, sonic tags orally inserted into the stomachs of Gadus morhua (Pisces: Gadiformes) found over-wintering in Trinity Bay, Newfoundland, the movements of individual fish were observed as surface waters warmed in early spring. Physiological measurements (antifreeze protein levels in the blood) indicate that many cold-adapted, bay cod change their thermal regime at this time. Fish acclimatized to subzero water temperatures enter the newly-formed thermocline and become available to a cod trap fishery. Most sonically-tagged fish resided in 0–1°C waters along the shoreline. Tracking data confirmed indications from declining antifreeze protein levels that cold-adapted cod, having moved into shallow waters in early spring, do not return to deeper, subzero-temperature waters for any appreciable time. At night some cod swam pelagically near the surface. Fish moved at times in the same direction as the tidal current, but ground speeds were several times greater than current velocities. Nocturnal pelagic swimming was also observed during the summer when temperatures within the thermocline exceeded 10°C.

Overwintering of Adult Northern Atlantic Cod (Gadus morhua) in Cold Inshore Waters as Evidenced by Plasma Antifreeze Glycoprotein Levels

1994 ◽  
Vol 51 (12) ◽  
pp. 2834-2842 ◽  
Author(s):  
Sally V. Goddard ◽  
J. S. Wroblewski ◽  
C. T. Taggart ◽  
K. A. Howse ◽  
W. L. Bailey ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Antifreeze Glycoproteins ◽  
Cold Temperatures ◽  
Antifreeze Glycoprotein ◽  
Trap Fishery ◽  
In The Wild ◽  
History Of ◽  
Inshore Waters ◽  
Trinity Bay

Adult Atlantic cod (Gadus morhua) are known to produce antifreeze glycoproteins in response to cold temperatures. Our laboratory studies demonstrated that blood plasma levels in adult cod were positively correlated with the number of days they spent in subzero water. Between April 1991 and June 1993, we monitored concentrations of antifreeze glycoproteins in the plasma of late juvenile and adult cod in Trinity Bay, Newfoundland, and used the results to estimate how long cod had been exposed to low water temperatures. A consideration of these data in conjunction with detailed temperature profiles of the area taken over the course of the study allowed us to deduce the distribution of cod in relation to the temperature field. This study provides evidence that (1) blood antifreeze glycoprotein levels can be used to deduce the recent thermal history of cod in the wild and (2) after their inshore summer feeding period, considerable numbers of adult cod overwintered inshore in Trinity Bay in subzero water, producing antifreeze glycoproteins as temperatures fell below 0 °C. From May onwards, "cold-adapted" cod moved into warming surface waters, where they became available to an early inshore trap fishery.

Movements of farmed and wild Atlantic cod (Gadus morhua) released in Trinity Bay, Newfoundland

1996 ◽  
Vol 124 (4) ◽  
pp. 619-627 ◽  
Author(s):  
J. S. Wroblewski ◽  
R. K. Smedbol ◽  
C. T. Taggart ◽  
S. V. Goddard
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Trinity Bay

Outcome of an inshore spawning event by northern Atlantic cod (Gadus morhua) at a low stock level

1998 ◽  
Vol 55 (10) ◽  
pp. 2283-2291 ◽  
Author(s):  
R K Smedbol ◽  
D C Schneider ◽  
J S Wroblewski ◽  
D A Methven
Keyword(s):  
Gadus Morhua ◽  
Direct Evidence ◽  
Atlantic Cod ◽  
Spatial Scales ◽  
Spawning Aggregation ◽  
Stock Level ◽  
Egg Density ◽  
Northern Atlantic ◽  
Northeast Coast ◽  
Trinity Bay

A large spawning aggregation of northern Atlantic cod (Gadus morhua) was discovered in a fjord of Trinity Bay, Newfoundland, in April 1995, 3 years after the collapse of this stock and 1 year after the last offshore spawning aggregation was recorded. We hypothesized that spawning by this aggregation would increase the abundance/density of eggs and settled 0-group juveniles above the level of spawning in the bay during recent years. Data from 1995 were compared with ichthyoplankton and postsettlement juvenile surveys conducted in recent years. Egg density was significantly higher in 1995 than the pooled average of two recent years (1991 and 1993). The hypothesized increase in numbers of postsettlement age 0 fish was tested at three different spatial scales: the entire northeast coast of Newfoundland, individual bays, and areas within Trinity Bay. There was no detectable increase in catches of settled age 0 juveniles at any spatial scale. Consequently, while this large spawning aggregation produced locally high egg concentrations, it did not lead to a detectable increase in abundance of newly settled age 0 juveniles in coastal nursery areas. This study did not provide any direct evidence for an increase in recruitment in the inshore region due to the spawning output of locally abundant spawners in Trinity Bay.

Was an increase in natural mortality responsible for the collapse off northern cod?

1995 ◽  
Vol 52 (6) ◽  
pp. 1274-1285 ◽  
Author(s):  
Ransom A. Myers ◽  
Noel G. Cadigan
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Natural Mortality ◽  
Correlated Errors ◽  
Estimation Errors ◽  
Research Survey ◽  
Northern Cod ◽  
Northern Atlantic ◽  
Invalid Inference ◽  
Trawl Surveys

The collapse of the northern Atlantic cod (Gadus morhua) fishery off southern Labrador and to the northern Grand Bank of Newfoundland, once the largest cod fishery in the world, was a social and economic disaster for the region. An analysis of traditional catch-at-age data in conjunction with research surveys, which assumed that research survey estimation errors of abundance by age and year were independent, led assessment biologists to the conclusion that the collapse was caused by an increase in natural mortality in the first half of 1991. We constructed a statistical model to test this hypothesis. The results do not support the hypothesis. There is ambiguous evidence that natural mortality has increased since 1991; however, these results are found only in a model that has extraordinary patterns in the residuals. Our analysis suggests that even if natural mortality has been higher in recent years (as estimated using a model with correlated errors for research surveys), overfishing was sufficiently high to cause a collapse of this population. We also demonstrate that the usual assumption that estimation errors from research trawl surveys are independent is not valid, and can lead to invalid inference and unreasonable estimates of abundance.

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